Surface Shot Peening Method for Improving High-Temperature Oxidation Resistance of Molybdenum-Silicon-Boron Alloy

Abstract

The present invention discloses a surface shot peening method for improving the high-temperature oxidation resistance of Mo-Si-B alloy. First, the Mo-Si-B alloy is prepared by powder metallurgy and subsequent heat treatment; then, the oxide layer on the surface of the alloy is polished and cleaned off and surface polishing treatment is carried out; the surface of the alloy is subjected to shot peening treatment to obtain a nanocrystalline / ultrafine-grained structure layer with a thickness of 10-30 μm; finally, the shot-peened alloy is ultrasonically cleaned to remove the impurities adhering to the surface of the alloy after shot peening processing; the cleaned alloy is dried, and thus the Mo-Si-B alloy with excellent oxidation resistance is obtained. The present invention solves the mismatch problem between the room-temperature toughness and the high-temperature oxidation resistance of Mo-Si-B alloy existing in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface modification, and particularly relates to a surface shot peening method for improving the high-temperature oxidation resistance of Mo-Si-B alloys. Background Art

[0002] With the development of aeroengines towards the goals of high thrust-to-weight ratio, high flow ratio, and high inlet temperature, the gas temperature and pressure in the combustion chamber are continuously increasing. Nickel-based superalloys, as high-temperature alloys widely used in the hot-end components of current aeroengines, have a service temperature of up to 1150°C, which is 90% of their melting point, and it is difficult to meet the requirements of higher working temperatures. Therefore, the development of new structural materials that can replace nickel-based superalloys and work stably above 1200°C has attracted extensive attention at home and abroad.

[0003] The Mo-Si-B alloy mainly consists of three phases: α-Mo, Mo3Si, and Mo5SiB2. Its melting point reaches above 2000°C, and it has excellent high-temperature creep resistance and oxidation resistance, making it one of the candidate materials for the new generation of high-temperature alloys. However, there is a significant negative correlation between the room-temperature toughness and high-temperature oxidation resistance of this alloy, that is, when the content of the α-Mo phase in the alloy increases to more than 40 vol.%, good room-temperature toughness can be obtained, but too much metal phase α-Mo makes it difficult to rapidly form a complete borosilicate passivation layer on the alloy surface at high temperatures (1000 - 1300°C), resulting in rapid weight loss of the alloy in the initial stage of oxidation. Therefore, how to significantly improve its oxidation resistance on the basis of maintaining the good mechanical properties of the alloy is a hot issue in the research field of Mo-Si-B alloys.

[0004] Using surface coating technology to prepare an oxidation-resistant coating on the surface of Mo-Si-B alloys is one of the effective ways to solve the above problems. However, although most coatings exhibit excellent oxidation resistance, their mechanical properties are generally poor, and the bonding force with the substrate is weak and the interdiffusion is serious, so they cannot provide a lasting oxidation protection effect for the substrate.

[0005] According to the current research results on the high-temperature oxidation behavior of Mo-Si-B alloys, it is found that grain boundaries in the alloy are the main channels for atomic diffusion at high temperatures. The increase in the number of grain boundaries can accelerate the diffusion and reaction of Si, B, and O atoms, and accelerate the growth of the borosilicate passivation layer on the alloy surface. In addition, it is generally believed that nanocrystalline / ultrafine-grained structural materials have advantages such as a large specific surface area and high surface activity. Their high volume fraction of grain boundaries provides a large number of ideal channels for atomic diffusion, significantly increasing the atomic diffusion coefficient. Moreover, the non-equilibrium defects such as vacancies, dislocations, and sub-grain boundaries existing at grain boundaries, as well as a large amount of stored energy, will also promote atomic chemical reactions. In the research of metal materials such as titanium-based, iron-based, and aluminum-based, it is found that when the alloy forms a nanocrystalline / ultrafine-grained structural organization, the surface and interface effect of this organization can accelerate the formation of the surface passivation layer during high-temperature oxidation. At the same time, the size effect of this organization increases the nucleation sites of oxidation products, contributing to the formation of a more stable and dense passivation layer.

[0006] Therefore, if a nanocrystalline / ultrafine-grained structural layer with a certain thickness is prepared on the surface of a Mo-Si-B alloy with good mechanical properties, and the surface and interface effect and size effect of this structural layer are used to promote the rapid diffusion of Si and B atoms and the nucleation and growth of the passivation layer, the oxidation resistance of its surface can be improved on the premise of maintaining the good mechanical properties of the alloy matrix, comprehensively improving the service life of the Mo-Si-B alloy and promoting its industrial application. Summary of the Invention

[0007] The purpose of the present invention is to provide a surface shot peening method for improving the high-temperature oxidation resistance of molybdenum-silicon-boron alloys, which solves the mismatch problem between the room-temperature toughness and high-temperature oxidation resistance of Mo-Si-B alloys in the prior art.

[0008] The technical solution adopted by the present invention is a surface shot peening method for improving the high-temperature oxidation resistance of molybdenum-silicon-boron alloys, which is specifically implemented according to the following steps:

[0009] Step 1: Prepare a Mo-Si-B alloy through powder metallurgy and subsequent heat treatment;

[0010] Step 2: Grind and clean the oxide layer on the surface of the alloy and perform surface polishing treatment;

[0011] Step 3: Perform shot peening treatment on the surface of the alloy to obtain a nanocrystalline / ultrafine-grained structural layer with a thickness of 10 - 30 μm;

[0012] Step 4: Ultrasonically clean the shot-peened alloy to remove the impurities attached to the surface of the alloy after shot peening;

[0013] Step 5: Dry the cleaned alloy, and thus obtain a Mo-Si-B alloy with excellent high-temperature oxidation resistance.

[0014] The features of the present invention also lie in that,

[0015] In step 1, molybdenum powder, silicon powder and boron powder are used as raw materials, wherein the mass percentage of molybdenum powder is 93.0 - 98.0%, the mass percentage of silicon powder is 1.6 - 4.2%, and the mass percentage of boron powder is 0.4 - 2.8%. The sum of the above mass fractions is 100%.

[0016] In step 1, the purity of molybdenum powder ≥ 99.995wt%, and the particle size of molybdenum powder < 5μm; the purity of silicon powder ≥ 99.995wt%, and the particle size of silicon powder < 5μm; the purity of boron powder ≥ 99.95wt%, and the particle size of boron powder < 1μm.

[0017] Step 1 is specifically as follows: First, weigh molybdenum powder, silicon powder and boron powder, then ball-mill and mix the molybdenum powder, silicon powder and boron powder. The ball-milling time is 6 - 10h, and then mechanical alloying treatment is carried out to obtain alloy powder. The mechanical alloying treatment time is 20 - 30h; Second, the alloy powder after being sieved through 200 - 300 meshes is subjected to vacuum hot-pressing sintering. Specifically: raise the temperature from room temperature to 1500 - 1700°C, then keep the temperature and pressure for 2 - 5h, and then reduce the pressure and cool down with the furnace to room temperature and take out the alloy block from the mold. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, and the heating rate is 5 - 10°C / min; Finally, the hot-pressed sintered alloy block is subjected to vacuum heat treatment. Specifically: heat the temperature from room temperature to 1700 - 1800°C, and keep the temperature for 2 - 5h, then cool down with the furnace to room temperature and take out the alloy block from the furnace. During the heat treatment process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, and the heating rate is 5 - 10°C / min. After the above steps are completed, the Mo - Si - B alloy is obtained.

[0018] In step 2, use 150# - 1200# sandpaper to polish off the oxide layer on the surface of the Mo - Si - B alloy, and polish the alloy surface.

[0019] In step 3, perform surface shot peening on the Mo - Si - B alloy. Select S110 cast steel shot with a diameter of 0.2 - 0.3mm as the shot material. The compressed gas pressure is 0.35 - 0.45MPa, the shot material flow rate is 5 - 7kg / min, the moving speed of the nozzle is 5.5 - 7.5mm / min, the shot peening time is 15 - 30min, and the spraying distance is 150 - 200mm. Finally, a nanocrystalline / ultrafine crystalline structure layer with a thickness of 10 - 30μm is prepared on the alloy surface.

[0020] In step 4, ultrasonically clean the shot-peened alloy with acetone for 5 - 10min.

[0021] In step 5, the cleaned alloy is dried at a drying temperature of 100 - 150 °C for 15 - 20 min.

[0022] The beneficial effects of the present invention are as follows.

[0023] (1) The present invention uses surface shot peening technology to refine the surface structure of the Mo - Si - B alloy. By means of the high - density grain boundaries and defects in the surface nanocrystalline / ultrafine - grained structure layer of the alloy, it promotes the rapid diffusion and mutual reaction of Si, B, and O atoms at high temperatures, thereby accelerating the formation of the borosilicate passivation layer, improving the oxidation resistance of the alloy, and providing new ideas and technical support for the microstructure design of refractory metal - based alloys and the optimization of their oxidation resistance.

[0024] (2) Compared with the preparation of an oxidation - resistant coating using traditional surface coating technology, the nanocrystalline / ultrafine - grained structure layer prepared by the present invention has good bonding strength with the alloy matrix. At the same time, there are no significant compositional differences and inter - diffusion phenomena between the nanocrystalline / ultrafine - grained structure layer and the matrix, improving the high - temperature stability of the nanocrystalline / ultrafine - grained structure layer. The process design of the method of the present invention is simple, the operation is convenient, the cost is low, the requirements for equipment are low, and it hardly limits the size and shape of the alloy material to be shot - peened, making it easy to realize industrial production.

[0025] (3) After testing the oxidation kinetic behavior of the Mo - Si - B alloy in air at 1000 - 1200 °C before and after shot peening, it is shown that: the oxidation weight loss rate of the shot - peened Mo - Si - B alloy is only 5 - 11 mg / cm 2 , which is much smaller than that of the non - shot - peened Mo - Si - B alloy (whose oxidation weight loss rate is 40 - 60 mg / cm 2 ); and after oxidation of the shot - peened Mo - Si - B alloy, a dense borosilicate passivation layer is formed on the alloy surface, and the borosilicate passivation layer and the alloy matrix maintain good bonding strength. In addition, the mechanical properties of the Mo - Si - B alloy matrix are not significantly affected after shot peening. Description of the Drawings

[0026] Figure 1 It is the oxidation kinetic curve of the Mo - 12Si - 8.5B alloy in air at 1100 °C before and after shot peening. Detailed Embodiments

[0027] The present invention will be described in detail below with reference to the drawings and specific embodiments.

[0028] The surface shot - peening method for improving the high - temperature oxidation resistance of molybdenum - silicon - boron alloy of the present invention is specifically implemented according to the following steps:

[0029] Step 1: Prepare the Mo - Si - B alloy by powder metallurgy and subsequent heat treatment;

[0030] In Step 1, molybdenum powder, silicon powder and boron powder are used as raw materials. Among them, the mass percentage of molybdenum powder is 93.0 - 98.0%, the mass percentage of silicon powder is 1.6 - 4.2%, and the mass percentage of boron powder is 0.4 - 2.8%. The sum of the above mass fractions is 100%.

[0031] In Step 1, the purity of molybdenum powder ≥ 99.995wt%, and the particle size of molybdenum powder < 5μm; the purity of silicon powder ≥ 99.995wt%, and the particle size of silicon powder < 5μm; the purity of boron powder ≥ 99.95wt%, and the particle size of boron powder < 1μm.

[0032] Step 1 is specifically as follows: First, weigh molybdenum powder, silicon powder and boron powder, then ball-mill and mix the molybdenum powder, silicon powder and boron powder. The ball-milling time is 6 - 10h, and then mechanical alloying treatment is carried out to obtain alloy powder. The mechanical alloying treatment time is 20 - 30h; Second, load the alloy powder screened by a 200 - 300 mesh Tyler sieve into a graphite mold and place it in a vacuum hot-pressing sintering furnace for vacuum hot-pressing sintering. Specifically: raise the temperature from room temperature to 1500 - 1700°C, then keep the temperature and pressure for 2 - 5h, and then reduce the pressure and cool down with the furnace to room temperature and take out the alloy block from the mold. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa to avoid alloy oxidation, and the heating rate is 5 - 10°C / min; Finally, carry out vacuum heat treatment on the hot-pressed sintered alloy block. Specifically: heat the temperature from room temperature to 1700 - 1800°C and keep it for 2 - 5h, and then cool down with the furnace to room temperature and take out the alloy block from the furnace. During the heat treatment process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa to avoid alloy oxidation, and the heating rate is 5 - 10°C / min. After the above steps are completed, the Mo - Si - B alloy is obtained.

[0033] In Step 2, grind and clean the oxide layer on the surface of the alloy and perform surface polishing treatment;

[0034] In Step 2, use 150# - 1200# sandpaper to grind off the oxide layer on the surface of the Mo - Si - B alloy, and use a polishing machine to polish the surface of the alloy.

[0035] In Step 3, perform shot peening treatment on the surface of the alloy to obtain a nanocrystalline / ultrafine crystalline structure layer with a thickness of 10 - 30μm;

[0036] In Step 3, the Mo-Si-B alloy is subjected to surface shot peening. The shot material is S110 cast steel shot with a diameter of 0.2 - 0.3 mm, the compressed gas pressure is 0.35 - 0.45 MPa, the shot material flow rate is 5 - 7 kg / min, the nozzle moving speed is 5.5 - 7.5 mm / min, the shot peening time is 15 - 30 min, and the spraying distance is 150 - 200 mm. Finally, a nanocrystalline / ultrafine-grained structure layer with uniform structure and no obvious cracks and a thickness of 10 - 30 μm is prepared on the alloy surface.

[0037] Step 4: The shot-peened alloy is put into an ultrasonic cleaning machine for ultrasonic cleaning to remove the impurities adhering to the alloy surface after shot peening.

[0038] In Step 4, the shot-peened alloy is ultrasonically cleaned with acetone for 5 - 10 min.

[0039] Step 5: The cleaned alloy is dried to obtain the Mo-Si-B alloy with excellent high-temperature oxidation resistance.

[0040] In Step 5, the cleaned alloy is put into a blast drying oven for drying. The drying temperature is 100 - 150 °C, and the drying time is 15 - 20 min.

[0041] The surface shot peening method of the present invention improves the high-temperature oxidation resistance of the molybdenum-silicon-boron alloy, thereby forming a nanocrystalline / ultrafine-grained structure layer with a certain thickness on the alloy surface. By means of the surface interface effect and size effect of this structure layer, the rapid formation of the borosilicate passivation layer at high temperature is promoted, thereby improving the oxidation resistance of the alloy and extending the service life, overcoming the long-existing mismatch problem between the room-temperature toughness and high-temperature oxidation resistance of the Mo-Si-B alloy, and promoting the industrial application of the alloy.

[0042] Example 1

[0043] A surface shot peening process for improving the high-temperature oxidation resistance of the Mo-Si-B alloy includes the following steps:

[0044] Step 1: Prepare the Mo-12Si-8.5B (at.%) alloy by powder metallurgy and subsequent heat treatment; specifically: using molybdenum powder, silicon powder, and boron powder as raw materials, where the mass percentages of molybdenum powder, silicon powder, and boron powder are 94.68%, 4.18%, and 1.14% respectively. First, ball-mill and mix the molybdenum powder, silicon powder, and boron powder for 10 h, and then carry out mechanical alloying treatment for 30 h to obtain alloy powder; secondly, load the alloy powder after being screened by a 200-mesh Tyler sieve into a graphite mold and perform hot-press sintering in a vacuum hot-press sintering furnace. During the sintering process, the vacuum degree is maintained at 6.5×10 -3 Pa to 1.5×10 -2Between Pa, the heating rate is 5 °C / min, the sintering temperature is 1600 °C, and after sintering, it is cooled to room temperature in the furnace and taken out from the mold; finally, the hot-pressed sintered alloy block is subjected to vacuum heat treatment, and the vacuum degree is maintained between 6.5×10 -3 Pa to 1.5×10 -2 Pa, the heating rate is 5 °C / min, the heat treatment temperature is 1700 °C, and the heat treatment time is 3 h.

[0045] Step 2, use 150#-1200# sandpaper to grind off the oxide layer on the surface of the Mo-12Si-8.5B alloy, and polish the alloy surface with a polishing machine.

[0046] Step 3, use a supersonic particle bombardment device to perform shot peening on the surface of the alloy specimen to obtain a surface nanocrystalline / ultrafine crystalline structure layer with a thickness of about 10 μm; specifically: put the Mo-12Si-8.5B alloy specimen into the supersonic particle bombardment device, and fix it on the stage with a fixture. Load the S110 cast steel shot with a diameter of 0.2 mm into the shot material tank, turn on the air compressor, set the compressed gas pressure to 0.45 MPa, the shot material flow rate to 7 kg / min, the nozzle moving speed to 5.5 mm / min, the shot peening time to 30 min, and the spraying distance to 150 mm, and perform shot peening on the alloy surface.

[0047] Step 4, put the shot-peened alloy specimen into an ultrasonic cleaner, and clean the specimen with acetone for 10 min to remove the impurities attached to the alloy surface during the shot peening process;

[0048] Step 5, put the cleaned Mo-12Si-8.5B alloy into a blast drying oven for drying, the drying temperature is 150 °C, and the drying time is 20 min.

[0049] Use a thermogravimetric oxidation-reduction analyzer to test the oxidation kinetic behavior of the Mo-12Si-8.5B alloy specimen before and after shot peening at 1100 °C. Figure 1 is the oxidation kinetic curve of the Mo-12Si-8.5B alloy before and after shot peening in air at 1100 °C. The experimental results show that after 30 h of oxidation, the oxidation weight loss rate of the shot-peened specimen is 6.3 mg / cm 2 while the oxidation weight loss rate of the specimen without shot peening is 40.5 mg / cm 2 indicating that shot peening can significantly improve the high-temperature oxidation resistance of the Mo-12Si-8.5B alloy.

[0050] Example 2

[0051] A surface shot peening process for improving the high-temperature oxidation resistance of Mo-Si-B alloys, including the following steps:

[0052] Step 1: Prepare the Mo-8Si-5B (at.%) alloy by powder metallurgy and subsequent heat treatment. Specifically: Use molybdenum powder, silicon powder, and boron powder as raw materials, where the mass percentages of molybdenum powder, silicon powder, and boron powder are 96.77%, 2.60%, and 0.63% respectively. First, ball-mill and mix the molybdenum powder, silicon powder, and boron powder for 9 h, and then perform mechanical alloying for 28 h to obtain alloy powder. Second, load the alloy powder screened by a 200-mesh Tyler sieve into a graphite mold and conduct hot-press sintering in a vacuum hot-press sintering furnace. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 7 °C / min, the sintering temperature is 1600 °C, and after sintering, it is cooled to room temperature in the furnace and taken out of the mold. Finally, perform vacuum heat treatment on the hot-press sintered alloy block. During the heat treatment process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 7 °C / min, the heat treatment temperature is 1700 °C, and the heat treatment time is 5 h.

[0053] Step 2: Use 150# - 1200# sandpaper to grind off the oxide layer on the surface of the Mo-8Si-5B alloy, and polish the alloy surface using a polishing machine.

[0054] Step 3: Perform shot peening on the surface of the alloy specimen using a supersonic particle bombardment device to obtain a surface nanocrystalline / ultrafine-grained structure layer with a thickness of about 12 μm. Specifically: Place the Mo-8Si-5B alloy specimen into the supersonic particle bombardment device and fix it on the stage with a clamp. Load S110 cast steel shot with a diameter of 0.2 mm into the shot material tank, turn on the air compressor, set the compressed gas pressure to 0.45 MPa, the shot material flow rate to 6.5 kg / min, the nozzle moving speed to 6.5 mm / min, the shot peening time to 25 min, and the spraying distance to 160 mm, and perform shot peening on the alloy surface.

[0055] Step 4: Place the shot-peened alloy specimen into an ultrasonic cleaning machine and clean the specimen with acetone for 9 min to remove the impurities adhering to the alloy surface during the shot peening process.

[0056] Step 5: Place the cleaned Mo-8Si-5B alloy into a blast drying oven for drying. The drying temperature is 140 °C and the drying time is 18 min.

[0057] The oxidation kinetic behavior of Mo-8Si-5B alloy specimens before and after shot peening was tested at 1100 °C using a thermogravimetric redox analyzer. The experimental results show that after 30 h of oxidation, the oxidation weight loss rate of the shot-peened specimen is 7.3 mg / cm 2 , while that of the non-shot-peened specimen is 42.1 mg / cm 2 , indicating that shot peening can significantly improve the high-temperature oxidation resistance of Mo-8Si-5B alloy.

[0058] Example 3

[0059] A surface shot peening process for improving the high-temperature oxidation resistance of Mo-Si-B alloy, comprising the following steps:

[0060] Step 1, preparing Mo-7Si-4B (at.%) alloy by powder metallurgy and subsequent heat treatment; specifically: using molybdenum powder, silicon powder, and boron powder as raw materials, wherein the mass percentages of molybdenum powder, silicon powder, and boron powder are 97.27%, 2.24%, and 0.49% respectively. First, ball-mill and mix the molybdenum powder, silicon powder, and boron powder for 8 h, and then perform mechanical alloying for 25 h to obtain alloy powder; secondly, load the alloy powder after screening through a 300-mesh Tyler sieve into a graphite mold, and perform hot-press sintering in a vacuum hot-press sintering furnace. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 8 °C / min, the sintering temperature is 1600 °C, and after sintering, it is cooled to room temperature with the furnace and taken out of the mold; finally, perform vacuum heat treatment on the hot-press sintered alloy block. During the heat treatment process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 8 °C / min, the heat treatment temperature is 1800 °C, and the heat treatment time is 3 h.

[0061] Step 2, using 150#-1200# sandpaper to polish off the oxide layer on the surface of Mo-7Si-4B alloy, and polishing the alloy surface using a polishing machine.

[0062] Step 3, performing shot peening on the surface of the alloy specimen using a supersonic particle bombardment device to obtain a surface nanocrystalline / ultrafine crystalline structure layer with a thickness of about 16 μm; specifically: placing the Mo-7Si-4B alloy specimen into the supersonic particle bombardment device, and fixing it on the stage with a fixture. Load S110 cast steel shot with a diameter of 0.3 mm into the shot material tank, turn on the air compressor, set the compressed gas pressure to 0.4 MPa, the shot material flow rate to 6.5 kg / min, the nozzle moving speed to 7.5 mm / min, the shot peening time to 30 min, and the spraying distance to 170 mm, and perform shot peening on the alloy surface.

[0063] Step 4: Place the shot-peened alloy specimen into an ultrasonic cleaning machine and clean the specimen with acetone for 8 min to remove the impurities adhering to the alloy surface during the shot-peening process;

[0064] Step 5: Place the cleaned Mo-7Si-4B alloy into a blast drying oven for drying. The drying temperature is 120 °C and the drying time is 17 min.

[0065] The oxidation kinetic behavior of the Mo-7Si-4B alloy specimen before and after shot peening at 1100 °C was tested using a thermogravimetric redox analyzer. The experimental results show that after 30 h of oxidation, the oxidation weight loss rate of the shot-peened specimen is 9.3 mg / cm 2 , while the oxidation weight loss rate of the specimen without shot peening is 45.4 mg / cm 2 , indicating that shot peening can significantly improve the high-temperature oxidation resistance of the Mo-7Si-4B alloy.

[0066] Example 4

[0067] A surface shot-peening process for improving the high-temperature oxidation resistance of Mo-Si-B alloys, comprising the following steps:

[0068] Step 1: Prepare a Mo-6Si-5B (at.%) alloy by powder metallurgy and subsequent heat treatment; specifically: using molybdenum powder, silicon powder, and boron powder as raw materials, where the mass percentages of molybdenum powder, silicon powder, and boron powder are 97.46%, 1.92%, and 0.62% respectively. First, ball-mill and mix the molybdenum powder, silicon powder, and boron powder for 7 h, and then carry out mechanical alloying for 23 h to obtain alloy powder; secondly, load the alloy powder sieved by a 300-mesh Tyler sieve into a graphite mold and perform hot-press sintering in a vacuum hot-pressing sintering furnace. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 9 °C / min, the sintering temperature is 1600 °C, and after sintering, it is cooled to room temperature with the furnace and taken out of the mold; finally, perform vacuum heat treatment on the hot-press sintered alloy block. During the heat treatment process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 9 °C / min, the heat treatment temperature is 1800 °C, and the heat treatment time is 4 h.

[0069] Step 2: Use 150#-1200# sandpaper to polish off the oxide layer on the surface of the Mo-6Si-5B alloy, and polish the alloy surface using a polishing machine.

[0070] Step 3: Shot peening treatment is carried out on the surface of the alloy specimen by using a supersonic particle bombardment device to obtain a surface nanocrystalline / ultrafine crystalline structure layer with a thickness of about 18 μm. Specifically: Put the Mo-6Si-5B alloy specimen into the supersonic particle bombardment device and fix it on the stage with a fixture. Load the S110 cast steel shot with a diameter of 0.3 mm into the shot can. Turn on the air compressor, set the compressed gas pressure to 0.40 MPa, the shot flow rate to 6 kg / min, the nozzle moving speed to 7 mm / min, the shot peening time to 25 min, and the spraying distance to 160 mm, and carry out shot peening treatment on the alloy surface.

[0071] Step 4: Put the shot-peened alloy specimen into an ultrasonic cleaner and clean the specimen with acetone for 6 min to remove the impurities attached to the alloy surface during the shot peening process.

[0072] Step 5: Put the cleaned Mo-6Si-5B alloy into a blast drying oven for drying. The drying temperature is 120 °C and the drying time is 16 min.

[0073] The oxidation kinetics behavior of the Mo-6Si-5B alloy specimen before and after shot peening treatment at 1100 °C is tested by using a thermogravimetric redox analyzer. The experimental results show that after 30 h of oxidation, the oxidation weight loss rate of the shot-peened specimen is 10.2 mg / cm 2 while that of the specimen without shot peening treatment is 56.7 mg / cm 2 indicating that shot peening treatment can significantly improve the high-temperature oxidation resistance of the Mo-6Si-5B alloy.

[0074] Example 5

[0075] A surface shot peening process for improving the high-temperature oxidation resistance of Mo-Si-B alloy, comprising the following steps:

[0076] Step 1: Prepare Mo-5Si-6B (at.%) alloy by powder metallurgy and subsequent heat treatment. Specifically: Use molybdenum powder, silicon powder, and boron powder as raw materials, and the mass percentages of molybdenum powder, silicon powder, and boron powder are 97.65%, 1.61%, and 0.74% respectively. First, ball mill and mix the molybdenum powder, silicon powder, and boron powder for 6 h, and then carry out mechanical alloying treatment for 20 h to obtain alloy powder. Secondly, load the alloy powder screened by a 300-mesh Tyler sieve into a graphite mold and carry out hot press sintering in a vacuum hot press sintering furnace. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, the heating rate is 10 °C / min, the sintering temperature is 1600 °C, and after sintering, it is cooled to room temperature with the furnace and taken out of the mold. Finally, carry out vacuum heat treatment on the hot press sintered alloy block, and the vacuum degree is maintained at 6.5×10 during the heat treatment process.-3 from Pa to 1.5×10 -2 Pa. The heating rate is 10 °C / min, the heat treatment temperature is 1800 °C, and the heat treatment time is 5 h.

[0077] Step 2: Use 150# - 1200# sandpaper to grind off the oxide layer on the surface of the Mo-5Si-6B alloy, and polish the alloy surface with a polishing machine.

[0078] Step 3: Use a supersonic particle bombardment device to perform shot peening on the surface of the alloy specimen to obtain a surface nanocrystalline / ultrafine crystalline structure layer with a thickness of about 20 μm. Specifically: Place the Mo-5Si-6B alloy specimen into the supersonic particle bombardment device, fix it on the stage with a fixture, load S110 cast steel shot with a diameter of 0.3 mm into the shot can, turn on the air compressor, set the compressed gas pressure to 0.35 MPa, the shot flow rate to 6.0 kg / min, the nozzle moving speed to 6.5 mm / min, the shot peening time to 30 min, and the spraying distance to 150 mm, and perform shot peening on the alloy surface.

[0079] Step 4: Place the shot-peened alloy specimen into an ultrasonic cleaner and clean the specimen with acetone for 5 min to remove the impurities attached to the alloy surface during the shot peening process.

[0080] Step 5: Place the cleaned Mo-5Si-6B alloy into a blast drying oven for drying. The drying temperature is 100 °C and the drying time is 15 min.

[0081] Use a thermogravimetric redox analyzer to test the oxidation kinetic behavior of the Mo-5Si-6B alloy specimen before and after shot peening at 1100 °C. The experimental results show that after 30 h of oxidation, the oxidation weight loss rate of the shot-peened specimen is 7.2 mg / cm 2 , while the oxidation weight loss rate of the specimen without shot peening is 51.1 mg / cm 2 , indicating that shot peening can significantly improve the high-temperature oxidation resistance of the Mo-5Si-6B alloy.

Claims

1. A surface shot peening method for improving the high-temperature oxidation resistance of a molybdenum-silicon-boron alloy, characterized in that, The implementation is specifically carried out according to the following steps: Step 1: Prepare the Mo-Si-B alloy through powder metallurgy and subsequent heat treatment; The specific steps of Step 1 are as follows: First, weigh molybdenum powder, silicon powder and boron powder, and then ball-mill and mix the molybdenum powder, silicon powder and boron powder for 6 - 10 h. Subsequently, mechanical alloying treatment is carried out to obtain alloy powder, and the mechanical alloying treatment time is 20 - 30 h. Second, the alloy powder after being sieved through 200 - 300 meshes is subjected to vacuum hot-pressing sintering. Specifically, the temperature is raised from room temperature to 1500 - 1700 °C, and then held at a constant temperature and pressure for 2 - 5 h. Subsequently, the pressure is reduced and the temperature is decreased with the furnace to room temperature, and the alloy block is taken out of the mold. During the sintering process, the vacuum degree is maintained between 6.5×10 -3 Pa and 1.5×10 -2 Pa, and the heating rate is 5 - 10 °C / min. Finally, the hot-pressed sintered alloy block is subjected to vacuum heat treatment. Specifically, the temperature is heated from room temperature to 1700 - 1800 °C and held for 2 - 5 h. Subsequently, the temperature is decreased with the furnace to room temperature, and the alloy block is taken out of the furnace. During the heat treatment process, the vacuum degree is maintained between 6.5×10 - 3 Pa and 1.5×10 -2 Pa, and the heating rate is 5 - 10 °C / min. After the above steps are completed, the Mo-Si-B alloy is obtained; Step 2: Grind and clean the oxide layer on the surface of the alloy and perform surface polishing treatment; Step 3: Perform shot peening on the alloy surface to obtain a nanocrystalline / ultrafine-grained structure layer with a thickness of 10 - 30 μm; Step 4: Ultrasonically clean the shot-peened alloy to remove the impurities adhering to the alloy surface after shot peening; Step 5: Dry the cleaned alloy to obtain the Mo-Si-B alloy with high-temperature oxidation resistance.

2. The surface shot peening method for improving the high-temperature oxidation resistance of molybdenum-silicon-boron alloy according to claim 1, characterized in that In Step 1, molybdenum powder, silicon powder, and boron powder are used as raw materials, where the mass percentage of molybdenum powder is 93.0 - 98.0%, the mass percentage of silicon powder is 1.6 - 4.2%, and the mass percentage of boron powder is 0.4 - 2.8%. The sum of the above mass fractions is 100%.

3. The surface shot peening method for improving the high-temperature oxidation resistance of the molybdenum-silicon-boron alloy according to claim 1, wherein In Step 1, the purity of molybdenum powder ≥ 99.995 wt%, and the particle size of molybdenum powder < 5 μm; the purity of silicon powder ≥ 99.995 wt%, and the particle size of silicon powder < 5 μm; the purity of boron powder ≥ 99.95 wt%, and the particle size of boron powder < 1 μm.

4. The surface shot peening method for improving the high-temperature oxidation resistance of a molybdenum-silicon-boron alloy according to claim 1, characterized in that, In Step 2, use 150# - 1200# sandpaper to grind off the oxide layer on the surface of the Mo-Si-B alloy and perform polishing treatment on the alloy surface.

5. The surface shot peening method for improving the high-temperature oxidation resistance of a molybdenum-silicon-boron alloy according to claim 1, characterized in that, In Step 3, perform surface shot peening on the Mo-Si-B alloy. The shot material is S110 cast steel shot with a diameter of 0.2 - 0.3 mm, the compressed gas pressure is 0.35 - 0.45 MPa, the shot material flow rate is 5 - 7 kg / min, the moving speed of the nozzle is 5.5 - 7.5 mm / min, the shot peening time is 15 - 30 min, and the spraying distance is 150 - 200 mm. Finally, a nanocrystalline / ultrafine-grained structure layer with a thickness of 10 - 30 μm is prepared on the alloy surface.

6. The surface shot peening method for improving the high-temperature oxidation resistance of a molybdenum-silicon-boron alloy according to claim 1, characterized in that, In Step 4, ultrasonically clean the shot-peened alloy with acetone for 5 - 10 min.

7. The surface shot peening method for improving the high-temperature oxidation resistance of the molybdenum-silicon-boron alloy according to claim 1, wherein In Step 5, dry the cleaned alloy. The drying temperature is 100 - 150 °C, and the drying time is 15 - 20 min.

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