EP1561830B1 - Verfahren zur Herstellung von Produkten aus Titanium-Legierungen durch Druckgiessen - Google Patents

Verfahren zur Herstellung von Produkten aus Titanium-Legierungen durch Druckgiessen Download PDF

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Publication number
EP1561830B1
EP1561830B1 EP05009895A EP05009895A EP1561830B1 EP 1561830 B1 EP1561830 B1 EP 1561830B1 EP 05009895 A EP05009895 A EP 05009895A EP 05009895 A EP05009895 A EP 05009895A EP 1561830 B1 EP1561830 B1 EP 1561830B1
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Prior art keywords
die
articles
charge
titanium
ppm
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French (fr)
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EP1561830A1 (de
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John Joseph Schirra
Christopher Anthony Borg
David William Anderson
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Raytheon Technologies Corp
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United Technologies Corp
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Priority claimed from EP99972440A external-priority patent/EP1141427A4/de
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
    • B22D17/14—Machines with evacuated die cavity
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing 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
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/14—Form or construction
    • F01D5/147—Construction, i.e. structural features, e.g. of weight-saving hollow blades
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/20—Manufacture essentially without removing material
    • F05D2230/21—Manufacture essentially without removing material by casting
    • F05D2230/211—Manufacture essentially without removing material by casting by precision casting, e.g. microfusing or investment casting
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/20—Manufacture essentially without removing material
    • F05D2230/25—Manufacture essentially without removing material by forging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2300/00—Materials; Properties thereof
    • F05D2300/10—Metals, alloys or intermetallic compounds
    • F05D2300/13—Refractory metals, i.e. Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W
    • F05D2300/133—Titanium

Definitions

  • the present invention relates generally to a method of producing a die cast gas turbine engine component composed of titanium alloy.
  • Titanium and titanium alloys are employed in applications which require light weight and high strength-weight ratios. These alloys exhibit good corrosion resistance, and are generally useful up to relatively high temperatures, e.g., up to about 1200 °F/ 650 °C. Broadly, the term "titanium alloys" is intended to include alloys composed of at least about 25 at. % titanium.
  • titanium alloys are employed in the compressor section of the engine, including but not limited to airfoils such as blades and vanes, as well as structural components such as intermediate and compressor cases and compressor disks.
  • a titanium alloy widely utilized in gas turbine engines is Ti 6-4, which includes about 6 w/o (percent by weight) aluminum, about 4 w/o vanadium, balance generally titanium, and is used in environments up to about 600° F.
  • Ti-6-2-4-2 may be employed, and includes about 6 w/o Al, about 2 w/o Sn (tin), about 4 w/o Zr (zirconium) and about 2 w/o Mo (molybdenum), balance generally titanium.
  • Other titanium-base alloys may also be employed, such as Ti 8-1-1, which includes about 8 w/o Al, 1 w/o Mo and I w/o V (vanadium), balance generally titanium, as well as titanium aluminides which are broadly composed of titanium and aluminum in stoichiometric amounts such as TiAl and TiAl 3 .
  • these materials must at least be capable of being formed into relatively complex, three dimensional shapes such as airfoils, and must be oxidation resistant - particularly at elevated temperatures.
  • Titanium and titanium alloys have in the past typically been precision forged to produce parts having a fine average grain size and a balance of high strength, low weight and durability or high cycle fatigue resistance.
  • forging is a preferred method used to produce parts having complex, three-dimensional shapes such as blades and vanes. When properly produced, forged parts do exhibit a balance of high strength, low weight, and durability.
  • an ingot of material is converted into billet form, typically cylindrical for blades and vanes, and is then thermomechanically processed, such as by heating and stamping several times between dies and/or hammers that are shaped progressively similar to the desired shape, in order to plastically deform the material into the desired component shape.
  • the forging dies typically may be heated.
  • Each component is typically heat treated to obtain desired properties, e.g., hardening/strengthening, stress relief, resistance to crack growth and a particular level of HCF resistance, and is also finished, e.g., machined, chem-milled and/or media finished, if necessary to provide the component with the precise shape, dimensions and/or surface features.
  • Forging typically includes a series of operation, each requiring separate dies and associated equipment.
  • the post-forging finishing operations e.g., machining the root portion of a blade and providing the appropriate surface finish, comprise a significant portion of the overall cost of producing forged parts, and include a significant portion of parts which must be discarded.
  • Titanium alloys may also some springback, e.g., the material is resilient, and the springback must be taken into account during forging, i.e., the parts must typically be "over forged". As noted above, finished components may still require extensive post forging processing.
  • Forged components may contain forging imperfections that tend to be difficult to inspect. Moreover, precise reproducibility is also a concern - forging does not result in components having dimensions that are precisely the same from part to part. After inspection, many parts must still be re-worked. As a general rule, forged parts must be scrapped or significantly re-worked about 20 % of the time. Moreover, newer, more advanced titanium based alloys will be increasingly difficult (if not impossible) and correspondingly more expensive to forge. These concerns will only intensify as more complex three-dimensional airfoil geometries are employed.
  • Casting has been extensively used to produce relatively near-finished-shape articles.
  • Investment casting in which molten metal is poured into a ceramic shell having a cavity in the shape of the article to be cast, can be used to produce such articles.
  • investment casting produces extremely large grains, e.g., ASTM 1 or larger (relative to the small average grain size achievable by forging), and in some cases the entire part comprises a single grain.
  • ASTM 1 or larger relative to the small average grain size achievable by forging
  • this process is expensive. Reproducibility of very precise dimensions from part to part is difficult to achieve.
  • molten material is typically melted, poured and/or solidified in air or other gas, which can result in parts having undesirable properties such as inclusions and porosity, particularly for materials containing reactive elements such as titanium or aluminum.
  • Permanent mold casting in which molten material is poured into a multipart, reusable mold and flows into the mold under only the force of gravity, has also been used to cast parts generally. See, e.g., U.S. Pat. No. 5,505,246 to Colvin.
  • permanent mold casting has several drawbacks. For thin castings, such as airfoils, the force of gravity may be insufficient to urge the material into thinner sections, particularly so where high melting temperature materials and low superheats are employed, and accordingly the mold does not consistently fill and the parts must be scrapped. Dimensional tolerances must be relatively large, and require correspondingly more post casting work, and repeatably is difficult to achieve. Permanent mold casting also results in relatively poor surface finish, which also requires more post cast work.
  • a conventional die casting machine includes a shot sleeve mounted to one (typically fixed) platen of a multiple part die, e.g., a two part die including fixed and movable platens which cooperate to define a die cavity.
  • the shot sleeve is oriented horizontally, vertically or inclined between horizontal and vertical.
  • the sleeve communicates with a runner of the die, and includes an opening on the sleeve through which molten metal is poured.
  • a plunger is positioned for movement in the sleeve, and a driving mechanism moves the plunger and forces molten metal from the sleeve into the die.
  • the shot sleeve is typically oriented horizontally and is unheated. Casting usually occurs under atmospheric conditions, i.e., the equipment is not located in a non-reactive environment such as a vacuum chamber or inert atmosphere.
  • the plunger since the shot sleeve is unheated, a skin or "can" of molten metal solidifies on the inside of the shot sleeve, and in order to move the plunger through the sleeve to inject the molten metal into the die, the plunger must overcome the resistance of the solidified metal, scraping the skin off of the sleeve and thereby "crushing the can".
  • the can forms a structurally strong member, e.g., in the form of cylinder which is supported by the sleeve, the plunger and/or associated structure for moving the plunger can be damaged or destroyed due to the resistance to plunger motion.
  • high melting temperature materials such as titanium alloys and superalloys.
  • superalloys generally refer to those materials characterized by high strength and which maintain high strength at high temperatures. Such materials are also characterized by relatively high melting points.
  • Past attempts to die cast high melting temperature materials such as titanium alloys and superalloys has resulted in inoperable die casting machinery, as well as articles characterized by inferior qualities such as impurities, excessive porosity, and relatively poor strength and fatigue properties.
  • a method of producing a die cast titanium alloy article is disclosed.
  • the article for example an airfoil for a gas turbine engine, has a transformed beta microstructure and preferably also has a fine average grain size for a cast article, e.g., ASTM 1 or smaller, and an absence of flow lines.
  • Exemplary titanium alloys include Ti 6Al-4V (composition including about 4 - 8 w/o Al and 3 - 5 w/o V, balance generally titanium) or Ti 6Al-2Sn-4Zr-2Mo (composition including about 5.5 - 6.5 w/o Al, about 1.75 - 2.25 w/o Sn (tin), about 3.5 - 4.5 w/o Zr, about 1.8 - 2.2 w/o Mo, balance generally titanium).
  • Other titanium alloys have also been successfully die cast, such as Ti 8Al-1Mo-1V and titanium aluminides.
  • the articles have both yield and ultimate tensile strengths at both room and elevated temperatures that are at least comparable to forged parts composed of the same material, and also have similar fatigue properties.
  • the present invention is advantageous in it obviates any need to prepare specially tailored billets of material. Accordingly, the time required to produce a part, from ingot to finished part, is reduced significantly.
  • Die casting broadly can be performed in a single operation, as opposed to multiple forging operations. In die casting, multiple parts can be produced in a single casting. Die casting enables the production of parts having more complex, three dimensional shapes than forging, thereby enabling new software design technology to be applied to and exploited in areas such as gas turbine engines and enabling production of more aerodynamically efficient airfoils and other components. Die casting enables the production of such articles utilizing materials that are difficult or impossible to forge into such shapes. Die cast parts are produced nearer to their finished shape, and with a superior surface finish, thereby minimizing post forming finishing operations, and reducing the cost of producing such parts.
  • a die cast titanium alloy article obtained by a method in accordance with the present invention is indicated generally by the reference numeral 10.
  • the article is a compressor blade 10 for a gas turbine engine, and includes an airfoil 12, a platform 14, and a root 16.
  • Ti-6Al-4V Ti-6Al-4V
  • Ti 6-4 typically also includes some impurities, and by way of example may also include up to 0.5 w/o Fe, up to 0.25 w/o O, up to 0.20 w/o C, up to 0.1 w/o N, up to 0.02 w/o H, up to 0.01 w/o Y, up to 0.4 w/o other elements.
  • Ti 6Al-2Sn-4Zr-2Mo (“Ti 6-2-4-2”) is used, and broadly includes about 5 - 7 w/o Al, 1.5 - 2.5 w/o Sn (tin), 3.0- 5.0 w/o Zr, 1.5 - 2.5 w/o Mo.
  • Ti 6-2-4-2 typically also includes some impurities, and by way of example may also include 0.05 - 0.15 5 w% Si, up to 0.2 w/o Fe, up to 0.25 w/o O, up to 0.15 w/o Cu, up to 0.1 w/o N, up to 0.02 w/o H, up to 0.010 Y, up to 0.4 w/o other elements.
  • Ti alloys include Ti 8-1-1 and titanium aluminides, which are composed of stoichiometric amounts of titanium and aluminum.
  • Ti 8-1-1 broadly includes about 7-8.5 w/o Al, 0.5-1.5 w/o Mo and 0.5-1.5 w/o V, balance generally titanium.
  • Ti 8-1-1 typically also includes some impurities, and by way of example may also include up to 0.22 w/o Si, up to 0.4 w/o Fe, up to 0.15 w/o O, up to 0.1 w/o C, up to 0.25 w/o Sn, up to 0.15 w/o Cu, up to 750 ppm N, up to 200 ppm H, up to 50 ppm B, up to 75 ppm Y.
  • titanium aluminides are composed primarily of titanium and aluminum in stoichiometric amounts, having compositions such as TiAl and TiAl 3 .
  • Titanium aluminides are discussed for example in U.S. Pat. Nos. 4,294,615 and 4,292,077 both to Blackburn et al., which are hereby expressly incorporated by reference herein.
  • Articles prepared in accordance with the method of present invention are characterized by a stable, predominately transformed beta microstructure, in contrast to the alpha + beta microstructure typically produced in forged titanium articles to date. While investment cast articles also typically exhibit a transformed beta microstructure, such microstructure typically consists both of larger grains and coarser alpha/beta laths than die cast article obtained by the method of present invention.
  • the particular, preferred average grain size and maximum allowable grain size will depend upon the application and cross sectional thickness of the part, e.g., whether the article is intended for use in a gas turbine engine versus other application, rotating vs. non-rotating parts operating in lower temperature versus higher temperature environments.
  • the average grain size should be ASTM 1 or smaller, more preferably ASTM 3 or smaller.
  • the titanium alloy articles, such as blades and vanes, obtained by the method in accordance with the present invention are preferably characterized by an absence of flow lines.
  • the articles may be thermomechanically processed after casting, if desired.
  • the die cast articles may subsequently serve as pre-forms for use in a forging operation.
  • the die cast articles be cast to near net shape, so as to minimize post-casting work and associated expense performed on the articles.
  • the die cast articles may be processed to heat any residual casting porosity that may be present, such as by isostatic pressing operations such as hot isostatic pressing (HIP).
  • HIP hot isostatic pressing
  • Careful selection of HIP parameters, such as temperature, pressure and time is required to heal any porosity without altering the fine grain, transformed beta microstructure.
  • the temperature must be sufficiently high to enable closing of the porosity under pressure, e.g., to enable creep, but not so high as to enable recrystallization of the material, e.g., below the beta transus temperature of the titanium alloy.
  • the HIP temperature preferably should not exceed 1750° F/ 950 °C, and is more preferably between about 1550 - 1650 ° F/ 845 - 900 °C.
  • Ti 6-4 may also be annealed at about 1550 F in a non-reactive environment, preferably argon or vacuum, for at least two hours after HIP'ing.
  • the HIP temperature should not exceed 1850° F/ 1010 °C, and is more preferably between 1650 - 1750 ° F/ 9900 950 °C.
  • Ti 6-2-4-2 may be heat treated at about 1100 F/ 595 °C in a non-reactive environment, preferably argon or vacuum, for at least 8 hours Additional post cast processing may also be performed, such as chemical milling of the surface to remove surface contaminants, media processing to improve surface finish, and additional thermal cycles to achieve a particular balance of mechanical properties. Such additional processing will vary on factors such as alloy composition and desired properties.
  • Die cast articles composed of Ti 6-4 were prepared in accordance with the method of present invention, as discussed in more detail below.
  • the articles included compressor airfoils and test bars, and also included the above-post cast processing.
  • Exemplary microstructures of a test bar and of an airfoil arc illustrated in FIGS. 2 and 3.
  • the microstructure of a corresponding airfoil composed of forged Ti 6-4 is illustrated in FIG. 4.
  • results from the die cast articles were compared to results from specimens machined from corresponding forged articles, and the results are shown in FIGS. 5, 6, 7 and 8.
  • the die cast articles are characterized, at room temperature and at about 300° F/ 150 °C, by comparable 0.2% yield strengths, ultimate tensile strengths, elongation at failure and impact strengths.
  • Compressor airfoils composed of Ti 6-4 should have a 0.2% yield strength at room temperature of at least 100 ksi/ 700 MPa and more preferably at least 110 ksi/ 770 MPa and most preferably at least 125 ksi/ 875 MPa: and at yield strength at 300° F/ 150 °C of at least 90 ksi/ 630 MPa and more preferably 100 ksi/ 700 MPa and most preferably at least 105 ksi/ 735 MPa.
  • Such articles have a ultimate tensile strength at room temperature of at least 110 ksi/ 770 MPa and more preferably at least 125 ksi/ 875 MPa and most preferably at least 135 ksi/ 945 MPa; and an ultimate tensile strength at 300° F/ 150 °C of at least 100 ksi/ 700 MPa and more preferably 110 ksi/ 770 MPa and most preferably at least 120 ksi/ 840 MPa.
  • Elongation (in 4D) at failure at room temperature is preferably at least 10% and more preferably at least 15%; and at 300° F/ 150 °C is preferably at least preferably at least 13% and more preferably at least 15%.
  • Impact strength at room temperature is preferably at least 15 ft-Ibs/ 2. 1mg-m and more preferably at least 17 ft-lbs/2.35 kg-m; and at 300 F/150 °C is preferably at least 15 ft-lbs/ 2.1 kg-m and more preferably at least 22 ft-lbs/3.04 kg-m.
  • Such components have equivalent durability properties, such as fatigue strength, and particularly high cycle fatigue capability.
  • Fatigue tests also compared die cast Ti 6-4 and corresponding forged parts, and as indicated in FIGS. 7 and 8 the die cast articles exhibit smooth and notched fatigue lives comparable to forged articles.
  • the above values are at least comparable to corresponding forged articles in compliance with AMS 4928 (Rev. N, Apr. 1993).
  • Other relevant specifications include AMS 4967, 4965 and 4930, which are all incorporated by reference herein. Again, the specific required values will differ depending upon the particular use to which the articles are being put.
  • Die cast articles composed ofTi 6-2-4-2 were also prepared in accordance with the method of present invention, as discussed in more detail below.
  • the articles included compressor airfoils and test bars, and also included the above-post cast processing.
  • Exemplary microstructures of a test bar and of an airfoil are illustrated in FIGS. 9 and 10.
  • the microstructure of a corresponding airfoil composed of forged Ti 6-2-4-2 is illustrated in FIG. 11.
  • die cast articles composed of Ti 6-2-4-2 to be used as compressor airfoils have strength and impact properties at least equivalent to those exhibited by corresponding forged articles produced for this application.
  • Compressor airfoils composed of Ti 6-2-4-2 should have a yield strength at 900 F/480 °C of at least 55 ksi/ 385 MPa and more preferably 65 ksi/ 455 MPa and most preferably at least 72 ksi/ 504 MPa.
  • Such articles should have an ultimate tensile strength at 900 ° F/ 480 °C of at least 75 ksi/ 525 MPa and more preferably 85 ksi/ 595 MPa and most preferably at least 95 ksi/ 665 MPa.
  • Elongation (in 4D) at failure at 900 F/ 480 °C is preferably at least preferably at least 10% and more preferably at least 13%.
  • Such components must have equivalent durability properties, such as fatigue strength, and particularly high cycle fatigue capability.
  • Fatigue tests also compared die cast Ti 6-2-4-2 and corresponding forged parts, and as indicated in FIG. 12 the die cast articles exhibit properties comparable to forged articles. The above values are comparable to corresponding forged articles in compliance with AMS 4976 (Rev. E, July 1994); other relevant specifications include AMS 4975, which are all incorporated by reference herein.
  • die casting may be used to produce articles composed of a broad range of titanium alloy compositions.
  • articles have also been die cast from Ti 8-1-1.
  • Exemplary microstructure of die cast Ti 8-1-1 is illustrated in FIG. 13. Fatigue tests comparing die cast Ti 8-1-1 and corresponding forged parts are expected to indicate that the die cast articles exhibit comparable properties to forged articles.
  • the above values will differ depending upon the particular use to which the articles are being put.
  • the above values are comparable to corresponding forged articles in compliance with AMS 4973 (Rev. D, Oct. 1990); other relevant specifications include AMS 4972, which are all incorporated by reference herein.
  • FIGS. 14,15 and 16 we prefer to use a die casting machine (FIGS. 14-15) of the type having an unheated shot sleeve ("cold chamber") to produce articles in accordance with the present invention.
  • a die casting machine (FIGS. 14-15) of the type having an unheated shot sleeve ("cold chamber") to produce articles in accordance with the present invention.
  • a charge of material is prepared (FIG. 16, step 44), and the material to be die cast is melted (step 46 - FIG. 16) in the apparatus 18.
  • molten titanium is an aggressive material, and attacks the material in which it is melted.
  • ISR induction skull remelting or melting
  • material is melted in a crucible defined a plurality of metal (typically copper) fingers retained in position next to one another.
  • the crucible is surrounded by an induction coil coupled to a power source 26.
  • the fingers include passages for the circulation of cooling water from and to a water source (not shown), to prevent melting of the fingers.
  • the field generated by the coil heats and melts material located in the crucible.
  • the field also serves to agitate or stir the molten metal.
  • a thin layer of the material e.g., the titanium, freezes on the crucible wall and forms the skull, thereby minimizing the ability of molten titanium to attack the crucible.
  • any gasses in the melting environment may become entrapped in the molten material and result in excess porosity in die cast articles, we prefer to melt the material in a vacuum environment rather than in an inert environment, e.g., argon. More preferably the material is melted in a melt chamber 20 coupled to a vacuum source 22 in which the chamber is maintained at a pressure of less than 100 ⁇ m, preferably less than 50 ⁇ m.
  • the material may be melted in other manners, such as by vacuum induction melting (VIM) and electron beam melting, so long as the material being melted is not significantly contaminated.
  • VIM vacuum induction melting
  • any equipment used to transfer the molten material must typically be capable of withstanding high temperatures and be positioned in the vacuum chamber, and consequently the chamber must be relatively large. The additional equipment adds cost, and the correspondingly large vacuum chamber takes longer to evacuate thus affecting the cycle time.
  • the material Since some amount of time will necessarily elapse between material melting and injection of the molten material into the die, the material is melted with a limited superheat - high enough to ensure that the material remains at least substantially molten until it is injected, but low enough to ensure that rapid solidification occurs upon injection enabling formation of small grains and also to minimize the thermal load upon the die casting apparatus (particularly those portions of the apparatus which come into contact with the molten metal).
  • titanium alloys We have melted titanium alloys to a controlled, limited superheat, e.g., we have successfully used superheats within about 100° F to 200° F/ 37 - 95 °C above the melting temperature of the alloy and more preferably within about 50° F to 100° F/ 10 - 37 °C, preferably using a ceramic free melting system such as an inducto-skull melting unit.
  • the material is sufficiently superheated to ensure that it remains molten until injected into the mold, but the amount of superheat is low enough to enable rapid solidification of the molten material after injection.
  • Molten alloy is then transferred to a horizontal shot sleeve of the machine, which is preferably located in a vacuum environment and the molten material is injected under pressure into a reusable mold.
  • a horizontal shot sleeve of the machine which is preferably located in a vacuum environment and the molten material is injected under pressure into a reusable mold.
  • the crucible In order to transfer molten material from the crucible to a shot sleeve 30 of the apparatus (step 48 - FIG. 16), the crucible is mounted for translation (arrow 31 in FIG. 15), and also for pivotal movement (arrow 33 of FIG. 14) about a pouring axis, and in turn is mounted to a motor (not shown) for rotating the crucible to pour molten material from the crucible through a pour hole 32 of the shot sleeve 30. Translation of the crucible occurs between the melt chamber 20 in which material is melted and a position in a separate vacuum chamber 34 in which the shot sleeve is located.
  • the pour chamber 34 is also maintained as a non-reactive environment, preferably a vacuum environment with a pressure level less than 100 ⁇ m and more preferably less than 50 ⁇ m.
  • the melt chamber 20 and pour chamber 34 are separated by a gate valve or other suitable means (not shown) to minimize the loss of vacuum in the event that one chamber is exposed to atmosphere, e.g., to gain access to a component in the particular chamber.
  • a gate valve or other suitable means not shown
  • the illustrated embodiment includes separate melting and pouring chambers, it is also possible to perform melting and pouring in a single chamber. We prefer to use separate chambers in order to minimize the loss of vacuum environment in the event that a given component must be exposed to atmosphere, e.g., to service the melting unit or the shot sleeve or to remove a casting.
  • the molten material is transferred from the crucible 24 into the shot sleeve 30 through a pour hole 34.
  • the shot sleeve 30 is coupled to a multipart, reusable die 36, which defines a die cavity 38
  • a sufficient amount of molten material is poured into the shot sleeve to fill the die cavity, which may include one part or more than one part.
  • the illustrated die 36 includes two sections, 36a, 36b (but may include more sections), which cooperate to define the die cavity 38, for example in the form of a compressor blade or vane for a gas turbine engine.
  • the die 36 is also preferably coupled directly to the vacuum source and also through the shot sleeve, to enable evacuation of the die prior to injection of the molten metal.
  • the die may be located in a vacuum chamber, instead of or in addition to being coupled directly to a vacuum source.
  • One section of the two sections 36a, 36b of the die is typically fixed, while the other part is movable relative to the one section, for example by a hydraulic assembly (not shown).
  • the die preferably includes ejector pins (not shown) to facilitate ejecting solidified material from the die.
  • the die may also include a stripper mechanism (not shown) for removing casting material from the die while the material is still hot, to further reduce thermal loads on the die.
  • the die may be composed of various materials, and should have good thermal conductivity, and be relatively resistant to erosion and chemical attack from injection of the molten material.
  • a comprehensive list of possible materials would be quite large, and includes materials such as metals, ceramics, graphite, ceramic matrix composites and metal matrix composites.
  • Each of various die material has attributes, e.g., ease of machining, strength at elevated temperatures and compromises of the two, that makes it desirable for different applications.
  • For titanium we currently prefer to use dies composed of mild carbon steel, e.g., 1018, due to its low cost and ease of machining. Coatings and surface treatments may be employed to enhance apparatus performance and the quality of resulting parts.
  • the die may also be attached to a source of coolant such as water or a source of heat such as oil (not shown) to thermally manage the die temperature during operation.
  • a die lubricant may be applied to one or more selected parts of the die and the die casting apparatus. Any lubricant should generally improve the quality of resultant cast articles, and more specifically should be resistant to thermal breakdown, so as not to contaminate the material being injected.
  • Molten metal is then transferred from the crucible to the shot sleeve.
  • a sufficient amount of molten metal is poured into the shot sleeve to partially fill the sleeve, and subsequently to fill the die.
  • the sleeve is less than 50% filled, more preferably less than about 40% filled, and most preferably less than 30% filled.
  • An injection device such as a plunger 40 cooperates with the shot sleeve 30 and hydraulics or other suitable assembly (not shown) drive the plunger in the direction of arrow 42, to move the plunger between the position illustrated by the solid lines and the position indicated by dashed lines, and thereby inject the molten material under pressure from the sleeve 30 into the die cavity 38 (step 50 - FIG. 15).
  • the plunger and sleeve cooperate to define a volume that is substantially greater than the amount of molten material that will be injected.
  • the volume is at least twice the volume of material to be injected, more preferably at least three times.
  • the volume of molten material transferred from the crucible to the sleeve fills less than one half and most preferably less than about one third of the sleeve volume. Since the sleeve is only partially filled, any material or skin that solidifies on the sleeve forms only a partial cylinder, e.g., an open arcuate surface, and is easily scraped or crushed during metal injection, and reincorporated into the molten material.
  • plunger speeds of between about 30 inches per second (ips) and 300 ips (with a shot sleeve having an inner diameter of about 3 inches), and currently prefer to use a plunger speed of between about 50 - 175 inches per second (ips)/1.2 - 4.5 m/s.
  • the plunger is typically moved at a pressure of at least 1200 psi/8.4 MPa, and more preferably at least 1500 psi/ 10.5 MPa.
  • the plunger approaches the ends of its stroke when the die cavity is filled, it begins to transfer pressure to the metal. It may then be desirable to intensify the pressure to ensure complete filling of the mold cavity, the particular intensification parameters will depend upon the desired result.
  • Intensification is performed to minimize porosity, and to reduce or eliminate any material shrinkage during cooling. We have used intensification above 1500 psi/ 10.5 MPa with satisfactory results. After a sufficient period of time has elapsed to ensure solidification of the material in the die, the ejector pins (not shown) arc actuated to eject parts from the die (step 52 - FIG. 16).
  • cast articles typically include some porosity, generally up to a few percent. Accordingly, and particularly where such articles are used in more demanding applications, such as compressor airfoils for gas turbine engines, there is a need to reduce and preferably eliminate porosity and otherwise treated as needed (step 54 - FIG. 16).
  • the parts are therefore preferably hot isostatically pressed (HIP'd) as described above to reduce and substantially eliminate porosity in the as cast parts.
  • HIP HIP at a temperature of above about 1500 - 1600 F/ 815 - 870 °C (and below the beta transus temperature of about 1850 F/ 1010 °C where it is desired to maintain existing beta phase), at a pressure of at least 14 ksi/ 98 MPa, more preferably above 14.5 ksi/ 101.5 MPa, and for at least 2 hours.
  • the articles may then be heat treated.
  • the articles may be heated to a temperature of between about 1500-1600 F/ 815 - 870 °C in an inert environment, e.g., argon or vacuum, for at least 2 hours.
  • the articles are preferably heated to a temperature of between about 1000-1200 F, more preferably about 1100 F/ 590 °C in an inert environment, e.g., argon or vacuum, for at least 8 hours.
  • HIP parameters may be varied depending upon the desired application for the article and target cycle time for the process, however the temperature, pressure and time used during HIP must be sufficient to eliminate substantially all porosity in the cast articles, but not to allow significant grain growth and coarsening of any alpha and the beta phases in the transformed beta microstructure.
  • the parts are inspected (step 56 - FIG. 16) using conventional inspection techniques, e.g., by fluorescent penetrant inspection (FPI), radiographic, visual, and after passing inspection may be used or further treated/re-treated if necessary (step 58 - FIG. 16).
  • FPI fluorescent penetrant inspection
  • radiographic visual
  • after passing inspection may be used or further treated/re-treated if necessary (step 58 - FIG. 16).
  • the melting, pouring and injection of material must be performed in a non-reactive environment, and we prefer to perform these operations in a vacuum environment maintained at a pressure preferably less than 100 ⁇ m and more preferably less than 50 ⁇ m.
  • the amount of superheat should be sufficient to ensure that the material remains substantially and completely molten from the time it is poured until it is injected, but also to enable rapid cooling and formation of small grains once injected. Due to the relatively low superheat, molten metal transfer and injection must be rapid enough to occur prior to metal solidification.
  • the resulting microstructure such as grain size appears to correspond to the sectional thickness of the part being cast as well as the die materials utilized and the superheat used, i.e., thinner sections tend to include smaller grains and thicker sections (particularly internal portions of thicker sections) tend to include larger grains.
  • Higher thermal conductivity die materials result in articles having smaller grains, as does use of lower superheats. We believe that this results from relative cooling rates.
  • the rate at which the plunger is moved, and correspondingly the rate at which material is injected into the mold appears to affect the surface finish of the articles as cast, although the design of the gating as well as the die material may also play a role in combination with the injection rate.
  • Die casting provides other significant advantages over forging. From the standpoint of required equipment, forging requires the production of multiple dies to make a new part, at significant cost. In contrast, only a single die set is required per part, at significantly reduced expense relative to forging. The time required to produce a part, from ingot to finished part, is reduced significantly, since there is no need to prepare specially tailored billets of material, and casting broadly is performed in a single step, as opposed to multiple forging operations. In die casting, multiple parts can be produced in a single casting. Die casting enables production of parts having more complex three dimensional shapes, thereby enabling new software design technology to be applied to and exploited in areas such as gas turbine engines and enabling production of more efficient airfoils and other components.
  • die casting will enable the production of articles having complex shapes utilizing materials that are difficult or impossible to forge into those shapes.
  • die cast parts can be produced nearer to their finished shape, and with a superior surface finish, which minimizes post forming finishing operations, all of which also reduces the cost of producing such parts.

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Claims (12)

  1. Verfahren zur Herstellung eines druckgegossenen Gasturbinenmaschinen-Bauteils, das aus Titanlegierung besteht, folgende Schritte aufweisend:
    a) Vorbereiten einer Material-Charge;
    b) Schmelzen der Material-Charge unter Verwendung einer Induktions-Schalenschmelzeinheit, die unter einer Vakuumumgebung von weniger als 100 µm arbeitet, und Erhitzen der Material-Charge auf eine Überhitzung innerhalb von 50°F bis 100°F/27,7 bis 55,5°C;
    c) Giesen der geschmolzenen Material-Charge in einen nicht erwärmten horizontalen Schusskanal einer Druckgussmaschine unter der Vakuumumgebung, so dass das geschmolzene Material weniger als 50 % des Schusskanal-Volumens füllt; und
    d) Einspritzen des geschmolzenen Materials unter Druck in eine wiederverwendbare Form;
    wobei die Material-Charge ausgewählt wird aus:
    i) 4 bis 8 Gew.-% Al und 3 bis 5 Gew.-% V, bis zu 0,5 Gew.-% Fe bis zu 0,25 Gew.-% O, bis zu 0,20 Gew.- % C, bis zu 0,1 Gew.- % N, bis zu 0,02 Gew.- % H, bis zu 0,01 Gew.- % Y, Rest Titan und Verunreinigungen;
    ii) 5 bis 7 Gew.-%, Al, 1,5 bis 2,5 Gew.-% Sn, 3,0 bis 5,0 Gew.-% Zr und 1,5 bis 2,5 Gew.-% Mo, gewünschtenfalls 0,05 bis 0,15 Gew.-% Si, bis zu 0,2 Gew.-% Fe, bis zu 0,25 Gew.-% O, bis zu 0,15 Gew.-% Cu, bis zu 0,1 Gew.-% N, bis zu 0,02 Gew.-% H, bis zu 0,010 Y, Rest Titan und Verunreinigungen; oder
    iii) 7 bis 8,5 Gew.-% Al, 0,5 bis 1,5 Gew.-% Mo und 0,5 bis 1,5 Gew.-% V, bis zu 0,22 Gew.-% Si, bis zu 0,4 Gew.-% Fe, bis zu 0,15 Gew.-% O, bis zu 0,1 Gew.-% C, bis zu 0,25 Gew.-% Sn, bis zu 0,15 Gew.-% Cu, bis zu 750 ppm N, bis zu 200 ppm H, bis zu 50 ppm B, bis zu 75 ppm Y, Rest Titan und Verunreinigungen.
  2. Verfahren wie in Anspruch 1 beansprucht, bei dem das Volumen an geschmolzenem Material, das in den Schusskanal überführt wird, weniger als 40 % des Schusskanal-Volumens beträgt.
  3. Verfahren wie in Anspruch 2 beansprucht, bei dem das Volumen an geschmolzenem Material, das in den Schusskanal überführt wird, weniger als 30 % des Schusskanal-Volumens beträgt.
  4. Verfahren wie in Anspruch 1, 2 oder 3 beansprucht, bei dem der Prozess des Gießens und Einspritzens des geschmolzenen Materials in weniger als 2 Sekunden durchgeführt wird.
  5. Verfahren wie in Anspruch 4 beansprucht, bei dem der Prozess des Gießens und Einspritzens des geschmolzenen Materials in weniger als einer Sekunde durchgeführt wird.
  6. Verfahren wie in irgendeinem vorangehenden Anspruch beansprucht, bei dem die geschmolzene Charge mit einer Kolbengeschwindigkeit von 1,2 bis 4,5 m/s (50 bis 175 inch/s) in die Form eingespritzt wird.
  7. Verfahren wie in irgendeinem der Ansprüche 1 bis 6 beansprucht, bei dem die Material-Charge aus 5 bis 7 Gew.-% Al, 3,5 bis 4,5 Gew.-% V, bis zu 0,5 Gew.-% Fe, bis zu 0,25 Gew.-% O, bis zu 0,20 Gew.-% C, bis zu 0,1 Gew.-% N, bis zu 0,02 Gew:-% H, bis zu 0,01 Gew.-% Y, Rest Titan und Verunreinigungen besteht.
  8. Verfahren wie in irgendeinem der Ansprüche 1 bis 6 beansprucht, bei dem die Material-Charge aus 5,5 bis 6,5 Gew.-% Al, 1,75 bis 2,25 Gew.-% Sn, 3,5 bis 4,5 Gew.-% Zr, 1,8 bis 2,2 Gew.-% Mo, bis zu 0,2 Gew.-% Fe, bis zu 0,15 Gew.-% C, bis zu 0,25 Gew.-% O, bis zu 0,1 Gew.-% N, bis zu 0,02 Gew.-% H, und bis zu 0,01 Y, Rest Titan und Verunreinigungen besteht.
  9. Verfahren wie in irgendeinem der Ansprüche 1 bis 6 beansprucht, bei dem die Material-Charge aus 7,35 bis 8,35 Gew.-% Al, 0,75 bis 1,25 Gew.-% Mo und 0,75 bis 1,25 Gew.-% V, bis zu 0,15 Gew.-% Si, bis zu 0,4 Gew.-% Fe, bis zu 0,15 Gew.-% O, bis zu 0,1 Gew.-% C, bis zu 0,25 Gew.-% Sn, bis zu 0,15 Gew.-% Cu, bis zu 750 ppm N, bis zu 200 ppm h, bis zu 50 ppm, bis zu 75 ppm Y, Rest Titan und Verunreinigungen besteht.
  10. Verfahren wie in irgendeinem vorangehenden Anspruch beansprucht, bei dem die Vakuum-Umgebung weniger als 50 µm beträgt.
  11. Verfahren wie in irgendeinem vorangehenden Anspruch beansprucht, bei dem das Bauteil bei einer Temperatur über 1500°F/815°C und unter 1850°F/1010°C bei einem Druck von mindestens 14 ksi/98 MPa für mindestens zwei Stunden heißisostatisch gepresst wird.
  12. Verfahren wie in irgendeinem vorangehenden Anspruch beansprucht, bei dem mehr als ein Teil in einem einzigen Schuss gegossen wird.
EP05009895A 1998-12-23 1999-12-22 Verfahren zur Herstellung von Produkten aus Titanium-Legierungen durch Druckgiessen Expired - Lifetime EP1561830B1 (de)

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CN114000076B (zh) * 2021-11-04 2022-05-27 四川大学 一种初始凝固相为β相的多取向片层组织TiAl合金及其制备方法和应用

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US4482398A (en) * 1984-01-27 1984-11-13 The United States Of America As Represented By The Secretary Of The Air Force Method for refining microstructures of cast titanium articles
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