RU2681089C2 - Titanium-based alloy billet for elastic elements with energy-intensive structure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, in particular to functional billets of a titanium-based alloy, which have increased strength, elasticity and ductility. Billet for the production of elastic elements made of the titanium-based alloy, containing, wt. %: aluminum 1.2–4.5, molybdenum 3.5–6.5, vanadium 3.0–6.0, iron ≤ 0.5, carbon ≤ 0.3, hydrogen ≤ 0.03, oxygen ≤ 0.3, nitrogen ≤ 0.15, silicon ≤ 0.5, zirconium ≤ 1.0. In this case, the alloy has a uniform, fine microstructure with a grain size of (1–10) microns of orthorhombic martensite α^//, on the boundaries of which globular particles of primary α - phase are placed.

EFFECT: billet is characterized by a stable energy-intensive structure with a high value of tensile strength σ_B, maximum shear stresses on torsion τ in the temperature range of 20 °C to 350 °C.

3 cl, 2 dwg, 2 tbl

Description

The invention relates to the field of functional metal billets from an alloy based on titanium for the implementation of an energy-intensive structure with increased strength, elasticity and ductility. This blank is intended for use in aircraft, shipbuilding, automotive, oil and gas, nuclear energy and other industries for the manufacture of elastic elements of various types and purposes.

Elastic elements, on the one hand, as products, have a huge assortment, on the other hand, according to operating conditions, for each specific case, must have a set of properties that satisfy these conditions. From this point of view, for the release of elastic elements that are different from each other, it is necessary that the material of the elastic element have a certain set of necessary elastic properties, and a set of sufficient material properties that satisfy various operating conditions.

In the technical literature, it is proposed to evaluate the titanium alloy for the manufacture of elastic elements by the ratio of the elastic limit σ _0.002 , when the residual deformation is 0.002%, and the elastic modulus E - σ _0.002 / E. Moreover, the larger the value of this parameter, the greater the elasticity and energy intensity of the material. The choice of this parameter is justified by the fact that the alloy with such parameters has high strength and ductility and a relatively low modulus of elasticity. In order to have high elasticity, the alloy must have a high ratio of σ _0.2 / σ _B , while the ultimate strength σ _B must be maximum. The value of the ratio σ _0.002 / E, which is the basis for the choice of material for elastic elements, is justified in a number of works. The value of σ _0.002 / E should be maximum and not lower than 0.5 × 10 ² for steel materials (V. Fedorovich, "Maraging steel - material for elastic elements", Metallurgy and heat treatment, 1988. No. 10). The characteristic σ _0.002 / Е for high-strength titanium alloys should be not less than (0.73-0.8) ⋅10 ² . (Belogur VP, “Elastic elements from titanium alloys.” Springs. Scientific and Technical Journal, 2016, No. 1 p. 12-14.). However, it should be noted that obtaining the value of this parameter characterizing the elasticity and energy intensity of the alloy is difficult. In the spring during operation, the material is twisted. It is known that in high-strength materials, the greater the tensile strength of the alloy σ _B , the higher the maximum shear stress σ ₃ during torsion. The studies presented in these works show that the higher τ ₃ , the higher the energy intensity of the spring (τ ₃ ² / G or τ ₃ ² / ρG - energy intensity parameters). Here G is the shear modulus, MPa; ρ is the density, g / cm ³ , τ ₃ is the shear stress in the material at the highest spring loading, MPa; σ _B - ultimate strength, MPa. The efficiency of using titanium alloys in elastic elements is advisable at levels of tensile strength σ _{B of the} material of at least 1500 MPa, with a tensile strength of τ _{3 of} at least 900 MPa, with a ratio of σ _0.2 / σ _B , at least 0.9, where σ _0.2 - yield strength, MPa, σ _B - tensile strength, MPa. In addition, the energy intensity of the alloy should be more than 20 in the parameter τ ² / G, and more than 4.7 in the parameter τ ² / ρG, where τ is the largest shear stress, MPa, G is the shear modulus, MPa, ρ is the density, g / cm ³ .

Known alloy based on titanium, which contains wt. %:

Aluminum 3.0-4.2

Zirconium 2.0-3.0

Silicon 0.02-0.12

Iron 0.05-0.25

Oxygen 0.03-0.14

Nitrogen 0.01-0.04

Carbon 0.05-0.10

Hydrogen 0.001-0.006

Ruthenium 0.05-0.15,

Niobium 0.7-1.5

Vanadium 0.7-1.5,

Titanium is the rest.

(RF patent No. 2582171, IPC С22С 14/00 (2006.1), published on 08/20/2011).

The alloy is characterized by high characteristics of resistance against crevice, pitting and hot salt corrosion in aggressive salt-containing environments with pH> 2 and temperatures up to 250 ° C. A significant disadvantage of this alloy is its low strength. The parameter ultimate strength in this case does not exceed 730 MPa. An assessment of its strength properties shows that it is not suitable as a material for the manufacture of elastic elements.

Known heat-resistant alloy based on titanium and a product made of it, which contains wt. %:

Aluminum 10.5-12.5

Niobium 38.5-42.0

Molybdenum 0.5-1.5

Vanadium 0.5-1.5

Zirconium 1.0-2.5

Tungsten 0.3-1.0

Tantalum 0.3-1.0

Silicon 0.1-0.25

Gadolinium 0.02-0.6

Titanium and impurities - the rest

(RF patent No. 2592657, IPC С22С 14/00 (2006.1), published on July 27, 2016).

A titanium-based alloy is used to manufacture a wide range of deformed semi-finished products and parts that can be used in power structures of aviation and space technology, power plants, rockets, long-term operating at temperatures up to 700 ° C. It has a low value of tensile strength, not exceeding 1190 MPa. Assessment of its strength properties shows that it is of little use as a material for the manufacture of elastic elements.

Known alloy of titanium with good corrosion resistance and high mechanical strength at elevated temperatures, containing wt. %:

Aluminum from 4.5 to 7.5;

Tin from 2.0 to 8.0;

Niobium from 1.5 to 6.5;

Molybdenum from 0.1 to 2.5;

Silicon from 0.1 to 0.6;

Titanium - the rest

(RF patent No. 2583221, IPC С22С 14/00 (2006.1), published on 05/10/2016).

According to the data provided, this titanium alloy provides good corrosion resistance at high temperatures, up to 750 ° C. The main disadvantage of this alloy is the insufficiently high strength at room temperature. Strength less than 1220 MPa. Evaluation of its strength properties shows that as a material for the manufacture of elastic elements, it is of little use.

Known alloy based on titanium, which contains wt. %:

Aluminum 1.5-3.5

Molybdenum 4.5-8.0

Vanadium 1.0-3.5,

Iron 1.5-3.8

Titanium - the rest

(RF patent No. 2211873, IPC С22С 14/00 (2006.1), published on 09/10/2003).

This metastable β-titanium alloy has a regulated optimal combination of β- and α-stabilizing alloying elements, which, after heat treatment, provide a relatively high level of strength and plastic characteristics, it can be used for the manufacture of parts for general purposes. Alloy with good ductility, has a relative elongation of δ = 20.2 and a tensile strength of 1250 MPa, which is not enough for the manufacture of elastic elements. The alloy has a high ratio of parameters σ _0.2 / σ _B = 0.95. With this ratio of parameters, the alloy could well be suitable for the manufacture of elastic elements. However, this alloy should not be used for this application. This is primarily due to the insufficient tensile strength, as well as the fact that this alloy is prone to the formation of refractory inclusions due to the high molybdenum content up to 8.0% and to the formation of dendritic or zonal segregation due to the high iron content (3.8 wt. %). The presence of such inhomogeneities and defects reduces the energy intensity of the alloy. The stored high energy of the alloy, in the presence of structural heterogeneities in the structure of the alloy, is quickly consumed, the reliability of the products is not high, which ultimately leads to the rapid destruction of the elastic element.

Known alloy used in the production of elastic elements of various types and purposes containing: aluminum, vanadium, molybdenum, chromium, zirconium, iron, oxygen, additionally contains tungsten in the following ratio of components, wt. %:

Aluminum 2.0-6.5,

Vanadium 3.0-6.0

Molybdenum 4.0-6.5

Chrome 1.8-7.0

Zirconium 0.55-2.5

Iron 0.03-0.45

Tungsten 0.001-0.095

Oxygen 0.02-0.2

The rest of titanium, while the product is made of an alloy based on titanium, is made of an alloy of this composition. (Patent RU No. 2356976, application: 2007121098 dated 06.06.2007, IPC С22С 14/00).

The alloy has high technological plasticity in terms of the minimum bending radius parameter expressed in sheet thicknesses. This alloy is alloyed with a complex of α-stabilizing elements (Al, O ₂ ), β-stabilizing elements (Mo, V, Cr, Fe, W) and neutral hardeners (Zr), which ensures effective hardening of α- and β-solid solutions and participation them in the process of loading.

The disadvantages of this alloy include many β-stabilizing elements and their ambiguous effect on the stability of mechanical properties at temperatures (300-350) ° C and low energy intensity of the alloy. The low tensile strength of 1190 MPa, with a high ratio of σ _0.2 / σ _B = 0.95.

The prototype of the proposed invention is an alloy based on titanium containing aluminum, molybdenum, vanadium, characterized in that, in order to increase the mechanical properties, it additionally contains silicon and hydrogen in the following ratio of components, wt. %:

Aluminum 1.2-3.8

Molybdenum 5.1-6.5

Vanadium 4.0-6.5

Silicon 0.01-0.05

Hydrogen 0.005-0.015

Titanium rest

(Patent RU No. 1584408, application No. 4434156 dated 04/12/1988, IPC С22С 14/00).

From the data presented in the technical solution, an alloy based on titanium provides good riveting, increased ductility during fractional deformation during rivet upsetting. The disadvantage of this alloy is its low tensile strength, not exceeding 900 MPa.

The objective of the proposed technical solution is to increase the safety and reliability of the elastic elements made of prefabricated alloys based on titanium, to increase the life of the elastic elements.

In the process of solving this problem, a technical result is achieved, which consists in increasing the strength and energy intensity of a titanium-based alloy billet determined by the parameters τ ² / G, τ ² / ρG, ratio σ _0.2 / σ _B , torsional strength, tensile strength in the temperature range from 20 ° C to 350 ° C, where σ _0.2 is the yield strength, MPa, σ _B is the tensile strength, MPa.

The specified technical result is achieved by the workpiece for the manufacture of elastic elements from an alloy based on titanium containing aluminum; molybdenum; vanadium; iron; carbon; hydrogen; oxygen; nitrogen; silicon; zirconium; titanium else, characterized in that it has the following ratio of components, wt. %:

Aluminum 1.2-4.5

Molybdenum 3.5-6.5

Vanadium 3.0-6.0

Iron ≤0.5

Carbon ≤0.3

Hydrogen ≤0.03

Oxygen ≤0.3

Nitrogen ≤0.15

Silicon ≤0.5

Zirconium ≤1.0

has a uniform, finely dispersed microstructure with a grain size (1-10) microns of orthorhombic martensitic α //, at the borders of which globular particles of the primary α - phase are located. In addition, the energy intensity of the workpiece in the parameter τ ² / G is more than 20, and the parameter τ ² / pG is more than 4.7, where τ is the largest shear stress, MPa, G is the shear modulus, MPa, ρ is the density, g / cm ³ , the tensile strength of the workpiece is not less than 900 MPa, the tensile strength is not less than 1500 MPa, with a ratio of σ _0.2 / σ _B , not less than 0.9, where σ _0.2 is the yield strength, MPa, σ _B - ultimate strength, MPa.

The authors of this technical solution carried out studies of various blanks, and also analyzed the available literature data, it was found that the ratio of the parameter σ _0.2 / σ _{B is} not less than 0.9 with a tensile strength σ _B not lower than 1500 MPa can serve as an estimated characteristic elastic properties and energy intensity of a titanium-based alloy billet when choosing a billet for manufacturing elastic elements. This technical solution proposes to evaluate the energy intensity of a titanium-based alloy billet and its suitability for use as a material for manufacturing elastic elements by a set of parameters: energy intensity parameters (τ ² / G or τ ² / ρG), torsional strength, parameter ratios σ _0.2 / σ _B and tensile strength. This assessment allows us to more correctly evaluate the energy intensity characteristic of the material after heat treatment of the titanium alloy.

The energy intensity of a titanium-based alloy billet, as well as its fatigue strength, depend on the specific composition of the chemical elements. The indicated parameters for the energy intensity of a titanium-based alloy preform are satisfied by alloys having a uniform, finely dispersed microstructure with grain sizes of 1-10 μm martensitic type with smaller substructural components at the periphery with the presence of globular particles of the primary α phase along the boundaries of individual grains, mainly from orthorhombic martensite α ''.

The proposed method is implemented on a billet of an alloy that relates to high strength α + β - martensitic type titanium alloys. The alloy contains a significant amount of β-stabilizing elements, and due to its heterophase, it can undergo effective hardening heat treatment. Two-phase α + β - alloys are very sensitive to observing the technological parameters of thermal hardening, in particular, to the cooling rate after annealing and aging.

The authors found that in order to realize high strength and ductility of the alloy, it is necessary to ensure the optimum content of α stabilizing alloying elements, such as aluminum, oxygen, carbon, nitrogen, and β stabilizing alloying elements, such as molybdenum, vanadium, and iron. The claimed aluminum content in the alloy provides high strength, as well as the ability to change the strength and plastic properties due to heat treatment. When the aluminum content is lower than the value specified in the alloy, the strength of the alloy decreases. Alloying with aluminum above the maximum value specified in the alloy leads to a decrease in the ductility of the alloy

Alloying the alloy with vanadium and molybdenum after heat treatment leads to the achievement of the required strength (σ _B ≥1500 MPa). When the content of vanadium and molybdenum is lower than the minimum declared value, the tensile strength of the alloy after heat treatment does not reach the declared value. An increase in the percentage of vanadium and molybdenum above 6.0% and 6.5%, respectively, leads to the formation of refractory inclusions in the smelting of ingots, which leads to heterogeneity of the alloy and the occurrence of defects. Since an increase in the concentration of vanadium and molybdenum above 6.5% is not desirable for a further increase in the β phase in the alloy, iron is added to the alloy. Iron is added in moderation (up to 0.5%), this amount does not lead to the formation of dendritic or zonal segregation.

The claimed content in the zirconium alloy stabilizes the α phase and also provides increased strength. An increase in the concentration of zirconium above 1.0% leads to a decrease in the ductility of the alloy during cold deformation, therefore, exceeding this value is undesirable.

The invention is as follows.

To obtain an energy-intensive preform from a titanium-based alloy having a uniform, finely dispersed microstructure with a grain size (1-10) microns of an orthorhombic martensitic α //, at the boundaries of which globular particles of the primary α-phase are located, with the energy intensity of the preform in the parameter τ ² / G more than 20, in the parameter τ ² / ρG more than 4.7, where τ is the largest shear stress, MPa, G is the shear modulus, MPa, ρ is the density, g / cm ³ and has a tensile strength of at least 900 MPa, tensile strength not less than 1500 MPa, pr and the ratio σ _0.2 / σ _B , not less than 0.9, where σ _0.2 is the yield strength, MPa, σ _B is the tensile strength, MPa, ingots with a diameter of 450 mm, with different chemical contents, were obtained by the triple vacuum arc remelting method elements, after which they grind to 420 mm; heated to a temperature of 960 ° C in a gas furnace and forged to a diameter of 115 mm The resulting preform was machined to remove the alpha layer.

The chemical composition of the ingots is presented in table. one.

Thermomechanical processing of the workpieces was carried out as follows. Before hot extrusion, the preforms were coated with a colloidal graphite preparation of the NPK grade, dried. The preforms were heated in the PN-15 furnace to a temperature of (960 ± 20) ° С and a holding time of (90-120) min. Several blanks were prepared. Hot billets were squeezed into water at a degree of deformation of (90-95)%. Next, each bar was machined to the required diameter in order to further conduct cold deformation. For example, in order to ultimately obtain a wire with a diameter of ∅14.5 mm, with a degree of cold deformation of 73%, a workpiece with a diameter of ∅28.1 mm was taken. This preform was obtained by turning from an extruded rod of 31.5 mm. After that, cold deformation was carried out with a degree of deformation of (23-73)%, then aging was carried out at a temperature of (390-490) ° C for 2-8 hours.

The physicomechanical properties of the workpieces were determined. Heat treatment was carried out in a laboratory resistance furnace SNOL 12/16. Microstructural studies of the workpieces were performed using an electron microscope. The research results are presented in FIG. 1. X-ray phase analysis of the composition of the preform was carried out when shooting a monolithic sample on a DRON-3 diffractometer with monochromatic CuK _α radiation. The research results are presented in FIG. 2.

Studies of tensile and torsional mechanical properties were carried out on a MI-40KU universal torsion-tensile testing machine combined with a PC. Samples for torsion tests were made with a length of 150 mm, in the form of a cylindrical rod, full-size, without grooves in the working part.

The research results are presented in table 2.

Due to the energy-intensive, strength, fatigue properties achieved, the workpiece can be used to manufacture elastic elements (springs, torsion bars, clamps, membranes, etc.). These properties of the titanium alloy workpiece in the proposed technical solution are achieved through strict control over the chemical composition of the alloy. In particular, aluminum, molybdenum, vanadium, zirconium should be controlled within the specified range to obtain a good combination of properties. Impurities of oxygen, nitrogen, should be kept at a very low level.

Thus, the use of the proposed blank allows to increase the manufacturability of the manufacture of products, to improve the quality and, consequently, the reliability of the elastic elements.

Claims (15)

1. A workpiece for the manufacture of elastic elements from an alloy based on titanium containing aluminum, molybdenum, vanadium, iron and titanium, characterized in that the alloy additionally contains carbon, hydrogen, oxygen, nitrogen, silicon and zirconium, in the following ratio of components, wt. %: Aluminum 1.2-4.5 Molybdenum 3.5-6.5 Vanadium 3.0-6.0 Iron ≤0.5 Carbon ≤0.3 Hydrogen ≤0.03 Oxygen ≤0.3 Nitrogen ≤0.15 Silicon ≤0.5 Zirconium ≤1.0, Titanium - the rest, and has a uniform, finely dispersed microstructure with a grain size (1-10) microns of orthorhombic martensite α ^// , at the boundaries of which globular particles of the primary α-phase are located. 2. The workpiece according to claim 1, characterized in that the energy intensity of the workpiece in the parameter τ ² / G is more than 20, and in the parameter τ ² / pG - more than 4.7, where τ is the largest tangential stress, MPa, G is the elastic modulus at shear, MPa, ρ - density, g / cm ³ . 3. The workpiece according to claim 1, characterized in that the tensile strength is not less than 900 MPa, the tensile strength is not less than 1500 MPa with a ratio of σ _0.2 / σ _B not less than 0.9, where σ _{0, 2} - yield strength, MPa, σ _B - tensile strength, MPa.

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