A heat treatment process for eliminating low plasticity of GH4099 nickel-based alloy components at medium temperature

Abstract

The present invention relates to the technical field of powder metallurgy high-temperature alloys, and in particular to a heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature. The process comprises the following steps: (1) placing the machined GH4099 alloy component in a vacuum heat treatment furnace; (2) performing a solution heat treatment: the heat treatment temperature is 1175°C and the holding time is 1 hour; (3) after the solution heat treatment holding stage is completed, heating is stopped, cooling to 700°C at a cooling rate of 5°C / min, and then cooling with the furnace, and taking out when the temperature is 150-200°C; (4) placing the solution heat treated GH4099 alloy component in a vacuum heat treatment furnace for aging heat treatment, the heat treatment temperature is 850°C and the holding time is 5 hours; (5) after the aging heat treatment holding stage is completed, heating is stopped, cooling to 700°C at a cooling rate of 5°C / min, and then cooling with the furnace, and taking out when the temperature is 150-200°C. The present invention can avoid the low plasticity of the alloy component at medium temperature and reduce the risk of cracking of the alloy component.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy high-temperature alloys, and in particular to a heat treatment process for eliminating the low plasticity of a GH4099 nickel-based alloy component at medium temperature. Background Art

[0002] GH4099 alloy is a high-temperature alloy developed in collaboration between my country's metallurgical and aviation industries. It was originally designed for afterburner barrels in aircraft gas turbine engines. With a composition similar to that of EP693 alloy, it is a typical age-hardened nickel-based high-temperature alloy with a Ni and Co matrix, solid-solution strengthening using alloying elements such as W, Mo, and Cr, and age-hardening elements such as Al and Ti. This alloy can be used for long periods below 900°C, with a maximum operating temperature of 1000°C, and exhibits excellent comprehensive mechanical properties.

[0003] Currently, rolling and forging are the most common methods for preparing GH4099 alloy. However, due to the high strength and hardness of nickel-based superalloys and their poor deformability during plastic working, specimens are prone to cracking, resulting in low yields. Furthermore, the material utilization rate of rolled and forged specimens is low, which leads to high costs for related products. Powder metallurgy (PM) has attracted widespread attention as an ideal method for preparing superalloys due to its advantages, such as low preparation temperature, fine microstructure, uniform composition without macrosegregation, excellent mechanical properties and stability, short manufacturing cycles, near-net-shape forming of complex parts, and high material utilization.

[0004] Based on the preparation method of this alloy, its main strengthening method is heat treatment. Selecting the appropriate heat treatment is a necessary step for the workpiece to meet the use requirements. Medium-temperature low plasticity is a common phenomenon. Most metals and alloys are in the medium temperature range, about 0.5 to 0.8 times the melting point. The elongation decreases and fracture occurs along the grain boundary. There is a plastic minimum on the temperature-plasticity curve. The heat treatment cooling rate affects the strength and plasticity of the alloy. In order to ensure the performance of the alloy, it is necessary to select a suitable cooling rate to avoid the medium-temperature low plasticity phenomenon affecting the normal service of the component. Summary of the Invention

[0005] The purpose of the present invention is to provide a heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, which can avoid the low plasticity of GH4099 alloy at medium temperature, thereby reducing the risk of component cracking.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, comprising the following steps:

[0008] (1) Placing the machined GH4099 alloy components in a vacuum heat treatment furnace;

[0009] (2) Solution heat treatment: After the GH4099 alloy component has completed the solution heat treatment and holding stage, it is cooled to 700°C at a cooling rate of 5°C / min, and then continues to cool in the vacuum heat treatment furnace. When the temperature is 150-200°C, the GH4099 nickel-based alloy component is taken out;

[0010] (3) Aging heat treatment: The GH4099 alloy component prepared in step (2) is subjected to aging heat treatment, cooled to 700°C at a cooling rate of 5°C / min, and then continued to cool in a vacuum heat treatment furnace. When the temperature is 150-200°C, the GH4099 nickel-based alloy component is taken out to obtain a GH4099 nickel-based alloy component that meets the requirements in terms of shape and mechanical properties.

[0011] In the heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, in step (1), the GH4099 alloy components are prepared by powder metallurgy process, and after mechanical processing, they are placed in a vacuum heat treatment furnace for heat treatment.

[0012] In the heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, in step (2), the solution heat treatment temperature is 1175° C. and the holding time is 1 hour.

[0013] In the heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, in step (3), the aging heat treatment temperature is 850° C. and the holding time is 5 hours.

[0014] In the heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, the heating rate during the solution aging heat treatment in step (2) and the aging heat treatment in step (3) is less than 8°C / min.

[0015] The design concept of the present invention is:

[0016] Most metals and alloys experience reduced elongation and reduction of area in the medium-temperature range, approximately 0.5 to 0.8 times their melting point. Fracture occurs along grain boundaries, and a plastic minimum is observed on the temperature-plasticity curve. This phenomenon is known as medium-temperature brittleness or medium-temperature low plasticity in metals and alloys. The long-term service temperature of the GH4099 alloy is 900°C, with a maximum operating temperature of 1000°C. To prevent cracking of components caused by the medium-temperature low plasticity phenomenon in GH4099 alloys under high-temperature service conditions, the present invention designs a heat treatment process that eliminates the medium-temperature low plasticity of GH4099 nickel-based alloy components by changing the cooling rate during the heat treatment process.

[0017] The advantages and beneficial effects of the present invention are:

[0018] The process of the present invention consists of two steps. The first step is a solution heat treatment: the heat treatment temperature is 1175°C and the holding time is 1 hour. After the solution heat treatment holding stage is completed, heating is stopped and the component is cooled to 700°C at a cooling rate of 5°C / min. Then, it is furnace-cooled. When the temperature reaches 150-200°C, the GH4099 nickel-based alloy component is removed. The second step is an aging heat treatment: the heat treatment temperature is 850°C and the holding time is 5 hours. After the aging heat treatment holding stage is completed, heating is stopped and the component is cooled to 700°C at a cooling rate of 5°C / min. Then, it is furnace-cooled. When the temperature reaches 150-200°C, the GH4099 nickel-based alloy component is removed. The process of the present invention can be performed in a conventional vacuum heat treatment furnace and is applicable to solution aging heat treatment of GH4099 powder alloy after machining.

[0019] 2. The process of the present invention is simple and practical, can avoid the low plasticity phenomenon of GH4099 alloy at medium temperature, improve the overall metallurgical quality of the powder alloy, ensure the plasticity and toughness of the alloy, and reduce its manufacturing cost.

[0020] 3. The process of the present invention is simple and practical, and can be applied to the solid solution aging heat treatment of powder metallurgy high-temperature alloy components formed by direct hot isostatic pressing after machining. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the process curve of solution heat treatment under different cooling methods (gas quenching, furnace cooling, 5℃ / min cooling).

[0022] In the figure, the horizontal axis Time is time (min), and the vertical axis Temperature is temperature (°C).

[0023] Figure 2 This is the aging heat treatment process curve. In the figure, the horizontal axis Time is time (min) and the vertical axis Temperature is temperature (℃).

[0024] Figure 3 The tensile strength and elongation curves of the alloy under different cooling methods (gas quenching, furnace cooling, 5℃ / min cooling). m is the tensile strength (MPa), and the right vertical axis A is the elongation (%).

[0025] Figure 4 This is the metallographic structure of the GH4099 alloy component obtained by solution aging heat treatment at a cooling rate of 5°C / min in Example 1. DETAILED DESCRIPTION

[0026] In the specific implementation process, the present invention proposes a heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, which is as follows:

[0027] 1. The machined GH4099 alloy components were solution heat treated in a vacuum heat treatment furnace at 1175°C for 1 hour. After the solution heat treatment, heating was stopped and the components were cooled to 700°C at a rate of 5°C / min. The components were then furnace cooled. When the temperature reached 150-200°C, the components were removed. Solution strengthening occurs by adding alloying elements to the superalloy matrix. The solute atoms occupy interstitial or node positions, distorting the matrix's crystal lattice and generating a stress field that increases the resistance to dislocation slip in the solid solution. The γ phase of the superalloy matrix can dissolve a large number of alloying elements. For example, Cr, W, and Mo are the primary solution strengthening elements in GH4099 alloy. Their atomic diameters are generally larger than those of Ni atoms. When dissolved in the γ matrix, the matrix γ lattice expands and distorts, creating a long-range internal stress field that hinders dislocation motion. The effect of solid solution strengthening is primarily related to the properties of the alloying elements themselves (such as the size of solute and solvent atoms, electrochemical properties) and their solubility in the matrix. The closer the properties, the greater the solubility and the better the strengthening effect. However, if the added element content exceeds the alloy solubility, a second phase will precipitate in the alloy, potentially deteriorating the alloy's properties.

[0028] 2. Aging heat treatment: The heat treatment temperature was 850°C for a holding time of 5 hours. After the holding stage, heating was stopped and the components were cooled to 700°C at a cooling rate of 5°C / min. The components were then furnace cooled. When the temperature reached 150-200°C, the GH4099 nickel-based alloy components were removed. The 5°C / min cooling rate was achieved by holding at 1175°C for 1 hour, then cooling the heat treatment furnace down to 700°C at a cooling rate of 5°C / min, and then furnace cooling. Age-precipitation strengthening (A-P-T) involves the precipitation of fine precipitates from a supersaturated solid solution. The strengthening effect is achieved through the interaction between dislocations and the precipitates. The strengthening effect is primarily related to the morphology of the precipitates and the mismatch between the precipitates and the matrix. A-P-T can be explained by coherent distortion between the precipitates and the matrix, dislocation shearing mechanisms, Orowan bypassing mechanisms, and dislocation climb mechanisms. γ phase is a common strengthening phase in superalloys. The γ' phase is typically coherent with the matrix γ phase. The two have the same crystal structure but different lattice constants. This creates lattice distortion at the interface, causing changes in the stress field and increasing resistance to dislocation motion, thereby strengthening the alloy. The greater the lattice mismatch between the γ' and γ phases, the greater the stress field intensity and the higher the alloy strength. When the precipitated phase in a superalloy is low in hardness and coherent with the matrix γ phase, dislocations will cross the barrier by cutting through the precipitated phase. When the precipitated phase is numerous, the cutting mechanism requires less stress than the bypassing mechanism. Precipitated phases in superalloys are generally harder and stronger than the matrix. When the precipitated phases are densely packed, dislocations pass through these hard points using the Orowan bypassing mechanism. Dislocations bend between the precipitated phases until adjacent curved segments of the precipitated phases connect. After passing through, dislocations leave dislocation loops around the precipitated phase. The alloy's strengthening effect is closely related to the distance between the precipitated phases; the smaller the distance, the higher the strength. At higher temperatures and lower stresses, dislocation cutting and bypassing mechanisms are ineffective, and dislocations can only climb through the precipitated phase. The Al, Ti, Nb and other elements in GH4099 alloy are precipitation strengthening elements and are the main forming elements of the strengthening phase γ phase.

[0029] The preferred embodiments and comparative examples of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0030] The compositions of the following comparative examples and example alloys are shown in Table 1:

[0031] Table 1. GH4099 alloy composition (wt.%)

[0032]

[0033] In the following examples and comparative examples, the machined powder GH4099 alloy components were prepared by hot isostatic pressing + solution aging heat treatment.

[0034] Example 1

[0035] In terms of weight percentage, the composition of GH4099 alloy components is: C: 0.038, Cr: 18.31, Co: 6.54, W: 6.03, Mo: 4.01, Al: 2.02, Ti: 1.24, Fe: 0.081, B: 0.003, Ce: 0.0014, Mn: 0.005, Si: 0.018, P: 0.005, S: 0.0004, Mg: 0.0005, and Ni: the rest.

[0036] In this embodiment, the powder GH4099 alloy component is subjected to hot isostatic pressing and heat treatment, and the specific process is as follows:

[0037] GH4099 alloy powder is prepared by plasma rotating electrode atomization method. The GH4099 alloy powder with a size of less than 106 microns is loaded into a stainless steel sleeve. After vacuum degassing, it is first subjected to low-temperature pressure holding treatment in a vacuum degassing furnace with a holding temperature of 400°C and a time of 8 hours. After completion, it is cooled to room temperature with the furnace; then hot isostatic pressing treatment is performed, and finally the GH4099 alloy components are subjected to solid solution aging heat treatment before delivery.

[0038] Hot isostatic pressing consists of two stages:

[0039] The first stage of temperature and pressure increase process: temperature and pressure increase with the furnace, the insulation temperature is selected at (T γ' +130)℃, gas pressure should be greater than or equal to 140MPa, time is 4h. γ' is the γ' dissolution temperature of GH4099 alloy, T γ' It is 1100℃.

[0040] The second stage of cooling and pressure relief process: cooling to room temperature with the furnace to obtain powder GH4099 alloy components.

[0041] After hot isostatic pressing, the powder GH4099 alloy components are subjected to solution treatment and aging heat treatment:

[0042] 1. Place the machined GH4099 alloy components in a vacuum heat treatment furnace;

[0043] 2. Solution heat treatment: heat treatment temperature is 1175℃, holding time is 1h( Figure 1 );

[0044] 3. After the solution heat treatment and holding stage is completed, the cooling rate is 5℃ / min to 700℃, and then it is continued to cool in the vacuum heat treatment furnace (the average cooling rate is about 2℃ / min). When the temperature is 150-200℃, the GH4099 nickel-based alloy component is taken out and air-cooled to room temperature ( Figure 1 ).

[0045] like Figure 4 As shown, the metallographic structure of the GH4099 alloy component obtained by solution heat treatment at a cooling rate of 5°C / min in Example 1 can be seen to be uniform without defects such as inclusions and pores.

[0046] 4. Perform aging heat treatment on GH4099 alloy components. Heat to 850℃ at a heating rate of 6℃ / min, keep warm for 5h, cool to 700℃ at a cooling rate of 5℃ / min, and then continue to cool in the vacuum heat treatment furnace (average cooling rate is about 2℃ / min). When the temperature is 150-200℃, take out the GH4099 nickel-based alloy components and air cool them to room temperature ( Figure 2 ).

[0047] The mechanical properties of the alloy obtained by solution aging heat treatment at room temperature, 550℃ and 900℃ are shown in Table 2 and Figure 3 .

[0048] Table 2 Mechanical properties of alloys cooled at 5℃ / min at room temperature, 550℃ and 900℃

[0049]

[0050]

[0051] Note: R m is the tensile strength; R p0.2 is the yield strength; A is the elongation.

[0052] Comparative Example 1

[0053] In this comparative example, the process for preparing the powdered GH4099 alloy component is the same as that in Example 1 and will not be described again here.

[0054] 1. Place the machined GH4099 alloy components in a vacuum heat treatment furnace;

[0055] 2. Solution heat treatment: heat treatment temperature is 1175℃, holding time is 1h( Figure 1 );

[0056] 3. After the solution heat treatment and holding stage is completed, the product is cooled in a vacuum heat treatment furnace (the average cooling rate is about 12℃ / min above 700℃ and the average cooling rate is about 2℃ / min below 700℃) to room temperature ( Figure 1 The cooling rate of 12°C / min is achieved by stopping the heating process after the heat treatment furnace is heated and allowing the furnace to cool naturally.

[0057] 4. Perform aging heat treatment on GH4099 alloy components, heating to 850℃ at a heating rate of 6℃ / min, then keeping the temperature for 5h, cooling to 700℃ at a cooling rate of 5℃ / min, and then continue to cool to room temperature in a vacuum heat treatment furnace ( Figure 2 ).

[0058] The mechanical tests of the alloy obtained by solution aging heat treatment were carried out, and the properties at room temperature, 550℃ and 900℃ were obtained as shown in Table 3 and Figure 3 .

[0059] Table 3 Mechanical properties of furnace-cooled alloys at room temperature, 550℃ and 900℃

[0060]

[0061] Comparative Example 2

[0062] In this comparative example, the process for preparing the powdered GH4099 alloy component is the same as that in Example 1 and will not be described again here.

[0063] 1. Place the machined GH4099 alloy components in a vacuum heat treatment furnace;

[0064] 2. Solution heat treatment: heat treatment temperature is 1175℃, holding time is 1h( Figure 1 );

[0065] 3. After the solution heat treatment and holding stage is completed, the product is gas quenched in a vacuum heat treatment furnace (the average cooling rate is about 95℃ / min above 700℃ and the average cooling rate is about 35℃ / min below 700℃) to room temperature ( Figure 1 The cooling rate of 95°C / min was achieved by filling the furnace with argon after the insulation was completed, and then starting the internal fan to rapidly reduce the temperature of the furnace.

[0066] 4. Perform aging heat treatment on GH4099 alloy components, heating to 850℃ at a heating rate of 6℃ / min, then keeping the temperature for 5h, cooling to 700℃ at a cooling rate of 5℃ / min, and then continue to cool to room temperature in a vacuum heat treatment furnace ( Figure 2 ).

[0067] The mechanical tests of the alloy obtained by solution aging heat treatment were carried out, and the properties at room temperature, 550℃ and 900℃ were obtained as shown in Table 4 and Figure 3 .

[0068] Table 4 Mechanical properties of gas quenched alloys at room temperature, 550℃ and 900℃

[0069]

[0070] In summary, the GH4099 nickel-based alloy complex components prepared by the hot isostatic pressing method of the present invention, after undergoing specific solution heat treatment and aging heat treatment, have a room temperature tensile strength of not less than 1145 MPa and an elongation of not less than 29%; a 550°C tensile strength of not less than 1050 MPa and an elongation of not less than 28%; and a 900°C tensile strength of not less than 390 MPa and an elongation of not less than 30%. The heat treatment process of the present invention can avoid the low plasticity of alloy components at medium temperatures, provide a processing foundation for subsequent processing, ensure component quality, expand the application range of GH4099 nickel-based alloy, and meet the strength and plasticity requirements of GH4099 nickel-based alloy components in aerospace products.

[0071] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various variations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A heat treatment process for eliminating the low plasticity of GH4099 nickel-based alloy components at medium temperature, characterized in that: The steps include: (1) Place the machined GH4099 alloy components in a vacuum heat treatment furnace; (2) Solution heat treatment: The solution heat treatment temperature is 1175 °C, and the holding time is 1 h. After the GH4099 alloy component is completed through the solution heat treatment holding stage, it is cooled to 700 °C at a cooling rate of 5 °C / min, and then continues to cool in the vacuum heat treatment furnace. When the temperature is 150-200 °C, the GH4099 nickel-based alloy component is taken out; (3) Aging heat treatment: The GH4099 alloy component in step (2) was subjected to aging heat treatment at a temperature of 850°C and a holding time of 5 h. The component was cooled to 700°C at a cooling rate of 5°C / min and then continued to cool in a vacuum heat treatment furnace. When the temperature was 150-200°C, the GH4099 nickel-based alloy component was taken out to obtain a GH4099 nickel-based alloy component that met the requirements in terms of shape and mechanical properties.

2. The heat treatment process for eliminating low plasticity of GH4099 nickel-based alloy components at medium temperature according to claim 1, characterized in that: In step (1), the GH4099 alloy component is prepared by powder metallurgy process, and is placed in a vacuum heat treatment furnace for heat treatment after mechanical processing.

3. The heat treatment process for eliminating low plasticity of GH4099 nickel-based alloy components at medium temperature according to claim 1, characterized in that: During the solution aging heat treatment of step (2) and the aging heat treatment of step (3), the heating rate is less than 8°C / min.

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