A hot extrusion forming method for a tapered thin-walled part of a NbZrTi-based refractory high-entropy alloy

Abstract

The present invention relates to a hot extrusion forming method for a NbZrTi series refractory high entropy alloy conical thin-walled part, and belongs to the field of alloy technology. The alloy ingot obtained after smelting is subjected to homogenization annealing treatment, and then a layer of high-temperature anti-oxidation coating is coated on the surface of the ingot and heated, and then hot extrusion forming is performed at high temperature, and finally step-by-step recrystallization annealing is performed to obtain a refractory high entropy alloy conical thin-walled part with high surface quality, no defects and fine structure.

Description

Technical Field

[0001] The invention relates to a hot extrusion forming method for a tapered thin-walled part of a NbZrTi series refractory high-entropy alloy, belonging to the technical field of alloys. Background Art

[0002] High entropy alloys have broken through the limitations of traditional alloys with a single principal element. By regulating the content and combination of multiple principal elements, high entropy alloys are endowed with excellent properties such as high strength, high hardness, high toughness and corrosion resistance, which have shown great application potential in many fields. Refractory high entropy alloys have good high-temperature softening resistance and high-temperature phase stability due to the use of high-melting-point elements as principal elements, and are expected to become new high-temperature structural materials.

[0003] The preparation methods of refractory high entropy alloys include melting casting, powder metallurgy and additive manufacturing. Among the many preparation methods, melting casting has become the most commonly used method for preparing refractory high entropy alloys due to its simple process. However, current refractory high entropy alloys generally contain elements such as Nb, Zr, and Ti. Due to the large variety of elements and large density differences, the casting composition is severely segregated; the alloy has a high melting point and poor fluidity, resulting in coarse casting structure and many shrinkage cavities / shrinkage; the elements are highly active and easily react with the shell, resulting in poor casting surface quality. These problems are especially serious when the casting is a tapered thin-walled part. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a hot extrusion forming method for a NbZrTi-based refractory high-entropy alloy conical thin-walled part, by subjecting the ingot to a homogenization annealing treatment, then coating a layer of high-temperature anti-oxidation coating on the surface of the ingot and heating the ingot, then hot extruding the ingot, and finally performing step-by-step recrystallization annealing and machining to obtain a refractory high-entropy alloy conical thin-walled part with high surface quality, no defects and fine structure.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A hot extrusion forming method for a tapered thin-walled part of a NbZrTi-based refractory high-entropy alloy, the method steps comprising:

[0007] (1) Under the protection of inert gas, the metal elements corresponding to the components in the NbZrTi refractory high entropy alloy are mixed according to atomic percentage, and the alloy ingot is obtained after smelting;

[0008] (2) subjecting the alloy ingot to a vacuum homogenization annealing treatment to obtain an annealed alloy ingot;

[0009] (3) coating a layer of yttria-based high-temperature anti-oxidation coating on the surface of the annealed alloy ingot, then placing the ingot in a heat treatment furnace, heating it in the alloy single-phase temperature range and keeping it warm for 30 to 120 minutes to obtain a blank, and then placing the blank in a preheated extrusion die, extruding it, and obtaining a blank; wherein the preheating temperature is 200 to 400° C., and the preheating time is more than 30 minutes; the thickness of the high-temperature anti-oxidation coating = (surface area of ​​the tapered thin-walled part ÷ surface area of ​​the annealed ingot) × (50 to 150) μm;

[0010] (4) In a local heat treatment device with a heating induction coil and a temperature measuring function, the blank is subjected to step-by-step recrystallization annealing, wherein the first step of recrystallization annealing is performed at the upper part of the thin-walled part, the annealing temperature is 0.5 to 0.7 times the melting point of the alloy, the holding time is 30 to 60 minutes, and water cooling is performed after the holding period is completed; the second step of recrystallization annealing is performed at the lower part of the thin-walled part, the annealing temperature is 100 to 300°C higher than the first step of recrystallization annealing, the holding time is 60 to 120 minutes, and water cooling is performed after the holding period is completed; after mechanical processing, a conical thin-walled part of a NbZrTi-based refractory high entropy alloy is obtained.

[0011] Preferably, in step (1), the chemical formula of the NbZrTi refractory high entropy alloy is Nb a Zr b Ti c M x , M is one or more of Hf, W, Ni, Al, Cr, Mo, and Fe, 15≤a≤35, 15≤b≤60, 15≤c≤65, 0≤x≤15, and a+b+c+x=100.

[0012] Preferably, in step (1), the maximum smelting current is 300-500A, the holding time is 2-5min, the furnace is cooled for 60-180min, and the smelting is repeated 3-6 times.

[0013] Preferably, in step (2), during the vacuum homogenization annealing treatment, the annealing temperature is 0.7 to 0.8 times the melting point of the alloy, and the holding time is 10 to 24 hours.

[0014] Preferably, in step (3), the yttrium oxide-based high temperature anti-oxidation coating is composed of yttrium oxide and zirconium acetate, and the mass ratio of yttrium oxide to zirconium acetate is 5:1~3:2.

[0015] Preferably, in step (3), the blank is placed in the extrusion die within 5 to 10 seconds.

[0016] Preferably, in step (3), during extrusion molding, the molding is preceded by pressing; during pressing, the pressure is tons, the extrusion speed is 20~50mm / s; during molding, the pressure is +(600~900) tons, extrusion speed is 60~100mm / s; among them, is the deformation resistance of the blank; is the diameter of the pressed part, mm; is the diameter of the die in the mold, mm; is the contact surface friction coefficient, =0.03~0.15; is the original height of the profiled part, mm; is the height of the die in the mold, mm; is the outer diameter of the molded part mouth, mm; is the inner diameter of the molded part mouth, mm.

[0017] Preferably, in step (4), the upper portion of the thin-walled part is the area from the mouth of the thin-walled part to 1 / 2 of the height; the lower portion of the thin-walled part is the area from the bottom of the thin-walled part to 1 / 2 of the height.

[0018] Preferably, in step (4), the ratio of the wall thickness to the diameter of the NbZrTi-based refractory high entropy alloy conical thin-walled part is 1 / 38 to 1 / 20, and the cone angle is 30 to 120°.

[0019] A NbZrTi series refractory high entropy alloy conical thin-walled part is prepared by the above method.

[0020] Beneficial effects:

[0021] The invention provides a method for preparing a tapered thin-walled part of a NbZrTi-based refractory high-entropy alloy, comprising the steps of performing vacuum homogenization annealing on a smelted ingot to eliminate component segregation inside the ingot; then coating the surface of the ingot with a high-temperature anti-oxidation coating to prevent cracking and poor surface quality caused by oxidation of the ingot surface during high-temperature heating and hot extrusion; immediately performing high-temperature hot extrusion after coating to close shrinkage cavities / shrinkage defects; and finally performing a step-by-step recrystallization annealing process to ensure uniformity of the structure of the unevenly deformed portion of the tapered thin-walled part and refine the grains.

[0022] The present invention provides a method for preparing a tapered thin-walled part of a NbZrTi series refractory high-entropy alloy. A high-temperature anti-oxidation coating of a specific thickness is prepared before hot extrusion heating. On the one hand, the presence of the high-temperature anti-oxidation coating can prevent the surface of the ingot from being oxidized to form an oxide film during the heating process, and then the tapered thin-walled part is extruded and cracked during the hot extrusion process due to the incoordination between the oxide film and the matrix deformation; on the other hand, the high-temperature anti-oxidation coating has a specific thickness, which can prolong the time for cracks in the coating to extend to the surface of the ingot, and avoid the coating from losing its protective effect due to cracking and peeling during hot extrusion. At the same time, before hot extrusion molding, the coating is kept warm at a single-phase temperature, which can not only improve the bonding strength between the coating and the NbZrTi series high-entropy alloy matrix, but also soften the NbZrTi series high-entropy alloy matrix.

[0023] The present invention provides a method for preparing a tapered thin-walled part of a NbZrTi-based refractory high-entropy alloy. The extrusion process is divided into two steps: pressing and forming. Pressing is a preforming process in the extrusion process. In the preforming process, the NbZrTi-based refractory high-entropy alloy material is pre-distributed to obtain a semi-finished product with a shape close to a thin-walled tapered part. Pressing (preforming process) can reduce the flow of materials during forming, reduce the degree of deformation and the wear of the mold; on the other hand, it can make the material easier to fill the cavity during forming, avoiding crack defects.

[0024] The present invention provides a method for preparing a tapered thin-walled part of a NbZrTi-based refractory high-entropy alloy. After hot extrusion, step-by-step recrystallization annealing is performed to ensure the uniformity of the grain size of the upper part of the thin-walled part with a large deformation amount and the lower part of the thin-walled part with a small deformation amount during the hot extrusion process, and refine the grains, thereby making the entire thin-walled part have a fine and uniform structure. Figure 1 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the step-by-step recrystallization annealing position of a thin-walled component. The upper part is the upward area of ​​1 / 2 of the height of the thin-walled component, and the lower part is the downward area of ​​1 / 2 of the height of the thin-walled component.

[0026] Figure 2 is the recrystallized Nb in Example 1 15 Zr 20 Ti 65 Macroscopic microstructure photographs of conical thin-walled parts of refractory high-entropy alloy before and after machining; (a) is the photograph before machining, and (b) is the photograph after machining.

[0027] Figure 3 Nb in different states in Example 1 15 Zr 20 Ti 65 Microstructure photos of conical thin-walled parts of refractory high-entropy alloys; among them, (a) is a photo of the cast state, (b) is a photo of the homogenization annealing state, and (c) is a photo of the recrystallized state.

[0028] Figure 4 The Nb after hot extrusion molding in Comparative Example 1 15 Zr 20 Ti 65 Macroscopic microstructure photographs of three conical thin-walled parts of refractory high-entropy alloys.

[0029] Figure 5 The Nb after hot extrusion molding in Comparative Example 2 15 Zr 20 Ti 65 Macrostructure photograph of conical thin-walled parts of refractory high-entropy alloy.

[0030] Figure 6 The primary recrystallized Nb in Comparative Example 3 15 Zr 20 Ti 65 Microstructure photograph of conical thin-walled parts of refractory high-entropy alloy. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below in conjunction with specific embodiments.

[0032] In the following examples and comparative examples, a camera was used to take macroscopic photos of the tapered thin-walled parts in different states. The samples for microscopic observation were taken from the ingot after smelting, the ingot after homogenization annealing, and the blank after recrystallization annealing. After the samples were ground, mechanically vibrated and polished, and stress-relieved, the microstructure was photographed and analyzed under an optical microscope.

[0033] Embodiment 1:

[0034] Nb 15 Zr 20 Ti 65 The hot extrusion forming method of refractory high entropy alloy conical thin-walled parts is as follows:

[0035] (1) Ingredients: According to the chemical formula Nb 15 Zr 20 Ti 65 A total of 2.2 kg of raw materials were weighed by atomic percentage, including 484.4 g of Nb block, 634.2 g of Zr particles, and 1081.5 g of Ti block. Before smelting, the surface oxide scale of the raw materials was polished off with a grinding wheel, then ultrasonically cleaned with alcohol for 5 minutes, and finally the residual alcohol on the surface of the raw materials was blown dry with a hair dryer.

[0036] (2) Melting: Place Ti blocks, Zr particles and Nb blocks in the crucible from the bottom of the Φ60×100 mm crucible upwards in order of melting point, and then turn on the mechanical pump and molecular pump to evacuate to 3.5×10 -2 Pa, the molecular pump and mechanical pump were turned off in turn, and argon was introduced as a protective atmosphere. When the pressure in the furnace increased to 4×10 -2 MPa, close the ventilation valve, and start smelting after introducing cooling water. During the smelting process, add 50A current per minute from 0A. When the current increases to 500A, keep warm for 5min and then turn off the power. Cool the furnace for 180min and get the ingot of Φ60×80mm. Then repeat the above smelting process and remelt the ingot 6 times to ensure its composition uniformity.

[0037] (3) Homogenization annealing treatment: The remelted ingot is placed in a quartz tube and sealed with vacuum, and then placed in a box-type heat treatment furnace for homogenization annealing treatment. The annealing temperature is 1200°C and the holding time is 24 hours. After cooling to room temperature with the furnace, the sealed tube is taken out and broken to obtain a homogenized annealed ingot.

[0038] (4) Coating: Use wire cutting to cut the homogenized annealed ingot into two cylindrical billets of Φ60×37mm (residue is retained). Use a grinder to polish the surfaces of the two cylindrical billets, and use alcohol ultrasonic treatment for 5 minutes to remove impurities and oil stains on the surface of the substrate. Then apply a 300μm thick yttrium oxide coating on the surface of the cylindrical billet (the mass ratio of yttrium oxide to zirconium acetate is 3:2). After coating, take out the cylindrical billet and place it in a box-type heat treatment furnace for heating at a heating temperature of 1050℃ and a holding time of 120min.

[0039] (5) Extrusion =0.1): A vertical extruder is used to extrude the cylindrical billet, and the extrusion process is divided into two steps: pressing and forming. Before pressing, a graphite lubricant is applied to the surface of the mold, and then the mold is disassembled and placed in a heating furnace for preheating. The preheating temperature is 400°C and the preheating time is 60 minutes. The pressing rod is preheated with an acetylene gun. The preheating temperature is 200°C and the preheating time is 60 minutes. After the preheating is completed, the mold and the pressing rod are taken out and loaded within 30 to 60 seconds, and then the cylindrical billet is taken out from the heat treatment furnace and placed in the mold for pressing within 5 to 10 seconds. The pressing process lasts for 4 to 7 seconds, with a pressure of 630 tons and an extrusion speed of 50 mm / s. After the pressing is completed, the sample is placed in a heating furnace for heating, and the heating system is the same as before pressing. Before forming, a graphite lubricant is applied to the surface of the mold, and the forming mold and the extrusion rod are preheated. The preheating system is the same as before pressing. After loading the mold and the pressure rod, the cylindrical blank is taken out of the heat treatment furnace and placed in the extrusion mold for extrusion molding within 5-10 seconds. The molding process lasts for 1-3 seconds, with a pressure of 1250 tons and an extrusion speed of 100 mm / s. After molding, the blank is taken out and air-cooled to room temperature; the diameter of the die in the mold is 10 mm, the height is 20 mm, the outer diameter of the molded part is 90 mm, and the inner diameter is 80 mm; finally, the above extrusion process is repeated with another cylindrical blank to ensure the reliability of the experiment.

[0040] (6) Step-by-step recrystallization annealing: fix the lower part of the blank (the area from the bottom of the thin-walled part to 1 / 2 of its height), and then place its upper part (the area from the mouth of the thin-walled part to 1 / 2 of its height) in the heating induction coil of the local heat treatment device for the first step of recrystallization annealing, the annealing temperature is 820℃, and the annealing time is 60min; after water cooling, fix the upper part of the blank, and then place its lower part in the heating induction coil of the local heat treatment device for the second step of recrystallization annealing, the annealing temperature is 920℃, the annealing time is 120min, and the cooling method is water cooling. The temperature of the heating induction coil is controlled and displayed by the temperature measuring device in the local heat treatment device during the whole process.

[0041] (6) Machining: According to the requirements of the part drawing, the recrystallized annealed blank is turned to remove 0.5~1mm of machining allowance to obtain a Nb with a thickness of 3mm, an inner diameter of 65mm, and a taper angle of 45°. 15 Zr 20 Ti 65 Conical thin-walled parts made of refractory high entropy alloy.

[0042] The macroscopic structure characterization of the recrystallized conical thin-walled parts shows that the surface quality of the conical thin-walled parts is high, and there are basically no shrinkage holes / shrinkage defects, such as Figure 2 shown.

[0043] For Nb in different states 15 Zr 20 Ti 65 The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears, with an average grain size of 1265μm. Hot extrusion of the homogenized ingot and recrystallization annealing can obtain fine equiaxed crystal structure with an average grain size of 432μm, and the grains are refined by 833μm. Figure 3 shown.

[0044] Embodiment 2:

[0045] In this embodiment, the alloy composition is Nb 30 Zr 55 Ti 15 The batching process is as follows: According to the chemical formula Nb 30 Zr 55 Ti 15 A total of 2.2 kg of raw materials were weighed by atomic percentage, including 719.5 g of Nb block, 1295.2 g of Zr particles, and 185.3 g of Ti block. Before smelting, the surface oxide scale of the raw materials was polished off with a grinding wheel, then ultrasonically cleaned with alcohol for 5 minutes, and finally the residual alcohol on the surface of the raw materials was blown dry with a hair dryer. The rest was the same as in Example 1.

[0046] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts is high and there are basically no shrinkage holes / shrinkage defects.

[0047] For Nb in different states 30 Zr 55 Ti 15 The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1260μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized to obtain a fine equiaxed crystal structure with an average grain size of 430μm. Compared with the homogenized structure, the grain size is reduced by 830μm, and the grains are effectively refined. The grain size is similar to that of Example 1. This is because the Nb a Zr b Ti c For alloys, if only the alloy composition is changed and other conditions remain unchanged, the grain size under different states remains basically unchanged.

[0048] Embodiment 3:

[0049] In this embodiment, the alloy composition is Nb 15 Zr 20 Ti 60 Hf5, the batching process is as follows: According to the chemical formula Nb 15 Zr 20 Ti 60 Hf5 weighs a total of 2.2kg of raw materials by atomic percentage, including 439.1g of Nb blocks, 574.8g of Zr particles, 904.9g of Ti blocks, and 281.2g of Hf particles. Before smelting, the surface oxide scale of the raw material is polished off with a grinding wheel, then ultrasonically cleaned with alcohol for 5 minutes, and finally the residual alcohol on the surface of the raw material is dried with a hair dryer. In this embodiment, the homogenization annealing temperature is 1300°C, and the homogenization annealing time is 12h. In this embodiment, the pressure during molding is 680 tons, the pressure during extrusion is 1300 tons, the first step recrystallization annealing temperature is 850°C, and the second step recrystallization annealing temperature is 950°C. The rest is the same as in Example 1.

[0050] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts is high and there are basically no shrinkage holes / shrinkage defects.

[0051] For Nb in different states 15 Zr 20 Ti 60The microstructure characterization of Hf5 alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1365μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 485μm. Compared with the homogenized structure, the grain size is reduced by 880μm, and the grains are effectively refined.

[0052] Embodiment 4:

[0053] In this embodiment, the alloy composition is Nb 15 Zr 20 Ti 55 W 10 The batching process is as follows: According to the chemical formula Nb 15 Zr 20 Ti 55 W 10 A total of 2.2 kg of raw materials were weighed by atomic percentage, including 398.7 g of Nb blocks, 522.0 g of Zr particles, 753.3 g of Ti blocks, and 526.0 g of W particles. Before smelting, the surface oxide scale of the raw materials was polished off with a grinding wheel, then ultrasonically cleaned with alcohol for 5 minutes, and finally the residual alcohol on the surface of the raw materials was dried with a hair dryer. In this embodiment, the homogenization annealing temperature is 1500°C, and the homogenization annealing time is 10 hours. In this embodiment, the pressure during molding is 600 tons, the pressure during extrusion is 1200 tons, the first step recrystallization annealing temperature is 950°C, and the second step recrystallization annealing temperature is 1050°C. The rest is the same as in Example 1.

[0054] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts is high and there are basically no shrinkage holes / shrinkage defects.

[0055] For Nb in different states 15 Zr 20 Ti 55 W 10 The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1460μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 531μm. Compared with the homogenized structure, the grain size is reduced by 929μm, and the grains are effectively refined.

[0056] Embodiment 5:

[0057] In this embodiment, the alloy composition is Nb 15 Zr20 Ti 50 Ni 15 The batching process is as follows: According to the chemical formula Nb 15 Zr 20 Ti 50 Ni 15 According to atomic percentage, a total of 2.2 kg of raw materials are weighed, including 472.3 g of Nb blocks, 618.3 g of Zr particles, 811.1 g of Ti blocks, and 298.4 g of Ni particles. Before smelting, the surface oxide scale of the raw materials is polished off with a grinding wheel, then ultrasonically cleaned with alcohol for 5 minutes, and finally the residual alcohol on the surface of the raw materials is dried with a hair dryer. In this embodiment, the homogenization annealing temperature is 1000°C, the pressure during the press molding is 550 tons, and the pressure during the extrusion is 1150 tons. The rest is the same as in Example 1.

[0058] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts is high and there are basically no shrinkage holes / shrinkage defects.

[0059] For Nb in different states 15 Zr 20 Ti 50 Ni 15 The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1271μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 436μm. Compared with the homogenized structure, the grain size is reduced by 835μm, and the grains are effectively refined.

[0060] Embodiment 6:

[0061] In this embodiment, the maximum value of the smelting current is 300A, the smelting holding time is 2 minutes, the furnace is cooled for 60 minutes after smelting, the smelting is repeated 3 times, and the rest is the same as in Example 1.

[0062] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts is lower than that of Example 1, and there are basically no shrinkage cavities / shrinkage defects on the surface.

[0063] For Nb in different states 15 Zr 20 Ti 65The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears, with an average grain size of 1255μm. The homogenized ingot is hot-extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 427μm. Compared with the homogenized structure, the grain size is reduced by 828μm, and the grains are effectively refined.

[0064] Embodiment 7:

[0065] In this embodiment, the extrusion heating temperature is 980°C, the heating time is 30 minutes, the mold preheating temperature is 200°C, the preheating time is 30 minutes, the extrusion speed of the press process is 20 mm / s, and the extrusion speed of the molding process is 60 mm / s. The rest is the same as in Example 1.

[0066] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts obtained is equivalent to that of Example 1, and there are basically no shrinkage cavities / shrinkage defects.

[0067] For Nb in different states 15 Zr 20 Ti 65 The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1165μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 382μm. Compared with the homogenized structure, the grain size is reduced by 783μm, and the grains are effectively refined.

[0068] Embodiment 8:

[0069] In this embodiment, the first step recrystallization annealing time is 30 minutes, the second step recrystallization annealing time is 60 minutes, and the rest is the same as in Embodiment 1.

[0070] The macroscopic structure characterization of the conical thin-walled parts after recrystallization shows that the surface quality of the conical thin-walled parts obtained is equivalent to that of Example 1, and there are basically no shrinkage cavities / shrinkage defects.

[0071] For Nb in different states 15 Zr 20 Ti 65The microstructure characterization of the alloy shows that its as-cast structure is composed of coarse dendrites. After homogenization, the dendrite structure disappears and coarse equiaxed crystal structure appears. The average grain size is 1265μm. A small amount of shrinkage defects can be observed in the matrix. The homogenized ingot is hot extruded and recrystallized annealed to obtain a fine equiaxed crystal structure with an average grain size of 400μm. Compared with the homogenized structure, the grain size is reduced by 865μm, and the grains are effectively refined.

[0072] Comparative Example 1:

[0073] In this comparative example, a 60 μm yttrium oxide coating was applied, and three cylindrical billets were extruded to verify the extrusion effect. The rest was the same as in Example 1.

[0074] The macroscopic structure characterization of the three conical thin-walled parts after hot extrusion showed that the surface quality of the conical thin-walled parts was poor and oxidation cracking occurred (such as Figure 4 ), but there are basically no shrinkage cavities / shrinkage defects on the surface.

[0075] Comparative Example 2:

[0076] In this comparative example, the hot extrusion heating temperature is 750° C., and the rest is the same as in Example 1.

[0077] The macroscopic structure characterization of the conical thin-walled parts after hot extrusion shows that the conical thin-walled parts have cracks and pieces (such as Figure 5 as shown).

[0078] Comparative Example 3:

[0079] In this comparative example, only the first step of recrystallization annealing is performed, and the other steps remain unchanged. The microstructure characterization of the conical thin-walled part after recrystallization annealing shows that the grain size of the upper part is 339μm (e.g. Figure 6 As shown in the figure), the grain size of the lower part is comparable to that after homogenization annealing, with an average grain size of 1270 μm. The grain sizes of the upper and lower parts of the thin-walled part are uneven.

[0080] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A hot extrusion forming method for a tapered thin-walled part of a NbZrTi refractory high entropy alloy, characterized in that: The method steps include: (1) Under the protection of inert gas, the metal elements corresponding to the components in the NbZrTi refractory high entropy alloy are mixed according to atomic percentage, and the alloy ingot is obtained after smelting; (2) subjecting the alloy ingot to a vacuum homogenization annealing treatment to obtain an annealed alloy ingot; (3) coating a layer of yttria-based high-temperature anti-oxidation coating on the surface of the annealed alloy ingot, then placing the ingot in a heat treatment furnace, heating it in the alloy single-phase temperature range and keeping it warm for 30 to 120 minutes to obtain a blank, and then placing the blank in a preheated extrusion die, extruding it, and obtaining a blank; wherein the preheating temperature is 200 to 400° C., and the preheating time is more than 30 minutes; the thickness of the high-temperature anti-oxidation coating = (surface area of ​​the tapered thin-walled part ÷ surface area of ​​the annealed ingot) × (50 to 150) μm; (4) performing step-by-step recrystallization annealing on the blank in a local heat treatment device with a heating induction coil and a temperature measuring function, wherein the first step of recrystallization annealing is performed at the upper part of the thin-walled part, the annealing temperature is 0.5 to 0.7 times the melting point of the alloy, the holding time is 30 to 60 minutes, and water cooling is performed after the holding is completed; the second step of recrystallization annealing is performed at the lower part of the thin-walled part, the annealing temperature is 100 to 300°C higher than the first step of recrystallization annealing, the holding time is 60 to 120 minutes, and water cooling is performed after the holding is completed; after mechanical processing, a conical thin-walled part of a NbZrTi-based refractory high entropy alloy is obtained; Wherein, in step (3), during extrusion molding, the molding is preceded by pressing; during pressing, the pressure is tons, the extrusion speed is 20~50mm / s; during molding, the pressure is +(600~900) tons, extrusion speed is 60~100mm / s; among them, is the deformation resistance of the blank; is the diameter of the pressed part, mm; is the diameter of the die in the mold, mm; is the contact surface friction coefficient, =0.03~0.15; is the original height of the profiled part, mm; is the height of the die in the mold, mm; is the outer diameter of the molded part mouth, mm; is the inner diameter of the molded part mouth, mm.

2. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1, characterized in that: In step (1), the chemical formula of the NbZrTi refractory high entropy alloy is Nb a Zr b Ti c M x , M is one or more of Hf, W, Ni, Al, Cr, Mo, and Fe, 15≤a≤35, 15≤b≤60, 15≤c≤65, 0≤x≤15, and a+b+c+x=100.

3. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: In step (1), the maximum smelting current is 300-500A, the holding time is 2-5min, the furnace is cooled for 60-180min, and the smelting is repeated 3-6 times.

4. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: In step (2), during the vacuum homogenization annealing treatment, the annealing temperature is 0.7 to 0.8 times the melting point of the alloy, and the holding time is 10 to 24 hours.

5. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: The yttrium oxide-based high temperature anti-oxidation coating is composed of yttrium oxide and zirconium acetate, and the mass ratio of yttrium oxide to zirconium acetate is 5:1-3:

2.

6. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: In step (3), the blank is placed in the extrusion die within 5 to 10 seconds.

7. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: In step (4), the upper portion of the thin-walled part is the area from the mouth of the thin-walled part to 1 / 2 of the height; the lower portion of the thin-walled part is the area from the bottom of the thin-walled part to 1 / 2 of the height.

8. A hot extrusion forming method for a tapered thin-walled NbZrTi refractory high entropy alloy according to claim 1 or 2, characterized in that: In step (4), the ratio of the wall thickness to the diameter of the NbZrTi-based refractory high entropy alloy conical thin-walled part is 1 / 38 to 1 / 20, and the cone angle is 30 to 120°.

9. A tapered thin-walled part of a NbZrTi refractory high entropy alloy, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

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