Method for improving high-temperature toughness of disc shaft parts

Abstract

The invention relates to a method for improving the high-temperature obdurability of disc shaft parts, which specifically comprises the following steps: firstly, carrying out pre-heating treatment: carrying out solution treatment on a metal shaft blank to eliminate the internal residual stress of the blank to obtain a pre-treated shaft blank; and then low-speed near yield temperature setting is conducted, specifically, after the temperature gradient of the pretreated shaft blank is eliminated, the temperature is kept unchanged, prestress is loaded till near yield is achieved, then cyclic torsional deformation aging treatment is conducted on the pretreated shaft blank, and after deformation is finished, cooling is conducted to the room temperature. According to the method, a low-speed near-yield setting process and a solid solution aging heat treatment process are dynamically, timely and synergistically coupled to form a brand-new low-speed near-yield-temperature setting process, and meanwhile, four strengthening mechanisms of solid solution strengthening, deformation strengthening, aging strengthening and fine grain strengthening and adjustment of an internal stress state are combined; and the high-temperature strength and toughness of the metal material are synchronously improved.

Description

Technical Field

[0001] The present invention relates to a metal material strengthening and toughening technology, and in particular to a method for improving the high-temperature toughness of disk-shaft parts. Specifically, it is a method for improving the comprehensive thermal performance of rotating parts by comprehensively utilizing heat treatment and low-speed near-yield temperature setting processes. Background Art

[0002] The development of advanced aviation technology requires the continuous improvement of the strength, life and reliability of aviation gas turbine engine components. Disc and shaft parts are key components of gas turbine engines, including fan discs, compressor discs, turbine discs, drum-shaped reinforcement discs, comb discs, gear shafts, power shafts and other rotating parts. The performance of the disc plays a vital role in the thrust-to-weight ratio, life, reliability and safety of aviation engines.

[0003] Gas turbines and turbojet engines are operated under harsh conditions. The internal rotating parts are subjected to the combined effects of centrifugal force, thermal stress, vibration stress and other loads during operation. The stress state is very complex and the working conditions are extremely harsh. The temperature, mechanical load and medium effect on different disc shaft parts and their different parts are quite different. Since the main components of the engine are usually made of high-value metal materials with excellent comprehensive performance. In order to pursue the advanced performance of the whole machine and take into account the potential of the existing material performance, the design generally fully explores the structure and strength potential of each component, reduces the strength margin, and reduces the overall design and manufacturing costs through reliability analysis.

[0004] Traditional disk-shaft parts are mostly strengthened by solution aging or deformation heat treatment. For example, application number CN202211715644.X "Heat treatment method of high-temperature alloy disk-shaft forgings and prepared disk-shaft forgings" and CN202311582543.4 "A method for preparing TC6 titanium alloy blade forgings for aircraft engines" respectively provide solution aging and deformation heat treatment process methods. Both processes can improve the strength and toughness of engine disk-shaft parts to a limited extent, and the shape of the parts will also change further during the processing process.

[0005] Overspeeding of disk-shaft parts before service can produce strain hardening, which can improve room temperature and high temperature tensile yield strength, fatigue life and crack propagation life while keeping the cross section of disk-shaft parts unchanged. As shown in the process methods of application number CN202321631195.0 "A workbench for overspeed experiments" and CN201821311850.3 "An impeller overspeed test equipment", the above overspeed setting process places extremely high requirements on the stiffness and centering of the equipment. It is difficult to use the coupling effect of multiple physical fields to strengthen the workpiece during overspeed rotation, and the internal stress of the workpiece cannot be precisely controlled and distributed. The process technology is difficult and costly. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems existing in the prior art and provide a method for improving the high-temperature toughness of disk-shaft parts, while improving the thermal strength of metal materials, ensuring that their thermoplasticity does not decrease significantly or is improved, and synchronously coordinating the improvement of the thermal strength and thermoplasticity of the material to adjust the internal stress distribution of the parts.

[0007] To achieve the above, the technical solution adopted by the present invention is: a method for improving the high temperature toughness of disk shaft parts, the specific steps are as follows: Step 1: Pre-heat treatment: The metal shaft blank is subjected to a solid solution treatment to eliminate the residual stress inside the blank to obtain a pre-treated blank; Step 2: Low speed near yield temperature setting: After eliminating the temperature gradient of the pretreated shaft blank, keep the temperature constant, load the prestress until it is close to yield, and then perform cyclic torsion deformation on one end of the pretreated shaft blank, that is, twist one end of the shaft blank in one direction until the shaft blank is deformed as a whole, and then immediately twist it in the opposite direction until the shaft blank is deformed as a whole, and in this way, cyclic torsion deformation is performed for 2-8 hours at a fixed temperature; Among them, the treatment temperature for eliminating the temperature gradient of the pre-treated shaft blank is determined according to the material of the metal shaft blank; in the cyclic torsion deformation, the fixed temperature and torsion speed are determined under the premise of ensuring that the material used for the shaft blank will not break due to excessive torsion speed; Step 3: Preparation of high temperature tough disk and shaft: After the cyclic torsional deformation is completed, the product is cooled to room temperature and the deformed section is directly taken to obtain a shaft having high temperature toughness or a disk of a corresponding shape is obtained by cutting off the deformed section.

[0008] Furthermore, in step one, the temperature of the solution treatment is determined according to the material of the metal shaft blank; when the metal shaft blank is a two-phase titanium alloy material, the solution temperature is 40~100°C below the β phase transformation point, the solution holding time is 0.5~2h, and the cooling method is water cooling or air cooling.

[0009] Furthermore, in step 2, prestress is applied to one end of the pretreated shaft blank, followed by cyclic torsion; wherein the prestress is tensile stress or compressive stress and is less than the material yield strength of the metal shaft blank.

[0010] Furthermore, the prestressing force is 30-50 MPa.

[0011] Furthermore, in step 2, the angle of the cyclic torsional deformation is 30 to 60 degrees; and the torsional speed of the cyclic torsional deformation is 1 to 5 cycles / min.

[0012] Furthermore, in the step 2, the duration of one cyclic torsional deformation cycle is 6 to 24 seconds.

[0013] Furthermore, the cooling described in step three is air cooling.

[0014] Furthermore, in step 2, the fixed temperature during the cyclic torsion deformation is 50-400° C., which is lower than the conventional aging temperature of the metal shaft blank.

[0015] Furthermore, the fixed temperature during the cyclic torsion deformation is 200° C. below the conventional aging temperature of the metal shaft blank.

[0016] Furthermore, the metal shaft blank of the disk or shaft is TC11 or Ti643 titanium alloy.

[0017] The beneficial effects of the present invention are as follows: the present invention couples low-speed near-yield setting with solid solution aging, and at the same time combines solid solution strengthening, deformation strengthening, aging strengthening and fine grain strengthening, and utilizes repeated shear deformation to promote dislocation rearrangement, forming a diffusion path to reduce the aging temperature and enhance the setting effect, breaking the shackles of traditional heat treatment processes that only rely on aging strengthening to limitedly improve the thermal strength of metal materials, and can greatly improve the strength and toughness of metal materials without losing or even improving thermoplasticity, so that they can meet more stringent service conditions.

[0018] The overspeed setting process for aircraft engine disk and shaft parts does not require expensive process equipment, does not require higher temperatures and longer times than traditional aging processes, and can simultaneously improve high-temperature strength and toughness compared to traditional mechanical heat treatment (deformation coupling heat treatment). While improving the thermal strength of metal materials, it ensures that their thermoplasticity does not decrease significantly or increases, and simultaneously coordinates the improvement of material thermal strength and thermoplasticity, adjusts the internal stress distribution of parts, and significantly reduces process costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a process flow chart of the present invention; Figure 2 It is a schematic diagram of the process of the present invention; Figure 3 It is a schematic diagram of the structure of a metal deformation specimen of a specific example; In the figure: 1-sample axis, 2-transition arc surface, 3-auxiliary clamping axis, 4-transition axis, 5-compression retaining axis, 6-tension retaining edge, 7-torsion axis; Figure 4 600°C high temperature tensile stress-strain curves of specific examples 1 and 2 of the present invention and comparative example 1; Figure 5 600°C high temperature tensile stress-strain curves of specific examples 1, 3, 4 of the present invention and comparative example 1; Figure 6 600°C high temperature tensile stress-strain curves of specific examples 1 and 5 of the present invention and comparative example 1; Figure 7 600°C high temperature tensile stress-strain curves of specific examples 6 and 7 of the present invention and comparative example 2. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is described in detail and completely below in conjunction with the accompanying drawings. However, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments.

[0021] Example 1: Figure 1 As shown, a method for improving the high temperature toughness of disk shaft parts, the specific steps are as follows: Step 1: Pre-heat treatment: The metal shaft blank is subjected to a solid solution treatment to eliminate the residual stress inside the blank to obtain a pre-treated blank; The temperature of the solution treatment is determined according to the material of the metal shaft blank; Step 2: Low speed near yield temperature setting: After eliminating the temperature gradient of the pretreated shaft blank, keep the temperature constant, load the prestress until it is close to yield, and then perform cyclic torsion deformation on one end of the pretreated shaft blank, that is, twist one end of the shaft blank in one direction until the shaft blank is deformed as a whole, and then immediately twist it in the opposite direction until the shaft blank is deformed as a whole, and in this way, cyclic torsion deformation is performed for 2-8 hours at a fixed temperature; Among them, the treatment temperature for eliminating the temperature gradient of the pre-treated shaft blank is determined according to the material of the metal shaft blank; in the cyclic torsion deformation, the fixed temperature and torsion speed are determined under the premise of ensuring that the material used for the shaft blank will not break due to excessive torsion speed; Step 3: Preparation of high temperature tough disk and shaft: After the cyclic torsional deformation is completed, the product is air-cooled to room temperature, and the deformed section is directly taken to obtain a shaft having high temperature toughness, or the deformed section is cut off and processed into a disk of corresponding shape.

[0022] The metal shaft blank of the disc or shaft is TC11 or Ti643 titanium alloy.

[0023] Example 2: The same as Example 1, except that in step 1, when the metal shaft blank is a two-phase titanium alloy material, the solid solution temperature is 40~100°C below the β phase transformation point, the solid solution holding time is 0.5~2h, and the cooling method is water cooling or air cooling.

[0024] Embodiment 3 is the same as Embodiment 1, except that: in step 2, a prestress is applied to one end of the pretreated shaft blank, and then cyclic torsion is performed; The prestress is a tensile stress or a compressive stress and is less than the material yield strength of the metal shaft blank. The prestress is 30 to 50 MPa.

[0025] Example 4: The same as Example 1, except that in step 2, the angle of the cyclic torsional deformation is 30 to 60°; the torsional speed is 1 to 5 cycles / min, and the duration of one cyclic torsional deformation cycle is 6 to 24 seconds.

[0026] The fixed temperature during cyclic torsion deformation is 50~400℃ below the normal aging temperature of the metal shaft blank.

[0027] Example 5: Same as Example 4, except that the fixed temperature during cyclic torsional deformation is 200°C below the conventional aging temperature of the metal shaft blank.

[0028] like Figure 2-7 To further illustrate the technical solutions and beneficial effects of the present invention, the present invention provides the following specific examples and comparative examples: First, the structure of the sample used in the specific example is explained: Figure 2 , Figure 3 As shown, like Figure 3 As shown, the specimen is machined as a whole by a CNC lathe, wherein one end of the specimen shaft 1 is connected to the transition shaft 4 through an arc surface 2, the end of the transition shaft 4 is fixed to the auxiliary clamping shaft 3, and the end of the auxiliary clamping shaft 3 is machined with a tensile retaining edge 6; the other end of the specimen shaft 1 is connected to the compression retaining shaft 5, and the end of the compression retaining shaft 5 is connected to the torsion shaft 7; the diameters of the transition shaft 4 and the compression retaining shaft 5 are both larger than those of the auxiliary clamping shaft 3 and the compression retaining shaft 5, and the diameter of the specimen shaft 1 is smaller than that of the transition shaft 4 and the compression retaining shaft 5; the circumference of the auxiliary clamping shaft 3 and the torsion shaft 7 are machined with three planes distributed at 120°, which are respectively used for tensile clamping specimens, compression clamping specimens, and torsion clamping specimens.

[0029] Directions: A three-jaw chuck is used to fix three torsion planes distributed at 120° on the auxiliary clamping shaft 3. When tensile stress is applied, the tensile flange 6 plays a fixing role, and when compressive stress is applied, the compression flange 5 plays a fixing role. Figure 3 As shown, during deformation, the prestressed load will cause the jaws to press against the tensile flange 6 or the compression shaft 5, thereby applying tensile / compressive stress; during torsion, the three jaws clamp the three torsion planes on the torsion shaft 7 distributed at 120°, and torsion them back and forth to achieve positive and negative torsion deformation of the sample. The sample shaft 1 is heated by a heating coil, and the deformation temperature is monitored in real time by a thermocouple. The processing process is as follows Figure 2 shown.

[0030] Specific example 1: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The TC11 titanium alloy to be treated is pre-solidified in the dual phase region at a temperature of 950°C. After being kept at this temperature for 1 hour, it is cooled to room temperature in air. (2) The TC11 titanium alloy specimen that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, preload the tensile stress with a magnitude of 50 MPa, and then perform cyclic torsion deformation with a torsion speed of 2 cycles / min and a torsion angle of 30° forward and then immediately reverse 30°. The duration of one cycle is 9 s. After setting at a low speed near the yield temperature for 4 h, stop deformation and heating, and air cool to room temperature.

[0031] The mechanical properties of the treated TC11 titanium alloy samples were tested, and the results are shown in Table 1. The stress-strain curve is shown in Figure 4 .

[0032] Performance test description: The high temperature tensile test was carried out on an Instron 3382 electronic universal testing machine, and the high temperature tensile mechanical properties test was carried out in accordance with GB / T228.2-2015 "Metallic Materials Tensile Test Part 2: High Temperature Test Method".

[0033] Comparative Example 1: The TC11 material was subjected to a solution aging heat treatment process. The material was first kept at 950°C for 1 hour and then air-cooled. It was then kept at 530°C for 6 hours and then cooled to room temperature in air.

[0034] The mechanical properties of the treated TC11 material were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 4 .

[0035] Specific example 2: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The TC11 titanium alloy to be treated is pre-solution treated in the dual phase region at a temperature of 950°C. After being kept at this temperature for 1 hour, it is water quenched to room temperature. (2) The TC11 titanium alloy specimen that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, preload the tensile stress with a magnitude of 50 MPa, and then perform cyclic torsion deformation with a torsion speed of 3 cycles / min and a torsion angle of 30° forward and then immediately reverse 30°. The duration of one cycle is 9 s. After setting at a low speed near the yield temperature for 4 h, stop deformation and heating, and air cool to room temperature.

[0036] The mechanical properties of the treated TC11 titanium alloy samples were tested, and the results are shown in Table 1. The stress-strain curve is shown in Figure 4 .

[0037] Specific example 3: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The TC11 titanium alloy to be treated is pre-solidified in the dual phase region at a temperature of 950°C. After being kept at this temperature for 1 hour, it is cooled to room temperature in air. (2) The TC11 titanium alloy specimen that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant and preload the compressive stress with a magnitude of 50 MPa. Then perform cyclic torsion deformation with a torsion speed of 2 cycles / min and a torsion angle of 30° forward and then immediately reverse 30°. The duration of one cycle is 9 s. After setting at a low speed near the yield temperature for 4 h, stop deformation and heating, and air cool to room temperature.

[0038] The mechanical properties of the treated TC11 titanium alloy samples were tested, and the results are shown in Table 1. The stress-strain curve is shown in Figure 5 .

[0039] Specific example 4: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The TC11 titanium alloy to be treated is pre-solidified in the dual phase region at a temperature of 950°C. After being kept at this temperature for 1 hour, it is cooled to room temperature in air. (2) The TC11 titanium alloy specimen that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, do not load prestress, and directly perform cyclic torsion deformation. The torsion speed is 4 cycles / min, the torsion angle is 30° forward, and then immediately reverse 30°. The duration of one cycle is 9s. After setting at a low speed near the yield temperature for 4h, stop deformation and heating, and air cool to room temperature.

[0040] The mechanical properties of the treated TC11 titanium alloy samples were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 5 .

[0041] Specific example 5: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The TC11 titanium alloy to be treated is pre-solidified in the dual-phase region at 950°C. After being kept at this temperature for 1 hour, it is cooled to room temperature in air. (2) The TC11 titanium alloy specimen that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, preload the tensile stress with a magnitude of 50 MPa, and then perform cyclic torsion deformation with a torsion speed of 1 cycle / min and a torsion angle of 10° forward and then immediately reverse 10°. The duration of one cycle is 5 s. After setting at a low speed near the yield temperature for 4 h, stop deformation and heating, and air cool to room temperature.

[0042] The mechanical properties of the treated TC11 titanium alloy samples were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 6 .

[0043] Specific Example 6: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The Ti643 titanium alloy to be treated is pre-solidified in the dual-phase region at a solution treatment temperature of 970°C. After being kept at this temperature for 1 hour, it is cooled to room temperature in air. (2) The Ti643 titanium alloy sample that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, do not load prestress, and directly perform cyclic torsion deformation. The torsion speed is 3 cycles / min, the torsion angle is 30° forward, and then immediately reverse 30°. The duration of one cycle is 9s. After setting at a low speed near the yield temperature for 4h, stop deformation and heating, and air cool to room temperature.

[0044] The mechanical properties of the treated Ti643 titanium alloy samples were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 7 .

[0045] Comparative Example 2: The Ti643 material was subjected to a solution aging heat treatment process. The material was first kept at 970°C for 1 hour and then air-cooled. It was then kept at 650°C for 4 hours and then cooled to room temperature in air.

[0046] The mechanical properties of the treated Ti643 material were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 7 .

[0047] Specific example 7: A method for improving the high temperature toughness of disk and shaft parts, the specific steps are as follows: (1) The Ti643 titanium alloy to be treated is pre-solidified in the dual-phase region at a solution treatment temperature of 970°C. After being kept at this temperature for 1 hour, it is water-cooled to room temperature. (2) The Ti643 titanium alloy sample that had been pre-solid solution treated was clamped on a low-speed near-yield temperature setting testing machine, heated to 200°C, and kept warm for 10 minutes to ensure that the temperature gradient was eliminated; (3) Keep the temperature constant, do not load prestress, and directly perform cyclic torsion deformation. The torsion speed is 3 cycles / min, the torsion angle is 30° forward, and then immediately reverse 30°. The duration of one cycle is 9s. After setting at a low speed near the yield temperature for 4h, stop deformation and heating, and air cool to room temperature.

[0048] The mechanical properties of the treated Ti643 titanium alloy samples were tested. The results are shown in Table 1 and the stress-strain curves are shown in Figure 7 .

[0049] Table 1 Mechanical properties test results

[0050] Combining Table 1 and Figure 4-Figure 7 It can be seen that compared with the traditional solution aging heat treatment process, after the process of the present invention, its high-temperature mechanical properties such as high-temperature yield strength, tensile strength and elongation have been greatly improved, and the cross-sectional shrinkage rate has also increased slightly.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the high temperature toughness of disk and shaft parts, characterized in that: The specific steps are as follows: Step 1: Pre-heat treatment: The metal shaft blank is subjected to a solid solution treatment to eliminate the residual stress inside the blank to obtain a pre-treated blank; Step 2: Low speed near yield temperature setting: After eliminating the temperature gradient of the pretreated shaft blank, keep the temperature constant, load the prestress until it is close to yield, and then perform cyclic torsion deformation on one end of the pretreated shaft blank, that is, twist one end of the shaft blank in one direction until the shaft blank is deformed as a whole, and then immediately twist it in the opposite direction until the shaft blank is deformed as a whole, and in this way, cyclic torsion deformation is performed for 2-8 hours at a fixed temperature; Among them, the treatment temperature for eliminating the temperature gradient of the pre-treated shaft blank is determined according to the material of the metal shaft blank; in the cyclic torsion deformation, the fixed temperature and torsion speed are determined under the premise of ensuring that the material used for the shaft blank will not break due to excessive torsion speed; Step 3: Preparation of high temperature tough disk and shaft: After the cyclic torsional deformation is completed, the product is cooled to room temperature and the deformed section is directly taken to obtain a shaft having high temperature toughness or a disk of a corresponding shape is obtained by cutting off the deformed section.

2. A method for improving high temperature toughness of disk shaft parts according to claim 1, characterized in that: In step 1, the temperature of the solution treatment is determined according to the material of the metal shaft blank; when the metal shaft blank is a two-phase titanium alloy material, the solution temperature is 40~100°C below the β phase transformation point, the solution holding time is 0.5~2h, and the cooling method is water cooling or air cooling.

3. A method for improving high temperature toughness of disk shaft parts according to claim 1, characterized in that: In step 2, prestress is applied to one end of the pretreated shaft blank, followed by cyclic torsion; wherein the prestress is tensile stress or compressive stress and is less than the material yield strength of the metal shaft blank.

4. A method for improving high temperature toughness of disk shaft parts according to claim 3, characterized in that: The prestressing force is 30-50MPa.

5. The method for improving high temperature toughness of disk and shaft parts according to claim 1, characterized in that: In step 2, the angle of the cyclic torsional deformation is 30 to 60 degrees; the torsional speed of the cyclic torsional deformation is 1 to 5 cycles / min.

6. The method for improving high temperature toughness of disk shaft parts according to claim 1, characterized in that: In the step 2, the duration of one cyclic torsional deformation cycle is 6 to 24 seconds.

7. A low-speed near-yield temperature setting method for improving high-temperature toughness of disk-shaft parts according to claim 1, characterized in that: The cooling described in step 3 is air cooling.

8. The method for improving high temperature toughness of disk shaft parts according to claim 1, characterized in that: In step 2, the fixed temperature during the cyclic torsion deformation is 50-400° C., which is lower than the conventional aging temperature of the metal shaft blank.

9. A low-speed near-yield temperature setting method for improving high-temperature toughness of disk-shaft parts according to claim 8, characterized in that: The fixed temperature during the cyclic torsion deformation is 200° C. below the conventional aging temperature of the metal shaft blank.

10. A low-speed near-yield temperature setting method for improving high-temperature toughness of disk-shaft parts according to any one of claims 1 to 9, characterized in that: The metal shaft blank of the disk or shaft is TC11 or Ti643 titanium alloy.

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