Heat treatment method for improving mechanical property of GH4099 high-temperature alloy

Abstract

The invention discloses a heat treatment method for improving the mechanical property of a GH4099 high-temperature alloy, which comprises the following steps: firstly, printing a GH4099 alloy material into a part by adopting an additive manufacturing method, and then sequentially carrying out annealing treatment, hot isostatic pressing treatment, solution treatment and aging treatment on the part to obtain a final part, annealing treatment, hot isostatic pressing treatment (HIP), solution treatment and aging treatment are sequentially conducted on the GH4099 alloy subjected to 3D printing, the defects and texture problems generated by printing are eliminated through hot isostatic pressing treatment, and then the mechanical property of the GH4099 alloy is further improved through solution treatment and aging treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy heat treatment, and in particular relates to a heat treatment method for improving the mechanical properties of GH4099 high temperature alloy. Background Art

[0002] Materials used in aircraft engines usually need to serve in high-temperature environments, and because the combustion chamber is under high temperature and high pressure for a long time, the quality of the material itself is greatly tested. If the existing materials are not modified and optimized, their properties are difficult to meet the requirements of use. At present, solid solution treatment and aging treatment are usually used to optimize the performance of GH4099, a material used in aircraft engines. However, since GH4099 high-temperature alloy is mainly obtained by additive manufacturing, the disadvantages of additive manufacturing will also be inherited in the formed GH4099. Its main disadvantages are divided into two categories. One is the defects such as holes and cracks generated during the printing process. These defects are difficult to eliminate through general heat treatment and will be preserved in the final parts, weakening the performance of the parts. Second, due to the inherent thermal gradient direction of the printing process, columnar grains and strong textures will be produced. The long axis direction of these columnar grains is parallel to the printing direction. When the columnar crystals are subjected to force in the long axis direction and the short axis direction, their deformation resistance is different, which ultimately leads to the anisotropy of the macroscopic properties of the material. The texture will also lead to the anisotropy of the mechanical properties, which greatly affects the actual use of the parts.

[0003] Chinese invention patent CN202311773508.0 discloses a heat treatment process to eliminate the low plasticity of GH4099 nickel-based high-temperature alloy at medium temperature. The process adopts solution treatment plus aging treatment technology, but it aims to improve medium and low temperature plasticity and reduce alloy cracking, and cannot solve the problem of anisotropy of mechanical properties of materials. Chinese invention patent CN202111310804.8 discloses a heat treatment method for GH4099 alloy components formed by laser selective melting. The method uses laser selective melting process to prepare GH4099 alloy, and then annealing to relieve stress, as well as solution and aging to improve performance, and obtains certain performance, but does not optimize the holes, orientation, and grain morphology generated in the printing process, and its hole problem and anisotropy of mechanical properties are still not solved. Summary of the invention

[0004] The purpose of the present invention is to provide a heat treatment method for improving the mechanical properties of GH4099 high temperature alloy, which overcomes the problems of defect cavities generated by printing and anisotropy of mechanical properties of materials.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A heat treatment method for improving the mechanical properties of a GH4099 high temperature alloy, comprising firstly printing a GH4099 alloy material into a part by a laser additive manufacturing method, and then sequentially performing annealing treatment, hot isostatic pressing treatment, solution treatment, and aging treatment on the part;

[0007] Wherein, the annealing temperature is 900°C and the holding time is 5h;

[0008] The hot isostatic pressing treatment is performed at a temperature of 1180°C, a time of 3 hours, and an applied pressure of 160 MPa;

[0009] The temperature of the solution treatment is 1140°C and the time is 1h;

[0010] The aging treatment temperature is 900°C and the time is 5h;

[0011] The heating rate of the above temperatures is 10°C / min, and air cooling is adopted.

[0012] Furthermore, the purity of the GH4099 alloy material is greater than 99.9%, the particle size is 15 to 53 μm, and the mass percentages of its alloy components are: Al 1.70-2.40%, Fe≤2.00%, Co 5.00-8.00%, Cr 17.00-20.00%, W3.50-4.50%, Ti 1.00-1.50%, Ni-balance.

[0013] Furthermore, the annealing is performed by vacuum annealing, and the vacuum degree reaches 10 -3 Pa.

[0014] Furthermore, the gas used for the air cooling is argon.

[0015] The present invention has the following beneficial effects:

[0016] (1) Using hot isostatic pressing technology under specific high temperature and high pressure conditions, the holes in the parts are eliminated and their density is further improved. At the same time, the recrystallization of the grains is promoted, the original columnar crystal morphology is changed, and the anisotropy of the mechanical properties of the material is eliminated.

[0017] (2) The high temperature annealing process is used for the printed parts. Compared with the general annealing treatment, it can better eliminate the residual stress and avoid the bending and deformation of the parts.

[0018] (3) Through optimized solid solution failure treatment, strengthening phase is precipitated, which greatly improves its mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a comparison chart of the performance of 900℃ high temperature tensile test.

[0020] Figure 2 This is a graph showing the changes in grain morphology.

[0021] Figure 3 This is the recrystallization change diagram.

[0022] Figure 4 This is a texture reduction diagram.

[0023] Figure 5 Defect statistics chart. DETAILED DESCRIPTION

[0024] This embodiment provides a heat treatment method for improving the mechanical properties of GH4099 high temperature alloy, which is suitable for additive manufacturing of GH4099 and includes the following steps:

[0025] Step 1: Laser additive manufacturing;

[0026] Commercial GH4099 high-temperature alloy powder (purity > 99.9%, particle size 15-53 μm, alloy composition (mass percentage): Al-1.70-2.40%, Fe-≤2.00%, Co-5.00-8.00%, Cr-17.00-20.00%, W-3.50-4.50%, Ti-1.00-1.50%, Ni-balance) was used and formed by laser powder bed process with appropriate printing parameters.

[0027] Step 2: annealing;

[0028] The formed alloy parts are annealed at a temperature of 900°C at a heating rate of 10°C / min and kept at this temperature for 5 hours. The annealing is performed in vacuum with a vacuum degree of 10 -3 Pa, and then rapidly cooled using argon gas to prevent oxidation and fix its microstructure.

[0029] Annealing the high-temperature alloy after printing can eliminate the huge residual stress generated during printing, prevent the material from deforming and twisting, and facilitate subsequent processing.

[0030] Step 3: hot isostatic pressing;

[0031] The annealed parts were subjected to hot isostatic pressing treatment. The hot isostatic pressing temperature was set to 1180°C, and argon gas was used for pressurization. The pressure was finally maintained at 160 MPa and maintained in this environment for 3 hours.

[0032] Hot isostatic pressing is to put the parts into a high temperature and high pressure environment, and soften the parts by high temperature close to the melting point. At the same time, in the hot isostatic pressing atmosphere, each part is subjected to inward static pressure. In this state, the holes, cracks and other defects inside the parts will be gradually compressed and eventually eliminated, thereby improving its density. Since the pores and cracks are eliminated by high temperature and high pressure, the subsequent heat treatment and use generally cause the eliminated cracks to regenerate, so the performance deterioration of the parts caused by defect distribution can be well eliminated.

[0033] Step 4: solution treatment;

[0034] The parts after hot isostatic pressing were subjected to solution treatment at a heating rate of 10°C / min to 1140°C and maintained at this temperature for 1 hour. The heat treatment atmosphere was vacuum with a vacuum degree of 10 -3 Pa, and then cooled by passing argon gas.

[0035] The parts after hot isostatic pressing are homogenized to dissolve the grain boundary carbides and unevenly precipitated γ′ and δ phases of different sizes produced by the previous heat treatment, so that the elements can re-enter the matrix to facilitate the precipitation of γ′ phases of specific sizes by aging.

[0036] Step 5: Aging treatment

[0037] The solutionized parts were aged at a heating rate of 10°C / min to 900°C and then kept at this temperature for 5 hours. The heat treatment atmosphere was vacuum to prevent oxidation. Argon cooling was used to control the size and distribution of the precipitated phase.

[0038] The solutionized parts are subjected to aging treatment to precipitate the main strengthening phase γ′ of the alloy and improve its mechanical properties.

[0039] Due to the high temperature conditions during the hot isostatic pressing process, while eliminating defects, it also promotes the recrystallization of grains (the driving force for recrystallization comes from two parts, one is the microscopic residual stress generated by printing, and annealing can only eliminate the macroscopic part. The second is the thermodynamic driving force provided by high temperature). The anisotropy of mechanical properties of the printed alloy is mainly due to the specific thermal gradient of the printing process. Due to the hot isostatic pressing treatment, the grains are recrystallized. The thermal gradient at this time has no specific direction and tends to generate equiaxed grains. At the same time, the texture generated by the thermal gradient is also weakened, so its final macroscopic anisotropy is basically eliminated.

[0040] In this embodiment, the 3D printed GH4099 alloy is subjected to annealing, hot isostatic pressing (HIP), solution treatment and aging treatment in sequence. The defects and texture problems caused by printing are eliminated by hot isostatic pressing, and the mechanical properties are further improved by solution aging treatment.

[0041] Figure 1 This is a comparison chart of the performance of the 900℃ high temperature tensile test. The sample without HIP treatment has a lower elongation in the vertical direction (as shown by the green line) and breaks quickly during the stretching process. In contrast, the elongation of the transverse sample is higher, and the elongation basically reaches 7% (as shown by the blue line). This shows that the sample without HIP treatment has anisotropy of mechanical properties due to its uneven microstructure. After HIP, its elongation increases significantly, and the mechanical properties are greatly improved.

[0042] Figure 2 is the grain morphology change diagram, such as Figure 2 (a), (b), (c), (d), and (e) represent the EBSD images of the deposited, annealed, hot isostatically pressed, solution, and aged states in the vertical direction, respectively. It can be seen from the figure that the grain morphology of the deposited and annealed states is mainly long columnar crystals. After HIP treatment, the columnar crystal morphology disappears and transforms into equiaxed crystals, indicating that HIP can promote the transformation of its grain morphology. As we all know, columnar crystals will greatly affect its macroscopic properties, resulting in differences in the vertical and horizontal properties of the macroscopic specimen. Through HIP treatment, the recrystallization of the grains is promoted, and the anisotropic columnar crystals are transformed into isotropic equiaxed crystals, which greatly improves the usability of the product. Subsequent solution and aging treatments basically do not change its grain morphology.

[0043] Figure 3 is the recrystallization change diagram, Figure 3 (a), (b), (c), (d), and (e) represent the recrystallization diagrams in the vertical direction of the deposited, annealed, hot isostatically pressed, solid solution, and aged states, respectively. In the deposited and annealed states, the grains are basically deformed grains, still maintaining the original columnar shape. After HIP treatment, the deformed grains basically disappear and are basically transformed into recovered grains and recrystallized grains, further confirming the changes in grain morphology mentioned above.

[0044] Figure 4 is the texture reduction map, Figure 4 (a), (b), (c), (d), and (e) represent the vertical texture diagrams of the deposited, annealed, hot isostatically pressed, solid solution, and aged states, respectively. It can be seen from the figures that the texture of the printed and annealed states is relatively strong, and the orientation factor is above 6. A larger orientation factor also corresponds to a stronger anisotropy. Through HIP treatment, a recrystallization process occurs, and its orientation factor is reduced to about 3, which also improves the anisotropy of its performance.

[0045] Figure 5 is the defect statistics chart, Figure 5(a), (b), (c) are the horizontal defect distribution diagrams of the deposition state, annealing state and thermal isostatic state, (d), (e), (f) are the vertical defect distribution diagrams of the deposition state, annealing and isostatic state, and (g) is the defect diagram. As can be seen from the figure, there are many defects in the vertical direction, both in the printing state and the annealing state. After HIP treatment, the defects are greatly eliminated, and the defect density in the horizontal and vertical directions is basically the same, and the anisotropy caused by the defects has been basically eliminated.

[0046] The above description is only a preferred implementation manner of the present invention, but the protection scope of the present invention is not limited thereto, and any modification and replacement based on the technical solution and inventive concept provided by the present invention should be included in the protection scope of the present invention.

Claims

1. A heat treatment method for improving the mechanical properties of GH4099 high temperature alloy, characterized in that: The process includes firstly printing GH4099 alloy material into parts by laser additive manufacturing method, and then sequentially performing annealing treatment, hot isostatic pressing treatment, solution treatment, and aging treatment on the parts; Wherein, the annealing temperature is 900°C and the holding time is 5h; The hot isostatic pressing treatment is performed at a temperature of 1180°C, a time of 3 hours, and an applied pressure of 160 MPa; The temperature of the solution treatment is 1140°C and the time is 1h; The aging treatment temperature is 900°C and the time is 5h; The heating rate of the above temperatures is 10°C / min, and air cooling is adopted.

2. A heat treatment method for improving the mechanical properties of GH4099 high temperature alloy according to claim 1, characterized in that: The purity of the GH4099 alloy material is greater than 99.9%, the particle size is 15-53 μm, and the mass percentage of its alloy components is: Al 1.70-2.40%, Fe≤2.00%, Co5.00-8.00%, Cr 17.00-20.00%, W 3.50-4.50%, Ti1.00-1.50%, Ni-balance.

3. A heat treatment method for improving the mechanical properties of GH4099 high temperature alloy according to claim 1, characterized in that: The annealing is performed by vacuum annealing, and the vacuum degree reaches 10 -3 Pa.

4. A heat treatment method for improving the mechanical properties of GH4099 high temperature alloy according to claim 1, characterized in that: The gas used for air cooling is argon.

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