CN110453164B - Processing method for enhancing oxidation resistance of forged Ni-Cr-Co-based alloy - Google Patents

Abstract

The invention discloses a processing method for enhancing the oxidation resistance of a forged Ni-Cr-Co-based alloy, which comprises the following steps of 1) stress relief annealing treatment; 2) pre-solid solution treatment; 3) multi-stage solution treatment; 4) pre-stretching treatment; 5) stress relief annealing treatment; 6) repeating the step 4) and the step 5) until the axial tensile deformation of the alloy reaches 8-10 percent; 7) and (5) aging treatment. The method starts from the alloy itself, improves the binding force of the protective oxide film and the matrix through a series of heat treatment means, greatly improves the oxidation resistance of the alloy, prolongs the service life of the alloy, and also improves the comprehensive mechanical property of the alloy.

Description

A treatment method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys

technical field

The invention belongs to the field of high-temperature alloy structural materials, in particular to a treatment method for enhancing the oxidation resistance of a forged Ni-Cr-Co base alloy.

Background technique

Superalloy is a kind of metal material that can work for a long time above 600 ℃ and under certain stress conditions. It has excellent high temperature strength, good fatigue performance, fracture toughness and other comprehensive properties. The characteristics of superalloys make them irreplaceable key materials in aero-engines. Nickel-based superalloy is a widely used superalloy, and many key components of aero-engine are made of nickel-based superalloy. Due to the harsh working environment of aero-engines, which often need to work under high temperature and high pressure, it is particularly important to improve the oxidation resistance of nickel-based superalloys.

In general, the oxidation resistance of nickel-based superalloys mainly depends on the protective oxide film formed on the surface of the alloy. The elements that play an anti-oxidation role in nickel-based superalloys are mainly Al and Cr elements. Al element reacts with oxygen in the air to form a dense Al ₂ O ₃ film, and Cr element also reacts with oxygen to form a Cr ₂ O ₃ film. Since the stability of Al ₂ O ₃ is obviously better than that of Cr ₂ O ₃ at high temperature above 1000℃, if the service temperature of the alloy is higher than 1000℃, the content of Al element will be significantly higher than that of Cr when designing the alloy composition element, the final alloy will form a protective oxide film mainly composed of Al ₂ O ₃ , and if the service temperature of the alloy is lower than 1000 ℃, the content of Cr element in the alloy will be more, and finally the formation of Cr ₂ O ₃ is Primary protective oxide film.

Coating is also an important method to improve the oxidation resistance of alloys. The basic principle of coating is similar to that of protective oxide film, and a barrier is artificially created to isolate the chemical reaction between oxygen and alloy. However, the coating method has an important disadvantage, that is, for some key components, if their own anti-oxidation ability is poor, once the coating fails, it will cause serious damage to the component. Even if antioxidant coatings are sufficiently reliable, manufacturable, and inexpensive, there are several fundamental issues to consider: (1) there must be a good thermal expansion match between the coating and the substrate, otherwise cracking or other failure behavior may occur; (2) There must be good chemical compatibility between the coating and the substrate, otherwise a poor phase will be formed; (3) From the point of view of mechanical properties, the high temperature strength of most anti-oxidation coating compositions is relatively low, so in the Fatigue or deformation problems may occur during use, thereby limiting their durability; (4) There may be long-term interdiffusion problems between the coating and the substrate. Therefore, there is a need for a new method for improving the oxidation resistance of alloys.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a treatment method for enhancing the oxidation resistance of the forged Ni-Cr-Co-based alloy.

The technical solution of the present invention to solve the technical problem is to provide a treatment method for enhancing the oxidation resistance of a forged Ni-Cr-Co-based alloy, characterized in that the method comprises the following steps:

1) Stress relief annealing treatment: the forged Ni-Cr-Co base alloy is kept at a temperature of 700-750 ° C for 1-3 hours, and then the furnace is cooled to room temperature and taken out;

2) Pre-solution treatment: keep the temperature at 820-870°C for 6-8 hours, and air-cool to room temperature after being released;

3) Multi-stage solution treatment: keep the temperature at 950-980°C for 1-3h; each solution treatment is based on the previous solution treatment with a temperature of 10-15°C and the same holding time, and finally air-cooled after being released from the furnace to room temperature;

4) Pre-stretching treatment: use a universal material testing machine for axial pre-stretching treatment at room temperature, the axial stretching amount is 2% to 5%, and the stretching rate is 0.1-0.3mm/min. After the stretching is completed water cooled to room temperature;

5) Stress relief annealing treatment: keep the temperature at 700～750℃ for 1～3h, then take it out after cooling to room temperature in the furnace;

6) Repeat steps 4) and 5) until the axial tensile deformation of the alloy reaches 8% to 10%;

7) Aging treatment: heat preservation at a temperature of 770-800°C for 2-8 hours; then furnace-cooled to a temperature of 680-710°C for 6-8 hours, and air-cooled to room temperature after being released from the furnace.

Compared with the prior art, the beneficial effects of the present invention are:

(1) This method starts from the alloy itself, and through a series of heat treatment methods and stretching treatments, improves the bonding force between the protective oxide film and the substrate, greatly improves the oxidation resistance of the alloy, prolongs the service life of the alloy, and improves the Comprehensive mechanical properties of alloys.

(2) The method is relatively simple to operate, reduces the cost of processing alloys, and has strong universality.

(3) The structure of the alloy after treatment is relatively uniform, and more γ' phases (size of 10-36 nm) with a relatively round shape are precipitated, which reduces the η phase oriented along the grain boundary and greatly improves the Cr ₂ O _3. The bonding force between the film and the substrate reduces the generation of porous NiO and improves the oxidation resistance of the alloy without sacrificing other mechanical properties of the alloy.

Description of drawings

Fig. 1 is the microstructure diagram of the alloy obtained in Example 1 of the present invention;

Fig. 2 is the microstructure diagram of alloy oxidation 80h obtained in Example 1 of the present invention;

FIG. 3 is an oxidation kinetic curve diagram of the forged Ni-Cr-Co-based alloy and the alloy obtained in Example 1 of the present invention oxidized for 80 h.

Detailed ways

Specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail, and do not limit the protection scope of the claims of the present application.

The invention provides a treatment method (method for short) for enhancing the oxidation resistance of a forged Ni-Cr-Co-based alloy, which is characterized in that the method comprises the following steps:

1) Stress relief annealing treatment: The forged Ni-Cr-Co base alloy (referred to as alloy) is kept in a box furnace at a temperature of 700-750 ° C for 1-3 hours, and then the furnace is cooled to room temperature and taken out; the purpose of stress relief annealing It is to eliminate the residual stress generated during the forging process of the alloy and effectively improve the bonding force between the oxide film and the substrate;

2) Pre-solution treatment: keep the alloy obtained in the previous step in a box furnace with a temperature of 820-870 ° C for 6-8 hours, and air-cool to room temperature after being released from the furnace; the function of pre-solution is to ensure that an appropriate amount of η is precipitated on the grain boundary. phase to improve the notch sensitivity of the alloy;

3) Multi-stage solution treatment: keep the alloy obtained in the previous step in a box furnace with a temperature of 950-980 ° C for 1-3 hours; each solution treatment is based on the previous solution treatment. ℃ and the same holding time, and finally air-cooled to room temperature after being released from the furnace; in this example, a total of three solid solution treatments were carried out; the purpose of the multi-stage solid solution was to fully dissolve the strengthening elements of the alloy into the nickel-based solid solution and dissolve the carbides and carbides in the matrix. γ' is equal to obtain a supersaturated solid solution, which is convenient for re-precipitating the γ' strengthening phase with fine particles during aging treatment;

4) Pre-stretching treatment: the alloy obtained in the previous step is subjected to axial pre-stretching treatment using a universal material testing machine at room temperature. min, water-cooled to room temperature after stretching; pre-stretching improves the mechanical properties and intergranular corrosion resistance of the alloy;

5) Stress relief annealing treatment: keep the alloy obtained in the previous step in a box furnace with a temperature of 700 ~ 750 ° C for 1 ~ 3 hours, and then take it out after the furnace is cooled to room temperature; stress relief annealing can eliminate the residues produced by the alloy after pre-stretching stress, increase the bonding force between the oxide film and the substrate;

6) Repeat steps 4) and 5) until the axial tensile deformation of the alloy reaches 8% to 10%;

7) Aging treatment: keep the alloy obtained in the previous step in a box furnace with a temperature of 770-800 ° C for 2-8 hours; then cool it to a temperature of 680-710 ° C in the furnace, keep it for 6-8 hours, and air-cool it to room temperature after being released from the furnace; Aging treatment can make the alloy precipitate a large amount of round and fine γ' strengthening phase, improve the bonding force between the oxide film and the matrix, reduce the generation of porous NiO during oxidation, improve the peeling resistance of the oxide film, and improve the comprehensive mechanical properties of the alloy;

Preferably, during the entire treatment process, the holding process is carried out in a uniform temperature zone of the chamber furnace. The box-type furnace can be a box-type resistance furnace; the box-type furnace has the functions of rapid heating and cooling and controlling the heating and cooling rate.

Preferably, the steps 1) to 3) and the steps 5) to 7) are all carried out under protective gas; the protective gas is argon, and the gas flow is 1-15 L/min.

Preferably, during the whole treatment process, the alloy is placed in a crucible made of high temperature resistant corundum, and the crucible needs to be heated at a temperature of 700° C. for 3 hours to dehumidify before use.

Preferably, the forged Ni-Cr-Co-based alloy is a well-known nickel-based superalloy, developed by China Aviation Development Beijing Institute of Aeronautical Materials, and its mass fraction composition is C element: 0.024%; Cr element: 18.53%; Al Element: 1.55%; Ti element: 0.80%; Nb element: 5.34%; W element: 1.08%; Mo element: 2.85%; Co element: 9.26%; Fe element: 8.82%; P element: 0.011%; B element: 0.0072%; the rest are Ni elements.

Preferably, before the whole treatment process, the alloy needs to be prepared: the forged Ni-Cr-Co-based alloy is cut into a cylindrical shape with a diameter of 8mm and a height of 8mm by a wire cutting machine, and then ultrasonically cleaned in alcohol for 10min , dried for use.

The equipment and operating techniques used in this method are well known in the art.

Example 1

Preparation before processing: Use a wire cutting machine to cut the forged Ni-Cr-Co base alloy into cylindrical alloy samples with a diameter of 8 mm and a height of 8 mm, then ultrasonically clean them in alcohol for 10 minutes, and dry them for use; the corundum crucible Put it at 700℃ for 3h to dehumidify.

1) Carry out stress relief annealing treatment: raise the temperature of the box furnace to 700°C, put the crucible containing the alloy sample into the uniform temperature zone of the box furnace after the temperature is stable, and pass argon gas for gas protection; alloy test The sample was kept in a box furnace for 1 h, the gas protection was stopped, and then the furnace was cooled to room temperature and taken out;

2) Carry out pre-solution treatment: raise the temperature of the box furnace to 820°C, and after the temperature is stable, put the crucible containing the alloy samples that have undergone stress relief annealing into the uniform temperature zone of the box furnace, and pass argon gas to carry out the process. Gas protection; the alloy sample is kept in a box furnace for 6 hours, the gas protection is stopped, and then the crucible containing the alloy sample is taken out and air-cooled to room temperature;

3) Carry out multi-stage solution treatment: raise the temperature of the box furnace to 950 °C, and after the temperature is stable, put the crucible containing the alloy sample that has undergone pre-solution treatment into the uniform temperature zone of the box furnace, and pass argon into it. The alloy sample was kept in the box furnace for 1 hour, then the box furnace was heated to 960 °C, kept for 1 hour, the box furnace was heated to 970 °C again, kept for 1 hour, and the gas protection was stopped, and then the alloy was filled with alloy. The crucible of the sample is taken out and air-cooled to room temperature;

4) Carry out pre-stretching treatment: the alloy obtained in the previous step is subjected to axial pre-stretching treatment with a universal material testing machine at room temperature, the axial stretching amount is 2%, the stretching rate is 0.15 mm/min, and the stretching is performed. After completion, water cooled to room temperature;

5) Carry out stress relief annealing treatment: raise the temperature of the box furnace to 700°C, and after the temperature is stable, put the crucible containing the pre-stretched alloy sample into the uniform temperature zone of the box furnace, and pass argon gas into it. Carry out gas protection; the alloy sample is kept in a box furnace for 1 hour, the gas protection is stopped, and then the furnace is cooled to room temperature and taken out;

6) Repeat steps 4) and 5) until the overall axial tensile deformation of the alloy reaches 8%;

7) Carry out aging treatment: raise the temperature of the box furnace to 770°C, and after the temperature is stable, put the crucible containing the alloy samples that have undergone tensile deformation into the uniform temperature zone of the box furnace, and pass argon gas for gas protection ; The alloy sample was kept in a box furnace for 2h, then the furnace was cooled to 680°C, kept for 6h, and the gas protection was stopped, then the crucible containing the alloy sample was taken out, and air-cooled to room temperature to obtain a nickel base with excellent oxidation resistance. Superalloy.

After treatment, the structure of the alloy is relatively uniform, and more γ' phases with a relatively rounded morphology (size of 10-36 nm) are precipitated, which reduces the η phase oriented along the grain boundary, and greatly improves the Cr ₂ O ₃ film. The bonding force of the matrix reduces the generation of porous NiO and improves the oxidation resistance of the alloy without sacrificing other mechanical properties of the alloy.

The treated alloy was subjected to a long-term oxidation experiment in a box furnace at a temperature of 700 °C and an oxidation time of 80 h. Before putting the alloy into the box furnace, use an electronic balance with an accuracy of 0.0001g to weigh it, and then test the alloy at the time points of 1h, 5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h of oxidation. The samples were taken out and weighed with an electronic balance. As shown in Figure 3, when oxidized at 700℃/80h, compared with the original alloy without heat treatment, the oxidation kinetic curve and oxidation rate curve of this alloy are relatively stable, and there is no obvious mass weight gain or The phenomenon of reduction indicates that the oxidation resistance of the alloy treated by this method is good.

Example 1 shows that the alloy obtained by this method not only enhances its oxidation resistance, but also improves its mechanical properties to a certain extent. Since the alloy is produced by forging, more stress is accumulated inside the alloy. If stress relief annealing is not performed, the oxide film will fall off easily under the action of stress, which will have a certain impact on the oxidation resistance of the alloy. The purpose of pre-solution treatment is to ensure that a small amount of η phase exists at the grain boundary. Although η phase is not the strengthening phase of the alloy, if all the η phase in the alloy is eliminated, then this situation is also unfavorable for the overall mechanical properties of the alloy. Yes, related studies have shown that the η phase existing in the alloy has a certain relationship with the notch fracture resistance. When the η phase mass fraction drops to about 1.1wt%, individual samples have higher notch sensitivity, and when the η phase mass fraction drops to about 1.1wt% Down to 0.06 wt%, all samples showed obvious signs of notch fracture. Therefore, for nickel-based superalloys, the η phase cannot be completely removed, and a part of the η phase still needs to be retained. The solution treatment is to dissolve the carbides and γ' in the matrix to obtain a uniform supersaturated solid solution, which is convenient for re-precipitating the γ' strengthening phase with fine particles and uniform distribution during the aging treatment, and at the same time eliminates the stress caused by hot and cold processing. In addition, solution treatment can also make the alloy obtain suitable grain size to ensure the high temperature creep resistance of the alloy. The alloy is subjected to a certain plastic deformation in advance and then aging treatment, which can effectively refine the grains, eliminate various harmful phases in the alloy, and precipitate a relatively round and fine γ' phase, which improves the gap between the oxide film and the matrix. binding force.

What is not described in the present invention applies to the prior art.

Claims (7)

1. a processing method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys, characterized in that the method comprises the following steps: 1) Stress relief annealing treatment: the forged Ni-Cr-Co base alloy is kept at a temperature of 700-750 ° C for 1-3 hours, and then the furnace is cooled to room temperature and taken out; 2) Pre-solution treatment: keep the temperature at 820-870°C for 6-8 hours, and air-cool to room temperature after being released; 3) Multi-stage solution treatment: keep the temperature at 950-980°C for 1-3h; each solution treatment is based on the previous solution treatment with a temperature of 10-15°C and the same holding time, and finally air-cooled after being released from the furnace to room temperature; 4) Pre-stretching treatment: use a universal material testing machine for axial pre-stretching treatment at room temperature, the axial stretching amount is 2% to 5%, and the stretching rate is 0.1-0.3mm/min. After the stretching is completed water cooled to room temperature; 5) Stress relief annealing treatment: keep the temperature at 700～750℃ for 1～3h, then take it out after cooling to room temperature in the furnace; 6) Repeat steps 4) and 5) until the axial tensile deformation of the alloy reaches 8% to 10%; 7) Aging treatment: keep the temperature at 770-800℃ for 2-8h; then cool to 680-710℃ in the furnace, keep the temperature for 6-8h, and air-cool to room temperature after being released from the furnace; The forged Ni-Cr-Co-based alloy is composed of C element: 0.024%; Cr element: 18.53%; Al element: 1.55%; Ti element: 0.80%; Nb element: 5.34%; W element: 1.08 %; Mo element: 2.85%; Co element: 9.26%; Fe element: 8.82%; P element: 0.011%; B element: 0.0072%; 2. The treatment method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys according to claim 1, characterized in that in the whole treatment process, the heat preservation process is carried out in the uniform temperature zone of the box furnace. 3 . The method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys according to claim 1 , wherein step 3) adopts three solid solution treatments. 4 . 4. The treatment method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys according to claim 1, wherein steps 1)-step 3) and steps 5)-step 7) are all carried out under protective gas . 5 . The method for enhancing the oxidation resistance of a forged Ni-Cr-Co-based alloy according to claim 4 , wherein the protective gas is argon, and the gas flow is 1-15 L/min. 6 . 6. The treatment method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys according to claim 1, characterized in that in the whole treatment process, the alloy is placed in a crucible made of high-temperature resistant corundum material, and the crucible is used before use. It needs to be heated at a temperature of 700°C for 3 hours. 7. The treatment method for enhancing the oxidation resistance of forged Ni-Cr-Co-based alloys according to claim 1, characterized in that before carrying out the entire treatment process, the forged Ni-Cr-Co-based alloys are treated with a wire cutting machine by using a wire cutting machine. Cut it into a cylindrical shape with a diameter of 8 mm and a height of 8 mm, then ultrasonically clean it in alcohol for 10 minutes, and dry it for use.

Images