EP3878997A1 - Method of forming precursor into a ti alloy article - Google Patents

Method of forming precursor into a ti alloy article Download PDF

Info

Publication number
EP3878997A1
EP3878997A1 EP20275056.8A EP20275056A EP3878997A1 EP 3878997 A1 EP3878997 A1 EP 3878997A1 EP 20275056 A EP20275056 A EP 20275056A EP 3878997 A1 EP3878997 A1 EP 3878997A1
Authority
EP
European Patent Office
Prior art keywords
range
true strain
total
article
transus
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP20275056.8A
Other languages
German (de)
French (fr)
Inventor
designation of the inventor has not yet been filed The
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BAE Systems PLC
Original Assignee
BAE Systems PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BAE Systems PLC filed Critical BAE Systems PLC
Priority to EP20275056.8A priority Critical patent/EP3878997A1/en
Priority to PL21711942.9T priority patent/PL4118251T3/en
Priority to AU2021235517A priority patent/AU2021235517A1/en
Priority to PCT/GB2021/050608 priority patent/WO2021181101A1/en
Priority to EP21711942.9A priority patent/EP4118251B1/en
Priority to CA3173617A priority patent/CA3173617A1/en
Priority to US17/802,031 priority patent/US20230106504A1/en
Priority to GB2103367.5A priority patent/GB2594573B/en
Publication of EP3878997A1 publication Critical patent/EP3878997A1/en
Pending legal-status Critical Current

Links

Images

Classifications

    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22FCHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18High-melting or refractory metals or alloys based thereon
    • C22F1/183High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon

Definitions

  • the present invention relates to thermomechanical forming of ⁇ + ⁇ Ti alloys.
  • Manufacturing of components, for example aerospace components, from ⁇ + ⁇ Ti alloys typically includes:
  • Components exhibiting such a relatively coarse prior ⁇ grain size are non-compliant, according to manufacturing specifications, and since remediation is not practical and/or possible, such components be disposed, thereby reducing the yield.
  • Such relatively coarse prior ⁇ grain size may be exhibited in only a relatively small proportion of components, for example 3% to 20% by number of the components, similarly manufactured from similar precursors.
  • characterisation of the prior ⁇ grain size may usually only be performed after machining of the articles, for example by non-destructive testing of the components, since such relatively coarse prior ⁇ grains are typically found more proximal to central portions of the articles and thus only revealed upon machining of the articles.
  • a time and/or a cost of manufacturing the non-compliant components has already been invested.
  • thermomechanically forming an article a method of manufacturing a component and/or such an article and/or such a component which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere.
  • a first aspect provides a method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, the method comprising:
  • a second aspect provides a method of manufacturing a component, for example an aerospace component such as a spar or a longeron, comprising:
  • a third aspect provides an article thermomechanically formed according to the first aspect or a component manufactured according to the second aspect, wherein a maximum prior ⁇ grain size of the ⁇ + ⁇ Ti alloy in the first portion is in a range from 10 ⁇ m to 25 mm, preferably in a range from 100 ⁇ m to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
  • thermomechanically forming an article as set forth in the appended claims. Also provided is a method of manufacturing a component from such an article, such an article and such a component.
  • a first aspect provides a method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, the method comprising:
  • portions of the precursor, such as the first portion, that are deformed by a total true strain ⁇ 1, total greater than the predetermined threshold true strain ⁇ threshold are susceptible to exhibiting a relatively coarse prior ⁇ grain size in the thermomechanically formed article.
  • the heating step (a) and the deforming step (b) are repeated, as necessary, until the heated first portion is deformed by the total true strain ⁇ 1, total .
  • the precursor is repeatedly heated and deformed until the desired shape or form of the article is achieved, while restricting the amount of deforming during each repetition to at most the predetermined threshold true strain ⁇ threshold .
  • thermomechanically forming for example forging, rolling, extruding or drawing, the article from the precursor thereof.
  • thermomechanical forming is a metallurgical process that combines mechanical or plastic deformation processes, such forging, rolling, extruding or drawing, with thermal processes, such as heat treating, quenching, heating and cooling at various rates, into a single process.
  • the thermomechanical forming comprises and/or is forging of the article from the precursor thereof.
  • Forging of ⁇ + ⁇ Ti alloys is known. As with other forging alloys, the mechanical properties of ⁇ + ⁇ Ti alloys are affected by forging and thermal processes as well as alloy content. However, when die filling is optimized, there is only a moderate change in tensile properties with grain direction, and comparable strengths and ductilities are obtainable in both thick and thin sections. ⁇ + ⁇ Ti alloys are more difficult to forge than most steels, for example. The metallurgical behaviour of the ⁇ + ⁇ Ti alloys imposes some limitations and controls on forging operations and influences the steps in the manufacturing operation. Special care is generally exercised throughout all processing steps to minimize surface contamination by oxygen, carbon or nitrogen.
  • Titanium alloys can be forged to precision tolerances. However, excessive die wear, the need for expensive tooling, and problems with microstructure control and contamination may make the cost of close tolerance (not machined) forging prohibitive except for simple shapes like compressor fan blades for turbo-fan engines. Close tolerance forgings in moderately large sizes are currently being developed using hot die and isothermal forging techniques.
  • the article comprises and/or is a semi-finished intermediate (also known as a preform), for subsequent machining.
  • a semi-finished intermediate is subject to subsequent thermomechanical processing, for example block and finish forging (also known as blocking or blocker die and finish forging), thereby providing a machining blank.
  • the semi-finished intermediate comprises and/or is a machining blank, suitable for subsequent rough and/or finish machining.
  • the method comprises providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate.
  • the precursor comprises and/or is a forging stock such as a round, square or rectangular bar or a billet, for example, such as having cross-sectional dimensions (i.e. width and height and/or diameter) in a range from 50 mm x 50 mm to 500 mm x 500 mm, preferably in a range from 100 mm x 100 mm to 300 mm x 300 mm, for example 200 mm x 200 mm and/or a length in a range from 50 mm to 5,000 mm, preferably in a range from 500 mm to 2,000 mm. Other sizes are known.
  • the precursor comprises, substantially comprises, essentially comprises and/or consists of the ⁇ + ⁇ Ti alloy having a beta transus temperature ⁇ transus .
  • ⁇ + ⁇ Ti alloys are described below in detail.
  • the ⁇ + ⁇ Ti alloy comprises and/or is according to Grade 5.
  • the ⁇ + ⁇ Ti alloy comprises and/or is according to Table 1.
  • the ⁇ + ⁇ Ti alloy comprises and/or is AMS 4928 (AMS 4928, AMS 4928 Rev. A - W or later), AMS 4930 (AMS 4930, AMS 4930 Rev. A - K or later), AMS 4965 (AMS 4965, AMS 4965 Rev. A - M or later), AMS 4967 (AMS 4967, AMS 4967 Rev.
  • the ⁇ + ⁇ Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof.
  • the ⁇ + ⁇ Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof.
  • the precursor defines the set of portions including the first portion.
  • the set of portions comprises and/or is a logical partitioning or divisions of the precursor and thus each portion is a respective volume of the precursor.
  • the respective portions of the set of portions may have the same or different shapes, sizes and/or volumes.
  • the set of portions corresponds with finite elements as used in finite element methods.
  • the respective portions of the set proportions may be deformed during the thermal mechanical forming by the same or different true strains. In other words, different portions may be subjected to different deformations, for example by forging, so as to provide the desired shape of the article.
  • the set of portions includes N portions, where N is a natural number greater than or equal to 1, for example 1, 10, 100, 1,000, 10,000, 100,000, 1,000,000 or more.
  • a regularly-shaped, simple precursor such as a square cross-sectional billet (i.e. a forging stock) may be forged into an irregularly-shaped, complex article, such that different portions are subjected to different deformations, for example in which the different portions are subjected to different total true strains ⁇ N,total spaning a factor of 10, 100 or more.
  • a regularly-shaped, simple precursor such as a rectangular cross-sectional billet (i.e.
  • a rolling stock may be rolled into an regularly-shaped, simple article, such that different portions are subjected to similar or the same deformations, for example in which the different portions are subjected to similar or the same total true strains ⁇ N,total spanning a factor of 5, 2 or less. Extrusion and/or drawing may be more analogous to rolling than forging, in this respect.
  • the method comprises thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by the total true strain ⁇ 1, total , wherein the total true strain ⁇ 1, total is greater than the predetermined threshold true strain ⁇ threshold .
  • the first portion is hot worked by the total true strain ⁇ 1, total , which exceeds the predetermined threshold true strain ⁇ threshold . That is, the predetermined threshold true strain ⁇ threshold is the limit beyond which relatively coarse prior ⁇ grain sizes may be exhibited in the article.
  • Thermomechanically forming the article from the precursor comprises i iterations of:
  • the heating step (a) and the deforming step (b) are repeated, as necessary, until the heated first portion is deformed by the total true strain ⁇ 1, total .
  • the precursor is repeatedly heated and deformed until the desired shape of the article is formed, while restricting the amount of deforming during each repetition to at most the predetermined threshold true strain ⁇ threshold .
  • a relatively coarse prior ⁇ grain size is avoided, thereby improving mechanical properties of the components, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the components and/or stress corrosion resistance of the components.
  • repeating steps (a) and (b) comprise reheating the first portion to the temperature T i during the time t i , wherein the temperature T i is at most the beta transus temperature ⁇ transus and further deforming the heated first portion by the true strain ⁇ 1, i , wherein the true strain ⁇ 1, i is at most the predetermined threshold true strain ⁇ threshold , respectively.
  • the precursor and the first portion are thus repeatedly heated and deformed by repeating steps (a) and (b), such that a shape of the precursor and the first portion is iteratively deformed.
  • the intermediate during these repeated steps is referred to as the precursor, until the final shape of the article is formed.
  • thermomechanically forming the article from the precursor comprises i iterations of:
  • the first portion is heated to the temperature T i during (i.e. for) the time t i , thereby heating the first portion to a temperature suitable for the deformation, for example forging, rolling, extruding or drawing.
  • deforming is an adiabatic process, such that the precursor heats during the deforming, notwithstanding that cooling occurs due to heat losses to the environment and/or the deforming apparatus, such as a forging press.
  • the deforming is isothermal, for example isothermal forging.
  • the temperature T i is in a range from ⁇ transus - 175°F to ⁇ transus - 5°F, preferably in a range from ⁇ transus - 150°F to ⁇ transus - 15°F, more preferably in a range from ⁇ transus - 125°F to ⁇ transus - 25°F. That is, the precursor is deformed below the beta transus temperature ⁇ transus , in the ⁇ + ⁇ phase. If the temperature T i is too high, the heated first portion may be further heated above the beta transus temperature ⁇ transus during the deforming, due to adiabatic heating thereof. Conversely, if the temperature T i is too low, deforming of the heated first portion may be problematic and/or more difficult.
  • the time t i is in a range from 0.25 hours to 24 hours, preferably in a range from 0.5 hours to 12 hours, more preferably in a range from 1 hour to 8 hours, most preferably in a range from 2 hours to 6 hours wherein i is equal to 1.
  • the time t i is in a range from 0.25 hours to 4 hours, preferably in a range from 0.5 hours to 2 hours, more preferably in a range from 0.75 hours to 1.5 hours, for example 1 hour, wherein i is greater than or equal to 2.
  • the precursor may be initially hot soaked, before the first iteration (i.e. wherein i is equal to 1) of the deforming step (b) for generally a longer time than subsequent reheats (i.e. wherein i is greater than 1) between repeated deforming steps (b).
  • the heated first portion is deformed, for example forged, rolled, extruded or drawn, by the true strain ⁇ 1, i , wherein the true strain ⁇ 1, i is at most the predetermined threshold true strain ⁇ threshold ;
  • the predetermined threshold true strain ⁇ threshold is in a range from 0.1 to 1, preferably in a range from 0.3 to 0.9, more preferably in a range from 0.5 to 0.85, most preferably in a range from 0.7 to 0.8, for example 0.75.
  • deforming the heated first portion by the total true strain ⁇ 1, total comprises elongating the heated first portion by a total elongation ( ⁇ L / L ) total , wherein the total elongation ( ⁇ L / L ) total is at least a predetermined threshold elongation ( ⁇ L / L ) threshold . That is, a length L of the heated first portion may be increased by a minimum increase in length ⁇ L .
  • the precursor may be elongated during forging, for example.
  • i is in a range from 2 to 10, for example 2, 3, 4, 5, 6, 7, 8, 9 or 10, preferably in a range from 2 to 5, for example 2, 3, 4 or 5.
  • providing the precursor comprises providing the precursor having a cross-sectional aspect ratio in a range from 1:2 to 2:1, preferably in a range from 2:3 to 3:2, more preferably in a range from 3:4 to 4:3, for example about 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and/or providing the precursor having a longitudinal aspect ratio in a range from 1,000:1 to 1:1, preferably in a range from 100:1 to 4:3, more preferably in a range from 50:1 to 3:2, for example at least 2:1.
  • the precursor may be a length of forging stock such as a round, square or rectangular bar or a billet, for example, such as having cross-sectional dimensions (i.e. width and height and/or diameter) in a range from 50 mm x 50 mm to 500 mm x 500 mm, preferably in a range from 100 mm x 100 mm to 300 mm x 300 mm, for example 200 mm x 200 mm and/or a length in a range from 50 mm to 5,000 mm, preferably in a range from 500 mm to 2,000 mm. Other sizes are known.
  • cross-sectional dimensions i.e. width and height and/or diameter
  • the method comprises thermomechanical processing of the thermomechanically formed article, for example block and finish forging of the thermomechanically formed article, such as before beta annealing.
  • the method comprises ⁇ annealing the article at a temperature T ⁇ anneal during a time t ⁇ anneal , wherein the temperature T ⁇ anneal is at least the beta transus temperature ⁇ transus .
  • ⁇ annealing is known. That is, the ⁇ annealing is of the thermomechanically formed article.
  • the method comprises stabilization annealing the article at a temperature T stabilization anneal during a time t stabilization anneal , wherein the temperature T stabilization anneal is less than the beta transus temperature ⁇ transus .
  • Stabilization annealing is known. That is, the stabilization annealing is of the thermomechanically formed article.
  • stabilization annealing the article comprises stabilization annealing the ⁇ annealed article (i.e. after ⁇ annealing the thermomechanically formed article).
  • providing the precursor comprises vacuum arc melting, plasma arc melting and/or electron beam melting and/or vacuum arc re-melting the ⁇ + ⁇ Ti alloy. In this way, a solute content and/or microstructure of the precursor may be improved.
  • providing the precursor comprises vacuum arc remelting the ⁇ + ⁇ Ti alloy, for example subsequent to vacuum arc melting, plasma arc melting and/or electron beam melting the ⁇ + ⁇ Ti alloy. That is, the ⁇ + ⁇ Ti alloy may be melted twice.
  • a maximum grain size of the prior ⁇ phase of the ⁇ + ⁇ Ti alloy in the first portion of the article is in a range from 10 ⁇ m to 25 mm, preferably in a range from 100 ⁇ m to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm. In this way, a relatively coarse prior ⁇ grain size is avoided, thereby improving mechanical properties of the article, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or stress corrosion resistance of the article.
  • the prior ⁇ grain size in the ⁇ + ⁇ Ti alloy may be determined by image analysis of polished or machined and etched surfaces, according to known metallographic techniques, of the article, for example using Beuhler OmniMet (RTM) or Clemex Vision PE (RTM) microstructural image analysis software. Additionally and/or alternatively, the prior ⁇ grain size in the ⁇ + ⁇ Ti alloy may be determined from visual inspection and direct measurement (i.e. using a ruler and/or a gauge), for example of the etched surface.
  • RTM Beuhler OmniMet
  • RTM Clemex Vision PE
  • a microstructure of the ⁇ + ⁇ Ti alloy in the first portion of the article comprises, substantially comprises, essentially comprises or consists of a fully transformed microstructure, for example having little (at most 5%, preferably at most 2 %, more preferable at most 0.5% by volume fraction) or no (at most 0.1% by volume fraction) primary or equiaxed ⁇ phase.
  • the method is of thermomechanically forming by forging the article from the precursor thereof, the method comprising:
  • Elements having an atomic radius within ⁇ 15% of the atomic radius of Ti are substitutional elements and have significant solubility in Ti.
  • Elements having an atomic radius less than 59% of the atomic radius of Ti, for example H, N, O and C, occupy interstitial sites and also have substantial solubility.
  • the relatively high solubilities of substitutional and interstitial elements in Ti makes it difficult to design precipitation-hardened Ti alloys.
  • B has a similar but larger radius than C, O, N and H and it is therefore possible to induce titanium boride precipitation.
  • Cu precipitation is also possible in some alloys.
  • the substitutional elements may be categorised according to their effects on the stabilities of the a and ⁇ phases.
  • Al, O, N and Ga are a stabilisers while Mo, V, W and Ta are all ⁇ stabilisers.
  • Cu, Mn, Fe, Ni, Co and H are also ⁇ stabilisers but form the eutectoid. The eutectoid reaction is frequently sluggish (since substitutional atoms involved) and is suppressed.
  • Mo and V have the largest influence on ⁇ stability and are common alloying elements. W is rarely added due to its high density.
  • Cu forms TiCu 2 , which makes such Ti alloys age-hardening and heat treatable.
  • Zr, Sn and Si are neutral elements.
  • BCC Ti Body-centred cubic (BCC) Ti has three octahedral interstices per atom while closed-packed hexagonal (CPH) Ti has one octahedral interstice per atom. The latter are therefore larger, so that the solubility of O, N, and C is much higher in the ⁇ phase.
  • ⁇ + ⁇ Ti alloys also known as ⁇ - ⁇ Ti alloys, alpha-beta titanium alloys, dual-phase titanium alloys or two-phase titanium alloys
  • ⁇ stabilisers which allow substantial amounts of ⁇ to be retained on quenching from the ⁇ ⁇ ⁇ + ⁇ phase fields.
  • a typical ⁇ + ⁇ Ti alloy is Ti - 6AI - 4V (all nominal compositions in wt.% unless noted otherwise), while other ⁇ + ⁇ Ti alloys include Ti - 6AI - 6V - 2Sn and Ti - 6AI - 2Sn - 4Zr - Mo.
  • Al reduces alloy density, stabilises and strengthens the ⁇ phase and increases the ⁇ + ⁇ ⁇ ⁇ transformation temperature while V provides a greater amount of the more ductile ⁇ phase for hot-working and reduces the ⁇ + ⁇ ⁇ ⁇ transformation temperature.
  • Table 1 shows nominal compositions of selected ⁇ + ⁇ Ti alloys. Table 1: Nominal compositions of selected ⁇ + ⁇ Ti alloys.
  • heat treatments applied to Ti - 6AI - 4V alloys and more generally to ⁇ + ⁇ Ti alloys include: partial annealing (600 - 650 °C for about 1 hour), full annealing (700 - 850 °C followed by furnace cooling to about 600 °C followed by air cooling) or solutioning (880 - 950 °C followed by water quenching) and ageing (400 - 600 °C).
  • ⁇ + ⁇ Ti alloys constitute a very important group of structural materials used in aerospace applications.
  • the microstructures of these ⁇ + ⁇ Ti alloys can be varied significantly during thermomechanical processing and/or heat treatment, allowing for tailoring of their mechanical properties, including fatigue behaviour, to specific application requirements.
  • microstructure of ⁇ + ⁇ Ti alloys are:
  • the lamellar microstructure is characterized by relatively low tensile ductility, moderate fatigue properties, and good creep and crack growth resistance.
  • Important parameters of the lamellar microstructure with respect to mechanical properties include the ⁇ grain size D, size d of the colonies of a phase lamellae, thickness t of the a phase lamellae and the morphology of the interlamellar interface ( ⁇ phase).
  • ⁇ phase the morphology of the interlamellar interface
  • an increase in cooling rate leads to refinement of the microstructure - both a phase colony size d and ⁇ phase lamellae thickness t are reduced.
  • new ⁇ phase colonies tend to nucleate not only on ⁇ phase boundaries but also on boundaries of other ⁇ phase colonies, growing perpendicularly to the existing ⁇ phase lamellae. This leads to formation of a characteristic microstructure called "basket weave" or Widmanooth microstructure.
  • the equiaxed microstructure has a better balance of strength and ductility at room temperature and fatigue properties which depend noticeably on the crystallographic texture of the HCP a phase.
  • An advantageous balance of properties can be obtained by development of bimodal microstructure consisting of primary a grains and fine lamellar a colonies within relatively small ⁇ grains (10 - 20 ⁇ m in diameter).
  • the phase composition of ⁇ + ⁇ Ti alloys after cooling from the ⁇ phase is controlled, at least in part, by the cooling rate.
  • the kinetics of phase transformations is related, at least in part, to the ⁇ phase stability coefficient K ⁇ due to the chemical composition of the ⁇ + ⁇ Ti alloy.
  • the range of the ⁇ + ⁇ ⁇ ⁇ phase transformation temperature determines, at least in part, conditions of thermomechanical processing intended for development of a desired microstructure. Start and finish temperatures of ⁇ + ⁇ ⁇ ⁇ phase transformation vary depending, at least in part, on the amounts of ⁇ stabilizing elements (Table 2).
  • the microstructure of ⁇ + ⁇ Ti alloys after deformation or heat treatment carried out above the beta transus temperature ⁇ transus depends, at least in part, on the cooling rate. Relatively higher cooling rates (> 18 °C s -1 ) result in martensitic ⁇ ' ( ⁇ " ) microstructure for alloys having ⁇ phase stability coefficient K ⁇ ⁇ 1 and metastable ⁇ M microstructure for alloys having higher ⁇ phase stability coefficient K ⁇ .
  • Low and moderate cooling rates lead to development of lamellar microstructures consisting of colonies of ⁇ phase lamellae within large ⁇ phase grains.
  • a decrease in cooling rate cause an increase in both the thickness t of individual ⁇ phase lamellae and size d of the a colonies. These in turn lower the yield stress and tensile strength of these ⁇ + ⁇ Ti alloys.
  • the lamellar a phase microstructure of ⁇ + ⁇ Ti alloys heat treated in the ⁇ phase has a beneficial effect on fatigue behaviour, due to frequent changes in crack direction and secondary crack branching.
  • ⁇ phase lamellae are too large, thin layers of ⁇ phase are not capable of absorbing large amounts of energy and retard crack propagation. In this case, the ⁇ phase colonies behave as singular element of the microstructure. This phenomenon is more pronounced in ⁇ + ⁇ Ti alloys having smaller ⁇ phase stability coefficients K ⁇ , such as Ti - 6Al - 4V.
  • K ⁇ such as Ti - 6Al - 4V.
  • the second aspect provides a method of manufacturing a component, for example an aerospace component such as a spar or a longeron, comprising:
  • the component is provided, at least in part, by machining the article. Since the article is formed by thermomechanically forming in which the true strain ⁇ 1, i of the heated first portion is limited during each deforming step (b) to at most the predetermined threshold true strain ⁇ threshold , a relatively coarse prior ⁇ grain size is avoided, thereby improving mechanical properties of the article and/or the component machined therefrom, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or the component machined therefrom and/or stress corrosion resistance of the article and/or the component machined therefrom.
  • the method comprises non-destructive testing of the component.
  • non-destructive testing of the component comprises non-destructive testing of the machined component.
  • non-destructive testing of the component comprises determination of a maximum prior ⁇ grain size in the ⁇ + ⁇ Ti alloy, for example as determined by image analysis of polished or machined and etched surfaces, according to known metallographic techniques, of the article, for example using Beuhler OmniMet (RTM) or Clemex Vision PE (RTM) microstructural image analysis software.
  • RTM Beuhler OmniMet
  • RTM Clemex Vision PE
  • machining comprises removing an amount of the first portion in a range from 10% to 99.5%, preferably in a range from 25% to 99%, more preferably in a range from 50% to 97.5% by volume of the first portion. In other words, a substantial amount (at least 10%) or even a major amount (at least 50%) of the article is removed during machining.
  • the third aspect provides an article thermomechanically formed according to the first aspect or a component manufactured according to the second aspect, wherein a maximum prior ⁇ grain size in the ⁇ + ⁇ Ti alloy in the first portion of the article or the component is in a range from 10 ⁇ m to 25 mm, preferably in a range from 100 ⁇ m to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
  • the maximum grain size may be as described with respect to the first aspect.
  • the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of other components.
  • the term “consisting essentially of” or “consists essentially of” means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like.
  • Figure 3 schematically depicts a method of thermomechanically forming an ⁇ + ⁇ Ti alloy. It should be understood that the exemplary method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof relates to at least the step of pre-form forging and optionally, to the steps of die forging and/or subsequent heat treatment.
  • Figure 4 is a CAD drawing of an article 10, particularly for machining into a rib for an aircraft (i.e. an aerospace component), according to an exemplary embodiment.
  • the article 10 was thermomechanically formed according to an exemplary embodiment, as described with respect to Figure 5 , from a precursor 1 wherein the precursor 1 is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47".
  • the article 10 has a length of about 96".
  • Figure 5 schematically depicts an exemplary method of thermomechanically forming the article 10 of Figure 4 .
  • Figure 5 compares a conventional method of thermomechanically forming a conventional article (labelled 'Current Process') and the exemplary method of thermomechanically forming the exemplary article 10 (labelled 'New Process').
  • the conventional method comprises:
  • the precursor is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47", while the length of the article is about 96".
  • 'Positions 1 to 12' are deformed during the 1 st iteration (i.e. wherein i is equal to 1) while only 'Positions 8 to 12' are deformed during the 2 nd iteration (i.e. wherein i is equal to 2).
  • the exemplary method is of thermomechanically forming by forging the article 10 from the precursor 1 (not shown) thereof, the method comprising:
  • the precursor 1 is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47", while the length of the article 10 is about 96".
  • 'Positions 1 to 12' are deformed during the 1 st iteration (i.e. wherein i is equal to 1), 'Positions 1, 2 and 4' are deformed during the 2 nd iteration (i.e. wherein i is equal to 2), 'Positions 8 to 12' are deformed during the 3 rd iteration (i.e. wherein i is equal to 3) and 'Positions 8 and 11' are deformed during the 4 th iteration (i.e. wherein i is equal to 4).
  • the predetermined threshold true strain ⁇ threshold is 0.75 (i.e. 75%).
  • the number of heating steps has been increased from 2 to 4 while the respective portions are deformed by at most the predetermined threshold true strain ⁇ threshold of 0.75 (i.e. 75%).

Landscapes

  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Forging (AREA)

Abstract

A method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, is described. The method comprises: providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate, comprising, substantially comprising, essentially comprising and/or consisting of an α + β Ti alloy having a beta transus temperature βtransus , wherein the precursor defines a set of portions including a first portion; and thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε 1,total , wherein the total true strain ε 1,total is greater than a predetermined threshold true strain εthreshold ; wherein thermomechanically forming the article from the precursor comprises i iterations of: (a) heating the first portion to a temperature Ti during a time ti , wherein the temperature Ti is at most the beta transus temperature βtransus ; (b) deforming the heated first portion by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold ; and (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε 1,total , wherein i is a natural number greater than or equal to 2.

Description

    Field
  • The present invention relates to thermomechanical forming of α + β Ti alloys.
  • Background to the invention
  • Manufacturing of components, for example aerospace components, from α + β Ti alloys typically includes:
    1. 1. thermomechanical forming, for example forging, rolling, extruding or drawing, of precursors, for example forging, rolling, extruding or drawing stock, at a temperature of at most the beta transus temperature βtransus of the α + β Ti alloys, thereby providing articles thermomechanically formed from the precursors;
    2. 2. optionally heat treatment, for example β annealing and/or stabilisation annealing of the articles; and
    3. 3. machining of the articles, thereby providing the components from the articles.
  • A problem arises in that such manufacturing may result in the prior β grain size in the components (i.e. the machined articles) being relatively coarse, for example greater than 0.20" (5.1 mm), thereby adversely affecting mechanical properties of the components, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the components and/or stress corrosion resistance of the components. Components exhibiting such a relatively coarse prior β grain size are non-compliant, according to manufacturing specifications, and since remediation is not practical and/or possible, such components be disposed, thereby reducing the yield. Particularly, such relatively coarse prior β grain size may be exhibited in only a relatively small proportion of components, for example 3% to 20% by number of the components, similarly manufactured from similar precursors. Furthermore, characterisation of the prior β grain size may usually only be performed after machining of the articles, for example by non-destructive testing of the components, since such relatively coarse prior β grains are typically found more proximal to central portions of the articles and thus only revealed upon machining of the articles. However, at such an end stage of manufacturing, a time and/or a cost of manufacturing the non-compliant components has already been invested.
  • Hence, there is a need to improve manufacturing of components, for example aerospace components, from α + β Ti alloys.
  • Summary of the Invention
  • It is one aim of the present invention, amongst others, to provide a method of thermomechanically forming an article, a method of manufacturing a component and/or such an article and/or such a component which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere. For instance, it is an aim of embodiments of the invention to provide a method of thermomechanically forming an article from an α + β Ti alloy having a relatively finer prior β grain size. For instance, it is an aim of embodiments of the invention to provide a method of manufacturing a component having a higher yield. For instance, it is an aim of embodiments of the invention to provide an article and/or a component having a relatively finer prior β grain size.
  • A first aspect provides a method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, the method comprising:
    • providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate, comprising, substantially comprising, essentially comprising and/or consisting of an α + β Ti alloy having a beta transus temperature βtransus , wherein the precursor defines a set of portions including a first portion; and
    • thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε 1,total , wherein the total true strain ε 1,total is greater than a predetermined threshold true strain εthreshold;
    • wherein thermomechanically forming the article from the precursor comprises i iterations of:
      1. (a) heating the first portion to a temperature Ti during a time ti , wherein the temperature Ti is at most the beta transus temperature βtransus;
      2. (b) deforming the heated first portion by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold; and
      3. (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε1,total , wherein i is a natural number greater than or equal to 2.
  • A second aspect provides a method of manufacturing a component, for example an aerospace component such as a spar or a longeron, comprising:
    • thermomechanically forming an article according to the first aspect; and
    • machining, for example milling, turning, boring or drilling, the first portion of the article, thereby providing, at least in part, the component.
  • A third aspect provides an article thermomechanically formed according to the first aspect or a component manufactured according to the second aspect, wherein a maximum prior β grain size of the α + β Ti alloy in the first portion is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
  • Detailed Description of the Invention
  • According to the present invention there is provided a method of thermomechanically forming an article, as set forth in the appended claims. Also provided is a method of manufacturing a component from such an article, such an article and such a component. Other features of the invention will be apparent from the dependent claims, and the description that follows.
  • Method of thermomechanically forming an article
  • A first aspect provides a method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, the method comprising:
    • providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate, comprising, substantially comprising, essentially comprising and/or consisting of an α + β Ti alloy having a beta transus temperature βtransus , wherein the precursor defines a set of portions including a first portion; and
    • thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε 1,total , wherein the total true strain ε 1,total is greater than a predetermined threshold true strain εthreshold;
    • wherein thermomechanically forming the article from the precursor comprises i iterations of:
      1. (a) heating the first portion to a temperature Ti during a time ti , wherein the temperature Ti is at most the beta transus temperature βtransus;
      2. (b) deforming the heated first portion by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold; and
      3. (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε 1,total , wherein i is a natural number greater than or equal to 2.
  • Particularly, the inventors have identified that portions of the precursor, such as the first portion, that are deformed by a total true strain ε 1,total greater than the predetermined threshold true strain εthreshold are susceptible to exhibiting a relatively coarse prior β grain size in the thermomechanically formed article. Hence, by limiting the true strain ε 1,i of the heated first portion during each deforming step (b) to at most the predetermined threshold true strain εthreshold, such a relatively coarse prior β grain size is avoided, thereby improving mechanical properties of the of the article and/or a component machined therefrom, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or a component machined therefrom and/or stress corrosion resistance of the article and/or a component machined therefrom. In order to thermomechanically form the article, the heating step (a) and the deforming step (b) are repeated, as necessary, until the heated first portion is deformed by the total true strain ε 1, total. In other words, the precursor is repeatedly heated and deformed until the desired shape or form of the article is achieved, while restricting the amount of deforming during each repetition to at most the predetermined threshold true strain εthreshold.
  • The method is of thermomechanically forming, for example forging, rolling, extruding or drawing, the article from the precursor thereof. Generally, thermomechanical forming, is a metallurgical process that combines mechanical or plastic deformation processes, such forging, rolling, extruding or drawing, with thermal processes, such as heat treating, quenching, heating and cooling at various rates, into a single process. In one example, the thermomechanical forming comprises and/or is forging of the article from the precursor thereof.
  • Forging of α + β Ti alloys is known. As with other forging alloys, the mechanical properties of α + β Ti alloys are affected by forging and thermal processes as well as alloy content. However, when die filling is optimized, there is only a moderate change in tensile properties with grain direction, and comparable strengths and ductilities are obtainable in both thick and thin sections. α + β Ti alloys are more difficult to forge than most steels, for example. The metallurgical behaviour of the α + β Ti alloys imposes some limitations and controls on forging operations and influences the steps in the manufacturing operation. Special care is generally exercised throughout all processing steps to minimize surface contamination by oxygen, carbon or nitrogen. These contaminants can severely impair ductility, fracture toughness, and the overall quality of a titanium forging if left on the surfaces. Hydrogen can also be absorbed by titanium alloys and can cause problems if levels exceed specified amounts. Hydrogen absorption, unlike that of oxygen, is not always confined to the surface. Titanium alloys can be forged to precision tolerances. However, excessive die wear, the need for expensive tooling, and problems with microstructure control and contamination may make the cost of close tolerance (not machined) forging prohibitive except for simple shapes like compressor fan blades for turbo-fan engines. Close tolerance forgings in moderately large sizes are currently being developed using hot die and isothermal forging techniques.
  • In one example, the article comprises and/or is a semi-finished intermediate (also known as a preform), for subsequent machining. Typically, such a semi-finished intermediate is subject to subsequent thermomechanical processing, for example block and finish forging (also known as blocking or blocker die and finish forging), thereby providing a machining blank. Alternatively, the semi-finished intermediate comprises and/or is a machining blank, suitable for subsequent rough and/or finish machining.
  • The method comprises providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate. In one example, the precursor comprises and/or is a forging stock such as a round, square or rectangular bar or a billet, for example, such as having cross-sectional dimensions (i.e. width and height and/or diameter) in a range from 50 mm x 50 mm to 500 mm x 500 mm, preferably in a range from 100 mm x 100 mm to 300 mm x 300 mm, for example 200 mm x 200 mm and/or a length in a range from 50 mm to 5,000 mm, preferably in a range from 500 mm to 2,000 mm. Other sizes are known.
  • The precursor comprises, substantially comprises, essentially comprises and/or consists of the α + β Ti alloy having a beta transus temperature βtransus. α + β Ti alloys are described below in detail. In one example, the α + β Ti alloy comprises and/or is according to Grade 5. In one example, the α + β Ti alloy comprises and/or is according to Table 1. In one example, the α + β Ti alloy comprises and/or is AMS 4928 (AMS 4928, AMS 4928 Rev. A - W or later), AMS 4930 (AMS 4930, AMS 4930 Rev. A - K or later), AMS 4965 (AMS 4965, AMS 4965 Rev. A - M or later), AMS 4967 (AMS 4967, AMS 4967 Rev. A - M or later), AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof. In one preferred example, the α + β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof.
  • The precursor defines the set of portions including the first portion. It should be understood that the set of portions comprises and/or is a logical partitioning or divisions of the precursor and thus each portion is a respective volume of the precursor. It should be understood that the respective portions of the set of portions may have the same or different shapes, sizes and/or volumes. Hence, the set of portions corresponds with finite elements as used in finite element methods. It should be understood that the respective portions of the set proportions may be deformed during the thermal mechanical forming by the same or different true strains. In other words, different portions may be subjected to different deformations, for example by forging, so as to provide the desired shape of the article. In one example, the set of portions includes N portions, where N is a natural number greater than or equal to 1, for example 1, 10, 100, 1,000, 10,000, 100,000, 1,000,000 or more. For example, a regularly-shaped, simple precursor such as a square cross-sectional billet (i.e. a forging stock) may be forged into an irregularly-shaped, complex article, such that different portions are subjected to different deformations, for example in which the different portions are subjected to different total true strains εN,total spaning a factor of 10, 100 or more. In contrast, a regularly-shaped, simple precursor such as a rectangular cross-sectional billet (i.e. a rolling stock) may be rolled into an regularly-shaped, simple article, such that different portions are subjected to similar or the same deformations, for example in which the different portions are subjected to similar or the same total true strains εN,total spanning a factor of 5, 2 or less. Extrusion and/or drawing may be more analogous to rolling than forging, in this respect.
  • The method comprises thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by the total true strain ε 1,total , wherein the total true strain ε 1,total is greater than the predetermined threshold true strain εthreshold. In other words, the first portion is hot worked by the total true strain ε 1,total , which exceeds the predetermined threshold true strain εthreshold. That is, the predetermined threshold true strain εthreshold is the limit beyond which relatively coarse prior β grain sizes may be exhibited in the article.
  • Generally, true strain ε (also called natural strain) may be defined by: ε = ln D f D i
    Figure imgb0001
    where Di is an initial dimension, for example an initial cross-sectional area of the first portion i.e. in the precursor, and Df is a corresponding final dimension, for example a final cross-sectional area of the first portion i.e. in the article.
  • The true strain ε is related to engineering strain εeng by ε = ln 1 + ε eng
    Figure imgb0002
    where ε eng = D f D i D i .
    Figure imgb0003
  • Thermomechanically forming the article from the precursor comprises i iterations of:
    1. (a) heating the first portion to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus ;
    2. (b) deforming the heated first portion by the true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold; and
    3. (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε 1,total , wherein i is the natural number greater than or equal to 2.
  • That is, the heating step (a) and the deforming step (b) are repeated, as necessary, until the heated first portion is deformed by the total true strain ε 1, total. In other words, the precursor is repeatedly heated and deformed until the desired shape of the article is formed, while restricting the amount of deforming during each repetition to at most the predetermined threshold true strain εthreshold. In this way, a relatively coarse prior β grain size is avoided, thereby improving mechanical properties of the components, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the components and/or stress corrosion resistance of the components.
  • It should be understood that repeating steps (a) and (b) (i.e. when i is greater than or equal to 2) comprise reheating the first portion to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus and further deforming the heated first portion by the true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold , respectively. It should understood that the precursor and the first portion are thus repeatedly heated and deformed by repeating steps (a) and (b), such that a shape of the precursor and the first portion is iteratively deformed. For convenience, the intermediate during these repeated steps is referred to as the precursor, until the final shape of the article is formed.
  • More generally, thermomechanically forming the article from the precursor comprises i iterations of:
    1. (a) heating the precursor, defining the set of portions including N portions wherein N is a natural number greater than or equal to 1, to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus ;
    2. (b) deforming respective portions of the set of portions of the heated precursor, by respective true strains εN,i, wherein the true strain ε N,i of each portion is at most the predetermined threshold true strain εthreshold; and
    3. (c) repeating steps (a) and (b) until the cumulative true strain εN,cumulative = ∑ iε N,i is the total true strain ε 1, total, wherein i is a natural number greater than or equal to 2.
  • It should be understood that the first portion is heated to the temperature Ti during (i.e. for) the time ti , thereby heating the first portion to a temperature suitable for the deformation, for example forging, rolling, extruding or drawing. Generally, deforming is an adiabatic process, such that the precursor heats during the deforming, notwithstanding that cooling occurs due to heat losses to the environment and/or the deforming apparatus, such as a forging press. In one example, the deforming is isothermal, for example isothermal forging.
  • In one example, the temperature Ti is in a range from βtransus - 175°F to βtransus - 5°F, preferably in a range from βtransus - 150°F to βtransus - 15°F, more preferably in a range from βtransus - 125°F to βtransus - 25°F. That is, the precursor is deformed below the beta transus temperature βtransus , in the α + β phase. If the temperature Ti is too high, the heated first portion may be further heated above the beta transus temperature βtransus during the deforming, due to adiabatic heating thereof. Conversely, if the temperature Ti is too low, deforming of the heated first portion may be problematic and/or more difficult.
  • In one example, the time ti is in a range from 0.25 hours to 24 hours, preferably in a range from 0.5 hours to 12 hours, more preferably in a range from 1 hour to 8 hours, most preferably in a range from 2 hours to 6 hours wherein i is equal to 1.
  • In one example, the time ti is in a range from 0.25 hours to 4 hours, preferably in a range from 0.5 hours to 2 hours, more preferably in a range from 0.75 hours to 1.5 hours, for example 1 hour, wherein i is greater than or equal to 2.
  • That is, the precursor may be initially hot soaked, before the first iteration (i.e. wherein i is equal to 1) of the deforming step (b) for generally a longer time than subsequent reheats (i.e. wherein i is greater than 1) between repeated deforming steps (b).
  • It should be understood that the heated first portion is deformed, for example forged, rolled, extruded or drawn, by the true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold;
    In one example, the predetermined threshold true strain εthreshold is in a range from 0.1 to 1, preferably in a range from 0.3 to 0.9, more preferably in a range from 0.5 to 0.85, most preferably in a range from 0.7 to 0.8, for example 0.75. In this way, a relatively coarse prior β grain size is avoided, thereby improving mechanical properties of the components, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or a component machined therefrom and/or stress corrosion resistance of the article and/or a component machined therefrom.
  • In one example, deforming the heated first portion by the total true strain ε 1,total comprises elongating the heated first portion by a total elongation (δL/L) total, wherein the total elongation (δL/L) total is at least a predetermined threshold elongation (δL/L) threshold. That is, a length L of the heated first portion may be increased by a minimum increase in length δL. For example, the precursor may be elongated during forging, for example.
  • In one example, the predetermined threshold elongation (δL/L) threshold is in a range from 0.1 to 10, preferably in a range from 0.25 to 5, more preferably in a range from 0.5 to 2.5, most preferably in a range from 0.75 to 1.25, for example 1. That is, the length L of the heated first portion may be increased by a minimum increase in length δL = L, when (δL/L) threshold = 1, for example.
  • In one example, i is in a range from 2 to 10, for example 2, 3, 4, 5, 6, 7, 8, 9 or 10, preferably in a range from 2 to 5, for example 2, 3, 4 or 5. Generally, it is desirable to minimise i while the true strain ε 1,i is at most the predetermined threshold true strain εthreshold. In this way, a number of repetitions of the (a) and (b) is reduced, thereby controlling cost and/or complexity. In one example, providing the precursor comprises providing the precursor having a cross-sectional aspect ratio in a range from 1:2 to 2:1, preferably in a range from 2:3 to 3:2, more preferably in a range from 3:4 to 4:3, for example about 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and/or providing the precursor having a longitudinal aspect ratio in a range from 1,000:1 to 1:1, preferably in a range from 100:1 to 4:3, more preferably in a range from 50:1 to 3:2, for example at least 2:1. In other words, the precursor may be a length of forging stock such as a round, square or rectangular bar or a billet, for example, such as having cross-sectional dimensions (i.e. width and height and/or diameter) in a range from 50 mm x 50 mm to 500 mm x 500 mm, preferably in a range from 100 mm x 100 mm to 300 mm x 300 mm, for example 200 mm x 200 mm and/or a length in a range from 50 mm to 5,000 mm, preferably in a range from 500 mm to 2,000 mm. Other sizes are known.
  • In one example, the method comprises thermomechanical processing of the thermomechanically formed article, for example block and finish forging of the thermomechanically formed article, such as before beta annealing.
  • In one example, the method comprises β annealing the article at a temperature Tβ anneal during a time tβ anneal, wherein the temperature Tβ anneal is at least the beta transus temperature βtransus . It should be understood that the β annealing is subsequent to step (c) (i.e. after repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε1,total , wherein i is the natural number greater than or equal to 2). β annealing is known. That is, the β annealing is of the thermomechanically formed article.
  • In one example, the method comprises stabilization annealing the article at a temperature Tstabilization anneal during a time tstabilization anneal , wherein the temperature Tstabilization anneal is less than the beta transus temperature βtransus . It should be understood that the β annealing is subsequent to step (c) (i.e. after repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε1,total , wherein i is the natural number greater than or equal to 2). Stabilization annealing is known. That is, the stabilization annealing is of the thermomechanically formed article. In one example, stabilization annealing the article comprises stabilization annealing the β annealed article (i.e. after β annealing the thermomechanically formed article).
  • In one example, providing the precursor comprises vacuum arc melting, plasma arc melting and/or electron beam melting and/or vacuum arc re-melting the α + β Ti alloy. In this way, a solute content and/or microstructure of the precursor may be improved. In one example, providing the precursor comprises vacuum arc remelting the α + β Ti alloy, for example subsequent to vacuum arc melting, plasma arc melting and/or electron beam melting the α + β Ti alloy. That is, the α + β Ti alloy may be melted twice.
  • In one example, a maximum grain size of the prior β phase of the α + β Ti alloy in the first portion of the article is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm. In this way, a relatively coarse prior β grain size is avoided, thereby improving mechanical properties of the article, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or stress corrosion resistance of the article. The prior β grain size in the α + β Ti alloy may be determined by image analysis of polished or machined and etched surfaces, according to known metallographic techniques, of the article, for example using Beuhler OmniMet (RTM) or Clemex Vision PE (RTM) microstructural image analysis software. Additionally and/or alternatively, the prior β grain size in the α + β Ti alloy may be determined from visual inspection and direct measurement (i.e. using a ruler and/or a gauge), for example of the etched surface.
  • In one example, a microstructure of the α + β Ti alloy in the first portion of the article, for example after beta annealing, comprises, substantially comprises, essentially comprises or consists of a fully transformed microstructure, for example having little (at most 5%, preferably at most 2 %, more preferable at most 0.5% by volume fraction) or no (at most 0.1% by volume fraction) primary or equiaxed α phase.
  • In one preferred example, the method is of thermomechanically forming by forging the article from the precursor thereof, the method comprising:
    • providing the precursor, wherein the precursor is a forging stock such as a round, square or rectangular bar or a billet, having cross-sectional dimensions in a range from 50 mm x 50 mm to 500 mm x 500 mm, preferably in a range from 100 mm x 100 mm to 300 mm x 300 mm, for example 200 mm x 200 mm and/or a length in a range from 50 mm to 5,000 mm, preferably in a range from 500 mm to 2,000 mm, consisting of the α + β Ti alloy having a beta transus temperature βtransus , wherein the precursor defines the set of portions including a first portion; and
    • thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by the total true strain ε 1,total , wherein the total true strain ε 1,total is greater than the predetermined threshold true strain εthreshold;
    • wherein thermomechanically forming the article from the precursor comprises i iterations of:
      1. (a) heating the first portion to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus ;
      2. (b) deforming the heated first portion by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold;
      3. (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulative = ∑ iε 1,i is the total true strain ε 1,total , wherein i is the natural number greater than or equal to 2;
    • thermomechanical processing the article, for example block and finish forging of the article;
    • β annealing the article at a temperature Tβ anneal during a time tβ anneal, wherein the temperature Tβ anneal is at least the beta transus temperature βtransus; and
    • stabilization annealing the (β annealed) article at a temperature Tstabilization anneal during a time tstabilization anneal , wherein the temperature Tstabilization anneal is less than the beta transus temperature βtransus ;
    • wherein the α + β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof;
    • wherein the predetermined threshold true strain εthreshold is in a range from 0.1 to 1, preferably in a range from 0.3 to 0.9, more preferably in a range from 0.5 to 0.85, most preferably in a range from 0.7 to 0.8, for example 0.75;
    • wherein deforming the heated first portion by the total true strain ε 1,total comprises elongating the heated first portion by a total elongation (δL/L) total, wherein the total elongation (δL/ L) total is at least a predetermined threshold elongation (δL/L) threshold;
    • wherein the predetermined threshold elongation (δL/L)threshold is in a range from 0.1 to 10, preferably in a range from 0.25 to 5, more preferably in a range from 0.5 to 2.5, most preferably in a range from 0.75 to 1.25, for example 1;
    • wherein providing the precursor comprises providing the precursor having a cross-sectional aspect ratio in a range from 1:2 to 2:1, preferably in a range from 2:3 to 3:2, more preferably in a range from 3:4 to 4:3, for example about 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and/or providing the precursor having a longitudinal aspect ratio in a range from 1,000:1 to 1:1, preferably in a range from 100:1 to 4:3, more preferably in a range from 50:1 to 3:2, for example at least 2:1;
    • wherein the temperature Ti is in a range from β transus - 175°F to βtransus - 5°F, preferably in a range from βtransus - 150°F to βtransus - 15°F, more preferably in a range from βtransus - 125°F to βtransus - 25°F;
    • wherein the time ti is in a range from 0.25 hours to 24 hours, preferably in a range from 0.5 hours to 12 hours, more preferably in a range from 1 hour to 8 hours, most preferably in a range from 2 hours to 6 hours wherein i is equal to 1;
    • wherein the time ti is in a range from 0.25 hours to 4 hours, preferably in a range from 0.5 hours to 2 hours, more preferably in a range from 0.75 hours to 1.5 hours, for example 1 hour, wherein i is greater than or equal to 2;
    • wherein a microstructure of the α + β Ti alloy in the first portion of the article, for example after beta annealing, comprises, substantially comprises, essentially comprises or consists of a fully transformed microstructure, for example having little (at most 5%, preferably at most 2 %, more preferable at most 0.5% by volume fraction) or no (at most 0.1% by volume fraction) primary or equiaxed α phase; and
    • wherein a maximum prior β grain size in the α + β Ti alloy in the first portion of the article is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
    α + β Ti alloys
  • Elements having an atomic radius within ±15% of the atomic radius of Ti are substitutional elements and have significant solubility in Ti. Elements having an atomic radius less than 59% of the atomic radius of Ti, for example H, N, O and C, occupy interstitial sites and also have substantial solubility. The relatively high solubilities of substitutional and interstitial elements in Ti makes it difficult to design precipitation-hardened Ti alloys. However, B has a similar but larger radius than C, O, N and H and it is therefore possible to induce titanium boride precipitation. Cu precipitation is also possible in some alloys.
  • The substitutional elements may be categorised according to their effects on the stabilities of the a and β phases. Hence, Al, O, N and Ga are a stabilisers while Mo, V, W and Ta are all β stabilisers. Cu, Mn, Fe, Ni, Co and H are also β stabilisers but form the eutectoid. The eutectoid reaction is frequently sluggish (since substitutional atoms involved) and is suppressed. Mo and V have the largest influence on β stability and are common alloying elements. W is rarely added due to its high density. Cu forms TiCu2, which makes such Ti alloys age-hardening and heat treatable. Zr, Sn and Si are neutral elements.
  • The interstitial elements do not fit properly in the Ti lattices and cause changes in the lattice parameters. Hydrogen is the most important interstitial elenent. Body-centred cubic (BCC) Ti has three octahedral interstices per atom while closed-packed hexagonal (CPH) Ti has one octahedral interstice per atom. The latter are therefore larger, so that the solubility of O, N, and C is much higher in the α phase.
  • Most α + β Ti alloys (also known as α - β Ti alloys, alpha-beta titanium alloys, dual-phase titanium alloys or two-phase titanium alloys) have high-strength and formability, and contain 4 - 6 wt.% of β stabilisers which allow substantial amounts of β to be retained on quenching from the βα + β phase fields. A typical α + β Ti alloy is Ti - 6AI - 4V (all nominal compositions in wt.% unless noted otherwise), while other α + β Ti alloys include Ti - 6AI - 6V - 2Sn and Ti - 6AI - 2Sn - 4Zr - Mo. Al reduces alloy density, stabilises and strengthens the α phase and increases the α + ββ transformation temperature while V provides a greater amount of the more ductile β phase for hot-working and reduces the α + ββ transformation temperature. Table 1 shows nominal compositions of selected α + β Ti alloys. Table 1: Nominal compositions of selected α + β Ti alloys.
    α + β Ti alloys designation Tensile strength (MPa, min) 0.2% yield strength (MPa, min) Composition (wt.%) Impurity limits (wt.%, max)
    Al Sn Zr Mo V Cu Mn Cr Si N C H Fe O
    Ti-6Al-4V (a) (g) (i) AMS 4928W 900 830 5.5 - 6.75 3.5 - 4.5 0.05 0.08 0.0125 0.30 0.20
    Ti-6Al-4V ELI (g) (h) AMS 4930K 830 760 5.5 - 6.5 3.5 - 4.5 0.05 0.08 0.0125 0.25 0.13
    Ti-6Al-4V (g) (i) AMS 4965K 890 820 5.5 - 6.75 3.5 - 4.5 0.05 0.08 0.0125 0.30 0.20
    Ti-6Al-4V (a) (g) (i) AMS 4967M 890 820 5.5 - 6.75 3.5 - 4.5 0.05 0.08 0.0125 0.30 0.20
    Ti-6Al-4V ELI (g) (h) (j) AMS 6932C 860 790 5.5 - 6.5 3.5 - 4.5 0.05 0.08 0.0125 0.25 0.13
    Ti-6Al-4V (g) (h) (i) AMS 4905F 860 790 5.6 - 6.3 3.6 - 4.4 0.03 0.05 0.0125 0.25 0.12
    Ti-6Al-6V-2Sn (a) (g) (i) AMS 4971L 1030 970 5.0 - 6.0 1.5 - 2.5 5.0 - 6.0 0.35 - 1.0 0.04 0.05 0.015 0.2
    Ti-6Al-4V (g) (h) TIMETAL 6-4 ASTM Grade 5 Mil T-9047 970 920 5.5 - 6.75 3.5 - 4.5 0.05 0.08 0.015 0.40 0.2
    Ti-6Al-4V (g) (h) TIMETAL 6-4 ELI ASTM Grade 23 AMS 4981 970 920 5.5 - 6.5 3.5 - 4.5 0.03 0.08 0.0125 0.25 0.13
    Ti-6AI-4V-0.1 Ru (g) (h) (k) ASTM Grade 29 970 920 5.5 - 6.5 3.5 - 4.5 0.03 0.08 0.015 0.25 0.13
    Ti-8Mn (a) 860 760 8 0.05 0.08 0.015 0.5 0.2
    Ti-7Al-4Mo (a) 1030 970 7 4 0.05 0.1 0.013 0.3 0.2
    Ti-6Al-2Sn-4Zr-6Mo (b) AMS 4981 1170 1100 6 2 4 6 0.04 0.04 0.0125 0.15 0.15
    Ti-5Al-2Sn-2Zr-4Mo-4Cr (b)(c) 1125 1055 5 2 2 4 4 0.04 0.05 0.0125 0.3 0.13
    Ti-6Al-2Sn-2Zr-2Mo-2Cr (c) 1030 970 5.7 2 2 2 2 0.25 0.03 0.05 0.0125 0.25 0.14
    Ti-3Al-2.5V (d) 620 520 3 2.5 0.015 0.05 0.015 0.3 0.12
    Ti-4Al-4Mo-2Sn-0.5Si 1100 960 4 2 4 0.5 (e) 0.02 0.0125 0.2 (e)
    (a) Mechanical properties given for the annealed condition; may be solution treated and aged to increase strength; (b) Mechanical properties given for the solution-treated-and-aged condition; alloy not normally applied in annealed condition; (c) Semicommercial alloy; mechanical properties and composition limits subject to negotiation with suppliers; (d) Primarily a tubing alloy; may be cold drawn to increase strength; (e) Combined O2 + 2N2 = 0.27%; (f) Also solution treated and aged using an alternative aging temperature (480 °C, or 900 °F); (g) other elements total (wt.%, max) 0.40; (h) other elements each (wt.%, max) 0.10; (i) Y (wt.%, max) 0.005; (j) Y (wt.%, max) 0.05; (k) Ru (wt.%, min) 0.08, Ru (wt.%, max) 0.14
  • Ti - 6AI - 4V (martensitic α + β Ti alloy; Kβ = 0.3) accounts for about half of all the titanium alloys produced and is popular because of its strength (1100 MPa), creep resistance at 300 °C, fatigue resistance, good castability, plastic workability, heat treatability and weldability. Depending on required mechanical properties, heat treatments applied to Ti - 6AI - 4V alloys and more generally to α + β Ti alloys include: partial annealing (600 - 650 °C for about 1 hour), full annealing (700 - 850 °C followed by furnace cooling to about 600 °C followed by air cooling) or solutioning (880 - 950 °C followed by water quenching) and ageing (400 - 600 °C).
  • α + β Ti alloys constitute a very important group of structural materials used in aerospace applications. The microstructures of these α + β Ti alloys can be varied significantly during thermomechanical processing and/or heat treatment, allowing for tailoring of their mechanical properties, including fatigue behaviour, to specific application requirements.
  • The main types of microstructure of α + β Ti alloys are:
    1. 1. lamellar, formed after slow cooling when deformation or heat treatment takes place at a temperature in the single-phase β field above the beta transus temperature βtransus, comprising colonies of HCP α phase lamellae within large BCC β phase grains of several hundred microns in diameter; and
    2. 2. equiaxed, formed after deformation in the two-phase α + β field (i.e. below the beta transus temperature βtransus ), comprising globular α-phase dispersed in a β phase matrix.
  • The beta transus temperature βtransus is the temperature at which the α + ββ transformation takes place and is thus the lowest temperature at which the Ti alloy is composed of a volume fraction Vf = 1 of the BCC β phase.
  • The lamellar microstructure is characterized by relatively low tensile ductility, moderate fatigue properties, and good creep and crack growth resistance. Important parameters of the lamellar microstructure with respect to mechanical properties include the β grain size D, size d of the colonies of a phase lamellae, thickness t of the a phase lamellae and the morphology of the interlamellar interface (β phase). Generally, an increase in cooling rate leads to refinement of the microstructure - both a phase colony size d and α phase lamellae thickness t are reduced. Additionally, new α phase colonies tend to nucleate not only on β phase boundaries but also on boundaries of other α phase colonies, growing perpendicularly to the existing α phase lamellae. This leads to formation of a characteristic microstructure called "basket weave" or Widmanstätten microstructure.
  • The equiaxed microstructure has a better balance of strength and ductility at room temperature and fatigue properties which depend noticeably on the crystallographic texture of the HCP a phase.
  • An advantageous balance of properties can be obtained by development of bimodal microstructure consisting of primary a grains and fine lamellar a colonies within relatively small β grains (10 - 20 µm in diameter).
  • The phase composition of α + β Ti alloys after cooling from the β phase is controlled, at least in part, by the cooling rate. The kinetics of phase transformations is related, at least in part, to the β phase stability coefficient Kβ due to the chemical composition of the α + β Ti alloy. The range of the α + ββ phase transformation temperature determines, at least in part, conditions of thermomechanical processing intended for development of a desired microstructure. Start and finish temperatures of α + ββ phase transformation vary depending, at least in part, on the amounts of β stabilizing elements (Table 2). Table 2: Start and finish temperature of the α + ββ phase transformation for selected α + β Ti alloys (vh = vc = 0.08 °C s-1); ns: nucleation start; ps: precipitation start; s: start; f: finish.
    Temperature (°C) Ti - 6Al - 4V Ti - 6AI - 2Mo - 2Cr Ti - 6AI - 5Mo - 5V - 1Cr - 1Fe
    T α + β β ns
    Figure imgb0004
    890 840 790
    T α + β β ps
    Figure imgb0005
    930 920 830
    T α + β β f
    Figure imgb0006
    985 980 880
    T β α + β s
    Figure imgb0007
    950 940 850
    T β α + β s
    Figure imgb0008
    870 850 810
  • The microstructure of α + β Ti alloys after deformation or heat treatment carried out above the beta transus temperature βtransus depends, at least in part, on the cooling rate. Relatively higher cooling rates (> 18 °C s-1) result in martensitic α'(α") microstructure for alloys having β phase stability coefficient Kβ < 1 and metastable βM microstructure for alloys having higher β phase stability coefficient Kβ . Low and moderate cooling rates lead to development of lamellar microstructures consisting of colonies of α phase lamellae within large β phase grains. A decrease in cooling rate cause an increase in both the thickness t of individual α phase lamellae and size d of the a colonies. These in turn lower the yield stress and tensile strength of these α + β Ti alloys.
  • The lamellar a phase microstructure of α + β Ti alloys heat treated in the β phase has a beneficial effect on fatigue behaviour, due to frequent changes in crack direction and secondary crack branching. When α phase lamellae are too large, thin layers of β phase are not capable of absorbing large amounts of energy and retard crack propagation. In this case, the α phase colonies behave as singular element of the microstructure. This phenomenon is more pronounced in α + β Ti alloys having smaller β phase stability coefficients Kβ, such as Ti - 6Al - 4V. A sufficient thickness of the β phase enables absorption of energy in the process of plastic deformation of regions ahead of crack tips, contributing to slowing a rate of crack propagation and therefore increasing fatigue life.
  • Method of manufacturing a component
  • The second aspect provides a method of manufacturing a component, for example an aerospace component such as a spar or a longeron, comprising:
    • thermomechanically forming an article according to the first aspect; and
    • machining, for example milling, turning, boring or drilling, the first portion of the article, thereby providing, at least in part, the component.
  • In this way, the component is provided, at least in part, by machining the article. Since the article is formed by thermomechanically forming in which the true strain ε 1,i of the heated first portion is limited during each deforming step (b) to at most the predetermined threshold true strain εthreshold , a relatively coarse prior β grain size is avoided, thereby improving mechanical properties of the article and/or the component machined therefrom, especially fatigue crack growth and to an extent fracture toughness, tensile strength and/or ductility of the article and/or the component machined therefrom and/or stress corrosion resistance of the article and/or the component machined therefrom.
  • In one example, the method comprises non-destructive testing of the component. In one example, non-destructive testing of the component comprises non-destructive testing of the machined component. In one example, non-destructive testing of the component comprises determination of a maximum prior β grain size in the α + β Ti alloy, for example as determined by image analysis of polished or machined and etched surfaces, according to known metallographic techniques, of the article, for example using Beuhler OmniMet (RTM) or Clemex Vision PE (RTM) microstructural image analysis software.
  • In one example, machining comprises removing an amount of the first portion in a range from 10% to 99.5%, preferably in a range from 25% to 99%, more preferably in a range from 50% to 97.5% by volume of the first portion. In other words, a substantial amount (at least 10%) or even a major amount (at least 50%) of the article is removed during machining.
  • Article and component
  • The third aspect provides an article thermomechanically formed according to the first aspect or a component manufactured according to the second aspect, wherein a maximum prior β grain size in the α + β Ti alloy in the first portion of the article or the component is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
  • The maximum grain size may be as described with respect to the first aspect.
  • Definitions
  • Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of other components. The term "consisting essentially of" or "consists essentially of" means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like.
  • The term "consisting of" or "consists of" means including the components specified but excluding other components.
  • Whenever appropriate, depending upon the context, the use of the term "comprises" or "comprising" may also be taken to include the meaning "consists essentially of" or "consisting essentially of", and also may also be taken to include the meaning "consists of" or "consisting of".
  • The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.
  • Brief description of the drawings
  • For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which:
    • Figure 1 schematically depicts a continuous cooling transformation (CCT) curve for a Ti - 6AI - 4V α + β Ti alloy;
    • Figure 2 shows an optical micrography of a lamellar microstructure of a Ti - 6AI - 4V α + β Ti alloy;
    • Figure 3 schematically depicts a method of thermomechanically forming an α + β Ti alloy;
    • Figure 4 is a CAD drawing of an article according to an exemplary embodiment; and
    • Figure 5 schematically depicts an exemplary method of thermomechanically forming the article of Figure 4.
    Detailed Description of the Drawings
  • Figure 3 schematically depicts a method of thermomechanically forming an α + β Ti alloy. It should be understood that the exemplary method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof relates to at least the step of pre-form forging and optionally, to the steps of die forging and/or subsequent heat treatment.
  • Figure 4 is a CAD drawing of an article 10, particularly for machining into a rib for an aircraft (i.e. an aerospace component), according to an exemplary embodiment.
  • The article 10 was thermomechanically formed according to an exemplary embodiment, as described with respect to Figure 5, from a precursor 1 wherein the precursor 1 is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47". The article 10 has a length of about 96".
  • Figure 5 schematically depicts an exemplary method of thermomechanically forming the article 10 of Figure 4.
  • In more detail, Figure 5 compares a conventional method of thermomechanically forming a conventional article (labelled 'Current Process') and the exemplary method of thermomechanically forming the exemplary article 10 (labelled 'New Process').
  • The conventional method comprises:
    • providing a precursor, consisting of the α + β Ti alloy having a beta transus temperature βtransus, wherein the precursor defines the set of 12 portions (labelled 'Position 1 to 12') including a first portion (labelled 'Position 1); and
    • thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by the total true strain ε 1,total = 1.39;
    • wherein thermomechanically forming the article from the precursor comprises 2 iterations of:
      1. (a) heating the first portion to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus;
      2. (b) deforming the heated first portion 100A by a true strain ε 1,i , wherein the true strain ε 1,i is the total true strain ε 1,total = 1.39;
    • β annealing the thermomechanically formed article 10 at a temperature Tβ anneal during a time tβ anneal , wherein the temperature Tβ anneal is at least the beta transus temperature βtransus; and stabilization annealing the (β annealed) article 10 at a temperature Tstabilization anneal during a time tstabilization anneal , wherein the temperature Tstabilization anneal is less than the beta transus temperature βtransus;
    • wherein the α + β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof;
    • wherein deforming the heated first portion 100A by the total true strain ε 1,total comprises elongating the heated first portion 100A by a total elongation (δL/L) total, wherein the total elongation (δL/L) total is at least a predetermined threshold elongation (δL/L) threshold; wherein the predetermined threshold elongation (δL/L) threshold is about 1";
    • wherein providing the precursor 1 comprises providing the precursor 1 having a cross-sectional aspect ratio of 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and providing the precursor 1 having a longitudinal aspect ratio of about 8:1;
    • wherein the temperature Ti is in a range from β transus - 125°F to βtransus - 25°F;
    • wherein the time ti is about 3 hours wherein i is equal to 1.
  • In this particular example according to the conventional method, the precursor is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47", while the length of the article is about 96".
  • In the conventional method, 'Positions 1 to 12' are deformed during the 1st iteration (i.e. wherein i is equal to 1) while only 'Positions 8 to 12' are deformed during the 2nd iteration (i.e. wherein i is equal to 2).
  • In the 1st iteration (i.e. wherein i is equal to 1), the heated first portion 'Position 1' is deformed by a true strain ε 1,1 = 1.39 and the heated eleventh portion 'Position 11' is deformed by a true strain ε 11,1 = 0.17, by way of example.
  • In the 2nd iteration (i.e. wherein i is equal to 2), the heated first portion 'Position 1' is deformed by a true strain ε 1,2 = 0 and the heated eleventh portion 'Position 11' is deformed by a true strain ε 1,2 = 1.30.
  • The exemplary method is of thermomechanically forming by forging the article 10 from the precursor 1 (not shown) thereof, the method comprising:
    • providing the precursor 1, consisting of the α + β Ti alloy having a beta transus temperature βtransus, wherein the precursor 1 defines the set of 12 portions 100 (labelled 'Position 1 to 12') including a first portion 100A (labelled 'Position 1'); and
    • thermomechanically forming the article 10 from the precursor 1 by heating the first portion 100A and deforming the heated first portion 100A by the total true strain ε 1,total , wherein the total true strain ε 1,total is greater than the predetermined threshold true strain εthreshold;
    • wherein thermomechanically forming the article 10 from the precursor 1 comprises 2 iterations of:
      1. (a) heating the first portion 100A to the temperature Ti during the time ti , wherein the temperature Ti is at most the beta transus temperature βtransus;
      2. (b) deforming the heated first portion 100A by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold;
      3. (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulatíve = ∑ iε 1,i is the total true strain ε1,total , wherein i is 4;
    • thermomechanical processing the thermomechanically formed article 10, for example block and finish forging of the thermomechanically formed article 10;β annealing the thermomechanically formed article 10 at a temperature Tβ anneal during a time tβ anneal , wherein the temperature Tβ anneal is at least the beta transus temperature βtransus; and
    • stabilization annealing the (β annealed) article 10 at a temperature Tstabilization anneal during a time tstabilization anneal , wherein the temperature Tstabilinzation anneal is less than the beta transus temperature βtransus ;
    • wherein the α + β Ti alloy comprises and/or is AMS 6932 (AMS 6932, AMS 6932 Rev. A - C or later), LMA-M5004 (LMA-M5004, LMA-M5004 Rev. A - F or later) and/or an equivalent and/or a variant thereof;
    • wherein the predetermined threshold true strain εthreshold is 0.75 (i.e. 75%);
    • wherein deforming the heated first portion 100A by the total true strain ε 1,total comprises elongating the heated first portion 100A by a total elongation (δL/L) total, wherein the total elongation (δL/L) total is at least a predetermined threshold elongation (δL/L) threshold;
    • wherein the predetermined threshold elongation (δL/L) threshold is about 1";
    • wherein providing the precursor 1 comprises providing the precursor 1 having a cross-sectional aspect ratio of 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and providing the precursor 1 having a longitudinal aspect ratio of about 8:1;
    • wherein the temperature Ti is in a range from β transus - 125°F to βtransus - 25°F;
    • wherein the time ti is about 3 hours wherein i is equal to 1;
    • wherein the time ti is about 1 hour, wherein i is greater than or equal to 2; and
    • wherein a maximum prior β grain size of the a + β Ti alloy in the first portion 100A of the article 10 is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
  • In this particular example according to the exemplary method, the precursor 1 is a forging stock particularly a square bar, having a width of 6", a height of 6" and a length of 47", while the length of the article 10 is about 96".
  • In the exemplary method, 'Positions 1 to 12' are deformed during the 1st iteration (i.e. wherein i is equal to 1), ' Positions 1, 2 and 4' are deformed during the 2nd iteration (i.e. wherein i is equal to 2), 'Positions 8 to 12' are deformed during the 3rd iteration (i.e. wherein i is equal to 3) and 'Positions 8 and 11' are deformed during the 4th iteration (i.e. wherein i is equal to 4).
  • Particularly, in the 1st iteration (i.e. wherein i is equal to 1), the heated first portion 100A ('Position 1) is deformed by a true strain ε 1,1 = 0.75, wherein the true strain ε 1,1 is at most the predetermined threshold true strain εthreshold , and the heated eleventh portion 100K ('Position 11') is deformed by a true strain ε 11,1 = 0.17, wherein the true strain ε 11,1 is at most the predetermined threshold true strain εthreshold , wherein the predetermined threshold true strain εthreshold is 0.75 (i.e. 75%).
  • Particularly, in the 2nd iteration (i.e. wherein i is equal to 2), the heated first portion 100A ('Position 1') is deformed by a true strain ε 1,2 = 0.64, wherein the true strain ε 1,2 is at most the predetermined threshold true strain εthreshold , and the heated eleventh portion 100K ('Position 11') is deformed by a true strain ε 11,2 = 0, wherein the true strain ε 11,2 is at most the predetermined threshold true strain εthreshold , wherein the predetermined threshold true strain εthreshold is 0.75 (i.e. 75%).
  • Particularly, in the 3rd iteration (i.e. wherein i is equal to 3), the heated first portion 100A ('Position 1') is deformed by a true strain ε 1,3 = 0, wherein the true strain ε 1,3 is at most the predetermined threshold true strain εthreshold , and the heated eleventh portion 100K ('Position 11') is deformed by a true strain ε 11,3 = 0.58, wherein the true strain ε 11,3 is at most the predetermined threshold true strain εthreshold , wherein the predetermined threshold true strain εthreshold is 0.75 (i.e. 75%).
  • Particularly, in the 4th iteration (i.e. wherein i is equal to 4), the heated first portion 100A ('Position 1') is deformed by a true strain ε 1,4 = 0, wherein the true strain ε 1,4 is at most the predetermined threshold true strain εthreshold , and the heated eleventh portion 100K ('Position 11') is deformed by a true strain ε11,4 = 0.72, wherein the true strain ε 11,4 is at most the predetermined threshold true strain εthreshold , wherein the predetermined threshold true strain εthreshold is 0.75 (i.e. 75%).
  • That is, compared with the conventional method, the number of heating steps has been increased from 2 to 4 while the respective portions are deformed by at most the predetermined threshold true strain εthreshold of 0.75 (i.e. 75%).
  • While the yield for the conventional process was about 80%, due to disposal of components having relatively coarse prior β grain size, the yield for the exemplary process was improved to approaching 100%.
  • Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims and as described above.
  • Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
  • All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.
  • Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
  • The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (15)

  1. A method of thermomechanically forming, for example forging, rolling, extruding or drawing, an article from a precursor thereof, the method comprising:
    providing the precursor, for example an ingot, a forging stock, a forging, a bar, a billet or a plate, comprising, substantially comprising, essentially comprising and/or consisting of an α + β Ti alloy having a beta transus temperature βtransus , wherein the precursor defines a set of portions including a first portion; and
    thermomechanically forming the article from the precursor by heating the first portion and deforming the heated first portion by a total true strain ε 1,total , wherein the total true strain ε 1,total is greater than a predetermined threshold true strain εthreshold;
    wherein thermomechanically forming the article from the precursor comprises i iterations of:
    (a) heating the first portion to a temperature Ti during a time ti , wherein the temperature Ti is at most the beta transus temperature βtransus;
    (b) deforming the heated first portion by a true strain ε 1,i , wherein the true strain ε 1,i is at most the predetermined threshold true strain εthreshold; and
    (c) repeating steps (a) and (b) until the cumulative true strain ε 1,cumulatíve = ∑ iε 1,i is the total true strain ε1,total , wherein i is a natural number greater than or equal to 2.
  2. The method according to claim 1, wherein the predetermined threshold true strain εthreshold is in a range from 0.1 to 1, preferably in a range from 0.3 to 0.9, more preferably in a range from 0.5 to 0.85, most preferably in a range from 0.7 to 0.8, for example 0.75.
  3. The method according to any previous claim, wherein deforming the heated first portion by the total true strain ε 1,total comprises elongating the heated first portion by a total elongation (δL/L) total, wherein the total elongation (δL/L) total is at least a predetermined threshold elongation (δL/L) threshold.
  4. The method according to claim 3, wherein the predetermined threshold elongation (δL/ L) threshold is in a range from 0.1 to 10, preferably in a range from 0.25 to 5, more preferably in a range from 0.5 to 2.5, most preferably in a range from 0.75 to 1.25, for example 1.
  5. The method according to any previous claim, providing the precursor comprises providing the precursor having a cross-sectional aspect ratio in a range from 1:2 to 2:1, preferably in a range from 2:3 to 3:2, more preferably in a range from 3:4 to 4:3, for example about 1:1, wherein the cross-sectional aspect ratio is the ratio of a mutually-orthogonal cross-sectional dimensions, and/or providing the precursor having a longitudinal aspect ratio in a range from 1,000:1 to 1:1, preferably in a range from 100:1 to 4:3, more preferably in a range from 50:1 to 3:2, for example at least 2:1.
  6. The method according to any previous claim, wherein the temperature Ti is in a range from βtransus - 175°F to βtransus - 5°F, preferably in a range from βtransus - 150°F to βtransus - 15°F, more preferably in a range from βtransus - 125°F to βtransus - 25°F.
  7. The method according to any previous claim, wherein the time ti is in a range from 0.25 hours to 24 hours, preferably in a range from 0.5 hours to 12 hours, more preferably in a range from 1 hour to 8 hours, most preferably in a range from 2 hours to 6 hours wherein i is equal to 1.
  8. The method according to any previous claim, wherein the time ti is in a range from 0.25 hours to 4 hours, preferably in a range from 0.5 hours to 2 hours, more preferably in a range from 0.75 hours to 1.5 hours, for example 1 hour, wherein i is greater than or equal to 2.
  9. The method according to any previous claim, comprising β annealing the article at a temperature Tβ anneal during a time tβ anneal , wherein the temperature Tβ anneal is at least the beta transus temperature βtransus .
  10. The method according to any previous claim, comprising stabilization annealing the article at a temperature Tstabilization anneal during a time tstabitization anneal , wherein the temperature Tstabilization anneal is less than the beta transus temperature βtransus.
  11. The method according to any previous claim, wherein providing the precursor comprises vacuum arc melting, plasma arc melting and/or electron beam melting and/or vacuum arc remelting the α + β Ti alloy.
  12. A method of manufacturing a component, for example an aerospace component such as a spar or a longeron, comprising:
    thermomechanically forming an article according to any previous claim; and
    machining, for example milling, turning, boring or drilling, the first portion of the article, thereby providing, at least in part, the component.
  13. The method according to claim 12, comprising non-destructive testing of the (machined) component.
  14. The method according to any of claims 12 to 13, wherein machining comprises removing an amount of the first portion in a range from 10% to 99.5%, preferably in a range from 25% to 99%, more preferably in a range from 50% to 97.5% by volume of the first portion.
  15. An article thermomechanically formed according to any of claims 1 to 11 or a component manufactured according to any of claim 12 to 14, wherein a maximum prior β grain size of the α + β Ti alloy in the first portion of the article or the component is in a range from 10 µm to 25 mm, preferably in a range from 100 µm to 13 mm, more preferably in a range from 0.3 mm to 2.5 mm.
EP20275056.8A 2020-03-11 2020-03-11 Method of forming precursor into a ti alloy article Pending EP3878997A1 (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
EP20275056.8A EP3878997A1 (en) 2020-03-11 2020-03-11 Method of forming precursor into a ti alloy article
PL21711942.9T PL4118251T3 (en) 2020-03-11 2021-03-11 Method of forming precursor into a ti alloy article
AU2021235517A AU2021235517A1 (en) 2020-03-11 2021-03-11 Method of forming precursor into a Ti alloy article
PCT/GB2021/050608 WO2021181101A1 (en) 2020-03-11 2021-03-11 Method of forming precursor into a ti alloy article
EP21711942.9A EP4118251B1 (en) 2020-03-11 2021-03-11 Method of forming precursor into a ti alloy article
CA3173617A CA3173617A1 (en) 2020-03-11 2021-03-11 Method of forming precursor into a ti alloy article
US17/802,031 US20230106504A1 (en) 2020-03-11 2021-03-11 Method of forming precursor into a ti alloy article
GB2103367.5A GB2594573B (en) 2020-03-11 2021-03-11 Thermomechanical forming process

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP20275056.8A EP3878997A1 (en) 2020-03-11 2020-03-11 Method of forming precursor into a ti alloy article

Publications (1)

Publication Number Publication Date
EP3878997A1 true EP3878997A1 (en) 2021-09-15

Family

ID=70108124

Family Applications (1)

Application Number Title Priority Date Filing Date
EP20275056.8A Pending EP3878997A1 (en) 2020-03-11 2020-03-11 Method of forming precursor into a ti alloy article

Country Status (1)

Country Link
EP (1) EP3878997A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114042847A (en) * 2021-09-18 2022-02-15 中国航发北京航空材料研究院 Forging method for improving fracture toughness of TB6 titanium alloy

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2526215A2 (en) * 2010-01-22 2012-11-28 ATI Properties, Inc. Production of high strength titanium alloys
EP2596143A1 (en) * 2010-07-19 2013-05-29 ATI Properties, Inc. Processing of alpha/beta titanium alloys
US20160201165A1 (en) * 2015-01-12 2016-07-14 Ati Properties, Inc. Titanium alloy

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2526215A2 (en) * 2010-01-22 2012-11-28 ATI Properties, Inc. Production of high strength titanium alloys
EP2596143A1 (en) * 2010-07-19 2013-05-29 ATI Properties, Inc. Processing of alpha/beta titanium alloys
US20160201165A1 (en) * 2015-01-12 2016-07-14 Ati Properties, Inc. Titanium alloy
EP3245308A1 (en) * 2015-01-12 2017-11-22 ATI Properties LLC Titanium alloy

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114042847A (en) * 2021-09-18 2022-02-15 中国航发北京航空材料研究院 Forging method for improving fracture toughness of TB6 titanium alloy

Similar Documents

Publication Publication Date Title
EP2526215B1 (en) Production of high strength titanium alloys
CN108291277B (en) Processing of alpha-beta titanium alloys
JP6104164B2 (en) High strength and ductile alpha / beta titanium alloy
EP1761654B1 (en) Metastable beta-titanium alloys and methods of processing the same by direct aging
EP3791003B1 (en) High strength titanium alloys
EP3546606A1 (en) Â+ß TITANIUM ALLOY EXTRUDED MATERIAL
WO1998022629A2 (en) A new class of beta titanium-based alloys with high strength and good ductility
EP4118251B1 (en) Method of forming precursor into a ti alloy article
EP3878997A1 (en) Method of forming precursor into a ti alloy article
EP0411537B1 (en) Process for preparing titanium and titanium alloy materials having a fine equiaxed microstructure
EP0388830A1 (en) Process for production of titanium and titanium alloy materials having fine equiaxial microstructure
JP2023092454A (en) Titanium alloy, titanium alloy bar, titanium alloy plate, and engine valve
JPH07180011A (en) Production of alpha+beta type titanium alloy extruded material
EP4317497A1 (en) Material for the manufacture of high-strength fasteners and method for producing same
RU2793901C9 (en) Method for obtaining material for high-strength fasteners
RU2793901C1 (en) Method for obtaining material for high-strength fasteners
CN115627387A (en) High-strength TiZr-based alloy and preparation method thereof
AT526906A2 (en) Method for producing an object from an alpha-beta titanium alloy and object produced thereby

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION HAS BEEN PUBLISHED

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR