A method of heat treatment for laser cladding forming near-alpha titanium alloy equiaxed

Abstract

The application discloses a heat treatment method for laser cladding forming near-alpha titanium alloy equalization, the near-alpha titanium alloy comprises the following components in mass percentage: Al 5.0%-8.0%, Mo 2.0%-5.0%, Zr 1.0%-3.0%, Si 0.1%-1.0%, x 0.1%-1.0%, x<=0.5%, x is other impurity elements including Fe, C, N, H, O, and the balance is Ti, and the heat treatment method comprises annealing, slow cooling, solid solution and aging. The application controls the microstructure and the morphology and content of alpha phase of the laser cladding forming near-alpha titanium alloy through multi-stage heat treatment, obtains an equiaxed microstructure or a duplex microstructure formed by equiaxed alpha and residual beta, effectively eliminates the residual stress and anisotropy generated in the laser cladding forming process of the near-alpha titanium alloy, improves the comprehensive mechanical properties, and is suitable for the fields of aerospace, ocean engineering, petroleum chemical industry, transportation and the like.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy heat treatment technology, specifically relating to a heat treatment method for laser cladding forming of near-α type titanium alloys to achieve equiaxedness. Background Technology

[0002] Titanium alloys are widely used in important fields such as aerospace, marine engineering, and petrochemicals. During the additive manufacturing process of titanium alloys, due to the layer-by-layer deposition and rapid solidification, columnar β-grains that grow along the deposition direction are easily formed, resulting in a significant anisotropy in the microstructure. Simultaneously, the rapid solidification process easily forms non-equilibrium phases, such as acicular α' martensite and Widmanstätten structure. The presence of these brittle phases reduces the material's plasticity and toughness.

[0003] Equiaxed grains, with their similar dimensions across three dimensions, significantly reduce the anisotropy commonly found in additive manufacturing, making the strength, plasticity, and toughness of the material more consistent in different directions. The uniform distribution of equiaxed grains can hinder crack propagation in a single direction, making the crack propagation path more tortuous and requiring more energy, thereby extending fatigue life, improving the material's fracture resistance, and enhancing structural safety. Therefore, titanium alloys with equiaxed grains are suitable for aerospace, medical implants, and other fields with stringent requirements for multi-directional mechanical properties, reducing the risk of failure due to directional differences. In summary, the application of equiaxed microstructure in additive manufacturing of titanium alloys can improve the overall performance of the material; therefore, optimizing the process parameters for equiaxing additive manufacturing titanium alloys will further promote its industrial application. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a heat treatment method for equiaxing near-α type titanium alloys formed by laser cladding. This method controls the microstructure and morphology and content of the α phase in the laser-clad near-α type titanium alloy through multi-stage heat treatment including annealing, slow cooling, solution treatment, and aging. This results in an equiaxed microstructure or a bimodal microstructure composed of equiaxed α phases and residual β phases, effectively eliminating residual stress and anisotropy generated during the laser cladding process, improving its comprehensive mechanical properties, and fulfilling the requirement for equiaxing of titanium alloys in existing additive manufacturing processes.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a heat treatment method for isoaxialization of laser cladding near-α type titanium alloy, characterized in that the near-α type titanium alloy comprises the following components by mass percentage: Al 5.0%~8.0%, Mo 2.0%~5.0%, Zr 1.0%~3.0%, Si 0.1%~1.0%, x≤0.5%, where x is other impurity elements including Fe, C, N, H, and O, and the balance is Ti. This heat treatment method controls the microstructure and morphology and content of the α phase of the laser cladding near-α type titanium alloy by performing multi-stage heat treatment including annealing, slow cooling, solution treatment, and aging, thereby obtaining a high-strength laser cladding near-α type titanium alloy.

[0006] Typically, the raw material used in the laser cladding forming of near-α type titanium alloys in this invention is titanium alloy powder. The titanium alloy powder does not exhibit bonding or agglomeration, has good sphericity, and the powder surface is free of pores, with a particle size mainly ranging from 80 μm to 110 μm.

[0007] The laser cladding process parameters for near-α type titanium alloys of this invention are as follows: laser power 6kW~8kW, scanning speed 800mm / min~1200mm / min, powder feeding speed 1000g / H~1200g / H, and overlap ratio 30%~50%.

[0008] The above-mentioned heat treatment method for laser cladding forming of near-α type titanium alloy equiaxed is characterized in that the heat treatment includes the following steps:

[0009] Step 1: Heat the laser-clad near-α type titanium alloy to 500℃~600℃ and hold for 4h~10h for annealing, then air cool;

[0010] Step 2: Heat the laser-clad near-α type titanium alloy that was air-cooled in Step 1 to T. β Incubate at -10℃ for 1 to 4 hours, then slowly cool; the T β The β phase transformation temperature is given by laser cladding forming of near-α type titanium alloys, in °C.

[0011] Step 3: The laser-clad near-α type titanium alloy, which was slowly cooled in Step 2, is then subjected to T... β -20℃~T β Solution treatment is performed by holding the solution at -150℃ for 1 to 4 hours, followed by air cooling.

[0012] Step 4: Hold the laser-clad near-α type titanium alloy that was air-cooled in Step 3 at 400℃~700℃ for 4h~8h, and then air-cool it to obtain the heat-treated laser-clad near-α type titanium alloy.

[0013] The above-mentioned heat treatment method for laser cladding forming of near-α type titanium alloy equiaxed is characterized in that the slow cooling rate in step two is no faster than 30℃ / min, and the cooling termination temperature is lower than the α+β phase temperature, which is beneficial to the equiaxed formation of the α phase.

[0014] The above-mentioned heat treatment method for laser cladding forming of near-α type titanium alloy to achieve equiaxedness is characterized by repeatedly performing the heating and slow cooling process described in step two until the α phase reaches the target degree of equiaxedness through phase transformation.

[0015] The above-mentioned heat treatment method for equiaxing near-α type titanium alloy by laser cladding is characterized in that the laser cladding near-α type titanium alloy after heat treatment in step four has an equiaxed structure or a bimodal structure composed of equiaxed α and residual β.

[0016] The above-mentioned heat treatment method for equiaxing near-α type titanium alloy by laser cladding is characterized in that the room temperature mechanical properties of the laser cladding near-α type titanium alloy after heat treatment are: tensile strength Rm≥1000MPa, elongation after fracture A≥8%.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention involves multi-stage heat treatment of laser-clad near-α titanium alloys to control the microstructure and morphology and content of the α phase, thereby obtaining an equiaxed microstructure or a bimodal microstructure composed of equiaxed α and residual β. This effectively eliminates the residual stress and anisotropy generated in the laser-clad near-α titanium alloy during the laser cladding process, resulting in a laser-clad near-α titanium alloy with excellent comprehensive mechanical properties.

[0019] 2. This invention applies a multi-stage heat treatment process to laser-clad near-α titanium alloys, including annealing, slow cooling, solution treatment, and aging. Stress-relief annealing and multi-stage heating and slow cooling are used, with controlled cooling rates to achieve low undercooling. Low undercooling is the dominant condition for α-phase precipitation, thereby regulating the aspect ratio of the α-phase and suppressing α-phase precipitation. s The precipitation of α phase achieves the goals of spheroidizing the α phase, realizing equiaxed structure, and avoiding lamellar α anisotropy. Furthermore, the α phase content and α phase in the titanium alloy are controlled through solution treatment and aging. s By utilizing the synergistic effect of precipitation strengthening and grain refinement strengthening, the comprehensive mechanical properties of near-α type titanium alloys formed by laser cladding are ultimately optimized and controlled.

[0020] 3. The room temperature mechanical properties of the laser cladding near-α type titanium alloy after heat treatment in this invention are: tensile strength Rm≥1000MPa, elongation after fracture A≥8%, which has high strength characteristics and has wide application value in aerospace, marine engineering, petrochemical, transportation and other fields.

[0021] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0022] Figure 1 This is a metallographic diagram of the near-α type titanium alloy after heat treatment and laser cladding in Example 1 of the present invention.

[0023] Figure 2 This is a metallographic diagram of the near-α type titanium alloy after heat treatment and laser cladding in Example 2 of the present invention. Detailed Implementation

[0024] Example 1

[0025] The nominal composition of the laser cladding near-α type titanium alloy in this embodiment is Ti-6Al-3Mo-1.5Zr-0.3Si, which includes the following components by mass percentage: Al 6%, Mo 3%, Zr 1.5%, Si 0.3%, x≤0.5%, where x is other impurity elements including Fe, C, N, H, and O, and the balance is Ti.

[0026] The laser cladding process parameters for near-α type titanium alloy are as follows: laser power 6kW, scanning speed 1000mm / min, powder feeding speed 1000g / H, and overlap ratio 30%.

[0027] The heat treatment method for laser cladding forming of near-α type titanium alloy equiaxed in this embodiment includes the following steps:

[0028] Step 1: Heat the laser-clad near-α type titanium alloy to 540℃ and hold for 6 hours for annealing, then air cool;

[0029] Step 2: Heat the laser-clad near-α titanium alloy that was air-cooled in Step 1 to 1005℃ and hold for 1 hour. Then cool it to 500℃ at a cooling rate of 5℃ / min. Repeat the heating and holding process twice, for a total of three times.

[0030] Step 3: The laser-clad near-α type titanium alloy that was slow-cooled for the third time in Step 2 is solution-treated by holding it at 890℃ for 2 hours, and then air-cooled to room temperature.

[0031] Step 4: The laser-clad near-α type titanium alloy that was air-cooled in Step 3 is held at 530℃ for 6 hours, and then air-cooled to obtain the heat-treated laser-clad near-α type titanium alloy.

[0032] Figure 1 This is a metallographic image of the laser-clad near-α type titanium alloy after heat treatment in this embodiment. Figure 1 It can be seen that the laser-clad near-α type titanium alloy after heat treatment has an equiaxed structure consisting of equiaxed α and residual β.

[0033] According to the test results, the room temperature mechanical properties of the laser cladding near-α type titanium alloy after heat treatment in this embodiment are: tensile strength Rm = 1085 MPa, elongation after fracture A = 14.5%.

[0034] Example 2

[0035] The nominal composition of the laser cladding near-α type titanium alloy in this embodiment is Ti-7.8Al-4Mo-2Zr-0.3Si, which includes the following components by mass percentage: Al 7.8%, Mo 4%, Zr 2%, Si 0.3%, Fe 0.2%, x≤0.3%, where x is other impurity elements including Fe, C, N, H, and O, and the balance is Ti;

[0036] The laser cladding process parameters for near-α type titanium alloy are as follows: laser power 6kW, scanning speed 1000mm / min, powder feeding speed 1000g / H, and overlap ratio 30%.

[0037] The heat treatment method for laser cladding forming of near-α type titanium alloy equiaxed in this embodiment includes the following steps:

[0038] Step 1: Heat the laser-clad near-α type titanium alloy to 540℃ and hold for 6 hours for annealing, then air cool;

[0039] Step 2: Heat the laser-clad near-α type titanium alloy that was air-cooled in Step 1 to 1005℃ and hold for 1 hour, then slowly cool it to room temperature at a cooling rate of 0.5℃ / min.

[0040] Step 3: The laser-clad near-α type titanium alloy that was slowly cooled in Step 2 is solution-treated at 990℃ for 2 hours, and then air-cooled to room temperature.

[0041] Step 4: The laser-clad near-α type titanium alloy that was air-cooled in Step 3 is held at 650℃ for 6 hours, and then air-cooled to obtain the heat-treated laser-clad near-α type titanium alloy.

[0042] Figure 2 This is a metallographic image of the laser-clad near-α type titanium alloy after heat treatment in this embodiment. Figure 2 It can be seen that the laser-clad near-α type titanium alloy after heat treatment has a dual-state structure consisting of equiaxed α and residual β.

[0043] According to the test results, the room temperature mechanical properties of the laser cladding near-α type titanium alloy after heat treatment in this embodiment are: tensile strength Rm = 1113 MPa, elongation after fracture A = 11.5%.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A heat treatment method for laser cladding forming of near-α-type titanium alloy to achieve equiaxed structure, characterized in that, The near-alpha titanium alloy comprises the following components by mass percentage: Al 5.0%~8.0%, Mo 2.0%~5.0%, Zr 1.0%~3.0%, Si 0.1%~1.0%, x≤0.5%, where x represents other impurity elements including Fe, C, N, H, and O, with the balance being Ti. This heat treatment method involves multi-stage heat treatment, including annealing, slow cooling, solution treatment, and aging, to control the microstructure and morphology and content of the alpha phase in the laser-clad near-alpha titanium alloy, resulting in a high-strength laser-clad near-alpha titanium alloy. The heat treatment includes the following steps: Step 1: Heat the laser-clad near-α type titanium alloy to 500℃~600℃ and hold for 4h~10h for annealing, then air cool; Step 2: Heat the laser-clad near-α type titanium alloy that was air-cooled in Step 1 to T. β Incubate at -10℃ for 1-4 hours, then slowly cool; the T β The β phase transformation temperature is given by laser cladding forming of near-α type titanium alloys, in °C. Step 3: The laser-clad near-α type titanium alloy, which was slowly cooled in Step 2, is then subjected to T... β -20℃~T β Solution treatment is performed by holding the solution at -150℃ for 1 to 4 hours, followed by air cooling. Step 4: Hold the laser-clad near-α type titanium alloy that was air-cooled in Step 3 at 400℃~700℃ for 4h~8h, and then air-cool it to obtain the heat-treated laser-clad near-α type titanium alloy.

2. The heat treatment method for achieving equiaxed near-α type titanium alloy by laser cladding as described in claim 1, characterized in that, The slow cooling rate described in step two is no faster than 30℃ / min, and the cooling termination temperature is lower than the temperature of the α+β phase region, which is beneficial to the equiaxed formation of the α phase.

3. The heat treatment method for achieving equiaxed near-α type titanium alloy by laser cladding as described in claim 1, characterized in that, Repeat the heating and slow cooling process described in step two multiple times until the α phase reaches the target equiaxed degree through phase transformation.

4. The heat treatment method for achieving equiaxed near-α type titanium alloy by laser cladding as described in claim 1, characterized in that, The laser-clad near-α type titanium alloy after heat treatment described in step four has an equiaxed structure or a bimodal structure consisting of equiaxed α and residual β.

5. The heat treatment method for laser cladding forming of near-α type titanium alloy to achieve equiaxed structure, as described in claim 1, is characterized in that... The room temperature mechanical properties of the laser-clad near-α type titanium alloy after heat treatment are: tensile strength Rm≥1000MPa, elongation after fracture A≥8%.

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