KR102221443B1 - An improved method for finishing extruded titanium products - Google Patents

Abstract

The present disclosure is to produce an extruded approximate work piece, cool the extruded approximate work piece to a cooled temperature below the beta transus temperature, and then roll the extruded approximate work piece at least once at a rolling temperature to have the desired properties. It relates to a method of finishing an extruded approximate workpiece by creating a final shaped workpiece.

Description

An improved method for finishing extruded titanium products

Titanium alloys are known for their low density (60% of the steel density) and their high strength. In addition, the titanium alloy may have excellent corrosion resistance. Pure titanium has an alpha (hcp) crystal structure at room temperature.

Broadly, this patent application relates to an improved process for forming shaped titanium workpieces through a process that combines hot extrusion and one or more rolling steps. The novel shaped workpiece can realize improved properties (eg, improved strength, improved isotropy) compared to conventional titanium materials.

In one embodiment, a method of producing a titanium alloy workpiece comprises: (a) heating a cast ingot or wrought billet of titanium alloy to a temperature above its beta transus temperature to produce a heated workpiece; (b) initiating extrusion of the heated work piece while the heated work piece is above the beta transus temperature to produce an extruded approximate work piece, (c) placing the extruded approximate work piece in a cooled state below the beta transus temperature. Cooling to a temperature, and (d) rolling the extruded approximate work piece at least once at a rolling temperature to produce a final shaped work piece, wherein the rolling temperature is below the initial melting temperature of the alloy And the beta transus temperature is within 600°F (333°C). In some embodiments, the titanium alloy is an alpha-beta alloy, such as Ti-6Al-4V. In some embodiments, heat treatment, such as annealing (eg, stress relief annealing) and/or heat treatment, may be used before or after any extrusion and/or rolling step to facilitate the creation of the final shape of the workpiece.

In some embodiments, the method may further comprise protecting the surface of the heated workpiece with a protective agent after heating step (a) and before initiating rolling step (b). The protective agent may be a lubricant or a release agent, and in some embodiments, the protective agent may be removed prior to the rolling step (d).

In some embodiments of the cooling step (c), the cooled temperature may be room temperature. In some embodiments, the method may further comprise cleaning/preparing the approximate workpiece after cooling step (c) and prior to rolling step (d) to remove any protective agents.

In some embodiments, the rolling step (d) is 0.1 s ^-1 to 100 It may further include the step of rolling at a strain rate of s ^-1. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 1% to 95% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 10% to 90% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 20% to 85% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 30% to 80% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 40% to 75% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 50% to 70% to achieve a final shaped workpiece. In some embodiments, the rolling step may include uniformly reducing the approximate workpiece by a relative reduction of 55% to 65% to achieve a final shaped workpiece.

In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 1% to 95% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 10% to 90% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 20% to 85% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 30% to 80% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 40% to 75% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may comprise reducing the first section of the approximate workpiece by a relative reduction of 50% to 70% to achieve a final shaped workpiece with the first section reduced. In some embodiments, the rolling step may include reducing the first section of the approximate workpiece by a relative reduction of 55% to 65% to achieve a final shaped workpiece with the first section reduced.

In some embodiments, the rolling step reduces at least a second section of the approximate workpiece (different from the first section) by a relative reduction of 1% to 95%, resulting in a reduction in at least the first and second sections. It may further comprise the step of achieving the shaped workpiece. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 10% to 90% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 20% to 85% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 30% to 80% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 40% to 75% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 50% to 70% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include. In some embodiments, the rolling step further comprises reducing at least a second section of the approximate workpiece by a relative reduction of 55% to 65% to achieve a final shaped workpiece with at least the first and second sections reduced. Can include.

In some embodiments, the rolling temperature can be a temperature above the beta transus temperature and below the initial melting temperature. In some embodiments, the rolling temperature may be above the beta transus temperature and within 500° F. (278° C.) of the beta transus temperature. In some embodiments, the rolling temperature may be above the beta transus temperature and within 250° F. (139° C.) of the beta transus temperature. In some embodiments, the rolling temperature may be above the beta transus temperature and within 100° F. (55.6° C.) of the beta transus temperature. In some embodiments, the rolling temperature may be above the beta transus temperature and within 50° F. (27.8° C.) of the beta transus temperature. In another embodiment, the rolling temperature may be a temperature below the beta transus temperature and within 600° F. (333° C.) of the beta transus temperature. In some embodiments, the rolling temperature may be a temperature below the beta transus temperature and within 300° F. (167° C.) of the beta transus temperature. In some embodiments, the rolling temperature may be a temperature below the beta transus temperature and within 100° F. (55.6° C.) of the beta transus temperature. In some embodiments, the rolling temperature can be a temperature below the beta transus temperature and within 50° F. (27.8° C.) of the beta transus temperature. In some embodiments, the rolling temperature is a temperature above 600° F. (333° C.) below the beta transus temperature, and the rolling step (d) is each to prevent the development of cracks or internal metallurgical defects in the final shape workpiece. It further comprises a step of limiting the reduction per pass of the rolling step of the.

The novel process described herein can produce final shaped workpieces with improved properties. In one approach, the new final shape of the workpiece realizes at least 3% higher strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body, wherein the referenced titanium alloy body is It has the same composition as the workpiece and is in the same temper as the final shape workpiece, but in the form of a sheet, strip or plate (eg according to AMS 4911, § 3.3.1-3.3.2) depending on the thickness of the final shape workpiece. The final shape workpiece and the referenced titanium alloy body should have the same final thickness within acceptable commercial tolerances (eg AMS 2242). In order to produce a reference-version titanium alloy body within the same temper, generally the same thermal history is provided to both the final shape workpiece and the referenced titanium alloy body.

In one embodiment, the new final shape of the workpiece realizes at least 5% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body. In one embodiment, the novel final shape of the workpiece realizes at least 7% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body. In one embodiment, the novel final shape of the workpiece realizes at least 9% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body. In one embodiment, the new final shape workpiece realizes at least 11% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body. In one embodiment, the new final shape workpiece realizes at least 12% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body. In one embodiment, the novel final shape of the workpiece realizes at least 13% higher tensile yield strength (TYS and/or UTS) (L) compared to the referenced titanium alloy body.

In one embodiment, the novel final shape of the workpiece realizes at least 5% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body. In one embodiment, the new final shape workpiece realizes at least 7% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body. In one embodiment, the novel final shape of the workpiece realizes at least 9% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body. In one embodiment, the new final shape workpiece realizes at least 11% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body. In one embodiment, the new final shape workpiece realizes at least 12% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body. In one embodiment, the new final shape of the workpiece realizes at least 13% higher tensile yield strength (TYS and/or UTS) (LT) compared to the referenced titanium alloy body.

In one embodiment, the new final shape work piece realizes isotropic, wherein the tensile yield strength (TYS) in the LT direction is within the tensile yield strength (TYS) of 10 ksi in the L direction. In one embodiment, the TYS(LT) is within 8 ksi of TYS(L). In one embodiment, the TYS(LT) is within 7 ksi of TYS(L). In one embodiment, the TYS(LT) is within 6 ksi of TYS(L). In one embodiment, the TYS(LT) is within 5 ksi of TYS(L). In one embodiment, the TYS(LT) is within 4 ksi of TYS(L). In one embodiment, the TYS(LT) is within 3 ksi of TYS(L). Similar isotropic properties can also be realized for ultimate tensile strength (UTS).

In one approach, the new final shape of the workpiece can also realize good ductility. In one embodiment, the new final shape of the workpiece realizes an elongation (L) of at least 6%. In one embodiment, the new final shape of the workpiece realizes an elongation (LT) of at least 6%. In one embodiment, the new final shape of the workpiece realizes an elongation (L) of at least 8%. In one embodiment, the new final shape of the workpiece realizes an elongation (LT) of at least 8%. In one embodiment, the new final shape of the workpiece realizes an elongation (L) of at least 10%. In one embodiment, the new final shape of the workpiece realizes an elongation (LT) of at least 10%. In one embodiment, the new final shape of the workpiece realizes an elongation (L) of at least 12%. In one embodiment, the new final shape of the workpiece realizes an elongation (LT) of at least 12%. Any of the above stretching can be realized in both the L and LT directions.

The novel processes described herein can provide improved properties to final shaped workpieces, which can be applied in a variety of product applications. In one embodiment, the titanium alloy product can be used in aerospace structural applications. For example, the titanium alloy product may be formed of various components for use in the aerospace industry, such as floor beams, seat rails, and fuselage frames, among others. Among other things, many potential benefits can be realized in these components due to improved tensile properties, improved bearings, and improved resistance to the initiation and growth of fatigue cracks. An improved combination of these properties can, for example, lead to improved reliability. The titanium alloy workpiece may also be useful in marine, automotive, and/or defense applications, for example.

As described above, the approximate workpiece can be produced through an extrusion process. In other embodiments, the approximate workpiece may be a forged product, shape cast product, or additionally manufactured product instead of an extruded product. However, the process techniques and parameters described herein still apply to the approximate workpieces made from forged products, shape cast products, or additionally manufactured products.

Justice

Titanium alloys are classified into five categories: alpha, near-alpha, beta, near-beta, and alpha-beta alloys according to their microstructure and chemical properties. “Alpha” or “alpha phase” refers to a hexagonal dense (hcp) crystal structure. “Beta” or “beta phase” refers to a body centered cubic (bcc) crystal structure. "Alpha alloy" is a titanium alloy that is essentially free of beta phases and cannot be strengthened by heat treatment. "Beta alloy" is a titanium alloy that maintains a beta phase upon initial cooling to room temperature, which can be heat treated and have high hardenability. An "approximate-beta alloy" is a titanium alloy that starts with a beta alloy, but can partially return to some alpha phase when heated or cooled. A "near-alpha alloy" is a titanium alloy that forms some limited beta phase upon heating, but appears microstructurally similar to the alpha alloy. “Alpha-beta alloy” is a titanium alloy consisting of an alpha phase and a partially retained beta phase, and the amount of retained beta phase depends on the composition of the alloy and/or the presence of beta stabilizers (eg, V, Mo, Cr, Cu). Dependent, the amount of beta phase is greater than that found in the near-alpha alloy. Alpha-beta alloys can be strengthened by heat treatment (eg, solution heat treatment) and/or aging.

Alpha-beta titanium alloys can be classified into grades based on the composition of the alloy as determined by ASTM B348 (e.g., titanium alloys with grade 5 (about 6% Al and 4% V, including Ti-6Al-4V). ), grade 6 (including titanium alloys with about 5% Al and 2.5% Sn), and grade 9 (including titanium alloys with about 3% Al and 2.5% V)). Alpha-beta titanium alloys can also be classified directly by their chemical composition (e.g., Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-Al-2Sn-4Zr-6Mo, Ti-6Al, among others. -2Mo-2Cr, and Ti-6Al-2Sn-4Zr-2Mo).

As used herein, "Ti-6Al-4V" is from about 5.5% by weight Al to about 6.75% by weight Al, from about 3.5% by weight V to about 4.5% by weight V, up to 0.40% by weight Fe, up to 0.2% by weight O , Up to 0.015% by weight H, up to 0.05% by weight N, up to 0.40% by weight other impurities, and the balance refers to a grade 5 alpha-beta titanium alloy comprising Ti. As can be seen, similar specifications exist for other titanium grades.

"Beta transus" is defined as the lowest equilibrium temperature at which the material is 100% beta phase. As shown in Fig. 9, under the beta transus, the titanium alloy may be a mixture of alpha and beta phases depending on the composition of the alloy. Figure 9 is [Tamirisakandala, S., RB Bhat, and BV Vedam. "Recent advances in the deformation processing of titanium alloys." Journal of Materials Engineering and Performance 12.6 (2003): 661-673.

As used herein, “cast ingot” means an ingot formed from a molten titanium alloy, wherein the alloy may be melted one or more times during formation of the cast ingot.

As used herein, "processed billet" means a billet of titanium alloy formed from a cast ingot of a titanium alloy that has been worked before or during formation of the billet (eg, by forging, rolling, or pilger).

As used herein, “extruded” or “extruded” means a process for producing an extruded titanium alloy workpiece using direct or indirect extrusion. "Direct extrusion" or "directly extruded" refers to a process used to produce an extruded titanium alloy workpiece by pushing a cast ingot or machined billet of titanium alloy through a stationary die having the desired cross-section or shape. it means. In contrast, "indirectly extruded" or "indirectly extruded" is used to create an extruded titanium alloy workpiece by pushing a die having a desired cross-section or shape through a fixed cast ingot or machined billet of titanium alloy. I mean fair.

As used herein, “approximate workpiece” means an extruded titanium alloy workpiece, the shape of which is sufficient to achieve the final shape workpiece (e.g., the shape of the final product Provided to). In some embodiments, the one or more rolling steps may reduce the physical properties of the approximate workpiece so that the change in physical characteristics from the approximate to final shaped workpiece can be expressed by the following equation: NNSWP(z) x ( 1-RR(%)) = FSWP(z). NNSWP(z) represents the value of the physical measurement z of the approximate workpiece (e.g., z can be volume, width, or thickness), and RR (%) represents the percent reduction achieved in the physical measurement by rolling. Means, and FSWP(z) means the physical measurement value of the final shape work piece. In some embodiments, the one or more rolling steps may be sufficient to achieve a relative reduction in the thickness of the approximate workpiece, where "relative reduction" is the thickness of the approximate workpiece after one or more rolling steps using the following equation: Is defined as the change after dividing by the thickness before one or more rolling steps: R = (h1-h2)/h1, where R is the relative decrease, h1 is the measure of the thickness before rolling, and h2 is the thickness after rolling. It's a measure. In other words, the relative reduction relates to the total reduction in material thickness irrespective of the number of rolling passes required to achieve the relative reduction. Typically, each rolling pass reduces the thickness of the material to 25% or less. In some embodiments, the relative reduction may be non-uniform, meaning that the relative reduction may vary for different features or portions of the approximate workpiece depending on the configuration of the rolling step, or only a portion of the approximate workpiece may be reduced. do. Alternatively, the relative reduction can be uniform across the entire workpiece, meaning that the thickness reduction is the same across the entire workpiece. Relative reduction (R) may mean a reduction in the thickness of at least a portion of the approximate workpiece by 1% to 95%, such as any relative reduction described above. As a non-limiting example, the approximate workpiece has an initial thickness after extrusion of 0.255 inches (6.48 mm) over the entire c-channel shaped workpiece, and a final thickness after one or more rolling steps of 0.055 inches (1.40 mm), and It may be an approximate c-channel shaped workpiece (like Fig. 4c) with a relative reduction of 78%.

As used herein, “rolling” refers to a metal forming process (step) in which an extruded titanium alloy product is passed through one or more rolls of a roller arrangement to reduce the volume or thickness of the product. As shown in FIG. 8, the roller arrangement 800 comprises a number of rolls 801, 802, 803 in which the rollers may be arranged to reduce the thickness in one or more dimensions of the extruded titanium alloy product. Can include. Figure 8 is [Tamirisakandala, S., RB Bhat, and BV Vedam. "Recent advances in the deformation processing of titanium alloys." Journal of Materials Engineering and Performance 12.6 (2003): 661-673.

As used herein, “final shaped workpiece” means an extruded and rolled titanium workpiece having a desired volume or thickness and suitable for its intended end-use purpose. In some embodiments, the final shaped workpiece may be further finished through mechanical or surface treatment. Some non-limiting examples of some final shape workpieces include final shape pi-box final shape C channels. As used herein, "pi-box" means a material having a cross section generally similar to the Greek letter pi (π).

As used herein, “stress relief annealing” refers to a heat treatment process that relieves stress in a product at relatively low temperatures.

As used herein, “heat treatment” refers to a heat treatment process that heats a material to an elevated temperature to change the properties of the material. Some non-limiting examples of heat treatments useful in accordance with the methods described herein include mill annealing, approximate beta transus annealing, recrystallization annealing, solution heat treatment, and artificial aging, among others.

1 to 3 are flow charts describing an embodiment of a method for producing a titanium alloy workpiece.
4A-4C show a C-channel shaped workpiece produced by the method according to the present disclosure.
5A-5C show a T-bracket-shaped work piece produced by the method according to the present disclosure.
6A-6C show an L-bracket-shaped workpiece with a uniform relative reduction and non-uniform thickness, produced by the method according to the present disclosure.
7A to 7C show an L-bracket-shaped work piece with a non-uniform thickness and a non-uniform relative reduction, produced by the method according to the present disclosure.
8 shows an embodiment of a rolling mill setup with three roll sets.
9 shows a map of the microstructure deformation mechanism for Ti-6Al-4V alloy.
10A and 10B are graphs showing the relationship between room temperature strength and ductility as a cooling function from the beta transus region.
11A and 11B show the yield strength between workpieces processed at various strain rates and temperatures above (11a) and below (11b) the beta transus temperature.
12A and 12B show the ultimate strength between workpieces processed at various strain rates and temperatures above (12a) and below (12b) the beta transus temperature.
13A and 13B show material elongation between workpieces processed at various strain rates and temperatures above (13a) and below (13b) the beta transus temperature.
14A and 14B show the reduction of the area between workpieces processed at various strain rates and temperatures above (14a) and below (14b) the beta transus temperature.
15 shows a micrograph of the material of Example 2 under extrusion and rolling conditions in the longitudinal direction (L) and in the long transverse direction (T).
16 shows the fatigue crack propagation speed of the material of Example 2.

It will now be described in detail with reference to the accompanying drawings which are at least helpful in describing various related embodiments of the novel technology provided by the present disclosure.

1-3 are flow charts of various embodiments of a method for producing a titanium workpiece according to the present disclosure. The work piece can be of any shape that can be extruded from a titanium alloy. For example, in some embodiments, the workpiece can be a C-channel bracket, T bracket, H or I shape, or L bracket. The method includes a first step 10 of heating the titanium alloy above its beta transus temperature to produce a heated workpiece. In some embodiments, the titanium alloy can be an alpha alloy, beta alloy, or alpha-beta alloy. In some embodiments, the alpha-beta alloy can be Ti-6Al-4V. In some embodiments, the titanium alloy comprises a cast ingot or machined billet.

In some embodiments, the method may further comprise, after the heating step 10, a protective step, wherein the surface of the heated workpiece is coated with a protective agent to protect the surface from damage that may occur during extrusion. do. In some embodiments, the protective agent may include a lubricant (eg, graphite, glass, molten salt (eg, molten alkali metal salt)), and/or a release agent, such as a ceramic material (eg, ceramic powder).

The method further comprises extruding the heated workpiece 20 to produce an extruded approximate workpiece. In some embodiments, the extrusion step 20 may include direct extrusion. Alternatively, the extrusion step 20 may comprise indirect extrusion. In some embodiments, the extruding step 20 may include extruding the heated workpiece at a temperature above the beta transus temperature of the alloy. In other embodiments, the extrusion step 20 may include initiating extrusion at a temperature above the beta transus temperature of the alloy, wherein at least a portion of the extrusion step 20 is below the beta transus temperature of the alloy. It can be carried out at a temperature of.

The method further comprises cooling (30) the approximate workpiece to a temperature below its beta transus temperature. In some embodiments, cooling step 34 includes cooling to a temperature within the beta transus of the alloy of 600° F. (333° C.). In some embodiments, cooling 30 is at a temperature within the beta transus of the alloy of 500° F. (278° C.). In some embodiments, cooling 30 is at a temperature within the beta transus of the alloy of 400° F. (222° C.). In some embodiments, cooling 30 is at a temperature within the beta transus of the alloy of 300° F. (167° C.). In some embodiments, cooling 30 is at a temperature within the beta transus of the alloy of 200° F. (111° C.). In some embodiments, cooling 30 is at a temperature within the beta transus of the alloy of 100° F. (55.6° C.). In some embodiments, cooling 30 is at a temperature below the beta transus of the alloy above 600° F. (333° C.). In some embodiments, as shown in FIGS. 2 and 3, the cooling step 31 may include cooling the approximate workpiece to any temperature below the beta transus of the alloy, in some embodiments, The temperature may be room temperature.

In some embodiments, the method further comprises, after the cooling step, a cleaning/preparing step, wherein the approximate workpiece is prepared for rolling by removing any residual protective agent through the cleaning/preparing step. In some embodiments, the cleaning and/or preparation step may include sandblasting some or all of the workpiece for conditions to remove protective agent residues (eg, residual lubricant or release agent) and adhere the surface. Dry powder or wet suspension can be applied to the surface. Excess powder or suspension can be removed via mechanical or high-speed air means, leaving a thin film of protective agent.

Referring to Figure 1, the method further includes one or more rolling steps 40, wherein the rolling step comprises the step of rolling the extruded approximate work piece at least once at a rolling temperature to produce a final shaped work piece. Include. In some embodiments, the rolling temperature is the same temperature for each of the one or more rolling steps. In some embodiments, the rolling temperature may be different for each of the one or more rolling steps. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 600° F. (333° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 500° F. (278° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 400° F. (222° C.) of the beta transus temperature. In some embodiments, the rolling temperature is a temperature below the initial melting temperature of the alloy and within 300° F. (167° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 250°F (139°C) of the beta transus temperature. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 100° F. (55.6° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the initial melting temperature of the alloy and within 50° F. (27.8° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 600° F. (333° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 500° F. (278° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 400° F. (222° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 300° F. (167° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 250° F. (139° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 100° F. (55.6° C.) of the beta transus temperature. In some embodiments, the rolling temperature is below the beta transus temperature and within 50° F. (27.8° C.) of the beta transus temperature.

In some embodiments, one or more rolling steps 40 are performed on one or more sides of the approximate workpiece to produce a final shaped workpiece having a relative reduction of 1% to 95% in one or more sides or portions compared to the approximate workpiece. And reducing the portion. In some embodiments, only one section of the approximate workpiece can be reduced. In some embodiments, one or more sections of the approximate workpiece may be reduced. In some embodiments, the total relative reduction can be between 1% and 95%. In some embodiments, the relative reduction may be 90% or less of the total relative reduction. In some embodiments, the relative reduction may be 85% or less of the total relative reduction. In some embodiments, the relative reduction can be 80% or less of the total relative reduction. In some embodiments, the relative reduction may be 75% or less of the total relative reduction. In some embodiments, the relative reduction can be no more than 70% of the total relative reduction. In some embodiments, the relative reduction may be 65% or less of the total relative reduction. In some embodiments, the relative reduction can be at least 1% of the total relative reduction. In some embodiments, the relative reduction can be at least 10% of the total relative reduction. In some embodiments, the relative reduction can be at least 20% of the total relative reduction. In some embodiments, the relative reduction can be at least 30% of the total relative reduction. In some embodiments, the relative reduction can be at least 40% of the total relative reduction. In some embodiments, the relative reduction can be at least 50% of the total relative reduction. In some embodiments, the relative reduction can be at least 55% of the total relative reduction.

In some embodiments, the rolling is 0.1 s ^-1 to 100 It may further include rolling at a strain rate of s ^−1. In some embodiments, the rate of deformation is 1 s ^-1 to 100 It can be a speed of ^{s -1.} In some embodiments, the rate of deformation may be a ^{rate of 1 s -1} to 50 s ^-1. In some embodiments, the rate of deformation is 1 s ^-1 to 10 It can be a speed of ^{s -1.}

In some embodiments, as can be seen in FIGS. 4A-4C, the relative reduction can be uniform, where all portions of the final shaped workpiece have a uniform relative reduction. 4A shows an extruded C-channel bracket prior to one or more rolling steps 40. Fig. 4b shows a final shape workpiece with a uniform relative reduction compared to an approximate workpiece (see Fig. 4c comparing the two shapes).

In some embodiments, referring to FIGS. 4A-4C and FIGS. 5A-5C, the relative reduction can be uniform, and the absolute measure of one or more sides of the final shaped workpiece can be the same across the entire final shaped workpiece ( For example, the thickness or volume may be the same over the entire final shaped workpiece). 5A shows an extruded T bracket prior to one or more rolling steps 40. Figure 5b has a uniform relative reduction compared to the approximate workpiece (see Figure 5c comparing the two shapes), and also the first section 501 has the same thickness as the second section 502 Shows the final shaped workpiece with a uniform absolute measure of thickness across all parts of the shaped workpiece.

In some embodiments, referring to FIGS. 6A-6C, the relative reduction can be uniform across the final shape workpiece, but the absolute measurements of one or more sides can be different (e.g., the percent reduction in thickness is the total final shape. It may be the same across the workpiece, but the absolute thickness from part to part of the final shape workpiece may be different). 6A shows an extruded L bracket prior to one or more rolling steps 40. Figure 6b has a uniform relative reduction compared to the approximate workpiece (see Figure 6c comparing the two shapes), but since the first section 601 has a different thickness than the second section 602, the final shape of the workpiece Shows the final shape workpiece with non-uniform thickness across the part.

In some embodiments, referring to FIGS. 7A-7C, the relative reduction and absolute measurements may be non-uniform across the final shaped workpiece. 7a shows the extruded L bracket before the rolling step 40. Fig. 7b has a non-uniform relative reduction compared to the approximate workpiece (see Fig. 7c comparing the two shapes), and the first section 701 has a different thickness than the second section 702 so that the final shape of the workpiece Shows the final shape workpiece with non-uniform thickness across the part.

Referring back to Figure 2, the method may further include a step of reheating (32) the approximate workpiece after the cooling step (31), wherein the step of reheating (32) is an alloy of the extruded approximate workpiece And reheating to a reheated temperature below the initial melting temperature of and within its beta transus of 600° F. (333° C.). In some embodiments, the reheated temperature is a temperature below the initial melting temperature of the alloy and within its beta transus of 500° F. (278° C.). In some embodiments, the reheated temperature is a temperature below the initial melting temperature of the alloy and within its beta transus of 400° F. (222° C.). In some embodiments, the reheated temperature is a temperature below the initial melting temperature of the alloy and within its beta transus of 300° F. (167° C.). In some embodiments, the reheated temperature is a temperature below the initial melting temperature of the alloy and within its beta transus of 200° F. (111° C.). In some embodiments, the reheated temperature is a temperature below the initial melting temperature of the alloy and within its beta transus of 100° F. (55.6° C.).

In some embodiments, after each rolling step of one or more rolling steps 40, the approximate workpiece may be reheated 32 so that a subsequent rolling step may be performed at the reheated temperature. In some embodiments, the approximate workpiece may alternatively be cooled (31) and reheated (32) between each rolling step of one or more rolling steps (40). In some embodiments, the one or more rolling steps 40 may all comprise a rolling temperature of greater than 600° F. (333° C.) below the beta transus, wherein each of the one or more rolling steps 40 It may further comprise limiting the relative reduction for each rolling step to prevent the development of cracks or internal metallurgical defects. In some embodiments, various adjustments to the time (e.g., longer time) and/or temperature (e.g., higher temperature) of reheating are used to relieve residual stress, allow dislocation motion, and relax crystallographic texture. Can be adjusted. This can ensure that adequate ductility can be maintained to withstand deformation at lower temperatures.

In some embodiments, referring to FIG. 3, the reheating step 33 may include heating the extruded approximate workpiece to a temperature above the beta transus temperature and below its initial melting temperature, wherein the reheating step (33) may be followed after one or more rolling steps 41 performed at a temperature above the beta transus temperature of the alloy. In some embodiments, the approximate workpiece may be reheated 33 if its temperature drops below the beta transus temperature of the alloy during any given rolling step of one or more rolling steps 41. In some embodiments, the method further comprises one or more other rolling steps 42, which may be carried out below the beta transus temperature of the alloy.

Example One

Four Ti-6Al-4V samples were produced by the extrusion process and processed through four different manufacturing routes. The selected material had a mil measured beta transus (BT) of about 1810° F. (988° C.). Two temperatures were selected for the treatment: BT+50°F (28°C) (1860°F (1016°C)) and BT-10°F (5.6°C) (1800°F (982°C)). The temperature above the beta transus (BT) was limited above the beta transus at 50° F. (28° C.) to limit grain growth during heating. By selecting the temperature below the beta transus as an attempt to keep the product in the work window, the spheronization type transition was expected to end at 1775°F (968°C). Below 1775° F. (968° C.) temperatures, the product can still break into a working structure, but this conversion was expected to be dominated by lamellae kinking.

The treatment speed of rolling reduction was selected as a high and low speed showing a deformation ^{rate of 10 s -1} and 2.5 s ^-1. Exit velocity of 20-30 inches/sec (50.8-76.2 cm/sec) for high speed and 5-6 inches/sec (12.7-15.2 cm/sec) for low speed.

The extruded sample was heated in a radiant heat furnace that had already been preheated to the desired temperature. The sample was suspended in the furnace and a track was added in the furnace to fit the inlet of the roller. The cold product was mounted on the track and sealed into the furnace for 8 minutes. According to the calculation, the product is at a temperature within 1-3 minutes, but the additional time was used to ensure that the furnace had time to homogenize after opening and to provide some factor of safety against heating non-uniformities. After 8 minutes, the product was pushed along the track towards the roller set-up using a rigid arm. Upon entering the roll bite, the product was pulled through by the spinning wheel. At the end of the channel, a guide structure was placed to center the two of the product entering the wheel and prevent the possibility of the advancing arm reaching the wheel.

The furnace was placed right next to the rolling mill. The product was exposed to ambient air at a distance of 15 inches (38 cm) until the roll bite started. This provides a vehicle for cooling the product, especially when it approaches 0.100 inches (2.54 mm) thick in the final pass.

The four pieces were heated and passed four times to reduce equal spacing in an extrusion of 0.205 to 0.100 inches (5.21 to 2.54 mm) thick. Each fin of the product was of the same thickness, but could be different. After each pass, the parts were placed in a tray to cool the air.

The rolling mill (shown in Fig. 8) was different from the conventional 2 or 4 height rolling mill. In this case, the rollers were arranged to provide contact pressure on the main (largest) surface of the product, and were independently advanced to create a gap between the different rollers. Roller designs of this type can be modified to produce channels, H, L, T, and various other structural members. In the case of small rollers and certain shapes, interference with the bearing housing begins to occur. In many cases interference can be mitigated by placing the bearings inside the wheel and only the power sprocket on the side. It also creates a more rigid structure to apply the load. Using a larger wheel can also provide more space and increase the likelihood of reduction per pass.

After processing the samples, after light annealing was performed on all samples, the pieces were heated to 1325° F. (718° C.) (+/-25° F. (14° C.)) and held for 1 hour. The parts were then removed and the air cooled. This light annealing is primarily aimed at removing most of the built-up dislocations in the crystal and not altering the resulting microstructure.

In some cases, the glass is applied to the sample piece to evaluate how well it performs as a lubricant or protective agent in the rolling process. It was observed that it was built up in front of the roller until it passed as a large glue. In all cases where glass was used, this type of defect occurred. In the glass pool press-in area, the previous roughness was maintained while the incompressible liquid filled the surface profile. The same effect may also occur when an excess of dry lubricant (graphite, molybdenum disulfide, and/or hexagonal boron nitride) is applied to the roller. Large quantities of these materials (versus thin films) can behave like fluids and produce results similar to liquid glass. The best surface can be lightly powdered titanium dioxide on a piece with some dry lubricant on the rollers or no additional roller lubricant.

A less common method for secondary high temperature operation of alpha/beta titanium alloys is beta machining. In this way, the work takes place above the beta transus temperature. This leads to a needle-like alpha phase or a Witmanstaton microstructure. The lamellar microstructure leads to higher fracture toughness, fatigue crack propagation resistance and creep resistance. A slight debit occurs in strength and ductility. The main benefits of beta high temperature operations including beta forging and beta extrusion are reduced flow stress and improved die or feature fill. Titanium extrusion is performed predominantly above the beta transition temperature, increasing the formability of titanium despite an increase in grain size. The cooling rate from above the beta transus after recrystallization has an important influence on the formation of the Witman Staten microstructure. During this cooling, the alpha grains form into a platelet/basketweave pattern within the previous beta grains. The faster cooling rate reduces the thickness of the grain boundary alpha phase and creates a finely deformed microstructure within the previous grain as possible. This helps to preserve the sub-transus high temperature workability later. This also affects the room temperature characteristics as can be seen in FIGS. 10A and 10B. Figures 10a and 10b are [Sieniawski, J., Ziaja, W., Kubiak, K. and Motyka, M., 2013. Microstructure and mechanical properties of high strength two-phase titanium alloys. Titanium Alloys-Advances in Properties Control , pp.69-80].

Optimal cooling rates exist when the material crosses the beta transus for Ti-6Al-4V. Ideally, a cooling rate of 4 to 9° C. per second is desirable to achieve optimum ductility while still achieving high strength. Exceeding 9° C. per second may lead to the formation of thinner alpha lamellas and may increase strength but decrease ductility. Cooling faster than 18° C. per second results in the formation of martensite. This further reduces the ductility with a slight increase in strength.

Processing on Beta Transus

Two samples were processed on the beta transus for each reduction pass. The expression of the material properties in relation to the amount of reduction shows how the properties change through the various rolling passes. The strength trends for the two samples at various stages after the extrusion rolling process are shown in FIG. 11A. Looking at the yield and ultimate strength graphs in Fig. 12A, the strength increases under both treatment conditions, but the pieces with lower strain rates show significantly higher yield and ultimate strength improvements. Some level of texturing is also observed in the test results. As can be seen in Figures 13A and 14A, a general reduction in both elongation and reduction in area was observed in all cases. The slower processed samples showed significantly lower elongation than the faster processed pieces. Working above the recrystallization temperature suggests that the cooling rate is the most fundamental cause. Observing the microstructure can explain some of the observed behavior.

The microstructure of the extruded material is characteristic of what is seen in extrusion. The standard way of air cooling of significantly thicker products produces air cooling rates of 2 to 7° C. per second and higher levels of ductility from the Witman Staten microstructure. Extruded products typically require water cooling to achieve martensite in Ti-6Al-4V. The microstructure after four passes showed a larger beta crystal grain than (a) and (b) a partially martensite structure compared to the unidirectional bundle of extrusion. Without being bound by any theory, this may be due to the rapid cooling of the thin section by both radiative and conduction losses for the roller.

The conduction cooling effect may explain why the effect is greater in the slowly processed pieces than in the case of longer contact times. Loss of ductility is undesirable in aerospace structures, but can be managed through warmer rolls, higher set temperatures, improved management of the environment leading to and from the roll bite. The heated outlet region slows down cooling during initial cooling to form the desired microstructure. Mixing (processing steps below beta transus and above beta transus) can produce the best combination of properties of the beta worked material.

Processing under beta transus

When assigning work under the beta transus, textures can arise in the material. Texture is what gives direction within a material and occurs when working in one main direction. When producing strips that can see a large amount of work in one direction, alloys with higher cooling workability, such as commercially pure grades, are used, or beta annealing is performed after hot work and between cold work passes to relieve directionality. It is possible to produce. After hot rolling of the strip before annealing, the transverse ductility was not measurable and the brittle behavior was observed in the transverse direction compared to the lateral direction of the rolling. In addition, the presence of anisotropy in titanium increases the susceptibility to stress corrosion cracking in aqueous solutions.

Contrary to expectations, when evaluating the sub-beta treated pieces, there was some anisotropy in the strength of the material. The yield and ultimate properties in the longitudinal and transverse directions correlated very strongly, especially when processed at slow strain rates. As shown in FIGS. 11B and 12B, the sample produced at a slower strain rate exhibited a higher enhancement effect than at a higher temperature, and the material produced through the operation under the beta transus was almost in terms of ultimate strength. It was isotropic. Despite the relatively limited texture demonstrated in the mechanical test, grain elongation occurs significantly in the longitudinal direction (see Fig. 13B). Data corresponding to FIGS. 11A to 14B are shown in Table 1 below.

[Table 1]

Data in Figs. 11A to 14B

20 내지 30 인치/초 출구 속도; 느림

5 내지 6 인치/초 출구 속도*speed

20 to 30 inches/second exit speed; Slow

5 to 6 inches/second exit speed

**Sample A rolled at 1860°F (1016°C); Sample B rolled at 1800°F (982°C)

Example 2

Several Ti-6Al-4V alloys were extruded into strips (4 inches (10.2 cm) wide) and then rolled to various final thicknesses due to various rolling reductions, which are shown in Table 2 below. Sample 1 was treated with a reduction of 55%, sample 2 was treated with a reduction of 65%, and sample 3 was treated with a reduction of 75%. The initial thickness of the extruded strip was 0.3 inches (7.62 mm). The extrusion step was carried out at 2200° F. (1204° C.). The rolling reduction step was performed at 1750° F. (954° C.). Light annealing (to relieve stress) was performed for 30 minutes at 1450° F. (788° C.) before air cooling the sample. The mechanical properties of the final strip were then tested, and the results are shown below.

Strength and elongation properties were measured according to ASTM E8, and the results are shown in Table 2 below. All strength values were expressed in ksi/(MPa).

[Table 2]

Room temperature properties of Example 2 alloy

The sample material realizes significantly higher strength compared to the conventional Ti-6Al-4V product (see, for example, AMS 4928 and AMS 4911). Additionally, the material realizes isotropy with a rolling reduction of about 65% while realizing a strength difference of less than 5 ksi between the L and LT directions.

The elevated temperature tensile properties were measured for Sample 2 (65% relative reduction) at 600° F. (316° C.) according to ASTM E21, and the results are shown in Table 3.

[Table 3]

Example 2 Rising Temperature Characteristics of Alloy

Fatigue measurements were performed on Sample 2 (65% relative reduction) according to ASTM E466 and the results are shown in Table 4.

[Table 4]

Fatigue measurements at Kt = 2.3 (open hole) and 30 Hz for sample 2 (65% RR)

Bearing measurements were performed on sample 2 (65% relative reduction) according to ASTM E238 and the results are shown in Table 5.

[Table 5]

Bearing measurement at e/D = 1.5 for sample 2 (65% RR)

Grain elongation in the axial direction was observed both in the case of high strain rates and in the case of low strain rates. The microstructure taken within the vertical section and viewed in the tangential direction shows that the previous beta grains are elongated in the longitudinal direction. As illustrated, the extrudate has a beta engineered microstructure, while the extruded and rolled material has an alpha-beta engineered microstructure according to AMS standards.

Figure 16 shows the fatigue crack growth rate performed according to ASTM E647 under test conditions of a stress ratio of 0.10, a frequency of 10 Hz, room temperature, and laboratory atmospheric pressure. The fatigue crack growth results are consistent with the AMS standard for alpha-beta sheet products.

While various embodiments of the present disclosure have been described in detail, it will be apparent to those skilled in the art that variations and modifications of these embodiments may be made. However, it should be clearly understood that such modifications and changes are within the spirit and scope of the present disclosure.

Claims (20)

As a method of producing a titanium alloy workpiece,
(a) heating a cast ingot or machined billet of titanium alloy to a temperature above its beta transus temperature to produce a heated workpiece;
(b) Initiating extrusion of the heated workpiece while the heated workpiece is above the beta transus temperature to create an extruded near net shape workpiece, wherein the extruded near net shape workpiece is a pie-box comprising a non-planar shape selected from the group consisting of (pi-box), C-shape, T-shape, H-shape, I-shape and L-shape;
(c) cooling the extruded approximate workpiece to a cooled temperature below the beta transus temperature; And
(d) rolling the extruded approximate work piece at least one time at one or more rolling temperatures to create a final shape work piece, wherein the rolling temperature is below the initial melting temperature of the alloy, below the beta transus temperature, and the beta transus temperature Step, which is within 600°F (333°C) of
Including,
The rolling step is achieved so that the final shape workpiece maintains the non-planar shape of the extruded approximate workpiece,
The final shape workpiece is thinner in one or more dimensions compared to the extruded approximate workpiece,
Way. The method of claim 1, wherein the titanium alloy is an alpha-beta titanium alloy. The method of claim 1, further comprising, after the heating step (a), protecting the surface of the heated workpiece with a protective agent. The method of claim 3, wherein the protective agent is a lubricant or a release agent. 4. The method of claim 3, wherein the method further comprises, after the cooling step (c), cleaning the approximate workpiece before the rolling step (d) to remove any protective agents. The method of claim 1, wherein the cooled temperature is within 500° F. (278° C.) of the beta transus temperature. The method of claim 1, wherein the cooled temperature is within 100° F. (55.6° C.) of the beta transus temperature. The method of claim 1, wherein the cooled temperature is room temperature. delete delete delete The method of claim 1, wherein the rolling temperature is below the beta transus temperature and within 50° F. (27.8° C.) of the beta transus temperature. The method of claim 1, wherein the rolling step (d) is 0.1 s ^-1 to 100 The method further comprising rolling at a strain rate of ^{s -1.} The method of claim 1, wherein the rolling step comprises the step of uniformly reducing the approximate workpiece by a relative reduction of 1% to 95% to achieve the final shaped workpiece. 15. The method of claim 14, wherein the relative reduction is 40-75%. The method of claim 1, wherein the rolling step comprises reducing a first section of an approximate workpiece by a first relative reduction of 1% to 95% to achieve a final shaped workpiece with the first section reduced. . The method of claim 16, wherein the rolling step reduces at least a second section of the approximate workpiece by a second relative reduction of 1% to 95% to achieve a final shaped workpiece with at least the first and second sections reduced. The method further comprises a step, wherein the first relative reduction is different from the second relative reduction. The method of claim 1, wherein the final shape workpiece realizes at least 3% higher tensile yield strength (L) than the referenced titanium alloy body, and the referenced titanium alloy body has the same composition as the final shape workpiece and the final shape The method being in the same temper as the workpiece. 19. The method according to claim 18, wherein the final shaped workpiece comprises isotropic strength properties, and the tensile yield strength in the LT direction is within 10 ksi of the tensile yield strength in the L direction. 20. The method according to claim 19, wherein the final shaped workpiece achieves an elongation of at least 6% (L) and an elongation of at least 6% (LT).

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