Preparation method of refractory alloy thin-wall part

Abstract

The invention discloses a preparation method of a refractory alloy thin-wall part, which comprises the following steps: firstly, pretreating refractory alloy powder, then mixing with a binder, granulating to obtain a feed, then obtaining a green body in an injection molding machine, and finally, sequentially annealing, degreasing, sintering and densifying the green body to obtain the part. Compared with the prior art, on the basis of powder injection molding, the high-performance refractory alloy thin-wall product is prepared through the technologies of high-melting-point powder ball-milling treatment, green body annealing and oxalic acid degreasing, and the method has the advantages of being high in size precision, low in production cost, easy to achieve batch production and the like and can well meet the commercialization requirement.

Description

Technical Field

[0001] The invention relates to a method for preparing a refractory alloy part, in particular to a method for preparing a refractory alloy thin-wall part. Background Art

[0002] Refractory alloys refer to a class of metal alloys with high melting point, high hardness, high wear resistance, oxidation resistance and corrosion resistance, such as WC, TiC and W. These alloys have good stability and chemical stability at high temperatures, so they are often used to manufacture high-temperature components, wear-resistant materials and corrosion-resistant materials. Due to its high melting point and high hardness, it is very difficult to process it through traditional manufacturing methods (casting, forging, etc.). At present, common preparation methods include powder metallurgy technology, directional solidification technology, chemical vapor deposition and plasma spraying process. However, these preparation methods have always been limited to situations where the workpiece shape is relatively simple and the amount of material removal is very small, and it is impossible to achieve preparation according to the ideal design requirements. This brings challenges to the preparation of refractory alloy components with complex structures, and severely limits the application and development of refractory alloy materials.

[0003] Metal injection molding (MIM) has become the fastest growing "near net shape" technology in the field of powder metallurgy, integrating the two traditional processes of plastic injection molding and powder metallurgy. The process flow is: first, the metal powder and the binder are evenly mixed (mixed), and the feed is made into a granulator, and then formed (injected) by an injection molding machine, and then the binder in the formed blank is removed (degreased), and finally the final product is obtained by sintering densification and necessary post-treatment. MIM technology has unique advantages in manufacturing near net shape parts with complex geometry, uniform structure and high performance. The emergence of MIM technology has brought new opportunities for the promotion and application of refractory alloy materials. Entering the 21st century, people's requirements for miniaturization and thin-walling of refractory alloys are increasing. With the continuous expansion of the field of thin-walled structures, more thin-walled structural parts will be required to meet the requirements of performance and large-scale production.

[0004] Liu Sunhe of Zhuzhou Diamond Cutting Tool Co., Ltd. disclosed a binder for cemented carbide injection molding and its application, the binder contains the following components by mass fraction: 60-74% paraffin, 20-30% high molecular polymer, 4-8% plasticizer and / or lubricant and 2-10% surfactant. The binder of the present invention has excellent shape retention and environmental crack resistance. The cemented carbide products made with it not only have a long life and good effect, but also improve process efficiency (CN101844227A). However, since the wax-based system binder contains more paraffin and less high molecular polymer, the shape retention is poor, which makes the system unable to produce thin-walled products and easily cracks during solvent degreasing.

[0005] Duan Mantang of Shanghai Fuchi High-Tech Co., Ltd. provides a tungsten alloy feed for MIM, including surface-modified tungsten alloy mixed powder and a binder, wherein the weight ratio of the surface-modified tungsten alloy mixed powder to the binder is (93-97): (3-7), and the binder includes POM, PP, HDPE, lubricant, and antioxidant (CN112846186A). The present invention uses a modifier to modify the surface of the tungsten alloy mixed powder to make the tungsten alloy The surface of the gold mixed powder is evenly coated with a layer of modifier, which can improve the wettability of the tungsten alloy mixed powder and the binder and its dispersion effect in the binder, improve the uniformity of the tungsten alloy material, and the modifier further cooperates with the binder to improve the stability of the binder, thereby solving the problem of poor stability of mass production of tungsten alloy feed for MIM. However, the introduction of the modifier increases the cost, and the binder contains more PP and HDPE, which is not conducive to the filling of thin-walled products.

[0006] Therefore, how to obtain high-performance refractory alloy thin-walled products based on MIM technology has become a major technical challenge faced by those skilled in the art. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a method for preparing refractory alloy thin-wall parts. On the basis of powder injection molding, high-melting-point powder ball milling treatment, green body annealing and oxalic acid degreasing techniques are adopted to prepare high-performance refractory alloy thin-wall products, which have the advantages of low production cost and easy mass production.

[0008] The present invention provides a method for preparing a refractory alloy thin-walled part, characterized by comprising the following steps: firstly pre-treating the refractory alloy powder, then mixing and granulating with a binder to obtain a feed material, then obtaining a green body in an injection molding machine, and finally sequentially annealing, degreasing, and sintering the green body to obtain a part; The refractory alloy powder is composed of a high melting point powder and a binder phase powder and inevitable impurity elements, wherein the high melting point powder is any one of TiC, WC, and W, and has an average particle size of 0.1 to 0.5 μm, and the binder phase powder is any one of Fe-Cr-Mo-C, Co, Ni-Fe, and Ni-Cu, and has an average particle size of 0.2 to 0.6 μm, and the mass percentage of the high melting point powder is 85 to 92%; The pretreatment process is as follows: firstly, the high melting point powder is ball-milled, then mixed with the binder phase powder in alcohol, and finally dried to obtain the refractory alloy powder, and the mixing time is 4-8 hours; The binder is composed of the following components by mass percentage: 70-80% polyoxymethylene, 5-15% peanut oil, 5-15% ethylene-vinyl acetate copolymer, 5-15% polypropylene, and 1-3% oleic acid; The annealing process is as follows: the green body is placed in a drying oven, heated to 80-100°C at a heating rate of 3-5°C / min, kept at that temperature for 1-2h, and then cooled to room temperature with the furnace; The degreasing is divided into catalytic degreasing and thermal degreasing. The catalytic degreasing process is as follows: the oxalic acid flow rate is 3-6 ml / min, the catalytic degreasing temperature is 110-150° C., and the catalytic degreasing time is 6-10 hours. The wall thickness of the part is 0.15-0.3 mm; the weight of the part is 0.2-0.5 g.

[0009] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein the total amount of impurity elements is ≤0.2wt.%, and the impurity elements include at least one of C, O, N and S in mass percentage, wherein the C content is ≤0.05%, the O content is ≤0.1%, the N content is ≤0.02%, and the S content is ≤0.03%.

[0010] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein the ball milling process comprises placing a high melting point powder and a grinding ball together in a rolling ball mill, with a ball-to-material ratio of (1-2):1, adding 300-500 ml of kerosene, rotating at a speed of 300-400 r / min, and a time of 12-16 hours, followed by drying after ball milling.

[0011] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein during the mixing, the mixing temperature is 180-220° C., the mixing time is 1-3 hours, and the mixer speed is 80-140 r / min.

[0012] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein in the feed, by volume ratio, binder: refractory alloy powder = 45-55%: 55-45%.

[0013] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein during the injection, the injection temperature is 160-200°C, the injection pressure is 100-170MPa, and the mold temperature is 40-70°C.

[0014] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein the thermal degreasing process is: under the protection of an argon atmosphere, first heating to 400-500°C at a heating rate of 1-3°C / min and keeping warm for 1-2 hours, then heating to 800-900°C at a heating rate of 1-3°C / min and keeping warm for 1-4 hours, and then cooling to room temperature with the furnace.

[0015] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein the sintering process is as follows: in a vacuum degree of ≤5×10 -3 Pa in a vacuum environment, heat up to 1350~1500℃ at a heating rate of 5~10℃ / min, keep warm for 2~4h, and then cool to room temperature with the furnace.

[0016] As a preferred embodiment, the present invention provides a method for preparing a refractory alloy thin-walled part, wherein the density of the obtained product is not less than 99% and the dimensional accuracy is ±0.3-0.5%.

[0017] Principles and advantages The present invention is based on powder injection molding technology. First, the refractory alloy powder is pretreated, then mixed with a binder and granulated to obtain feed, then a green body is obtained in an injection molding machine, and finally the green body is annealed, degreased, and sintered to obtain a part. Due to the thin-walled characteristics of the product, the entire process has more stringent requirements than the traditional MIM technology. Therefore, it is necessary to study each aspect of powder processing, binder preparation, green body processing, degreasing process, and sintering process.

[0018] Powder plays a key role in the entire MIM process. The average particle size of conventional refractory alloy powder is generally 2~5um, and high melting point powder is mostly irregular, hexagonal, and polygonal. There are two problems with this powder feature. First, the powder particle size is not fine enough and the activity is not enough. The sintering process of cemented carbide or tungsten alloy usually uses pressure sintering (hydrogen or argon to give pressure) or special sintering (microwave sintering, spark plasma sintering), which leads to a significant increase in cost and does not use large-scale production; second, the irregular high melting point powder generates a lot of heat due to high-speed friction during the mixing process, which will accelerate the decomposition of polyoxymethylene in the binder. Therefore, the industry currently generally uses wax-based binders to prepare refractory alloy feedstocks, but the green body strength of this feedstock is low, and the product is prone to defects such as bruises and missing corners during repeated handling, and the defect rate is high. At the same time, the shape retention is poor, which makes the system unable to produce thin-walled products. Therefore, the present invention adopts micron-level high melting point powder to greatly improve the activity of the powder, and matches it with a suitable proportion of binding phase powder (8-15%) to provide sufficient liquid phase, laying the foundation for the subsequent pressureless sintering. At the same time, ball milling in kerosene is adopted to destroy the agglomerated and adhered parts of the powder through ball-to-material ratio, rotation speed and time and other ball milling processes, eliminate the polygons on the powder, make its surface smooth, and reduce the friction heat in the mixing process, thereby ensuring the smooth introduction of the plastic-based binder.

[0019] As mentioned before, wax-based binder system is the main system of MIM refractory alloys at present. For the plastic-based system based on polyoxymethylene, it has the characteristics of better strength and can maintain the shape of the product well, especially thin-walled products. Therefore, the polyoxymethylene selected in the present invention is the matrix, and a small amount of peanut oil is added as a flow agent, polypropylene and ethylene-vinyl acetate copolymer are used as skeleton materials to provide sufficient strength for the green body, and a small amount of oleic acid is used as a surface dispersant or activator, which can not only play a bridging role between the binder and the powder particles to prevent the two-phase separation and ensure uniform mixing, but also can play a lubricating role between the powder particles and between the powder particles and the mold wall. A new type of binder for MIM refractory alloy thin-walled parts with high fluidity and high strength is obtained by adjusting the formula ratio.

[0020] The injection molding process refers to the process of injection molding the mixed material (feed material). The defects formed in this process cannot be eliminated in the subsequent process, so the process parameters must be strictly controlled. The present invention adjusts important injection parameters such as injection temperature, injection pressure and mold temperature to obtain a good green body, preventing defects such as blistering, cracks, and pores on the product surface. The inventor found that a good green body cracked in the subsequent catalytic degreasing process, and no matter how the degreasing process parameters were adjusted, it could not be solved. Analysis found that the green body was cooled in a short time, and the rapid contraction of the binder caused the polymer chains of the polymer in it to be in a forced freezing state before adjustment, so that its elastic energy was stored in the body to cause internal stress. In the degreasing process, due to the removal of polyoxymethylene, the free volume of the polymer chains in the polymer becomes larger, and the residual internal stress is released, so that the crack source in the body can appear and expand, resulting in cracks in the body. Therefore, the present invention places the green body in a drying oven, heats it to a certain temperature and keeps it warm for a period of time, and then cools it with the furnace to eliminate internal stress, which helps to improve the toughness of the body.

[0021] The degreasing process is the most time-consuming and difficult to control link, which includes several different stages. Each stage can only remove one or several components in the binder. The purpose of staged degreasing is to maintain the shape of the green body and avoid collapse. Catalytic degreasing is a degreasing process that can quickly remove the binder in an acidic atmosphere at a certain temperature, with a binder system based on polyaldehyde resin as the main component. Polyaldehyde resin is composed of many repeated CO bonds. Under acidic atmosphere conditions of 110~150℃, the O atom is very sensitive to acidic gas, and two adjacent O atoms have a strong activation effect on the methylene H atom. At this time, the macromolecular polyaldehyde resin can be continuously cracked into small molecular formaldehyde gas, and the gas continuously escapes through the porous area generated in the early stage of degreasing, thereby removing most of the binder in the green body. The decomposition reaction in the catalytic degreasing process is carried out at the acidic atmosphere-binder interface, and is continuously promoted from the outside of the green body to the inside, and its speed can reach 1~4mm / h. The degreasing rate is 10~20 times that of other degreasing methods. At the same time, the reaction is a direct gas-solid transition, which avoids the generation of liquid phase, is conducive to maintaining the shape of the blank and controlling the dimensional accuracy of the product. The present invention adopts oxalic acid as the catalytic degreasing atmosphere. The acidic atmosphere for catalytic degreasing generally uses nitric acid or oxalic acid. Nitric acid is currently the most commonly used catalytic degreasing atmosphere. When nitric acid is used as the degreasing atmosphere, the degreasing rate and the final degreasing rate are higher. However, it also has the following disadvantages: ① The chemical properties of nitric acid itself have not changed during the degreasing process, and nitric acid is still discharged as nitric acid gas or nitrogen oxide waste gas. Nitrogen oxides can react photochemically with hydrocarbons in the air under the radiation of ultraviolet rays to produce photochemical smog, which can form acid rain and cause serious pollution to the natural environment such as water quality and soil. ② Concentrated nitric acid easily reacts with most metal powders. ③ Nitric acid gas will have a certain corrosive effect on the cavity of the catalytic degreasing furnace, and it is easy to react with reducing formaldehyde gas to cause explosion, exacerbating the safety hazards of the equipment. After catalytic debinding is completed, thermal debinding is used to remove the remaining binder, and the corresponding heating rate and holding time are effectively controlled to control the oxygen increment within the minimum range, while ensuring that the organic binder is completely removed to avoid the residual organic binder from forming carbides during the sintering process, causing an increase in carbon content. Compared with the traditional debinding process, the production efficiency is improved.

[0022] Sintering is a very important process in the MIM process, which plays a decisive role in the organization, density and chemical uniformity of the product. The sintering of refractory alloys is generally liquid phase sintering. During the heating process, when the temperature reaches the eutectic temperature of the bonding phase, the liquid phase begins to form. The high melting point particles are pushed by the surface tension of the liquid phase to displace. The capillary force formed by the liquid phase and the viscous flow of the liquid phase itself cause the high melting point particles to adjust their positions and redistribute to achieve the most compact arrangement. Since the high melting point particles have a large solubility in the bonding phase and its solid solution, the atoms on the surface of the high melting point particles will dissolve in the liquid phase, and the high melting point atoms will also precipitate, so that the high melting point particles can be evenly distributed in the bonding phase. After the solid phase dissolution and precipitation process is completed, the solid phase skeleton formation stage begins. At this time, the high melting point particles contact each other and produce solid phase sintering phenomenon, and grain growth occurs on the basis of diffusion. In this stage, the alloy density rises to the maximum value and is close to full density. Usually, the dissolution and re-precipitation of high melting point particles are accelerated by increasing the sintering temperature to improve the relative density of the product, but it is difficult to prevent the growth of grains, resulting in performance degradation. Therefore, the specific surface area of ​​the micron-sized particles used in the present invention is larger than that of conventional MIM large-particle powders, and the driving force is large during sintering. The vacuum sintering method can be used, and at a lower sintering temperature, the grains will not be aggregated and grown, and densification is completed more quickly. Thus, by applying this sintering process, refractory alloy products can reach 100% density, and have fine grains, uniform organization, good microstructures such as no segregation of components. Then, the heating rate and the holding time are controlled to avoid the defects such as deformation and cracking of the blank during the sintering process.

[0023] Compared with the prior art, the present invention, based on the powder injection molding technology, adopts the technology of high melting point powder ball milling, green body annealing and oxalic acid degreasing to prepare high-performance refractory alloy thin-walled products, and its characteristics are as follows: (1) High density, high dimensional accuracy and excellent product performance; (2) Powder ball milling modification, no new additives, low cost; (3) Annealing stress relief combined with oxalic acid degreasing has good formability and is easy to achieve mass production; In summary, based on the powder injection molding technology, the present invention adopts the technology of high melting point powder ball milling, green body annealing and oxalic acid degreasing, and simultaneously optimizes the binder and sintering process parameters to obtain high-performance refractory alloy thin-walled products, which have the advantages of high dimensional accuracy, low production cost, and easy mass production, and can well meet commercial needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of a thin-walled product.

[0025] Figure 2is the SEM picture of the high melting point powder after ball milling. DETAILED DESCRIPTION

[0026] The method of the present invention is further described below in conjunction with three embodiments. Example 1

[0027] A method for preparing a refractory alloy thin-walled part, the process is as follows: A. Raw material preparation: The composition of the refractory alloy is 90% TiC-10% Fe-Cr-Mo-C (wt.%). First, the high melting point TiC powder with an average particle size of 0.2μm is ball-milled, and it is placed in a rolling ball mill with a ball-to-material ratio of 1:1, and 300ml kerosene is added. The speed is 300r / min, and the time is 12h. After ball milling, it is dried, and then mixed with Fe-Cr-Mo-C powder with an average particle size of 0.3μm in alcohol, and finally dried to obtain the refractory alloy powder. The mixing time is 4h; B. Preparation of a binder: According to mass percentage, 75% of polyoxymethylene, 5% of peanut oil, 8% of ethylene-vinyl acetate copolymer, 10% of polypropylene, and 2% of oleic acid are used to prepare a binder; C. Prepare feed: Mix the binder and refractory alloy powder in a volume ratio of 50%:50%, granulate to prepare feed, mix at 180°C, mix at 90r / min, and mix for 2h; D. Injection molding: The feed material is injected into the mold cavity by an injection molding machine to obtain a green product. The injection temperature is 180°C, the injection pressure is 120MPa, and the mold temperature is 60°C; E. Annealing: Place the green body in a drying oven, heat to 100°C at a heating rate of 5°C / min, keep warm for 1h, and then cool to room temperature in the furnace; F. Degreasing: Degreasing is divided into catalytic degreasing and thermal degreasing. First, the product is placed in an oxalic acid catalytic furnace with an oxalic acid flow rate of 4 ml / min, a catalytic degreasing temperature of 120°C, and a catalytic degreasing time of 10 hours. Then, the product is thermally degreased in a vacuum degreasing furnace. In an argon atmosphere, the product is first heated to 450°C at a heating rate of 2°C / min and kept warm for 1 hour, then heated to 800°C at a heating rate of 1°C / min and kept warm for 2 hours, and then cooled to room temperature with the furnace; G. Sintering: The degreased product body is sintered in a vacuum furnace with a vacuum degree of 5*10 -3 Pa, heated to 1400℃ at a heating rate of 10℃ / min and kept at that temperature for 2h, and then cooled to room temperature with the furnace to obtain the finished product; H. Performance testing: the density of the obtained product is 99.2% and the dimensional accuracy is ±0.4%. Example 2

[0028] A method for preparing a refractory alloy thin-walled part, the process is as follows: A. Raw material preparation: The composition of the refractory alloy is 92% WC-8% Co (wt.%). First, the high melting point WC powder with an average particle size of 0.4 μm is ball-milled and placed in a rolling ball mill with a ball-to-material ratio of 1.2:1. 400 ml of kerosene is added, and the speed is 350 r / min for 14 hours. After ball milling, it is dried and then mixed with Co powder with an average particle size of 0.2 μm in alcohol. Finally, it is dried to obtain the refractory alloy powder. The mixing time is 4 hours. B. Preparation of a binder: According to mass percentage, 77% of polyoxymethylene, 6% of peanut oil, 8% of ethylene-vinyl acetate copolymer, 8% of polypropylene, and 1% of oleic acid are used to prepare a binder; C. Prepare feed: Mix the binder and refractory alloy powder in a volume ratio of 52%:48%, granulate to prepare feed, mix at 190°C, mix at 100r / min, and mix for 2h; D. Injection molding: Use an injection molding machine to inject the feed into the mold cavity to obtain a green product. The injection temperature is 190°C, the injection pressure is 130MPa, and the mold temperature is 50°C; E. Annealing: Place the green body in a drying oven, heat to 90°C at a heating rate of 5°C / min, keep at this temperature for 2h, and then cool to room temperature in the furnace; F. Degreasing: Degreasing is divided into catalytic degreasing and thermal degreasing. First, the product is placed in an oxalic acid catalytic furnace with an oxalic acid flow rate of 3 ml / min, a catalytic degreasing temperature of 130°C, and a catalytic degreasing time of 8 hours. Then, the product is thermally degreased in a vacuum degreasing furnace. In an argon atmosphere, the product is first heated to 450°C at a heating rate of 2°C / min and kept warm for 1 hour, then heated to 900°C at a heating rate of 1°C / min and kept warm for 1 hour, and then cooled to room temperature with the furnace; G. Sintering: The degreased product body is sintered in a vacuum furnace with a vacuum degree of 5*10 -3 Pa, heated to 1450℃ at a heating rate of 8℃ / min, kept at that temperature for 2h, and then cooled to room temperature with the furnace to obtain the finished product; H. Performance testing: the density of the obtained product is 99.5% and the dimensional accuracy is ±0.35%. Example 3

[0029] A method for preparing a refractory alloy thin-walled part, the process is as follows: A. Raw material preparation: The composition of the refractory alloy is 93% W-4% Ni-3% Fe (wt.%). First, the high melting point W powder with an average particle size of 0.3 μm is ball-milled and placed in a rolling ball mill with a ball-to-material ratio of 1.5:1. 300 ml of kerosene is added, and the speed is 360 r / min for 16 hours. After ball milling, it is dried and then mixed with Ni-Fe powder with an average particle size of 0.4 μm in alcohol. Finally, it is dried to obtain the refractory alloy powder. The mixing time is 4 hours. B. Preparation of binder: According to mass percentage, 78% of polyoxymethylene, 5% of peanut oil, 8% of ethylene-vinyl acetate copolymer, 8% of polypropylene and 1% of oleic acid are used to prepare a binder; C. Prepare feed: Mix the binder and refractory alloy powder in a volume ratio of 52%:48%, granulate to prepare feed, mix at 200°C, mix at 100r / min, and mix for 3h; D. Injection molding: The feed material is injected into the mold cavity by an injection molding machine to obtain a green product. The injection temperature is 190°C, the injection pressure is 140MPa, and the mold temperature is 60°C; E. Annealing: Place the green body in a drying oven, heat to 90°C at a heating rate of 5°C / min, keep at this temperature for 2h, and then cool to room temperature in the furnace; F. Degreasing: Degreasing is divided into catalytic degreasing and thermal degreasing. First, the product is placed in an oxalic acid catalytic furnace with an oxalic acid flow rate of 3 ml / min, a catalytic degreasing temperature of 140°C, and a catalytic degreasing time of 6 hours. Then, the product is thermally degreased in a vacuum degreasing furnace. In an argon atmosphere, the product is first heated to 450°C at a heating rate of 2°C / min and kept warm for 1 hour, and then heated to 900°C at a heating rate of 2°C / min and kept warm for 1 hour, and then cooled to room temperature with the furnace; G. Sintering: The degreased product body is sintered in a vacuum furnace with a vacuum degree of 5*10 -3 Pa, heated to 1400℃ at a heating rate of 8℃ / min and kept at that temperature for 3h, and then cooled to room temperature with the furnace to obtain the finished product; H. Performance testing: the density of the obtained product is 99.6% and the dimensional accuracy is ±0.3%.

[0030] Comparative Example 1: This comparative example adopts a method substantially the same as that of Example 3, except that a powder with an average particle size of 3 μm is used. The density of the obtained alloy product is 97%, and the dimensional accuracy is ±0.6%.

[0031] Comparative Example 2: This comparative example adopts a method substantially the same as that of Example 3, except that the ball milling of W powder is eliminated. The density of the obtained alloy product is 90%, and cracks occur.

[0032] Comparative Example 3: This comparative example adopts a method substantially the same as that of Example 3, except that the annealing of the green body is omitted. The density of the obtained alloy product is 92%, and cracks occur.

[0033] Comparative Example 4: This comparative example adopts a method substantially the same as that of Example 3, except that the temperature of catalytic degreasing is 100° C., the density of the obtained alloy product is 93%, and cracking occurs.

[0034] The above-described examples are only preferred implementation methods of the present invention, and therefore cannot be used to limit the scope of implementation of the present invention. Other equivalent changes, modifications, substitutions and combinations made in accordance with the principles and contents of the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a refractory alloy thin-walled part, characterized in that: The following steps are involved: First, the refractory alloy powder is pretreated, then mixed with a binder and granulated to obtain feed material, then a green body is obtained in an injection molding machine, and finally the green body is sequentially annealed, degreased, and sintered to obtain a part; The refractory alloy powder is composed of a high melting point powder and a binder phase powder and inevitable impurity elements, wherein the high melting point powder is any one of TiC, WC, and W, and has an average particle size of 0.1 to 0.5 μm, and the binder phase powder is any one of Fe-Cr-Mo-C, Co, Ni-Fe, and Ni-Cu, and has an average particle size of 0.2 to 0.6 μm, and the mass percentage of the high melting point powder is 85 to 92%; The pretreatment process is as follows: firstly, the high melting point powder is ball-milled, then mixed with the binder phase powder in alcohol, and finally dried to obtain the refractory alloy powder, and the mixing time is 4-8 hours; The binder is composed of the following components by mass percentage: 70-80% polyoxymethylene, 5-15% peanut oil, 5-15% ethylene-vinyl acetate copolymer, 5-15% polypropylene, and 1-3% oleic acid; The annealing process is as follows: the green body is placed in a drying oven, heated to 80-100°C at a heating rate of 3-5°C / min, kept at that temperature for 1-2h, and then cooled to room temperature with the furnace; The degreasing is divided into catalytic degreasing and thermal degreasing. The catalytic degreasing process is as follows: the oxalic acid flow rate is 3-6 ml / min, the catalytic degreasing temperature is 110-150° C., and the catalytic degreasing time is 6-10 hours. The wall thickness of the part is 0.15-0.3 mm; the weight of the part is 0.2-0.5 g.

2. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: The total amount of the impurity elements is ≤0.2wt.%, and includes at least one of C, O, N and S in terms of mass percentage, wherein the content of C is ≤0.05%, the content of O is ≤0.1%, the content of N is ≤0.02%, and the content of S is ≤0.03%.

3. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: The ball milling process is to place the high melting point powder and grinding balls together in a rolling ball mill, with a ball-to-material ratio of (1-2):1, and add 300-500 ml of kerosene, with a rotation speed of 300-400 r / min, a time of 12-16 hours, and dry after ball milling.

4. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: During the mixing, the mixing temperature is 180-220° C., the mixing time is 1-3 hours, and the mixer speed is 80-140 r / min.

5. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: In the feed material, by volume ratio, binder: refractory alloy powder = 45~55%: 55~45%.

6. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: During the injection, the injection temperature is 160-200°C, the injection pressure is 100-170MPa, and the mold temperature is 40-70°C.

7. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: The thermal debinding process is as follows: under the protection of argon atmosphere, firstly heating to 400-500°C at a heating rate of 1-3°C / min and keeping the temperature for 1-2h, then heating to 800-900°C at a heating rate of 1-3°C / min and keeping the temperature for 1-4h, and then cooling to room temperature with the furnace.

8. The method for preparing a refractory alloy thin-walled part according to claim 1, characterized in that: The sintering process is as follows: in a vacuum degree of ≤5×10 -3 Pa in a vacuum environment, heat up to 1350~1500℃ at a heating rate of 5~10℃ / min, keep warm for 2~4h, and then cool to room temperature with the furnace.

9. A method for preparing a refractory alloy thin-walled part according to any one of claims 1 to 8, characterized in that: The density of the obtained product is not less than 99%, and the dimensional accuracy is ±0.3~0.5%.

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