A nanoscale yttria shell carburized and a method for preparing the same

Abstract

The application discloses a carburized nanoscale yttrium oxide shell and a preparation method thereof. The preparation method comprises the following steps: preparing a nanoscale yttrium oxide shell embryo by using a grouting method; and placing the shell embryo after high-temperature sintering in a vacuum induction melting furnace filled with high-concentration active carbon to perform carburization treatment. The nanoscale yttrium oxide shell treated by using the carburization technology has excellent high-temperature resistance and chemical inertness, can reduce the pollution of yttrium oxide particles to a TiAl alloy melt, hinder the occurrence of a TiAl alloy melt-shell interface reaction, and make the surface of the TiAl alloy after melting more smooth, so that columnar grains on the surface of an alloy ingot can be clearly observed. Moreover, the shell has high bending strength and Vickers hardness, and the relative density is increased, so that the problem of the cracking of the yttrium oxide shell after the melting of the TiAl alloy is solved. The bending strength of the yttrium oxide shell prepared by the application can reach 24.3 MPa, and the Vickers hardness can reach 152 HV.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oxide shell and particularly relates to a nanoscale yttrium oxide shell treated by carburization and a preparation method thereof. BACKGROUND

[0002] Precision casting technology is one of the important methods for preparing turbine blades of an aero-engine. In recent years, with the increasingly complex component design of high-temperature alloys and the increasingly harsh process requirements, the interface reaction problem between the high-temperature alloy melt and the ceramic core / shell material gradually emerges. In the precision casting process of the high-temperature alloy, the ceramic core / shell material is in contact with the alloy melt at a high temperature of 1500 DEG C for a long time of tens of minutes or even more than one hour. The TiAl alloy in the molten state has high high-temperature activity and can almost react with any refractory material to form an oxygen-rich alpha contaminated layer, pores, shrinkage and other problems on the surface of the casting, thereby reducing the use performance and surface quality of the casting and seriously limiting the application and development of the TiAl alloy. Therefore, how to control the interface reaction between the titanium alloy and the casting material and obtain a pollution-free TiAl alloy casting is very important for the selection of the shell material.

[0003] The oxide shell material is widely available and low in price, and can reduce the preparation cost of the TiAl alloy. Therefore, in recent years, the research on the casting of the TiAl alloy mainly focuses on the oxide shell. However, the common oxide shell material generally reacts with the TiAl alloy melt to form a certain thickness of the reaction layer. It is found that the Y2O3 shell has the best stability and is not easy to react with the molten TiAl alloy, and is one of the current research hotspots of the shell material. Meanwhile, according to the analysis of the standard free energy of the common oxide, the Y2O3 shell has the highest stability in the interface reaction with the high-temperature molten alloy. However, the Y2O3 shell still has two deficiencies: firstly, the nanoscale yttrium oxide shell obtained by ordinary slurry forming has poor thermal shock resistance and is easy to crack in the alloy smelting process, thereby affecting the alloy smelting and secondary use; and secondly, there are more or less yttrium oxide particles at the interface of the smelted alloy, which affects the surface quality of the smelted TiAl alloy. Therefore, it is urgent to develop a new preparation method of the yttrium oxide shell to solve the above problems. SUMMARY

[0004] In view of the deficiencies of the above-mentioned yttrium oxide shell, the application provides a nanoscale yttrium oxide shell treated by carburization and a preparation method thereof, which can not only prevent the cracking of the shell in the TiAl alloy smelting process, but also help to improve the surface quality of the alloy.

[0005] The purpose of the application is achieved in the following manner:

[0006] The preparation method of the carburized nanoscale yttria shell comprises the following steps: using nanoscale yttria slurry to make a shell embryo, and performing carburization treatment in a vacuum induction melting furnace after sintering of the embryo is completed.

[0007] The preparation method of the carburized nanoscale yttria shell comprises the following steps,

[0008] (1) Preparation of nanoscale yttria slurry

[0009] The nanoscale yttria powder, ceramic dispersant and deionized water are mixed and placed in a ball mill for ball milling.

[0010] (2) A grouting model is made using water and gypsum, and then is placed in a drying box for drying treatment;

[0011] (3) The nanoscale yttria slurry ball-milled in step (1) is poured into the dried gypsum model in step (2), and after standing, the remaining slurry is poured out, and the operation is repeated for several times to obtain a nanoscale yttria shell embryo with a certain thickness;

[0012] (4) The yttria shell embryo in step (3) is placed in a place with air circulation and naturally dried, and when a gap of 1-2 mm is generated between the gypsum model and the yttria shell embryo, the yttria shell embryo is demolded, and then is placed in a drying box for drying;

[0013] (5) The nanoscale yttria shell embryo dried in step (4) is placed in a high-temperature muffle furnace for sintering;

[0014] (6) The nanoscale yttria shell sintered in step (5) is placed in a vacuum induction melting furnace filled with high-concentration activated carbon for carburization treatment.

[0015] In step (1), the particle size of the nanoscale yttria powder is 500 nm-850 nm, the ceramic dispersant is sodium polyacrylate or ammonium polyacrylate, the content is 2.2 %-3.1 %, the solid content in the nanoscale yttria slurry is 35 %-50 %, and the rotation speed of the ball mill is 310 r / min-420 r / min, and the ball milling time is 8 h-12 h.

[0016] The solid content of the slurry should be controlled within a proper range to ensure the smoothness of the grouting process. If the solid content is too low, the bonding force of the green body will not be enough to resist the shrinkage stress and cracking will occur. On the contrary, if the solid content is too high, the viscosity of the slurry will be too large, the permeability of the slurry itself will be affected, the humidity gradient difference in the thickness direction of the green body will be too large, the ion exchange between the slurry and the model will be hindered, the demolding will be affected, and cracking will occur due to different shrinkage stresses.

[0017] Before the wet mixing process of the slurry, electronic slurry grinding zirconium beads are used, and large, medium and small grinding zirconium beads are mixed, wherein the ratio of large: medium: small is 1: 1: 2, so as to fully exert the grinding effect of the electronic slurry grinding zirconium beads and make the powder evenly distributed in the slurry.

[0018] Deionized water is selected for slurry preparation to eliminate ionic impurities in water and avoid adverse effects on the properties of the slurry. The ceramic dispersant will decompose and escape after high-temperature sintering, preventing the dispersant components from affecting the purity of the shell. Moreover, the ceramic dispersant can make the powder uniformly suspended in the solution, stabilizing the spatial distribution of the powder in the solvent.

[0019] In step (2), the slurry injection model is a circular truncated cone, the water and gypsum ratio is 3:8, the ratio of the upper top surface to the lower bottom surface diameter is 1:2, the drying temperature is 39℃-45℃, and the drying time is 72 h-100 h.

[0020] The slurry injection model is designed as a circular truncated cone because the gravity of the slurry will cause the slurry to accumulate at the bottom of the yttria shell embryo, the capillary action rates of the upper and lower halves of the gypsum mold are different, leading to cracks in the shell embryo, and the volume of the lower half of the circular truncated cone model is larger than that of the upper half, promoting the water absorption rate of the lower half and making the water absorption rates of the upper and lower halves tend to be balanced, preventing the shell embryo from cracking. Then, the slurry injection model is dried in a drying box with a temperature of 39℃-45℃ and a drying time of 72 h-100 h. The temperature rise speed should not be too fast, otherwise it will cause cracks in the gypsum model and affect the slurry injection effect.

[0021] In step (3), the slurry is left to stand for 6 min-7.5 min, and the yttria shell embryo obtained by repeating this process 5 times has a thickness of 2 mm-3 mm. Specifically, the slurry is poured into the model and left to stand for 60 s-80 s in the first pouring, 65 s-85 s in the second pouring, the excess slurry is poured out, 70 s-90 s in the third pouring, 75 s-95 s in the fourth pouring, and 80 s-100 s in the fifth pouring. The shape of the mold inside is the embryo required, and the water in the slurry is removed by the capillary water absorption of the gypsum mold, thereby solidifying.

[0022] In step (4), the natural drying temperature is 15℃-38℃, and the natural drying time is 120 h-180 h; the drying temperature set in the drying box is 70℃-80℃, and the drying time is 48 h-60 h. The drying temperature should be as low as possible, and the drying time should be as long as possible to ensure that the combined water in the blank body is removed. If the temperature is too high and the drying time is too fast, the residual water in the nanoscale yttria crucible embryo will evaporate too quickly, causing the embryo to crack.

[0023] The sintering temperature of the embryo body in step (5) is 1700-1800 ℃, and the sintering time is 31-40 h. Since the Y2O3 porcelainizing temperature is relatively high, the highest sintering temperature is set to 1800 ℃. The sintering process is divided into four stages. In the first stage, the temperature is slowly increased from room temperature to 200 ℃ within 9-10 h to prevent the embryo body from cracking due to rapid temperature rise; in the second stage, the temperature is rapidly increased to 1650 ℃ within 4-6 h to improve the sintering efficiency; in the third stage, the temperature is slowly increased from 1650 ℃ to 1800 ℃ within 8-9 h; in the fourth stage, the temperature is kept at 1800 ℃ for 10-15 h to ensure the porcelainization of the shell, and the sintering is completed after the furnace is cooled to room temperature.

[0024] The carburizing treatment in step (6) is solid carburizing, which is composed of solid carburizing sources such as charcoal and / or graphite blocks, and a carburizing agent sodium carbonate; the carburizing treatment power is 20-75 kw, and the carburizing time is 37-62 min.

[0025] Before carburizing treatment, the air in the furnace body is first pumped to 5×10 -3 Pa, high-purity argon is used for two times of gas washing, and finally argon is filled to 0.7×10 5 Pa. The carburizing process is divided into five heating stages and four cooling stages. The heating process: the first stage is heated to 20 kw, and the temperature is kept for 5-8 min; the second stage is heated to 40 kw, and the temperature is kept for 4-5 min; the third stage is heated to 60 kw, and the temperature is kept for 3-5 min; the fourth stage is heated to 70 kw, and the temperature is kept for 2-3 min; the fifth stage is heated to 75 kw, and the temperature is kept for 1-2 min; the cooling process: the first stage is cooled to 65 kw, and the temperature is kept for 2-3 min; the second stage is cooled to 40 kw, and the temperature is kept for 5-6 min; the third stage is cooled to 30 kw, and the temperature is kept for 5-10 min; the fourth stage is cooled to 20 kw, and the temperature is kept for 10-20 min. After the nanoscale yttrium oxide shell is cooled to room temperature in the vacuum induction melting furnace, it is taken out to obtain a gray-black nanoscale yttrium oxide shell.

[0026] A carburized nanoscale yttrium oxide shell is prepared by any of the above preparation methods.

[0027] Beneficial effects:

[0028] 1. The surface profile of the carburized nanoscale yttrium oxide shell is clear, smooth and flat, without obvious cracks and holes, and has high bending strength and Vickers hardness, the bending strength can reach 24.3 MPa, and the Vickers hardness can reach 152 HV.

[0029] 2. The surface grain size of the nano-sized yttrium oxide shell treated with carburizing technology is more uniform, ranging from approximately 5 μm to 22 μm. The grain boundaries are clearer, the grain arrangement is more orderly, and the relative density is increased, which improves the thermal shock resistance of the yttrium oxide shell. The shell remains intact after melting without any cracks.

[0030] 3. The TiAl alloy ingots smelted using this shell have a clear boundary with the Y2O3 shell and are not adhered to. The surface of the alloy ingot after peeling is smooth and free of adhering substances, and obvious columnar crystals can be directly observed with the naked eye. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the carburizing treatment in this invention.

[0032] Figure 2 This is a schematic diagram of a frustum-shaped plaster casting model.

[0033] Figure 3 This is a physical image of the nanoscale yttrium oxide shell prepared by carburizing according to the present invention.

[0034] Figure 4 Schematic diagram of the surface microstructure of yttrium oxide shell: (a) without carburizing treatment; (b) after carburizing treatment.

[0035] Figure 5 The following are actual images of Ti-48Al alloy ingots: (a) induction melting using an uncarburized yttrium oxide shell; (b) induction melting using the carburized nanoscale yttrium oxide shell prepared according to this invention.

[0036] Figure 6 Microstructure of Ti-48Al alloy ingot surface: (a) induction melting using uncarburized yttrium oxide shell; (b) induction melting using the carburized nanoscale yttrium oxide shell prepared according to the present invention.

[0037] Figure 1 In the middle: 1-furnace shell, 2-induction coil, 3-arc-shaped copper petal block, 4-solid carburizing agent, 5-yttrium oxide shell, 6-graphite sheet. Detailed Implementation

[0038] The technical solution of the present invention will be further described in detail below with reference to specific implementation examples, but the present invention is not limited to these embodiments.

[0039] Example 1:

[0040] like Figure 1 As shown, a nanoscale yttrium oxide shell treated with carburizing is prepared by means of the following steps:

[0041] 1. Weigh 50 g of nano-yttria (nano-yttria powder particle size of 500 nm-850 nm) and 1.1 g of ceramic dispersant sodium polyacrylate, add to 93 ml of deionized water to obtain an initial solution, and put the initial solution into a planetary ball mill for ball milling for 12 h, wherein the rotation speed of the ball mill is 310 r / min, the ball milling medium is electronic slurry grinding zirconium beads, 10 large balls, 10 medium balls, and 20 small balls.

[0042] 2. Weigh 240 g of gypsum powder into 90 ml of water and stir until uniform, to make a circular table-shaped grouting gypsum model, as shown in Figure 2 , and then place the gypsum model in a drying oven and dry for 72 h at a temperature of 45 ℃.

[0043] 3. Repeat pouring the nano-yttria slurry into the grouting model 5 times. Pour the slurry into the model for the first time and let it stand for 60 s, pour out the excess slurry, and after the surface of the slurry in the gypsum model naturally dries and loses its luster, continue to pour in the slurry; pour the slurry into the model for the second time and let it stand for 65 s, repeat the above operation; pour the slurry into the model for the third time and let it stand for 70 s, repeat the above operation; pour the slurry into the model for the fourth time and let it stand for 75 s, repeat the above operation; pour the slurry into the model for the fifth time and let it stand for 80 s, and pour out the excess slurry.

[0044] 4. Place the grouted yttria shell embryo and the gypsum model in a place with air circulation and let it dry naturally for 120 h, until a gap is formed between the gypsum model and the yttria shell embryo, and the shell is loose. Then, demold the nano-yttria shell embryo, and then place the nano-yttria shell embryo in a drying oven and set the drying temperature to 80 ℃ and the drying time to 48 h.

[0045] 5. Place the dried nano-yttria shell embryo in a high-temperature muffle furnace and sinter it in four stages. In the first stage, slowly raise the temperature from room temperature to 200 ℃ in 9 h; in the second stage, quickly raise the temperature to 1650 ℃ in 4 h; in the third stage, slowly raise the temperature from 1650 ℃ to 1800 ℃ in 8 h; in the fourth stage, when the temperature rises to 1800 ℃, keep the temperature for 10 h; after sintering is completed, cool the furnace to room temperature, and obtain the nano-yttria shell finished product.

[0046] 6. Place the sintered nano-yttria shell into a vacuum induction melting furnace, then surround the yttria shell with charcoal and sodium carbonate powder. First, pump the air in the furnace body to 5×10 -3 Pa, use high-purity argon to wash twice, and finally fill argon to 0.7×10 5The carburizing heating process consists of five stages: the first stage is heating to 20 kW and holding for 5 min; the second stage is heating to 40 kW and holding for 4 min; the third stage is heating to 60 kW and holding for 3 min; the fourth stage is heating to 70 kW and holding for 2 min; and the fifth stage is heating to 75 kW and holding for 1 min. The cooling process consists of four stages: the first stage is cooling to 65 kW and holding for 2 min; the second stage is cooling to 40 kW and holding for 5 min; the third stage is cooling to 30 kW and holding for 5 min; and the fourth stage is cooling to 20 kW and holding for 10 min. After the nanoscale yttrium oxide shell is cooled to room temperature in a vacuum induction melting furnace, it is removed, yielding a gray-black nanoscale yttrium oxide shell.

[0047] The Ti-48Al (at. %) alloy was placed in a carburized yttrium oxide shell and then placed in a vacuum induction melting furnace, where a vacuum of 3 × 10⁻⁶ was applied. -3 Pa, then purge with high-purity argon gas, and finally purge with argon gas to 0.7 × 10⁻⁶. 5 Induction melting is performed after Pa. The alloy state is constantly observed through the external observation port of the furnace. After the alloy is completely melted, it is held for 5 minutes, then the power is turned off, and the alloy is taken out after cooling to room temperature.

[0048] like Figure 3 As shown, the surface of the nanoscale yttrium oxide shell treated with carburizing technology has a clear outline, is smooth and flat, and has no obvious cracks or pores. Figure 4 As shown, a comparison of the microstructures of nanoscale yttrium oxide shells treated with carburizing technology and those without reveals that the shells treated with carburizing technology have more uniform grain sizes on the surface, ranging from approximately 5 μm to 22 μm, clearer grain boundaries, more orderly grain arrangement, and increased relative density. This improves the thermal shock resistance of the yttrium oxide shells, and the shells remain intact without any cracks after melting.

[0049] like Figure 5 As shown, a comparison of alloy ingots induction melted using nanoscale yttrium oxide shells treated with carburizing technology and those without carburized nanoscale yttrium oxide shells reveals that the alloy ingots induction melted using carburized shells have a clear boundary with the yttrium oxide shells and are not adhered to. The surface of the alloy ingots after peeling is smooth, without any adhering substances, and obvious columnar crystals can be directly observed with the naked eye. Figure 6 As shown, alloy ingots formed by induction melting with two different shell types were examined under a scanning electron microscope to observe their surface microstructure. No Y element or any impurities were found on the alloy surface. Therefore, the nanoscale yttrium oxide shell treated with carburizing technology is very suitable for melting TiAl alloys.

[0050] Example 2:

[0051] 1. Weigh 80 g of nano-yttria (nano-yttria powder particle size of 500 nm-850 nm) and 2.16 g of ammonium polyacrylate into 90 ml of deionized water to obtain an initial solution, and put the initial solution into a planetary ball mill for ball milling for 10 h, wherein the rotation speed of the ball mill is 370 r / min, the ball milling medium is electronic slurry zirconium beads, 11 large balls, 11 medium balls, and 22 small balls.

[0052] 2. Weigh 300 g of gypsum powder into 112 ml of water and stir uniformly to make a circular table-shaped gypsum model, and then put the gypsum model into a drying oven and dry for 85 h, with a temperature setting of 41 ℃.

[0053] 3. Repeat pouring the nano-yttria slurry into the injection molding model 5 times. Pour the slurry into the model for the first time and stand for 70 s, pour out the excess slurry, and after the surface of the slurry in the gypsum model naturally dries and loses its luster, continue to pour in the slurry; pour the slurry into the model for the second time and stand for 80 s, repeat the above operation; pour the slurry into the model for the third time and stand for 85 s, repeat the above operation; pour the slurry into the model for the fourth time and stand for 90 s, repeat the above operation; pour the slurry into the model for the fifth time and stand for 95 s, pour out the excess slurry.

[0054] 4. Place the yttria shell embryo after injection molding and the gypsum model in a place with air circulation and naturally dry for 150 h, and when a gap is generated between the gypsum model and the yttria shell embryo, the nano-yttria shell embryo is demolded after the shell is loose. Then put the nano-yttria shell embryo into a drying oven and set the drying temperature to 75 ℃ and the drying time to 55 h.

[0055] 5. Put the dried nano-yttria shell embryo into a high-temperature muffle furnace and sinter it in three stages, the first stage is to slowly rise from room temperature to 200 ℃ in 9.5 h; the second stage is to quickly rise to 1650 ℃ in 5.5 h; the third stage is to slowly rise from 1650 ℃ to 1800 ℃ in 8.5 h. The fourth stage is to keep the temperature at 1800 ℃ for 13 h after the temperature rises to 1800 ℃; after sintering is completed, the furnace is cooled to room temperature, and the nano-yttria shell finished product is obtained.

[0056] 6. Put the sintered nano-yttria shell into a vacuum induction melting furnace, then put graphite blocks and sodium carbonate powder around the yttria shell. The air in the furnace body is pumped to 5×10 -3 Pa, use high-purity argon to wash twice, and finally fill argon to 0.7×10 5Pa. The carburizing heating process is divided into five stages: the first stage is heated to 20 kw, holding for 6 min; the second stage is heated to 40 kw, holding for 4.5 min; the third stage is heated to 60 kw, holding for 4 min; the fourth stage is heated to 70 kw, holding for 2.5 min; the fifth stage is heated to 75 kw, holding for 90 s. The cooling process is divided into four stages: the first stage, cooling to 65 kw, holding for 2.5 min; the second stage, cooling to 40 kw, holding for 5.5 min; the third stage, cooling to 30 kw, holding for 8 min; the fourth stage, cooling to 20 kw, holding for 15 min. After the nanoscale yttrium oxide shell is cooled to room temperature in the vacuum induction melting furnace, it is removed to obtain a gray-black nanoscale yttrium oxide shell.

[0057] The Ti-46Al (at. %) alloy is placed in the carburized yttrium oxide shell and placed in a vacuum induction melting furnace, vacuumed to 3 x 10 -3 Pa, then washed with high-purity argon, and finally filled with argon to 0.7 x 10 5 Pa and induction melted. The alloy state is observed at all times through the observation port outside the furnace body. After the alloy is completely melted, it is held for 5 min, then the power is turned off, and the alloy is removed after cooling to room temperature. The surface profile of the nanoscale yttrium oxide shell treated by the carburizing technology is clear, smooth, and free of obvious cracks and holes. The alloy ingot is clearly separated from the yttrium oxide shell without adhesion, and the surface of the peeled alloy ingot is smooth without adhesion. The obvious columnar crystals can be directly observed with the naked eye. The alloy ingot is placed in a scanning electron microscope to observe the surface microstructure, and no Y element or any impurities are found on the alloy surface. Therefore, the nanoscale yttrium oxide shell treated by the carburizing technology is very suitable for the melting of TiAl alloys.

[0058] Example 3:

[0059] 1. 100 g of nanometer yttrium oxide and 3.1 g of ammonium polyacrylate were weighed and added to 100 ml of deionized water to obtain an initial solution. The initial solution was placed in a planetary ball mill to ball mill for 8 h, wherein the rotation speed of the ball mill was 420 r / min, the ball milling medium was electronic slurry zirconium beads, 10 large balls, 10 medium balls, and 20 small balls.

[0060] 2. 300 g of gypsum powder was weighed and poured into 112 ml of water and stirred uniformly to make a gypsum model. Then the gypsum model was placed in a drying oven and dried for 100 h, with a temperature setting of 39 ℃.

[0061] 3. Repeat pouring the nano-yttria slurry into the slurry injection model for 5 times. Pour the slurry into the model for the first time and let it stand for 80 s, pour out the excess slurry, and after the surface of the slurry in the gypsum model is naturally dried and has no luster, continue to pour the slurry; pour the slurry into the model for the second time and let it stand for 85 s, repeat the above operation; pour the slurry into the model for the third time and let it stand for 90 s, repeat the above operation; pour the slurry into the model for the fourth time and let it stand for 95 s, repeat the above operation; pour the slurry into the model for the fifth time and let it stand for 100 s, pour out the excess slurry.

[0062] 4. Place the yttria shell body after slurry injection and the gypsum model in a place with air circulation and naturally dry for 180 h, until a gap is generated between the gypsum model and the yttria shell body, and the shell body is loose, then demold the nano-yttria shell body. Then, place the nano-yttria shell body into a drying oven, set the drying temperature to 70 ℃, and the drying time to 60 h.

[0063] 5. Place the dried nano-yttria shell body into a high-temperature muffle furnace for sintering in three stages, in the first stage, increase the temperature from room temperature to 200 ℃ within 10 h; in the second stage, rapidly increase the temperature to 1650 ℃ within 6 h; in the third stage, slowly increase the temperature from 1650 ℃ to 1800 ℃ within 9 h. In the fourth stage, when the temperature is increased to 1800 ℃, keep the temperature for 15 h; after sintering is completed, cool the furnace to room temperature, and obtain the nano-yttria shell finished product.

[0064] 6. Place the sintered nano-yttria shell into a vacuum induction melting furnace, then, place charcoal + graphite blocks and sodium carbonate powder around the yttria shell. Pump the air in the furnace body to 5×10 -3 Pa, use high-purity argon to wash the air twice, and finally fill argon to 0.7×10 5 Pa. The carburizing temperature process is divided into 5 stages: in the first stage, heat to 20 kw, keep for 8 min; in the second stage, heat to 40 kw, keep for 5 min; in the third stage, heat to 60 kw, keep for 5 min; in the fourth stage, heat to 70 kw, keep for 3 min; in the fifth stage, heat to 75 kw, keep for 2 min. The cooling process is divided into 4 stages: in the first stage, cool to 65 kw, keep for 3 min; in the second stage, cool to 40 kw, keep for 6 min; in the third stage, cool to 30 kw, keep for 10 min; in the fourth stage, cool to 20 kw, keep for 20 min. After the nano-yttria shell is cooled to room temperature in the vacuum induction melting furnace, take it out, and obtain the gray-black nano-yttria shell.

[0065] Place the Ti-46Al (at. %) alloy into the yttria shell after carburizing and place it in the vacuum induction melting furnace, pump the vacuum to 3×10 -3Pa, and then washed with high-purity argon gas, and finally filled with argon gas to 0.7*10 5 Pa, and then washed with high-purity argon gas, and finally filled with argon gas to 0.7*10

[0066] The bending strength and Vickers hardness of the carburized nanoscale yttrium oxide shell prepared in Examples 1-3 were tested by three-point bending test method and indentation method, respectively, and the test results are shown in Table 1.

[0067]

[0068] As can be seen from Table 1, the yttrium oxide shell prepared by the preparation method of the present application has excellent bending strength and Vickers hardness, and the bending strength can reach 24.1 MPa, and the Vickers hardness can reach 152 HV.

[0069] The nanoscale yttrium oxide shell treated by carburization technology has excellent high-temperature resistance and chemical inertness, can reduce the pollution of yttrium oxide particles to the TiAl alloy melt, hinder the occurrence of the TiAl alloy melt-shell interface reaction, and the surface of the TiAl alloy after melting is smoother, and the columnar grains on the surface of the alloy ingot can be clearly observed. Moreover, the shell has high bending strength and Vickers hardness, and the relative density is increased, solving the problem of cracking of the yttrium oxide shell after TiAl alloy melting.

[0070] The above description is only a further description of the technical solutions of the present application, and for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a nanoscale yttrium oxide shell after carburizing treatment, characterized in that: The process includes the following steps: a preform is made using nano-sized yttrium oxide slurry; after the preform is sintered, it is carburized in a vacuum induction melting furnace. Specifically, it includes the following steps: (1) Preparation of nano-scale yttrium oxide slurry Nanoscale yttrium oxide powder, ceramic dispersant, and deionized water are mixed and then placed in a ball mill for ball milling. (2) Use water and plaster to make a grouting model, and then place it in a drying oven for drying treatment; (3) Pour the ball-milled nano-sized yttrium oxide slurry from step (1) into the gypsum mold dried in step (2), let it stand, pour out the excess slurry, and repeat this process multiple times to obtain a nano-sized yttrium oxide shell preform with a certain thickness. (4) Place the yttrium oxide shell preform and plaster model from step (3) in a well-ventilated place and let them dry naturally. When a gap of 1-2 mm is formed between the plaster model and the yttrium oxide shell preform, demold the nano-sized yttrium oxide shell preform and then put it into a drying oven for drying. (5) The nanoscale yttrium oxide shell preform dried in step (4) is placed in a high-temperature muffle furnace for sintering; (6) The nanoscale yttrium oxide shell sintered in step (5) is placed in a vacuum induction melting furnace filled with high concentration of activated carbon for carburizing treatment. In step (3), the slurry is left to stand for 6 min-7.5 min. Repeating this process 5 times will result in a yttrium oxide shell preform with a thickness of 2 mm-3 mm. The slurry is poured into the mold for the first time and left to stand for 60 s-80 s. The slurry is poured into the mold for the second time and left to stand for 65 s-85 s. Excess slurry is then poured out. The slurry is poured into the mold for the third time and left to stand for 70 s-90 s. The slurry is poured into the mold for the fourth time and left to stand for 75 s-95 s. The slurry is poured into the mold for the fifth time and left to stand for 80 s-100 s. Step (5) The sintering temperature of the green body is 1700 ℃-1800 ℃, and the sintering time is 31 h-40 h. The sintering process is carried out in four stages. In the first stage, the temperature is slowly increased from room temperature to 200 ℃ within 9 h-10 h. In the second stage, the temperature is rapidly increased to 1650 ℃ within 4 h-6 h. In the third stage, the temperature is slowly increased from 1650 ℃ to 1800 ℃ within 8 h-9 h. In the fourth stage, after the temperature is raised to 1800 ℃, it is held for 10 h-15 h. The carburizing treatment in step (6) is solid carburizing, which is a solid carburizing agent composed of solid carburizing source charcoal and / or graphite blocks and carburizing catalyst sodium carbonate; the carburizing power is 20 kw-75 kw and the carburizing time is 37 min-62 min.

2. The preparation method as described in claim 1, characterized in that: In step (1), the particle size of the nano-sized yttrium oxide powder is 500 nm-850 nm, the ceramic dispersant is sodium polyacrylate or ammonium polyacrylate with a content of 2.2%-3.1%, the solid content in the nano-sized yttrium oxide slurry is 35%-50%, the ball mill speed is 310 r / min-420 r / min, and the ball milling time is 8 h-12 h.

3. The preparation method as described in claim 1, characterized in that: Step (2) The grouting model is frustum-shaped, the ratio of water to gypsum is 3:8, the ratio of the diameter of the top surface to the bottom surface is 1:2; the drying temperature is 39 ℃-45 ℃, and the drying time is 72 h-100 h.

4. The preparation method as described in claim 1, characterized in that: Step (4) The natural drying temperature is 15 ℃-38℃ and the natural drying time is 120 h-180 h; the drying temperature of the drying oven is 70 ℃-80 ℃ and the drying time is 48 h-60 h.

5. A nanoscale yttrium oxide shell treated with carburizing, characterized in that: It is prepared by any one of the preparation methods described in claims 1-4.

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