Heat treatment method for additive manufacturing of GH4099 alloy

Abstract

The invention relates to the technical field of additive manufacturing, in particular to a heat treatment method for improving the high-temperature toughness of an additive manufacturing nickel-based superalloy GH4099. Comprising the following steps: (1) a first-step high-temperature solution treatment system: preserving heat at 1180-1225 DEG C for 1-4 hours, and cooling to below 900 DEG C at the speed of 0.1-10 DEG C / min; (2) a second-step low-temperature solution treatment system: keeping the temperature at 980-1050 DEG C for 2-5 hours, and cooling (or air-cooling) to 900 DEG C or below at the speed of 10-50 DEG C / min; and (3) the aging treatment system is that heat preservation is conducted for 4-16 h at the temperature of 780-900 DEG C, and air cooling is conducted. According to the method, stable control of carbides, formation of zigzag grain boundaries, increase of twin crystal structures and size bimodal distribution of gamma'phases are achieved through high-temperature and low-temperature two-step solid solution and regulation and control of the cooling rate; the GH4099 nickel-based high-temperature alloy formed through additive manufacturing has the advantages that the tensile property at the high temperature of 900 DEG C is greatly improved under the condition that the tensile property at the room temperature is basically kept, the yield strength is improved by 15-50%, and the elongation is increased by 100-350%.

Description

Technical Field

[0001] The present invention relates to the field of laser powder bed fusion (LPBF) additive manufacturing and material heat treatment, and specifically to a high-low temperature two-step solution and aging treatment, and a method for regulating the microstructure of an LPBF-GH4099 high-temperature alloy by a heat treatment method that controls the cooling rate, thereby simultaneously improving the high-temperature strength and plasticity of the alloy. Background Art

[0002] Laser powder bed fusion (LPBF), as an advanced additive manufacturing technology, has the ability to manufacture complex shapes, quickly realize prototyping, flexible customized design, reduce assembly time, speed up iteration cycle, and improve supply chain flexibility and stability, giving it unique advantages in the manufacturing of complex high-temperature alloy parts for aerospace engines.

[0003] GH4099 is a high-temperature alloy with comprehensive strengthening of cobalt, tungsten, molybdenum, aluminum, titanium and other elements, with high thermal strength and excellent organizational stability. The alloy can serve for a long time at a high temperature of 900℃, and the maximum operating temperature can reach 1000℃. It is suitable for manufacturing complex high-temperature load-bearing structural parts such as combustion chambers and afterburner chambers of aircraft and aero-engines.

[0004] During the LPBF process of preparing nickel-based superalloys, the high temperature gradient (≥10 5 K / cm) and high cooling rates (10 6 -10 8 K / s), the microstructure of the alloy is generally composed of fine columnar crystals epitaxially grown at the bottom boundary of the molten pool and equiaxed crystals at the top of the molten pool. The rapid solidification process accumulates high residual stress, microsegregation and other structural inhomogeneities; because the laser heat source always acts on the top of the formed part and undergoes repeated thermal cycles, the microstructure is prone to anisotropy. These microstructural characteristics seriously affect the room temperature and high temperature mechanical properties of the GH4099 nickel-based high-temperature alloy, limiting its application in extreme environments such as high temperature and high pressure. Traditional heat treatment methods have certain limitations in improving the microstructure of LPBF-GH4099 alloy. Therefore, it is necessary to develop a heat treatment method in a targeted manner to effectively regulate its microstructure, thereby optimizing the mechanical properties of the LPBF-GH4099 alloy. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of existing heat treatment and provide a heat treatment method for GH4099 alloy for additive manufacturing to solve the problem that it is difficult to simultaneously meet the requirements of high temperature strength and plasticity of GH4099 alloy formed by laser powder bed melting.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] Step 1: Forming GH4099 alloy for the first step of high temperature solution treatment: the solution temperature is 1180-1225℃ (60-100℃ higher than the traditional GH4099 alloy solution treatment temperature), and the holding time is 1-4 h.

[0008] Step 2: For the GH4099 alloy that has been first solution treated in step 1, a second solution treatment at a relatively low temperature is performed: the solution temperature is 1000-1050°C (conventional GH4099 alloy heat treatment usually does not have this step), and the holding time is 2-5h;

[0009] The two-step solid solution in step 1 and step 2 are cooled at a rate of 0.1-10°C / min and 10-50°C / min (or air cooling) respectively.

[0010] Step 3: Perform aging treatment on the GH4099 alloy subjected to two-step solution treatment in step 2: the aging temperature is 780-900°C, the aging insulation is 4-16 h, and then air-cooled to room temperature.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The present invention achieves sufficient recrystallization through a reasonable heat treatment process, thereby eliminating the microstructure anisotropy of the LPBF-GH4099 alloy;

[0013] In a specific embodiment of the present invention, the first step of step 2 is solid solution cooled at a controlled temperature of 0.1-10°C / min to obtain a tortuous grain boundary, and at the same time promotes the formation of a large number of tetragonal γ' precipitation phases and annealing twins under controlled cooling conditions;

[0014] In a specific embodiment of the present invention, compared with the traditional GH4099 solution treatment, the present invention adopts a high-low temperature two-step solution treatment, the second step of step three has a solution temperature of 1000-1050°C and a holding time of 2-5 h; the particle carbide M with a size of 400-1200 nm is promoted. 23 C 6 The phase precipitates uniformly and discontinuously at the grain boundary (to avoid carbides from forming a film), and there are some 50-200 nm M 23 C 6 Carbide phase.

[0015] In a specific embodiment of the present invention, step three aging treatment: temperature 780-900°C, insulation 4-16 h, to ensure that the γ' phase formed in the solution cooling process continues to grow, the Al and Ti atoms dissolved in the matrix re-nucleate and transform and grow to the γ' phase, and achieve a bimodal distribution of the γ' phase with 20-200 nm and 100-1000 nm.

[0016] In a specific embodiment of the present invention, the GH4099 high temperature alloy material obtained by the heat treatment has greatly improved tensile properties at 900°C:

[0017] Room temperature tensile properties: tensile strength 1170-1240 MPa, yield strength 690-750 MPa, elongation after fracture 30%-35%, section shrinkage 28%-36%;

[0018] 900℃ high temperature tensile properties: tensile strength 405-495 MPa, yield strength 360-480 MPa, elongation after break 17%-31%, and section shrinkage 20%-28%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the heat treatment process of the present invention;

[0020] Figure 2 This is a microstructure photo of the LPBF-GH4099 alloy after the first step of high temperature solution treatment in the present invention;

[0021] Figure 3 The microstructure photo of the LPBF-GH4099 alloy after high and low temperature two-step solution treatment in the present invention;

[0022] Figure 4 The microstructure photo of the LPBF-GH4099 alloy after high and low temperature two-step solid solution and aging treatment in the present invention;

[0023] Figure 5 The room temperature tensile properties of LPBF-GH4099 alloy samples after heat treatment in different embodiments and comparative examples;

[0024] Figure 6 900°C high temperature tensile properties of LPBF-GH4099 alloy samples after heat treatment in different embodiments and comparative examples; DETAILED DESCRIPTION

[0025] The present invention proposes a heat treatment method for additive manufacturing of GH4099 alloy, and the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only the parts related to the present invention are shown in the accompanying drawings, not all.

[0026] Example 1

[0027] This embodiment provides a method for improving the high temperature strength and plasticity of GH4099 nickel-based high temperature alloy manufactured by additive manufacturing, comprising the following steps:

[0028] (1) The deposited GH4099 alloy sample was kept at 1210℃ for 1 h and then cooled to room temperature at a cooling rate of 3℃ / min;

[0029] (2) The GH4099 sample treated in (1) was kept at 1010°C for 3 h, and then air-cooled to room temperature;

[0030] (3) The GH4099 sample treated in (2) was kept at 850°C for 8 h, then taken out and air-cooled to room temperature.

[0031] Example 2

[0032] This example is based on the preparation method of Example 1, except that the first step of solid solution temperature and cooling rate are different, and step (1) is different:

[0033] (1) The deposited GH4099 alloy sample was kept at 1190℃ for 2 h and then cooled to 600℃ at a cooling rate of 0.5℃ / min;

[0034] (2) The GH4099 sample treated in (1) was kept at 1010°C for 3 h, and then air-cooled to room temperature;

[0035] (3) The GH4099 sample treated in (2) was kept at 850°C for 8 h, then taken out and air-cooled to room temperature.

[0036] Example 3

[0037] This example is based on the preparation method of Example 1, except that the second step solid solution temperature and cooling method are different, and step (2) is different:

[0038] (1) The deposited GH4099 alloy sample was kept at 1210℃ for 1 h and then cooled to room temperature at a cooling rate of 3℃ / min;

[0039] (2) The GH4099 sample treated in (1) was kept at 1040°C for 3 h, and then cooled to 500°C at a rate of 50°C / min;

[0040] (3) The GH4099 sample treated in (2) was kept at 850°C for 8 h and then air-cooled to room temperature.

[0041] Example 4

[0042] This example is based on the preparation method of Example 1, except that the aging and heat preservation temperature and time are different, and step (1) is different:

[0043] (1) The deposited GH4099 alloy sample was kept at 1210℃ for 1 h and then cooled to room temperature at a cooling rate of 3℃ / min;

[0044] (2) The GH4099 sample treated in (1) was kept at 1010°C for 3 h and then air-cooled to room temperature;

[0045] (3) The GH4099 sample treated in (2) was kept at 790°C for 15 h and then air-cooled to room temperature.

[0046] In Examples 1-4, the room temperature tensile properties of the LPBF-GH4099 alloy obtained by the treatment are: transverse and longitudinal tensile strength 1170 MPa~1240 MPa, yield strength 690 MPa~750 MPa, elongation 30%~35%, and cross-sectional shrinkage 28%~36%.

[0047] In Examples 1-4, the high temperature tensile properties of the LPBF-GH4099 alloy obtained by the treatment at 900°C are: transverse and longitudinal tensile strength 405 MPa-495 MPa, yield strength 360 MPa-480 MPa, elongation 17%-31%, and cross-sectional shrinkage 20%-28%.

[0048] Comparative Example 1

[0049] Comparative Example 1 adopts a conventional heat treatment method, comprising the following steps:

[0050] (1) The printed GH4099 alloy sample was kept at 1140℃ for 2 h and then air-cooled to room temperature.

[0051] (2) The GH4099 sample treated in (1) was kept at 850°C for 8 h and then air-cooled to room temperature;

[0052] Comparative Example 2

[0053] Comparative Example 3 adopts a one-step high-temperature solution and aging heat treatment method, comprising the following steps:

[0054] (1) The printed GH4099 alloy sample was kept at 1210℃ for 2 h and then air-cooled to room temperature.

[0055] (2) The GH4099 sample treated in (1) was kept at 850°C for 8 h and then air-cooled to room temperature;

[0056] Comparative Example 3

[0057] Comparative Example 3 provides a two-step solution and aging heat treatment method, comprising the following steps:

[0058] (1) The printed GH4099 alloy sample was kept at 1210℃ for 2 h and then air-cooled to room temperature.

[0059] (2) The GH4099 sample treated in (1) was kept at 1010°C for 3 h and then air-cooled to room temperature;

[0060] (3) The GH4099 sample treated in (2) was kept at 850°C for 8 h and then air-cooled to room temperature.

Claims

1. A heat treatment method for additive manufacturing of GH4099 alloy, characterized in that: The following steps are involved: The GH4099 nickel-based high-temperature alloy powder is formed by laser powder bed melting; then, the formed GH4099 alloy is subjected to high-low temperature two-step solution treatment and aging treatment; The first step is high temperature solution treatment: heating from room temperature to 1180-1225℃, keeping warm for 1-4 hours, and then cooling to below 900℃ at 0.1-10℃ / min; The second step of low temperature solution treatment is: heating from the temperature reached in the first step of solution cooling to 1000-1050℃, keeping it at that temperature for 2-5 hours, and then cooling at 10-50℃ / min (or air cooling) to below 900℃; The aging treatment is as follows: heating from the temperature reached in the second step of solution cooling to 780-900°C, keeping the temperature for 4-16 hours, and then air cooling to room temperature.

2. The forming of GH4099 alloy according to claim 1, characterized in that: The following steps are involved: 1) The GH4099 alloy cast bar is atomized and powdered in a vacuum induction gas atomization furnace, and the powder with a specification of 15-63 μm is sieved; 2) Place the alloy powder in step 1 in an oven for drying at 80-150°C for 2-5 hours; 3) The dried powder in step 2 is subjected to laser powder bed fusion (LPBF), wherein the parameters of the LPBF are: laser power 250-350 W, laser scanning speed 1000-1500 mm / s, scanning spacing 70-130 μm, layer thickness 30-60 μm, preheating temperature 10-180°C, oxygen content in the forming chamber is less than 500 ppm, and the scanning strategy is a strip interlayer rotation of 67°.

3. The heat treatment process of the LPBF-GH4099 alloy according to claim 1, characterized in that: The aging temperature is 780-900℃ and the holding time is 4-16 h.

4. A heat treatment method for the LPBF-GH4099 alloy according to claims 1-3, characterized in that: The microstructure of the treated GH4099 material presents a tortuous grain boundary, a bimodal distribution of the size of the γ' phase, reasonable control of the morphology and distribution of carbides, and an increase in twin crystal structure, so that the GH4099 nickel-based high-temperature alloy formed by additive manufacturing can increase the high-temperature tensile yield strength at 900°C by 15-50% and the elongation by 100-350% while the room temperature tensile properties are basically maintained.

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