Nb-Si-Ti-Cr-Al-Hf alloy turbine ultrahigh-temperature investment casting method

Abstract

The invention discloses an Nb-Si-Ti-Cr-Al-Hf alloy turbine ultrahigh-temperature investment casting method. The method comprises the following steps: preparing an alloy turbine ultrahigh-temperature investment casting shell; performing ultrahigh-temperature investment casting on the alloy turbine; and post-processing the alloy turbine casting. The microstructure and the mechanical property of the Nb-Si-based alloy are improved through alloying, the solidification path of the alloy is changed, the eutectoid reaction of metastable-phase Nb3Si is promoted, and the comprehensive performance is improved. Through the rare earth yttrium oxide shell, the problem that the alloy reacts with the shell is solved; high surface quality, strength and thermal shock resistance of the alloy turbine are ensured by regulating and controlling the powder-liquid mass ratio of the slurry and the number of shell layers; and a casting of which the tail end of the blade can be completely filled and has no metallurgical defect is cast through an induction suspension smelting technology, so that the alloy turbine cast by the ultra-high-temperature investment casting can meet the actual application requirement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ultra-high temperature investment casting forming process, and particularly relates to a preparation method of Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting. BACKGROUND

[0002] The sixth generation of aircraft engines is the core power system of fighter aircraft, and puts forward more stringent performance requirements for ultra-high temperature materials; the turbine front temperature of the sixth generation engine needs to break through 1800 DEG C, and even exceed 2000 DEG C for a short time, which is far higher than the 1600 DEG C limit of the existing engine, and the material needs to maintain structural stability at a high temperature. However, the widely used nickel-based high-temperature alloy has a use temperature limit of 1150 DEG C, and it is difficult to meet the temperature resistance requirements of the new generation of aerospace engine blades. The melting point of niobium alloy is 2400 DEG C, and it still maintains excellent mechanical properties at a high temperature of 2100 DEG C, and becomes the preferred material for the turbine blades of the new generation of aircraft engines, and is regarded as the core research material of the sixth generation of variable cycle engines and oblique detonation engines, and is expected to completely solve the 'heart disease' problem in the field of aircraft engines. However, room temperature brittleness limits the industrial application of Nb-Si-based alloys, and the room temperature fracture toughness of Nb-16Si alloy is only 5.4 MPa·m 1 / 2 , which is less than 1 / 5 of the conventional nickel-based high-temperature alloy, and seriously affects the processing performance and engineering application of the Nb-Si-based alloy. Existing researches have shown that when the brittle Nb5Si3 phase is dispersedly distributed in the continuous ductile Nb SS phase matrix, the Nb-Si-based alloy can obtain the balance of strength and toughness, and alloying is an important way to realize the balance of strength and toughness; during the alloying process, active elements such as Cr, Hf, Ti and Al are added to evolve into the Nb-Si-Ti-Cr-Al-Hf six-element system alloy which has been proved to have good comprehensive performance, and the alloy smelting temperature is higher than 2000 DEG C. The high active elements are easy to have interface reactions with the crucible and the shell material, and the traditional casting method is difficult to form a complex thin-walled turbine blade, and investment casting is the most promising forming process.

[0003] The high-temperature melt of metal elements in the Nb-Si-Ti-Cr-Al-Hf alloy has high activity, and the traditional induction melting method of the ceramic crucible is not suitable for the melting of the Nb-Si-Ti-Cr-Al-Hf alloy; the mature precision casting technology of the high-temperature alloy mainly adopts the alumina ceramic shell with a using temperature below 1600 DEG C, and the refractory metal surface shell, yttrium oxide and zirconium oxide shell are developed for the titanium-based alloy to ensure the forming of the titanium-based alloy. Since the melting point of the Nb-Si-Ti-Cr-Al-Hf alloy is more than 1700 DEG C, the casting melt temperature is more than 1900 DEG C, and the high-temperature activity of each metal element in the alloy is large, the precision casting technology of the high-temperature alloy and the titanium-based alloy cannot be applied to the precision casting of the Nb-Si-Ti-Cr-Al-Hf alloy. In view of the preparation of the ultra-high-temperature low-reaction shell and the heating of the ultra-high-temperature melt in the precision casting of the Nb-Si-Ti-Cr-Al-Hf alloy, it is urgent to solve the problems of the reaction of the Nb-Si-Ti-Cr-Al-Hf alloy with the shell and the alloy melting and pouring. SUMMARY

[0004] The purpose of the present application is to provide a Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high-temperature investment casting method, which is prepared by studying the shell formula of investment casting and exploring the suspension melting and pouring process.

[0005] The present application is realized by the following technical solutions.

[0006] The Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high-temperature investment casting method comprises the following steps.

[0007] Step 1, preparing a shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high-temperature investment casting.

[0008] a. preparing a wax mold: designing and drawing a three-dimensional graphic model of the turbine wax mold, and then preparing the wax mold by printing rapid prototyping method, wherein the wax mold module is composed of a bottom support, a blade, an upper edge plate and a riser.

[0009] b. preparing slurry: preparing the binder in proportion, adding the filler powder into the stirring binder, and then adding the wetting agent and defoaming agent to obtain the slurry after stirring; the binder ratio of the shell surface layer and the adjacent layer is that the mass ratio of deionized water, zirconium acetate and ammonium metatungstate is 0.5-1.5:1.0-2.0:4.0-5.0, and the powder-liquid mass ratio of the filler powder and the binder in the shell surface layer and the adjacent layer slurry is 2-4:1; the binder of the shell back layer and the sealing slurry layer is silica sol, the powder-liquid mass ratio of the filler powder and the binder in the back layer slurry is 1-3:1, and the powder-liquid mass ratio of the filler powder and the binder in the sealing slurry layer slurry is 1-2:1.

[0010] c. Preparation of shell: the wax mold module is first cleaned with a cleaning solution, then immersed in slurry and sand is scattered, dried at a temperature of 23±3°C and humidity of 70±5, repeated for 6-12 times of slurry hanging, sand scattering and drying process, finally immersed in slurry for sealing and drying; the shell surface layer and the adjacent layer are scattered with yttria sand of 40-100 mesh, dried for 20-30h; the shell back layer is scattered with bauxite sand of 16-80 mesh, dried for 10-20h; dried for 24h after sealing.

[0011] d. Shell dewaxing and sintering: the sealed and dried shell is placed upside down for dewaxing, the dewaxing temperature is 300-400°C, the dewaxing time is 2-5h; the dewaxed shell is placed in an air atmosphere sintering furnace, the sintering temperature is 900-1100°C, the sintering time is 3-8h, and the shell is cooled in the furnace, and the shell preparation is completed.

[0012] Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting.

[0013] a. Preparation of alloy ingot: calculate the alloy density according to the composition ratio of Nb-Si-Ti-Cr-Al-Hf alloy, determine the pouring weight of the entire casting according to the product model and the final group tree scheme, and calculate the weight of various metals in proportion; first, add Nb, Ti and Hf metals with high melting points into a water-cooled copper crucible, perform vacuum extraction treatment to make the vacuum degree ≤10 -3 Pa, close the gas filling valve or introduce a small amount of argon into the furnace, immediately turn on the induction heating power, heat and melt the alloy, keep heating for 3-10min, the alloy is in a suspended state and completely mixed and uniform, then cool to room temperature to obtain an alloy ingot; then turn over the alloy ingot and add Si, Cr and Al metals with low melting points into the water-cooled copper crucible, continue to melt and melt the alloy with the same smelting process, and cool to room temperature to obtain an alloy ingot; finally, turn over the ingot and continue to melt with the same smelting process to obtain an Nb-Si-Ti-Cr-Al-Hf alloy ingot with good microstructure uniformity.

[0014] b. Shell preheating: the dewaxed shell is subjected to local area cotton wrapping and heat insulation treatment, after the cotton wrapping is completed, the inside of the shell is cleaned by blowing gun, after cleaning, the shell is placed in a preheating furnace for preheating at a temperature of 1000±30°C for 2-4h.

[0015] c. Melting and pouring: the melted alloy ingot is placed in a water-cooled copper crucible, the shell is quickly transferred from the preheating furnace to the furnace, then the furnace door is closed to maintain the sealing of the furnace, and vacuum extraction treatment is performed to make the vacuum degree ≤10 -3Pa; closing the gas valve or introducing a small amount of argon into the furnace, immediately opening the induction heating power, heating and melting the alloy, maintaining heating for 3-10 min, when observing that the alloy is in a suspended state, immediately carrying out the pouring operation, tilting the water-cooled copper crucible, pouring the alloy liquid in the crucible into the preheated mold shell, and then cooling the mold shell to room temperature.

[0016] Step 3, post-processing of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: after the mold shell is taken out of the furnace, first, the shell is cleaned, then, cutting, grinding and polishing are carried out to obtain the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting.

[0017] Further, in step 1, the shell surface layer and the temporary surface layer filler powder are 300-400 mesh yttrium oxide powder, and the back layer filler powder is 100-300 mesh bauxite powder.

[0018] Further, in step 2, the atomic percentage of the Nb-Si-Ti-Cr-Al-Hf alloy composition is Nb-(10-20)Si-(20-25)Ti-(1-5)Cr-(2-6)Al-(2-10)Hf.

[0019] Further, in step 3, the shell cleaning is carried out by hydraulic shell cleaning, and the riser and the runner are cut off by wire electrical discharge machining or diamond cutting.

[0020] Further, in step 3, sand blasting or grinding head polishing is used to polish and surface polish the turbine casting.

[0021] The present application has the advantages and beneficial effects.

[0022] (1) The present application improves the microstructure and mechanical properties of the Nb-Si-based alloy by alloying, changes the alloy solidification path, promotes the eutectoid reaction of metastable phase Nb3Si, and improves the comprehensive performance. The addition of Ti element improves the room temperature fracture toughness and high temperature oxidation resistance, the addition of Al element inhibits the formation of Nb3Si phase and improves the high temperature oxidation resistance, the addition of Cr element generates Cr2Nb and is beneficial to the strength, and the addition of Hf element inhibits the formation of Nb3Si phase and improves the room temperature toughness, high temperature strength and high temperature oxidation resistance.

[0023] (2) The present application innovates the preparation technology of rare earth yttrium type shell, solves the problem of reaction between Nb-Si-Ti-Cr-Al-Hf alloy and the shell, and ensures that the finally formed Nb-Si-Ti-Cr-Al-Hf alloy turbine has high surface quality and high strength and thermal shock resistance by adjusting the powder-liquid mass ratio of the slurry and the shell layer; the problem of super-high temperature smelting of the alloy is solved by the induction suspension smelting technology, and the castings without metallurgical defects are poured, and then the Nb-Si-Ti-Cr-Al-Hf alloy turbine is obtained after shell cleaning and cutting, polishing and polishing. By adjusting the process parameters, the castings without porosity, porosity, shrinkage and other metallurgical defects are obtained, thereby meeting the demand of aerospace engine on Nb-Si-Ti-Cr-Al-Hf alloy material; at the same time, the castings are smooth by near-net forming, meeting the high quality requirement of aerospace engine parts. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The three-dimensional model of the wax mold of the Nb-Si-Ti-Cr-Al-Hf alloy turbine.

[0025] Figure 2 The appearance of the Nb-Si-Ti-Cr-Al-Hf alloy turbine shell.

[0026] Figure 3 The appearance of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting.

[0027] Figure 4 The microstructure of the Nb-Si-Ti-Cr-Al-Hf alloy turbine blade. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples are commercially available unless otherwise specified. Example 1

[0030] Step 1, preparation of a shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine super-high temperature investment casting.

[0031] a. Preparation of wax mold: design and draw three-dimensional model of turbine wax mold, then prepare wax mold by printing rapid prototyping method, wax mold module is composed of bottom support, blade, upper edge plate and riser.

[0032] b. Preparation of slurry: prepare binder in proportion, add filler powder to stirring binder, then add wetting agent and defoaming agent to obtain slurry after stirring; the binder ratio of shell surface layer and temporary surface layer is 1.0:1.5:4.0 in terms of mass ratio of deionized water: zirconium acetate: ammonium metatungstate; the powder-liquid mass ratio of filler powder and binder in shell surface layer and temporary surface layer slurry is 3.0:1; the binder of shell back layer and sealing slurry layer is silica sol, the powder-liquid mass ratio of filler powder and binder in back layer slurry is 2.0:1; the powder-liquid mass ratio of filler powder and binder in sealing slurry layer slurry is 1.5:1.

[0033] c. Preparation of shell: first wash wax mold module with cleaning solution, then immerse the module in slurry and sprinkle sand, dry under the condition of temperature 25℃ and humidity 70, repeat the process of slurry hanging, sand sprinkling and drying for 8 times, finally immerse in slurry for sealing and drying; the sand sprinkled on shell surface layer and temporary surface layer is yttrium oxide sand 40-70 mesh, dry for 24h; the sand sprinkled on shell back layer one and back layer two is bauxite sand 40-70 mesh, dry for 12h after back layer three; dry for 24h after sealing.

[0034] d. Shell dewaxing and sintering: dewax the shell with dried sealing slurry with riser downward, dewaxing temperature is 300℃, dewaxing time is 2h; place the dewaxed shell in air atmosphere sintering furnace, sintering temperature is 1000℃, sintering time is 4h, cool down with furnace, and the shell preparation is completed.

[0035] Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting.

[0036] a. Preparation of alloy ingot: the composition of Nb-Si-Ti-Cr-Al-Hf alloy is selected as Nb-14Si-20Ti-3Cr-3Al-2Hf in terms of atomic percentage, calculate the density according to the proportion, determine the pouring weight of the entire casting according to the product model and the final group tree scheme, and calculate the weight of various metals in proportion; first add Nb, Ti and Hf metals with high melting point into water-cooled copper crucible, vacuumize to a vacuum degree of 6.0×10 -3Pa, close the gas valve or introduce a small amount of argon into the furnace, immediately open the induction heating power, heat and melt the alloy, keep heating for 10 min, after the alloy is in a suspended state and completely mixed and uniform, cool down to room temperature to obtain an alloy ingot; then turn over the alloy ingot and add the remaining low-melting-point Si, Cr and Al metals into a water-cooled copper crucible, continue to melt and melt the alloy by using the same smelting process, and cool down to room temperature to obtain an alloy ingot; finally, turn over the cast ingot and continue to smelt by using the same smelting process to obtain a Nb-Si-Ti-Cr-Al-Hf alloy cast ingot with good microstructure uniformity.

[0037] b. Shell preheating: after the wax removal is completed, the shell is subjected to local area cotton wrapping and heat insulation treatment, after the cotton wrapping is completed, the inside of the shell is cleaned by blowing with a blowing gun, and after the cleaning is completed, the shell is placed in a preheating furnace for preheating, the temperature is 1000±30℃, and the holding time is 3h.

[0038] c. Melting and pouring: the smelted alloy ingot is placed in a water-cooled copper crucible, the shell is quickly transferred from the preheating furnace to the furnace, then the furnace door is closed to maintain the sealing property of the furnace, vacuumizing treatment is performed, and finally the vacuum degree is 7.0×10 -3 Pa; close the gas valve or introduce a small amount of argon into the furnace, immediately open the induction heating power, heat and melt the alloy, keep heating for 10 min, when it is observed that the alloy is in a suspended state, immediately perform the pouring operation, quickly tilt the water-cooled copper crucible, pour the alloy liquid in the crucible into the preheated shell, and then cool down to room temperature to take out the shell.

[0039] Step 3, post-treatment of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: after the shell is taken out from the furnace, first clean the shell, then perform cutting, polishing and polishing treatment to obtain the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting. Example 2

[0040] Step 1, preparation of a shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine superhigh-temperature investment casting.

[0041] a. Preparation of a wax mold: design and draw a three-dimensional graphic model of a turbine wax mold, and then prepare the wax mold by using a printing rapid prototyping method, the wax mold module is composed of a bottom support, a blade, an upper edge plate and a riser.

[0042] b. Preparation of slurry: the binder was prepared according to the proportion, the filler powder was added into the stirring binder, and then the wetting agent and defoaming agent were added to obtain the slurry after stirring; the proportion of the shell surface layer and the shell surface layer binder was 1.0:2.0:4.0 in terms of the mass ratio of deionized water: zirconium acetate: ammonium metatungstate; the powder-liquid mass ratio of the filler powder and the binder in the shell surface layer and the shell surface layer slurry was 2.5:1; the binder of the shell back layer and the sealing slurry layer was silica sol; the powder-liquid mass ratio of the filler powder and the binder in the back layer slurry was 2.5:1; the powder-liquid mass ratio of the filler powder and the binder in the sealing slurry layer slurry was 1.5:1.

[0043] c. Preparation of shell: the wax mold module was first cleaned with cleaning liquid, then the module was immersed in the slurry and sand was scattered, and the temperature was 23°C and the humidity was 70; the slurry hanging, sand scattering and drying process was repeated for 8 times, and finally the slurry was immersed for sealing and drying; the shell surface layer and the shell surface layer were scattered with yttrium oxide sand 40-70 mesh, and dried for 24h; the shell back one and back two layers were scattered with bauxite sand 40-70 mesh, and dried for 12h; the sealing slurry was dried for 24h.

[0044] d. Shell dewaxing and sintering: the shell with dried sealing slurry was placed with the riser downward for dewaxing, the dewaxing temperature was 300°C, and the dewaxing time was 2h; the dewaxed shell was placed in an air atmosphere sintering furnace, the sintering temperature was 1000°C, the sintering time was 5h, and the shell was cooled with the furnace, and the shell preparation was completed.

[0045] Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine ultrahigh temperature investment casting.

[0046] a. Preparation of alloy ingot: the Nb-Si-Ti-Cr-Al-Hf alloy was selected with the composition of Nb-14Si-20Ti-3Cr-3Al-2Hf in terms of atomic percentage, the density was calculated according to the proportion, the pouring weight of the entire casting was determined according to the product model and the final group tree scheme, and the weight of various metals was calculated according to the proportion; first, the metals with high melting point, such as Nb, Ti and Hf, were added into a water-cooled copper crucible, the vacuum degree was 6.0×10 -3 Pa after vacuumizing, the gas filling valve was closed or a small amount of argon was introduced into the furnace, the induction heating power was immediately turned on, the alloy was melted and kept heating for 10min, the alloy was in a suspended state and completely mixed and uniform, and then the alloy ingot was obtained after the furnace was cooled to room temperature; then, the alloy ingot was turned over, and the remaining metals with low melting point, such as Si, Cr and Al, were added into the water-cooled copper crucible, and the alloy was continuously melted by the same melting process, and the alloy ingot was obtained after the furnace was cooled to room temperature; finally, the alloy ingot was turned over again, and the same melting process was used to continue melting to obtain the Nb-Si-Ti-Cr-Al-Hf alloy ingot with good microstructure uniformity.

[0047] b. Shell preheating: After the dewaxing of the shell is completed, the shell is locally wrapped with cotton for heat insulation treatment. After the wrapping is completed, the inside of the shell is cleaned by blowing with a blowing gun. After the cleaning is completed, the shell is placed in a preheating furnace for preheating at a temperature of 1000±30℃ for 3h.

[0048] c. Melting and pouring: The melted alloy ingot is placed in a water-cooled copper crucible. The shell is quickly transferred from the preheating furnace to the furnace, and then the furnace door is closed to maintain the sealing property of the furnace. Vacuum is extracted, and the final vacuum degree is 6.0×10 -3 Pa; the gas filling valve is closed or a small amount of argon gas is introduced into the furnace. The induction heating power is immediately turned on to melt the alloy. The heating is maintained for 10 min. When it is observed that the alloy is in a suspended state, pouring is immediately performed. The water-cooled copper crucible is quickly tilted to pour the alloy liquid in the crucible into the preheated shell. The shell is cooled to room temperature with the furnace, and then taken out.

[0049] Step 3, Post-treatment of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: After the shell is taken out of the furnace, it is first cleaned, and then cut, polished and polished to obtain the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting. Example 3

[0050] Step 1, Preparation of a shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine superhigh-temperature investment casting.

[0051] a. Preparation of wax mold: design and draw a three-dimensional graphic model of the turbine wax mold, and then prepare the wax mold by printing rapid prototyping. The wax mold module is composed of a bottom support, a blade, an upper edge plate and a riser.

[0052] b. Preparation of slurry: prepare the binder in proportion, add the filler powder to the stirring binder, and then add the wetting agent and defoaming agent to obtain the slurry after stirring; the binder ratio of the shell surface layer and the temporary surface layer is 1.0:2.0:4.5 in terms of the mass ratio of deionized water: zirconium acetate: ammonium metatungstate; the powder-liquid mass ratio of the filler powder and the binder in the shell surface layer and the temporary surface layer slurry is 3.0:1; the binder of the shell back layer and the sealing slurry layer is silica sol; the powder-liquid mass ratio of the filler powder and the binder in the back layer slurry is 2.0:1; and the powder-liquid mass ratio of the filler powder and the binder in the sealing slurry layer is 1.5:1.

[0053] c. Shell preparation: The wax mold module is first cleaned with a cleaning solution, then immersed in slurry and sand is scattered, dried at a temperature of 26°C and humidity of 75, repeated for 8 times, and finally immersed in slurry for sealing and drying; the shell surface layer and the adjacent layer are scattered with yttrium oxide sand 40-70 mesh, dried for 24h; the first and second back layers of the shell are scattered with bauxite sand 40-70 mesh, and the third and subsequent back layers are scattered with bauxite sand 16-30 mesh, dried for 12h; after sealing, dry for 24h.

[0054] d. Shell dewaxing and sintering: The shell with dried sealing slurry is dewaxed with the riser facing down, the dewaxing temperature is 300°C, and the dewaxing time is 2h; the dewaxed shell is placed in an air atmosphere sintering furnace, the sintering temperature is 1000°C, the sintering time is 5h, and the shell is cooled with the furnace, and the shell preparation is completed.

[0055] Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting.

[0056] a. Preparation of alloy ingot: The Nb-Si-Ti-Cr-Al-Hf alloy composition is selected with atomic percentage of Nb-14Si-20Ti-3Cr-3Al-2Hf, the density is calculated according to the proportion, the pouring weight of the entire casting is determined according to the product model and the final group tree scheme, and the weight of various metals is calculated according to the proportion; first, the high melting point Nb, Ti and Hf metals are added to the water-cooled copper crucible, the vacuum degree is 6.0×10 -3 Pa after vacuumizing, the gas filling valve is closed or a small amount of argon is introduced into the furnace, the induction heating power is immediately turned on, the alloy is melted and kept for 10min, the alloy is in a suspended state and completely mixed and uniform, then cooled to room temperature to obtain the alloy ingot; then the alloy ingot is turned over and the remaining low melting point Si, Cr and Al metals are added to the water-cooled copper crucible, the same melting process is continued to melt the alloy, and the alloy ingot is cooled to room temperature; finally, the ingot is turned over again and the same melting process is used to continue melting to obtain the Nb-Si-Ti-Cr-Al-Hf alloy ingot with good microstructure uniformity.

[0057] b. Shell preheating: The dewaxed shell is subjected to local area cotton wrapping heat insulation treatment, after the cotton wrapping is completed, the inside of the shell is cleaned by blowing, after cleaning, the shell is placed in a preheating furnace for preheating at a temperature of 1000±30°C for 4h.

[0058] c. Melting and pouring: The melted alloy ingot is placed in a water-cooled copper crucible, the shell is quickly transferred from the preheating furnace to the furnace, then the furnace door is closed to maintain the sealing of the furnace, vacuumizing treatment is performed, and the final vacuum degree is 5.8×10 -3Pa; close the gas valve or pass a small amount of argon into the furnace, immediately open the induction heating power, heat and melt the alloy, keep heating for 10 min, when the alloy is observed in the suspension state, immediately pour the alloy into the preheated mold shell, then pour the alloy liquid in the crucible into the preheated mold shell, and then take out the mold shell after the furnace is cooled to room temperature.

[0059] Step 3, post-processing of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: after the mold shell is taken out of the furnace, the mold shell is first cleaned, then cut, polished and polished to obtain the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting.

[0060] Test example Step 1, preparation of a mold shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine super-high-temperature investment casting.

[0061] a. Preparation of wax mold: design and draw the three-dimensional model of the turbine wax mold, then prepare the wax mold by printing rapid prototyping method, and the wax mold module is composed of a bottom support, a blade, an upper edge plate and a riser.

[0062] b. Preparation of slurry: prepare the binder in proportion, add the filler powder into the stirring binder, then add the wetting agent and defoaming agent to obtain the slurry after stirring; the binder ratio of the mold shell surface layer and the temporary surface layer is 1.0:2.0:4.5 in terms of the mass ratio of deionized water: zirconium acetate: ammonium metatungstate; the powder-liquid mass ratio of the filler powder and the binder in the mold shell surface layer and the temporary surface layer slurry is 3.0:1; the binder of the mold shell back layer and the sealing slurry layer is silica sol, the powder-liquid mass ratio of the filler powder and the binder in the back layer slurry is 2.0:1; the powder-liquid mass ratio of the filler powder and the binder in the sealing slurry layer slurry is 1.5:1.

[0063] c. Preparation of mold shell: the wax mold module is first cleaned with cleaning liquid, then immersed in slurry and sand is scattered, dried under the conditions of temperature 23℃ and humidity 75, repeated slurry hanging, sand scattering and drying process 7 times, finally immersed in slurry for sealing and drying; the sand scattered on the mold shell surface layer and the temporary surface layer is yttria sand 40-70 mesh, dried for 24h; the sand scattered on the mold shell back one and back two layers is bauxite sand 40-70 mesh, dried for 12h after the back three; the sealing slurry is dried for 24h.

[0064] d. Mold shell dewaxing and sintering: the mold shell with dried sealing slurry is dewaxed with the riser downward, the dewaxing temperature is 300℃, the dewaxing time is 2h; the dewaxed mold shell is placed in an air atmosphere sintering furnace, the sintering temperature is 1000℃, the sintering time is 4h, and the furnace is cooled, and the mold shell preparation is completed.

[0065] Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine super-high-temperature investment casting.

[0066] a. Preparation of alloy ingot: the Nb-Si-Ti-Cr-Al-Hf alloy composition is selected as Nb-14Si-20Ti-3Cr-3Al-2Hf in atomic percentage, the density is calculated according to the proportion, the pouring weight of the entire casting is determined according to the product model and the final group tree scheme, and the weight of various metals is calculated according to the proportion; first, the metals with high melting points, Nb, Ti, and Hf, are added to a water-cooled copper crucible, the vacuum degree is 6.0x10 -3 Pa after vacuumizing, the gas filling valve is closed or a small amount of argon is introduced into the furnace, the induction heating power is immediately turned on to heat and melt the alloy, the heating is maintained for 10 min, after the alloy is in a suspended state and completely mixed and uniform, the furnace is cooled to room temperature to obtain an alloy ingot; then the alloy ingot is turned over and the remaining metals with low melting points, Si, Cr, and Al, are added to the water-cooled copper crucible, the same smelting process is continued to smelt and melt the alloy, and the furnace is cooled to room temperature to obtain an alloy ingot; finally, the ingot is turned over again and the same smelting process is used to continue smelting to obtain an Nb-Si-Ti-Cr-Al-Hf alloy ingot with good microstructure uniformity.

[0067] b. Shell preheating: after the wax removal is completed, the shell is locally wrapped with cotton for heat insulation treatment, after the cotton wrapping is completed, the inside of the shell is cleaned by blowing with a blow gun, after the cleaning is completed, the shell is placed in a preheating furnace for preheating, the temperature is 1000±30℃, and the holding time is 4h.

[0068] c. Melting and pouring: the smelted alloy ingot is placed in a water-cooled copper crucible, the shell is quickly transferred from the preheating furnace to the furnace, then the furnace door is closed to maintain the sealing of the furnace, vacuumizing treatment is performed, and the final vacuum degree is 5.5x10 -3 Pa; the gas filling valve is closed or a small amount of argon is introduced into the furnace, the induction heating power is immediately turned on to heat and melt the alloy, the heating is maintained for 10 min, after the alloy is observed to be in a suspended state, pouring operation is immediately performed, the water-cooled copper crucible is quickly tilted, the alloy liquid in the crucible is poured into the preheated shell, and then the shell is taken out after the furnace is cooled to room temperature.

[0069] Step 3, post-treatment of the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: after the shell is taken out from the furnace, it is first cleaned, then cut, polished, and polished to obtain an Nb-Si-Ti-Cr-Al-Hf alloy turbine casting.

[0070] Figure 1 is a three-dimensional model of the Nb-Si-Ti-Cr-Al-Hf alloy turbine wax mold, the model is composed of a base, blades, and an upper rim plate, wherein the blades are typical complex thin-walled blades with a minimum thickness of 2.5mm.

[0071] Figure 2is an Nb-Si-Ti-Cr-Al-Hf alloy turbine shell appearance diagram, by adjusting the preparation formula of the shell, a shell with high strength and good thermal shock resistance is obtained.

[0072] Figure 3 is an Nb-Si-Ti-Cr-Al-Hf alloy turbine casting appearance diagram, the casting surface is smooth and has no obvious metallurgical defects.

[0073] Figure 4 is a microstructure diagram of an Nb-Si-Ti-Cr-Al-Hf alloy turbine blade, wherein the left diagram is a microstructure diagram at low magnification, and the right diagram is a local enlarged view. Figure 4 It can be seen that the microstructure is mainly composed of ductile phase Nbss, α-Nb5Si3 phase, HfO2 phase and a small amount of γ-Nb5Si3 phase. Since the melting point of Ti and Hf is lower than that of Nb, they are excluded from the liquid phase during solidification and segregate in front of the solid-liquid interface, which promotes the formation of a small amount of γ-Nb5Si3 phase. The surface activity of Hf element is large, and it reacts with oxygen in the melt to form HfO2 phase, which solves the problem of oxygen gap pollution to a certain extent and improves the performance of the Nb-Si-Ti-Cr-Al-Hf alloy.

[0074] The Nb-Si-Ti-Cr-Al-Hf alloy castings obtained in the above examples and comparative examples were subjected to room temperature mechanical property and dimensional accuracy detection. Room temperature tensile test was carried out on the alloy casting furnace test bar according to ASTM E8 / E8M-24 "Metallic Materials Tensile Test Method", and room temperature fracture toughness test was carried out on the alloy casting furnace test bar according to ASTM E399-2020a "Standard Test Method for Linear Elastic Plane Strain Fracture Toughness of Metallic Materials". The detection results are shown in Table 1.

[0075] Table 1 Performance test results of Nb-Si-Ti-Cr-Al-Hf alloy castings of examples and comparative examples

[0076] From the comparison of examples 1-3 and test examples, it can be seen that the test examples have the highest tensile strength, and also have a higher elongation, while the examples have no elongation and fracture before yielding; from the test results of fracture toughness, it can be seen that the alloying regulation of Nb-Si based alloy has excellent effect on fracture toughness, and the room temperature fracture toughness of Nb-16Si alloy is 5.4 MPa·m 1 / 2 , and the alloying treatment improves the fracture toughness and improves the comprehensive performance.

[0077] Through the above comparison results can be found, tested three groups of examples and a group of test examples, innovation of rare earth yttrium type shell preparation technology to solve the problem of Nb-Si-Ti-Cr-Al-Hf alloy and shell reaction, by controlling the powder liquid mass ratio of slurry, shell layer to ensure the final forming of Nb-Si-Ti-Cr-Al-Hf alloy turbine with high surface quality and high strength and thermal shock resistance; Through the induction suspension melting technology solves the problem of alloy ultra-high temperature melting, pouring out of no metallurgical defects of castings, verify the best process at the same time to ensure the castings filling completely, no porosity, porosity, shrinkage cavity and other metallurgical defects, get the required Nb-Si-Ti-Cr-Al-Hf alloy turbine castings.

[0078] The above only describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, without departing from the principles of the present application, which should be covered within the protection scope of the present application.

Claims

1. A Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting method, characterized by It comprises the following steps: Step 1, preparation of the shell suitable for Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting: a. Preparation of wax mold: design and draw the three-dimensional model of turbine wax mold, then prepare the wax mold by printing rapid prototyping method, the wax mold module is composed of bottom support, blade, upper edge plate and riser; b. Preparation of slurry: prepare the binder in proportion, add the filler powder into the stirring binder, then add the wetting agent and defoaming agent to obtain the slurry after stirring; the binder ratio of shell surface layer and temporary surface layer is deionized water: zirconium acetate: ammonium metatungstate, the mass ratio is 0.5-1.5:1.0-2.0:4.0-5.0, the powder-liquid mass ratio of filler powder and binder in the shell surface layer and temporary surface layer slurry is 2-4:1; the binder of shell back layer and sealing slurry layer is silica sol, the powder-liquid mass ratio of filler powder and binder in the back layer slurry is 1-3:1; the powder-liquid mass ratio of filler powder and binder in the sealing slurry layer slurry is 1-2:1; c. Preparation of shell: the wax mold module is first cleaned with cleaning liquid, then immersed in slurry and sand is scattered, dried under the condition of temperature 23±3℃ and humidity 70±5, repeat the process of slurry hanging, sand scattering and drying for 6-12 times, finally immerse in slurry for sealing and drying; the sand scattering of shell surface layer and temporary surface layer is yttria sand 40-100 mesh, dried for 20-30h; the sand scattering of shell back layer is bauxite sand 16-80 mesh, dried for 10-20h; dried for 24h after sealing; d. Shell dewaxing and baking: the shell with dried sealing is dewaxed with the riser downward, the dewaxing temperature is 300-400℃, the dewaxing time is 2-5h; the dewaxed shell is placed in the air atmosphere sintering furnace, the baking temperature is 900-1100℃, the baking time is 3-8h, and the shell is cooled with the furnace, the shell preparation is completed; Step 2, Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting: a. Preparation of alloy ingot: according to the proportion of Nb-Si-Ti-Cr-Al-Hf alloy composition, the alloy density is calculated, the pouring weight of the whole casting is determined according to the product model and the final group tree scheme, and the weight of various metals is calculated in proportion; first, Nb, Ti and Hf are added to the water-cooled copper crucible, vacuumizing treatment is carried out to make the vacuum degree ≤10 -3 Pa, the gas filling valve is closed or a small amount of argon is introduced into the furnace, the induction heating power is immediately turned on, the alloy is heated and melted, the alloy is kept in the suspended state and completely mixed and uniform for 3-10 min, and then the alloy ingot is obtained by cooling in the furnace to room temperature; then the alloy ingot is turned over and Si, Cr and Al are added to the water-cooled copper crucible, and the same smelting process is used to continue smelting the alloy, and the alloy ingot is obtained by cooling in the furnace to room temperature; finally, the cast ingot is turned over again, and the same smelting process is used to continue smelting to obtain the Nb-Si-Ti-Cr-Al-Hf alloy ingot with good microstructure uniformity; b. Shell preheating: after the dewaxing is completed, the shell is locally treated with cotton insulation, then the inside of the shell is cleaned by blowing gun, after the cleaning is completed, the shell is preheated in the preheating furnace, the temperature is 1000±30℃, and the holding time is 2-4h; c. Smelting pouring: the smelted alloy ingot is put into a water-cooled copper crucible, the mold shell is quickly transferred from a preheating furnace to the furnace, the furnace door is closed to keep the furnace sealed, vacuumizing treatment is carried out, and the vacuum degree is ≤10 -3 Pa; the gas filling valve is closed or a small amount of argon is introduced into the furnace, the induction heating power is immediately turned on, the alloy is melted and heated, the heating is kept for 3-10 min, the pouring operation is immediately carried out after it is observed that the alloy is in a suspended state, the water-cooled copper crucible is tilted, the alloy liquid in the crucible is poured into the preheated mold shell, and then the mold shell is taken out after the furnace is cooled to room temperature. Step 3, post-treatment of Nb-Si-Ti-Cr-Al-Hf alloy turbine casting: After the shell is taken out from the furnace, it is first cleaned, then cut, polished and polished to obtain the Nb-Si-Ti-Cr-Al-Hf alloy turbine casting.

2. The Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting method according to claim 1, characterized in that In step 1, the filler powder of shell surface layer and temporary surface layer is yttria powder 300-400 mesh, and the filler powder of back layer is bauxite powder 100-300 mesh.

3. The Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting method according to claim 1, characterized in that In step 2, the atomic percentage of Nb-Si-Ti-Cr-Al-Hf alloy composition is Nb-(10-20)Si-(20-25)Ti-(1-5)Cr-(2-6)Al-(2-10)Hf.

4. The Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting method according to claim 1, characterized in that In step 3, the shell is cleaned by hydraulic cleaning, and the riser and runner are cut off by wire electrical discharge machining or diamond cutting.

5. The Nb-Si-Ti-Cr-Al-Hf alloy turbine ultra-high temperature investment casting method according to claim 1, characterized in that In step 3, the turbine casting is polished and surface polished by sand blasting or grinding head polishing.

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