A heat treatment method for improving tensile properties of additive manufactured high-temperature titanium alloy

Abstract

The application provides a heat treatment method for improving tensile properties of an additive manufacturing high-temperature titanium alloy, and relates to the technical field of additive manufacturing preparation.The heat treatment method provided by the application comprises the following steps: (1) heating the additive manufacturing high-temperature titanium alloy to 350 DEG C, keeping warm for 4-6 hours, first air cooling to room temperature, and obtaining a first treated titanium alloy; (2) heating the first treated titanium alloy to 20-30 DEG C below the beta transformation temperature, keeping warm for 1-2 hours, and performing water quenching treatment to obtain a second treated titanium alloy; and (3) heating the second treated titanium alloy to 500-600 DEG C, keeping warm for 4-6 hours, second air cooling to room temperature, and obtaining a high-performance high-temperature titanium alloy.The application can simultaneously improve the strength and ductility of the additive manufacturing high-temperature titanium alloy, and expand the application range of the additive manufacturing high-temperature titanium alloy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of additive manufacturing preparation, and particularly relates to a heat treatment method for improving the tensile property of high-temperature titanium alloy prepared by additive manufacturing. BACKGROUND

[0002] High-temperature titanium alloy is a kind of titanium alloy with good thermal stability and high-temperature strength and excellent processing performance, which is widely used in aerospace industry for aircraft load-bearing parts and gas turbine engine compressor disc parts. Taking the common high-temperature titanium alloy TA15 as an example, TA15 (Ti-6.5Al-2Zr-1Mo-1V), (corresponding to Russian brand BT20) titanium alloy is a relatively typical near-alpha alloy, which has suitable room temperature and high-temperature (500℃) strength, good thermal stability and welding performance, and the processing plasticity is also close to alpha + beta titanium alloy, and the beta transition temperature is about 975℃. Compared with the most common titanium alloy Ti-6Al-4V (Ti-6Al-4V is the world's most popular titanium alloy, which accounts for nearly half of the market share of titanium products used in the world today), TA15 titanium alloy has higher room temperature and high-temperature strength, fracture toughness, fatigue limit, corrosion resistance and welding performance. Large TA15 titanium alloy integral components have the characteristics of thin abdomen and high ribs, complex shape (such as cabin wall) and the like, which can effectively reduce the weight of the equipment and improve the structural performance, and are increasingly widely used in the field of aerospace. The key to the successful use of TA15 titanium alloy lies in its ability to perform thermal mechanical processing and heat treatment in the alpha + beta two-phase region (i.e. good formability), therefore, TA15 titanium alloy is widely used in load-bearing structural parts, and compressor blades and compressor discs of gas turbine engine and other fields with high temperature requirements.

[0003] In recent years, the emergence of additive manufacturing technology can directly manufacture parts with complex geometry, near full density and high precision from a 3D model. Most importantly, the unique thermal history of additive manufacturing technology can introduce fine microstructure in the formed parts, which can achieve excellent strength that cannot be achieved by conventional processes. Therefore, additive manufacturing technology further promotes the application of high-temperature titanium alloy in multiple industries, including nuclear power, marine and aerospace.

[0004] Considering that the working temperature of high-temperature titanium alloy (such as TA15 alloy) is as high as 500℃, it is more valuable to evaluate its mechanical properties at service temperature for most industrial applications, therefore, it is crucial to improve the high-temperature performance of additive manufacturing high-temperature titanium alloy. The performance optimization of additive manufacturing high-temperature titanium alloy in the industry is currently completed by simple annealing heat treatment, which can effectively improve the high-temperature plasticity of the formed parts, but the high-temperature tensile strength will be significantly reduced. SUMMARY

[0005] The application aims to provide a heat treatment method for improving the tensile property of an additively manufactured high-temperature titanium alloy.

[0006] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions.

[0007] The application provides a heat treatment method for improving the tensile property of an additively manufactured high-temperature titanium alloy, comprising the following steps.

[0008] (1) heating the additively manufactured high-temperature titanium alloy to 350 DEG C, keeping for 4-6 hours, first air cooling to room temperature to obtain a first treated titanium alloy;

[0009] (2) heating the first treated titanium alloy to 20-30 DEG C below the beta transformation temperature, keeping for 1-2 hours, and then water quenching to obtain a second treated titanium alloy;

[0010] (3) heating the second treated titanium alloy to 500-600 DEG C, keeping for 4-6 hours, and then second air cooling to room temperature to obtain a high-performance high-temperature titanium alloy.

[0011] Preferably, the additively manufactured high-temperature titanium alloy comprises an additively manufactured TA15 titanium alloy or an additively manufactured BT20 titanium alloy.

[0012] Preferably, the heating rate of step (1) from room temperature to 350 DEG C is 10-20 DEG C / min.

[0013] Preferably, the cooling rate of the first air cooling of step (1) is 3-5 DEG C / s.

[0014] Preferably, the heating rate of step (2) from room temperature to 20-30 DEG C below the beta transformation temperature is 10-20 DEG C / min.

[0015] Preferably, the heating rate of step (3) from room temperature to 500-600 DEG C is 10-20 DEG C / min.

[0016] Preferably, the cooling rate of the second air cooling of step (3) is 3-5 DEG C / s.

[0017] The application provides a heat treatment method for improving tensile properties of an additive manufacturing high-temperature titanium alloy, the additive manufacturing high-temperature titanium alloy is heated to 350 DEG C, and the heat preservation time is 4-6 hours, so that the residual stress is removed, then the first air cooling is performed to room temperature, and a first treated titanium alloy is obtained; the first treated titanium alloy is heated to 20-30 DEG C below the beta transformation temperature, and the heat preservation time is 1-2 hours, so that the martensite existing in the as-deposited state and the lath are completely decomposed, and part of the alpha phase is transformed into the beta phase, the short-time high-temperature heat treatment is different from the traditional long-time aging, the transformed alpha phase is equiaxed, and the proportion of the primary alpha phase is small, so that the plasticity of the alloy is improved; then the water quenching treatment is performed, so that part of the beta phase is transformed into fine and dense secondary alpha phase, in the process, the growth of the grain boundary alpha phase is inhibited, so that the grain boundary alpha phase with a discontinuous morphology is formed, and the microstructure is beneficial to improving the high-temperature tensile properties and the fracture resistance; the second treated titanium alloy is heated to 500-600 DEG C, the heat preservation time is 4-6 hours, and the second air cooling is performed to room temperature, so that the fine and dense secondary alpha phase is coarsened, the plasticity is further improved, and the grain boundary alpha phase with a discontinuous morphology can be retained, and then the high-performance high-temperature titanium alloy is obtained.

[0018] The application obtains the fine secondary alpha phase structure by using the multi-pass heat treatment process close to the beta phase transformation point of the high-temperature titanium alloy, so that the high-temperature tensile properties and the fracture toughness are good. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a process route diagram of the heat treatment of the embodiment 1 of the application;

[0020] Figure 2 It is the microstructure SEM and EBSD diagram of the as-deposited TA15 (comparative example 1) and the high-performance TA15 titanium alloy obtained after the heat treatment of the embodiment 1; Figure 2 a is the EBSD diagram of the comparative example 1, b is the SEM diagram of the comparative example 1, c is the EBSD diagram of the embodiment 1, and d is the SEM diagram of the embodiment 1;

[0021] Figure 3 It is the microstructure SEM and EBSD diagram of the TA15 titanium alloy obtained after the heat treatment of the comparative example 2;

[0022] Figure 4 It is the microstructure SEM and EBSD diagram of the TA15 titanium alloy obtained after the heat treatment of the comparative example 3;

[0023] Figure 5 It is the microstructure SEM diagram of the TA15 titanium alloy obtained after the heat treatment of the comparative example 4 and the comparative example 5; Figure 5 a is the comparative example 4, and b is the comparative example 5. DETAILED DESCRIPTION

[0024] The application provides a heat treatment method for improving the tensile property of an additive manufacturing high-temperature titanium alloy, comprising the following steps:

[0025] (1) heating the additive manufacturing high-temperature titanium alloy to 350 DEG C, holding for 4-6 hours, first air cooling to room temperature to obtain a first treated titanium alloy;

[0026] (2) heating the first treated titanium alloy to 20-30 DEG C below the beta transformation temperature, holding for 1-2 hours, and then performing water quenching treatment to obtain a second treated titanium alloy;

[0027] (3) heating the second treated titanium alloy to 500-600 DEG C, holding for 4-6 hours, and then second air cooling to room temperature to obtain a high-performance high-temperature titanium alloy.

[0028] In the application, the additive manufacturing high-temperature titanium alloy preferably comprises an additive manufacturing TA15 titanium alloy or an additive manufacturing BT20 titanium alloy. In the application, the additive manufacturing high-temperature titanium alloy is preferably a laser additive manufacturing high-temperature titanium alloy, and more preferably a selective laser melting forming high-temperature titanium alloy. Compared with other high-temperature titanium alloys, the additive manufacturing high-temperature titanium alloy is generally difficult to obtain a balance between high-temperature strength and plasticity, and the heat treatment method of the application can make the additive manufacturing high-temperature titanium alloy simultaneously realize excellent high-temperature strength and high-temperature plasticity.

[0029] In the application, the heating rate from room temperature to 350 DEG C is preferably 10-20 DEG C / min.

[0030] In the application, the cooling rate of the first air cooling is preferably 3-5 DEG C / s.

[0031] After obtaining the first treated titanium alloy, the first treated titanium alloy is heated to 20-30 DEG C below the beta transformation temperature, held for 1-2 hours, and then subjected to water quenching treatment to obtain a second treated titanium alloy. In the application, the heating rate from room temperature to 20-30 DEG C below the beta transformation temperature is preferably 10-20 DEG C / min. The first treated titanium alloy is preferably heated to 25 DEG C below the beta transformation temperature.

[0032] In the application, the water quenching treatment is preferably cooled to room temperature.

[0033] After obtaining the second treated titanium alloy, the second treated titanium alloy is heated to 500-600 DEG C, held for 4-6 hours, and then second air cooled to room temperature to obtain a high-performance high-temperature titanium alloy.

[0034] In the application, the heating rate from room temperature to 500-600 DEG C is preferably 10-20 DEG C / min.

[0035] In the present application, the cooling rate of the second air cooling is preferably 3-5℃ / s.

[0036] In the present application, the heat treatment method for improving the tensile property of the additively manufactured high-temperature titanium alloy is preferably performed in air.

[0037] The technical solutions in the present application will be described clearly and completely below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0038] Example 1

[0039] Taking the selective laser melting formed TA15 titanium alloy as an example, the beta transformation temperature thereof is 975℃, and the microstructure of the as-deposited state is shown in FIGS. 1a and 1b. Figure 2 The heat treatment was performed in a KJY OTF-1200X tube furnace, and the heat treatment route is shown in FIG. 2. Figure 1 The specific steps are as follows:

[0040] (1) A 100mm×10mm×10mm selective laser melting formed TA15 sample was placed in a tube furnace, the tube furnace was heated to 350℃ at a rate of 10℃ / min, and then the sample was cooled to room temperature in air at a rate of 3℃ / s after being kept at 350℃ for 4 hours;

[0041] (2) The sample treated in step (1) was placed in a tube furnace, the tube furnace was heated to 950℃ at a rate of 10℃ / min, and then the sample was taken out of the tube furnace and quickly placed in water to cool to room temperature after being kept at 950℃ for 2 hours;

[0042] (3) The sample treated in step (2) was placed in a tube furnace, the tube furnace was heated to 500℃ at a rate of 10℃ / min, and then the sample was cooled to room temperature in air at a rate of 3℃ / s after being kept at 500℃ for 4 hours, to obtain a high-performance TA15 titanium alloy.

[0043] After the high-performance TA15 titanium alloy was polished by metallographic grinding and polishing, the microstructure thereof was observed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), as shown in FIGS. 3c and 3d. Figure 2 It can be observed that there are obvious fine secondary α phase and discontinuous grain boundary α phase.

[0044] Comparative Example 1

[0045] The preparation method is basically the same as that of Example 1, except that the TA15 titanium alloy subjected to selective laser melting is not subjected to any heat treatment, and the microstructure is shown in Figure 2 a and b of FIG. 1, and no secondary α phase and grain boundary α phase are observed.

[0046] Comparative Example 2

[0047] The preparation method is basically the same as that of Example 1, except that the holding temperature of the heat treatment in step (2) is adjusted from “950℃” to “850℃”, and the microstructure is shown in Figure 3 No secondary α phase is observed, but there is discontinuous grain boundary α phase.

[0048] Comparative Example 3

[0049] The preparation method is basically the same as that of Example 1, except that the holding temperature of the heat treatment in step (2) is adjusted from “950℃” to “800℃”; and after the heat treatment is held for 2 hours, “quickly put into water to cool to room temperature” is adjusted to “air cooling to room temperature at a speed of 8℃ / s”, and the microstructure is shown in Figure 4 No secondary α phase and grain boundary α phase are observed, but the martensite is completely decomposed into uniform α+β phase.

[0050] Comparative Example 4

[0051] The preparation method is basically the same as that of Example 1, except that step (1) is not performed, and the microstructure is shown in Figure 5 a of FIG. 1, at this time, the grain boundary α phase is continuous, and blocky α phase appears.

[0052] Comparative Example 5

[0053] The preparation method is basically the same as that of Example 1, except that step (3) is not performed, and the microstructure is shown in Figure 5 b of FIG. 1, at this time, no obvious secondary α phase is observed.

[0054] Test Example 1

[0055] The samples heat treated according to Example 1, Comparative Examples 1-5 were machined using a lathe to produce tensile samples that met the ASTM E8 standard, specifically: 4 mm diameter parallel section, 20 mm gauge length, and a standard tensile rate of 0.0001 / s. High temperature tensile testing was performed on an INSTRON 5892 instrument at 500°C. Prior to each tensile test, the sample and the environment were homogenized using a heating rate of 10°C / min and a 30 minute dwell at the set temperature. The elongation was measured throughout the test using an INSTRON E001 contact extensometer. The high temperature tensile properties presented are the average of three replicate tests. The samples heat treated according to Example 1, Comparative Examples 1-5 were machined using a CNC lathe to produce compact tension (CT) size specimens that met the ASTM E399 standard for fracture toughness testing, with a thickness of 25 mm. The testing was performed on an INSTRON 8001 machine at a constant rate of 1 mm / min.

[0056] The test results were:

[0057] The high temperature tensile ultimate tensile strength of the sample of Example 1 was 949.5 MPa, the high temperature ductility was 20.7%, and the fracture toughness was 88 MPa-m 1 / 2 .

[0058] The high temperature tensile ultimate tensile strength of the sample of Comparative Example 1 was 945.0 MPa, the high temperature ductility was 10.0%, and the fracture toughness was 46 MPa-m 1 / 2 .

[0059] The high temperature tensile ultimate tensile strength of the sample of Comparative Example 2 was 730.5 MPa, the high temperature ductility was 16.1%, and the fracture toughness was 53 MPa-m 1 / 2 .

[0060] The high temperature tensile ultimate tensile strength of the sample of Comparative Example 3 was 770.3 MPa, the high temperature ductility was 17.5%, and the fracture toughness was 61 MPa-m 1 / 2 .

[0061] The high temperature tensile ultimate tensile strength of the sample of Comparative Example 4 was 701.9 MPa, the high temperature ductility was 7.1%, and the fracture toughness was 51 MPa-m 1 / 2 .

[0062] The high temperature tensile ultimate tensile strength of the sample of Comparative Example 5 was 693.3 MPa, the high temperature ductility was 11.7%, and the fracture toughness was 45 MPa-m 1 / 2 .

[0063] The test results show that the high-temperature tensile ultimate tensile strength (UTS) of the sample of Example 1 is increased from 945.0 MPa before heat treatment to 949.5 MPa after heat treatment, and the high-temperature plasticity is increased from 10.0% before heat treatment to 20.7% after heat treatment, the high-temperature plasticity is greatly improved by 100%, and the high-temperature performance of the additive manufacturing high-temperature titanium alloy is optimized. The fracture toughness of the additive manufacturing high-temperature titanium alloy is increased from 46 MPa·m 1 / 2 after heat treatment to 88 MPa·m 1 / 2 after heat treatment, and the fracture toughness is increased by about 100%. This shows that the fracture resistance of the additive manufacturing high-temperature titanium alloy is significantly enhanced after the heat treatment of Example 1.

[0064] The present application adopts multi-pass heat treatment, and simultaneously obtains fine secondary alpha phase and non-continuous grain boundary alpha phase, thereby realizing good high-temperature tensile performance of the additive manufacturing high-temperature titanium alloy.

[0065] The above only describes the preferred embodiments of the present application, and it should be noted that, for those skilled in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1.A heat treatment method for improving the tensile properties of an additively manufactured high-temperature titanium alloy, comprising the following steps: (1) heating the additively manufactured TA15 titanium alloy to 350 ℃, holding for 4 hours, first air cooling to room temperature at a cooling rate of 3 ℃ / s to obtain a first treated titanium alloy; (2) heating the first treated titanium alloy to 950 ℃ at a heating rate of 10 ℃ / min, holding for 2 hours, and then water quenching to obtain a second treated titanium alloy; (3) heating the second treated titanium alloy to 500 ℃ at a heating rate of 10 ℃ / min, holding for 4 hours, and then second air cooling to room temperature at a cooling rate of 3 ℃ / s to obtain a high-performance high-temperature titanium alloy.

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