A heat treatment method for α-phase of titanium alloy lamellar manufactured by spheroidizing laser additive manufacturing

Abstract

The present invention discloses a heat treatment method for spheroidized laser additive manufacturing titanium alloy sheet α phase, the specific process is: firstly, the laser additive manufacturing titanium alloy is heated to T β ‑(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β ‑(15℃~35℃), continue to control the heating rate at 5℃ / min~6℃ / min to T β ‑(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β The present invention adopts multiple temperature-controlled heating-insulating-temperature-controlled cooling processes to transform the needle-shaped lamellar structure in laser additive manufacturing titanium alloy into a nearly spheroidized structure, so that the titanium alloy has excellent plasticity.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy material processing, and in particular relates to a heat treatment method for spheroidizing laser additive manufacturing of titanium alloy lamellae α phase. Background Art

[0002] Titanium alloy has excellent comprehensive properties such as high specific strength, good thermal strength and corrosion resistance. It is widely used in aerospace, chemical and marine fields and is known as the "third generation metal".

[0003] Laser additive manufacturing technology uses high-power melting and synchronous powder delivery to form parts layer by layer. It has the advantages of short cycle, high forming freedom, digitalization, and fewer subsequent forming steps, making it an important path to achieve integrated structural and functional manufacturing of complex structural parts such as aircraft engines and gas turbines.

[0004] The laser deposition process has the characteristics of rapid heating and rapid cooling, so the structure obtained by laser additive manufacturing of titanium alloys is usually needle-shaped widmanstattenite, which generally has high strength and poor plasticity. Therefore, how to improve strength and plasticity has become a hot issue in laser additive manufacturing of titanium alloys. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a heat treatment method for spheroidized laser additively manufactured titanium alloy lamellar α phase in view of the deficiencies of the above-mentioned prior art. The method comprehensively considers the influence of changes in parameters such as heat treatment temperature, heating rate, holding time, cooling rate, etc. on the alloy structure, and evolves the needle-like fine lamellar structure in the laser additively manufactured titanium alloy into a near-spheroidized structure by adopting multiple temperature-controlled heating-holding-temperature-controlled cooling processes, so that the laser additively manufactured titanium alloy obtains excellent plasticity, solving the problem of poor plasticity of the laser additively manufactured titanium alloy.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a heat treatment method for spheroidizing laser additive manufacturing titanium alloy sheet α phase, characterized in that the specific process of the heat treatment method is: firstly heat the laser additive manufacturing titanium alloy to T β -(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β -(15℃~35℃), continue to control the heating rate at 5℃ / min~6℃ / min to T β -(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β-(15°C~35°C), cycle the above temperature-controlled heating-heat preservation-temperature-controlled cooling process, and finally cool to room temperature at a cooling rate of 5°C / min~10°C / min to obtain a laser additive manufacturing titanium alloy after heat treatment; the T β is the β transition temperature, in °C.

[0007] Aiming at the problem that the needle-shaped widmanstattenite lamellar structure in laser additive manufacturing titanium alloy leads to high strength but poor plasticity of titanium alloy, the present invention develops a heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase: first heating to T β -(5℃~10℃) and keep warm for 15min~20min, so that the primary lamellar α phase undergoes Ostwald ripening mechanism, spheroidizes the primary α phase, and then cools to T β -(15℃~35℃) makes the α phase precipitate and grow on the spheroidized primary α phase, further promoting the spheroidization of the α phase, and then controls the temperature and heats to T β -(5℃~10℃) and keep warm for 15min~20min, then cool to T β -(15℃~35℃), further promote the spheroidization of the primary α phase, and continue the temperature-controlled heating-heat preservation-temperature-controlled cooling process in a cycle, and finally cool to room temperature. The needle-like lamellar structure in the laser additively manufactured titanium alloy is gradually spheroidized by multiple temperature-controlled heating-heat preservation-temperature-controlled cooling processes, and evolved into a nearly spheroidized structure, so that the laser additively manufactured titanium alloy obtains excellent plasticity and maintains a certain strength, solving the problem of poor plasticity of laser additively manufactured titanium alloy.

[0008] The above-mentioned heat treatment method for spheroidizing laser additively manufactured titanium alloy lamellar α phase is characterized in that the laser additively manufactured titanium alloy is an α+β type titanium alloy.

[0009] The above-mentioned heat treatment method for spheroidizing laser additively manufactured titanium alloy lamellar α phase is characterized in that the initial structure of the laser additively manufactured titanium alloy is a needle-shaped lamellar structure.

[0010] The above-mentioned heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase is characterized in that the number of times the cycle continues the temperature-controlled heating-heat preservation-temperature-controlled cooling process is 2 to 3 times. By controlling the number of times the cycle continues the temperature-controlled heating-heat preservation-temperature-controlled cooling process, the primary α phase is not coarsened while ensuring the spheroidization of the primary α phase, thereby not significantly reducing the strength of the titanium alloy.

[0011] The above-mentioned heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase is characterized in that the structure of the laser additive manufacturing titanium alloy after the heat treatment is a near-spheroidized structure with an aspect ratio of 1.8 to 2.0. The present invention does not need to spheroidize the primary α phase through traditional thermal deformation and subsequent solution heat treatment. The structure of the laser additive manufacturing titanium alloy after heat treatment is a near-spheroidized structure with an aspect ratio of 1.8 to 2.0, thereby enabling the titanium alloy to obtain a better strength-plasticity match.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. Compared with the traditional heat treatment process, the present invention comprehensively considers the influence of changes in parameters such as heat treatment temperature, heating rate, holding time, cooling rate, etc. on the alloy structure, and evolves the needle-like fine lamellar structure in the laser additively manufactured titanium alloy into a near-spheroidized structure by adopting multiple temperature-controlled heating-holding-temperature-controlled cooling processes, so that the laser additively manufactured titanium alloy obtains excellent plasticity and solves the problem of poor plasticity of the laser additively manufactured titanium alloy.

[0014] 2. The process of the present invention is simple, easy to operate, and suitable for industrial production.

[0015] 3. The present invention promotes primary α spheroidization and improves alloy plasticity through a temperature-controlled heating-heat-insulation-temperature-controlled cooling process, and finally obtains a heat treatment process with better strength-plasticity matching.

[0016] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a temperature curve diagram of the heat treatment method in Example 1 of the present invention.

[0018] Figure 2 The initial microstructures of the titanium alloy manufactured by laser additive manufacturing in Example 1 of the present invention and Comparative Example 1 are shown in FIG.

[0019] Figure 3 This is a microstructure diagram of the laser additively manufactured titanium alloy after heat treatment in Example 1 of the present invention.

[0020] Figure 4 It is a temperature curve diagram of the heat treatment method in Comparative Example 1 of the present invention.

[0021] Figure 5 This is a microstructure diagram of the laser additively manufactured titanium alloy after heat treatment in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0022] Example 1

[0023] like Figure 1As shown, the specific process of this embodiment is: first, a needle-shaped lamellar tissue (such as Figure 2 The laser additively manufactured TC4-DT titanium alloy (shown in FIG. 1 ) is placed in a high temperature resistance furnace and heated to 960° C. and kept warm for 15 min, then cooled to 950° C. at a cooling rate of 0.3° C. / min, and then heated to 960° C. at a heating rate of 5° C. / min and kept warm for 15 min, then cooled to 950° C. at a cooling rate of 0.3° C. / min, and then the temperature control heating-heat holding-temperature control cooling process is repeated twice, and finally cooled to room temperature at a cooling rate of 10° C. / min to obtain a laser additively manufactured titanium alloy after heat treatment; the T β It is 965℃.

[0024] Figure 3 The microstructure of the laser additively manufactured titanium alloy after heat treatment in this embodiment is shown in FIG. Figure 3 It can be seen that the microstructure of the laser additively manufactured titanium alloy after heat treatment is a near-spheroidized structure with an aspect ratio close to 1.8.

[0025] After testing, the strength of the laser additively manufactured titanium alloy in this embodiment is 1210 MPa, and the elongation after fracture is 2.5%. The strength of the laser additively manufactured titanium alloy after heat treatment is 1010 MPa, and the elongation after fracture is 25%.

[0026] Comparative Example 1

[0027] like Figure 4 As shown, the specific process of this comparative example is: Figure 2 The laser additively manufactured TC4-DT titanium alloy (shown) was placed in a high-temperature resistance furnace and heated to 960°C and kept warm for 60 minutes, and then cooled to room temperature at a cooling rate of 10°C / min.

[0028] Figure 5 This is the microstructure of the laser additively manufactured titanium alloy after heat treatment in this comparative example. Figure 5 It can be seen that the microstructure of the laser additively manufactured titanium alloy after heat treatment is a coarse lamellar structure, and the primary α phase is almost not spheroidized.

[0029] According to the test, the strength of the laser additively manufactured titanium alloy after heat treatment in this comparative example is 948 MPa, and the elongation after fracture is 19%.

[0030] Will Figure 2 , Figure 4 and Figure 5 By comparison, it can be seen that compared with conventional heat treatment methods, the present invention adopts multiple temperature-controlled heating-heat preservation-temperature-controlled cooling processes to gradually spheroidize the needle-like flake layer structure in the laser additively manufactured titanium alloy, and evolve it into a near-spheroidized structure, thereby improving its plasticity.

[0031] Example 2

[0032] The specific process of this embodiment is: first, the laser additively manufactured TC4-DT titanium alloy with needle-like lamellar structure is placed in a high-temperature resistance furnace and heated to 960°C and kept warm for 15 minutes, then cooled to 950°C at a cooling rate of 1°C / min, and then controlled to heat to 960°C at a heating rate of 5.5°C / min and kept warm for 15 minutes, and then controlled to cool to 950°C at a cooling rate of 1°C / min, and the above temperature-controlled heating-heat-keeping-temperature-controlled cooling process is repeated for 3 times, and finally cooled to room temperature at a cooling rate of 8°C / min to obtain the laser additively manufactured titanium alloy after heat treatment; the T β It is 965℃.

[0033] After detection, the microstructure of the laser additively manufactured titanium alloy after heat treatment in this embodiment is a near-spheroidized structure with an aspect ratio close to 2.0.

[0034] According to the test, the strength of the laser additively manufactured titanium alloy after heat treatment in this embodiment is 998 MPa, and the elongation after fracture is 22%.

[0035] Example 3

[0036] The specific process of this embodiment is: first, the laser additively manufactured TC4-DT titanium alloy with needle-like lamellar structure is placed in a high-temperature resistance furnace and heated to 955°C and kept at this temperature for 20 minutes, then cooled to 930°C at a cooling rate of 0.3°C / min, and then continued to control the heating to 955°C at a heating rate of 6°C / min and kept at this temperature for 20 minutes, and then controlled to cool to 930°C at a cooling rate of 0.3°C / min, and the above temperature-controlled heating-heat-keeping-temperature-controlled cooling process is repeated for 3 times, and finally cooled to room temperature at a cooling rate of 5°C / min to obtain the laser additively manufactured titanium alloy after heat treatment; the T β It is 965℃.

[0037] After detection, the microstructure of the laser additively manufactured titanium alloy after heat treatment in this embodiment is a near-spheroidized structure with an aspect ratio close to 1.8.

[0038] According to the test, the strength of the laser additively manufactured titanium alloy after heat treatment in this embodiment is 975 MPa, and the elongation after fracture is 22%.

[0039] Example 4

[0040] The specific process of this embodiment is: first, the laser additively manufactured TC4-DT titanium alloy with needle-like lamellar structure is placed in a high-temperature resistance furnace and heated to 960°C and kept at this temperature for 17 minutes, then cooled to 940°C at a cooling rate of 0.7°C / min, and then continued to control the heating to 960°C at a heating rate of 5.5°C / min and kept at this temperature for 17 minutes, and then controlled to cool to 940°C at a cooling rate of 0.7°C / min, and the above temperature-controlled heating-heat-keeping-temperature-controlled cooling process is repeated for 3 times, and finally cooled to room temperature at a cooling rate of 8°C / min to obtain the laser additively manufactured titanium alloy after heat treatment; the T β It is 965℃.

[0041] After detection, the microstructure of the laser additively manufactured titanium alloy after heat treatment in this embodiment is a near-spheroidized structure with an aspect ratio close to 1.8.

[0042] According to the test, the strength of the laser additively manufactured titanium alloy after heat treatment in this embodiment is 980 MPa, and the elongation after fracture is 23%.

[0043] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase, characterized in that: The specific process of the heat treatment method is: first, the laser additive manufacturing titanium alloy is heated to T β -(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β -(15℃~35℃), continue to control the heating rate at 5℃ / min~6℃ / min to T β -(5℃~10℃) and keep warm for 15min~20min, then cool to T at a cooling rate of 0.3℃ / min~1℃ / min β -(15°C~35°C), cycle the above temperature-controlled heating-heat preservation-temperature-controlled cooling process, and finally cool to room temperature at a cooling rate of 5°C / min~10°C / min to obtain a laser additive manufacturing titanium alloy after heat treatment; the T β is the β transformation temperature, in degrees Celsius; the initial structure of the laser additively manufactured titanium alloy is a needle-shaped lamellar structure; the structure of the laser additively manufactured titanium alloy after heat treatment is a near-spheroidized structure with an aspect ratio of 1.8 to 2.

0.

2. The heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase according to claim 1 is characterized in that: The laser additively manufactured titanium alloy is an α+β type titanium alloy.

3. The heat treatment method for spheroidizing laser additive manufacturing titanium alloy lamellar α phase according to claim 1 is characterized in that: The cycle continues the temperature-controlled heating-heat-insulation-temperature-controlled cooling process 2 to 3 times.

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