A phase boundary coherent refractory alloy and its preparation method and application

Abstract

The present invention provides a phase boundary coherent refractory alloy and its preparation method and application, which belong to the field of powder metallurgy. In the phase boundary coherent refractory alloy, the oxide of the second phase high melting point metal forms a coherent phase interface with the refractory metal, and the oxide of the second phase high melting point metal is dispersed in the refractory metal. The preparation method is to prepare a nano-core-shell refractory alloy powder by a gel-combustion method combined with hydrogen reduction, and then quickly achieve densification by a two-step sintering technology to obtain a phase boundary coherent refractory alloy; the average particle size of the refractory alloy powder is less than 50nm, the relative density of the refractory alloy exceeds 98%, and the grain size is less than 1.0μm. The refractory alloy powder with a nano-core-shell structure of the present invention can effectively reduce the densification temperature, effectively prevent the growth of grains through a two-step sintering technology, reduce porosity, and increase density, and finally obtain an ultrafine-grained high-density refractory alloy material with a coherent phase interface.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy and relates to a phase boundary coherent refractory alloy and a preparation method and application thereof. Background Art

[0002] Tungsten (W), molybdenum (Mo), and rhenium (Re) possess a range of excellent properties, including high melting points, high elastic moduli and strength, and low thermal expansion coefficients. They play a vital role in modern defense, atomic energy, and vacuum engineering applications, and are irreplaceable in some specialized high-temperature applications. However, tungsten and molybdenum exhibit high room-temperature brittleness and high ductile-brittle transition temperatures (DBTT). This not only prevents them from being deformed at room temperature but also limits their full performance and application. Therefore, improving the room-temperature brittleness of tungsten and molybdenum is crucial to the development of their products.

[0003] For refractory alloy materials, heterogeneous interfaces often become the source of crack initiation and material failure due to stress-strain incompatibility. Coherent interfaces can maintain high-strength interfacial bonding and achieve uniform deformation and dislocation propagation, and therefore play an important role in ensuring the interfacial bonding of heterogeneous materials. As typical refractory metals, the preferred preparation strategy for W, Mo and Re is powder metallurgy. However, during the powder sintering process, densification is coupled with grain growth. Due to the low density limitation, traditional processes have to sinter at temperatures above 1800°C, sacrificing grain size to increase the relative density of the material. Therefore, effectively controlling the grain growth of nanopowders, achieving complete densification and obtaining excellent interfacial bonding are of great significance to the development of refractory alloys.

[0004] Modifiers are a class of chemical substances that can alter a material's performance by manipulating its microstructure or surface properties. They interact with the material surface through physical or chemical means, improving its wettability and adhesion. They can enhance the dispersibility and anti-agglomeration properties of metal powders and improve their compatibility and wettability in organic polymer materials. Surface modifiers have a wide range of applications in materials science, chemical engineering, and manufacturing, effectively enhancing the performance and service life of materials. Summary of the Invention

[0005] In order to solve the problem of coupling between densification and grain growth in the prior art, the present invention proposes a method for preparing phase-boundary coherent refractory alloys by a gel-combustion method based on the sol-gel method and spark plasma sintering technology. The method first adopts the gel-combustion method to prepare core-shell structure refractory alloy powder, and then uses the spark plasma two-step sintering technology to prepare phase-boundary coherent refractory alloys. The refractory alloy prepared by the method of the present invention can eliminate pores while ensuring a fine particle size, and ultimately obtain a high density.

[0006] A first aspect of the present invention provides a phase boundary coherent refractory alloy, wherein the oxide of a second phase high melting point metal forms a coherent phase interface with the refractory metal, and the oxide of the second phase high melting point metal is dispersed in the refractory metal;

[0007] The refractory metal is selected from one of tungsten (W), molybdenum (Mo) or rhenium (Re); the second phase high melting point metal is selected from one of zirconium (Zr), yttrium (Y), aluminum (Al), lutetium (Lu), cerium (Ce), hafnium (Hf), thorium (Th) and lanthanum (La);

[0008] The volume fraction of the second phase high melting point metal oxide in the phase boundary coherent refractory alloy is 3%-30%.

[0009] Furthermore, the volume fraction of the second phase high melting point metal oxide in the phase boundary coherent refractory alloy is 5.0% to 15.0%.

[0010] Furthermore, the relative density of the phase boundary coherent refractory alloy is not less than 98.0%, and the grain size is less than 1.0 μm;

[0011] Furthermore, the relative density is not less than 98.5%, and the grain size is 0.5 μm-0.8 μm.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned phase boundary coherent refractory alloy, the preparation method comprising the following steps:

[0013] Step 1. Prepare raw materials: a water-soluble salt of a refractory metal, a water-soluble salt of a second-phase high-melting-point metal, a modifier, ammonium nitrate, and glycine as raw materials; wherein the ratio of the water-soluble salt of the refractory metal to the water-soluble salt of the second-phase high-melting-point metal is such that, based on the sum of the volume of the refractory metal in the water-soluble salt of the refractory metal and the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal being 100%, the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal is 3%-30%; the refractory metal is selected from one of tungsten (W), molybdenum (Mo), or rhenium (Re); the second-phase high-melting-point metal is selected from one of zirconium (Zr), yttrium (Y), aluminum (Al), lutetium (Lu), cerium (Ce), hafnium (Hf), thorium (Th), and lanthanum (La); and the modifier is a water-soluble small molecule compound or a polymer;

[0014] Step 2, preparing alloy powder: mixing the raw materials and preparing a uniform aqueous solution, and in-situ compounding under heating conditions to form a core-shell complex gel; then heating to 500°C to 700°C to cause a combustion reaction to prepare a coated core-shell precursor powder comprising a refractory metal oxide and a second phase high melting point metal oxide; further reducing the coated core-shell precursor powder in a reducing gas at a temperature of 600°C to 1200°C to prepare an alloy powder with a core-shell structure in which the refractory metal is coated with the second phase high melting point metal oxide;

[0015] Step 3, forming and sintering: The alloy powder obtained in step 2 is pressed and formed, and a two-step spark plasma sintering method is adopted. The temperature is first raised to a pre-sintering temperature by a spark plasma sintering method and kept warm for 1 minute to 2 minutes, and then the temperature is reduced to a densification sintering temperature and kept warm for 3 minutes to 6 minutes to obtain a phase boundary coherent refractory alloy; wherein the pre-sintering temperature is 1500°C to 1800°C, and the densification sintering temperature is 120°C to 350°C lower than the pre-sintering temperature.

[0016] Furthermore, in step 1, the water-soluble salt of the refractory metal is selected from ammonium metatungstate, sodium tungstate, ammonium tungstate, ammonium molybdate, sodium molybdate, potassium molybdate, ammonium rhenate, sodium rhenate, and potassium rhenate.

[0017] Furthermore, in step 1, the water-soluble salt of the second phase high melting point metal is selected from aluminum nitrate, zirconium nitrate, yttrium nitrate, lutetium nitrate, cerium nitrate, hafnium nitrate, thorium nitrate, lanthanum nitrate, zirconium chloride, yttrium chloride, aluminum chloride, lutetium chloride, cerium chloride, hafnium chloride, thorium chloride, and lanthanum chloride.

[0018] Furthermore, in step 1, based on the sum of the volume of the refractory metal in the water-soluble salt of the refractory metal and the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal being 100%, the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal is 5.0% to 15.0%.

[0019] Furthermore, in step 1, the modifier is selected from one of stearic acid (SA), polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS).

[0020] Furthermore, in step 1, the amount of the modifier added is 0.1% to 0.5% of the mass of the refractory metal in the water-soluble salt of the refractory metal, preferably in the range of 0.15% to 0.25%.

[0021] Furthermore, in step 1, the molar ratio of the water-soluble salt of the refractory metal, ammonium nitrate and glycine is 1:1.3-2.6:3-6; preferably, the molar ratio of ammonium nitrate to glycine is 1:1.4-2.5:3.2-5.4.

[0022] Furthermore, in step 2, the temperature used for in-situ compounding to form the core-shell complex gel under heating conditions is 150°C-300°C.

[0023] Furthermore, in step 2, the solvent in the aqueous solution is evaporated and concentrated under heating conditions to obtain an in-situ composite core-shell complex gel.

[0024] Furthermore, in step 2, the temperature of the combustion reaction is preferably 500°C-650°C.

[0025] Furthermore, in step 2, the reduction temperature range is 700°C to 800°C.

[0026] Furthermore, in step 2, the reducing gas is hydrogen.

[0027] Furthermore, in step 2, the average particle size of the obtained alloy powder is less than 50 nm, preferably 20 nm-40 nm.

[0028] Furthermore, in step 3, the pre-sintering temperature is 1550° C. to 1650° C., and the holding time is 1 min to 2 min.

[0029] Furthermore, in step 3, the densification sintering temperature is 150° C. to 300° C. lower than the pre-sintering temperature, and the temperature is maintained for 4 to 5 minutes.

[0030] Furthermore, the relative density of the phase boundary coherent refractory alloy is not less than 98.0%, and the grain size is less than 1.0 μm; furthermore, the relative density is not less than 98.5%, and the grain size is 0.5 μm-0.8 μm.

[0031] A third aspect of the present invention provides a phase boundary coherent refractory alloy prepared by the above preparation method.

[0032] A fourth aspect of the present invention provides the use of the above-mentioned phase boundary coherent refractory alloy as a material for turbine blades and combustion chambers.

[0033] Beneficial effects

[0034] 1. The present invention provides a simple and rapid process for preparing alloy powders, enabling a one-step synthesis of alloy powders without the need for a subsequent calcination step. This allows for the controlled synthesis of alloy powders with core-shell structures. The alloy powders are fine in particle size, enabling large-scale powder production, significantly reducing alloy powder preparation time.

[0035] 2. The introduction of modifiers can effectively improve the dispersion state of raw material molecules and ions in solution, promote the formation of a gel with a coating complex structure, and the highly homogenized gel formed can better achieve the elemental uniformity of the precursor and the reduced powder, thereby achieving the dispersed distribution of the second phase oxide of the high melting point metal in the refractory metal.

[0036] 3. The use of pressure sintering technology can effectively improve the density of the sintered body. The spark plasma sintering technology has a fast heating rate and a short sintering time, which can effectively prevent excessive grain growth and shorten the sintering cycle.

[0037] 4. The two-step sintering process can inhibit grain growth by taking advantage of the differences in grain boundary diffusion and grain boundary migration kinetics. This method not only reduces the sintering densification temperature, but also effectively prevents non-uniform grain growth, reduces porosity, and improves density.

[0038] 5. The oxide of the second phase high melting point metal in the phase boundary coherent refractory alloy provided by the present invention forms a coherent phase interface with the refractory metal, and the second phase oxide of the high melting point metal is dispersed in the refractory metal. The alloy has high-density ultrafine grain characteristics, with a density greater than 98.0%, a grain size not exceeding 1 μm, and a high-temperature compressive strength of more than 1000 MPa at 600°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments.

[0040] Figure 1 TEM image of the nano-alumina coherent reinforced tungsten alloy prepared in Example 1 of the present invention, showing the dispersed distribution of alumina in the tungsten matrix.

[0041] Figure 2 1 is a HRTEM photograph of the nano-alumina coherent reinforced tungsten alloy prepared in Example 1 of the present invention, showing the coherent interface formed by the alumina and the tungsten matrix.

[0042] Figure 3 This is a TEM photograph of an alumina reinforced tungsten alloy prepared without applying the method provided by the present invention. The second phase particles appear as huge agglomerates.

[0043] Figure 4 This is a HRTEM photograph of an alumina reinforced tungsten alloy that is not prepared using the method provided by the present invention. It is difficult for the two to form a coherent interface. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0045] Example 1

[0046] Step 1: Prepare raw materials: ammonium metatungstate, aluminum nitrate, ammonium nitrate, stearic acid and glycine are used as raw materials, and the ratio of ammonium metatungstate and aluminum nitrate is calculated so that the total volume of aluminum oxide generated by the metal tungsten in the ammonium metatungstate and the aluminum in the aluminum nitrate is 100%, and the volume of aluminum oxide generated by the aluminum in the aluminum nitrate is 15.0%; the ratio of ammonium metatungstate, ammonium nitrate and glycine is calculated according to the molar ratio of 1:1.5:3.2, and the amount of stearic acid is 0.2% of the mass of the metal tungsten in the ammonium metatungstate.

[0047] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent and uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 750°C to obtain a tungsten-coated nano-alumina core-shell alloy powder with a powder size of 27 nm.

[0048] Step 3: Molding and sintering: The tungsten-coated nano-alumina core-shell alloy powder obtained in step 2 is pressed to form a formed body, and the formed body is pre-sintered by spark plasma in a vacuum at a pre-sintering temperature of 1600°C for 1 minute, and then cooled to a densification sintering temperature of 1400°C and kept for 5 minutes to prepare a nano-alumina coherent reinforced tungsten alloy.

[0049] The obtained nano-alumina coherent reinforced tungsten alloy has a relative density of 99.7%, an average grain size of 0.5 μm, and a compressive strength of more than 1000 MPa at 600°C.

[0050] Example 2

[0051] Step 1: Prepare raw materials: Using ammonium metatungstate, zirconium nitrate, ammonium nitrate, stearic acid and glycine as raw materials, calculate the ratio of ammonium metatungstate and zirconium nitrate so that the total volume of zirconium oxide generated by the metal tungsten in the ammonium metatungstate and the zirconium in the zirconium nitrate is 100%, and the volume of zirconium oxide generated by the zirconium in the zirconium nitrate accounts for 5.0% of the total volume; the ratio of ammonium metatungstate, ammonium nitrate and glycine is calculated according to a molar ratio of 1:1.7:3.2, and the ratio of stearic acid is calculated according to 0.2% of the mass of the metal tungsten in the ammonium metatungstate.

[0052] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, evaporate the solution and concentrate it to form a transparent uniform gel, raise the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 700°C to obtain a tungsten-coated nano-zirconia core-shell alloy powder with a powder size of 33nm.

[0053] Step 3: Forming and Sintering: After compaction, the formed body undergoes spark plasma pre-sintering in a vacuum at 1550°C for 1 minute. The temperature is then lowered to the densification sintering temperature of 1250°C and held for 5 minutes. This results in a nano-zirconia coherent reinforced tungsten alloy with a relative density of 98.9%, an average grain size of 0.7 μm, and a compressive strength exceeding 1000 MPa at 600°C.

[0054] Example 3

[0055] Step 1: Prepare raw materials: ammonium molybdate, lanthanum nitrate, ammonium nitrate, stearic acid and glycine are used as raw materials, and the ratio of ammonium molybdate and lanthanum nitrate is calculated so that the total volume of lanthanum oxide generated by the metallic molybdenum in the ammonium molybdate and the lanthanum in the lanthanum nitrate is 100%, and the volume of lanthanum oxide generated by the lanthanum in the lanthanum nitrate accounts for 10.0% of the total volume; the ratio of ammonium molybdate, ammonium nitrate and glycine is calculated according to a molar ratio of 1:1.4:3.3, and the ratio of stearic acid is calculated according to 0.2% of the mass of the metallic molybdenum in the ammonium molybdate.

[0056] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 800°C to obtain a molybdenum-coated nano-lanthanum oxide core-shell alloy powder with a powder size of 31 nm.

[0057] Step 3: Forming and Sintering: After compaction, the formed body undergoes spark plasma pre-sintering in a vacuum at 1650°C for 1 minute. The pre-sintering temperature is then lowered to 1400°C for 5 minutes, resulting in a nano-lanthanum oxide coherent-reinforced molybdenum alloy. This alloy has a relative density of 99.2%, an average grain size of 0.6 μm, and a compressive strength exceeding 1000 MPa at 600°C.

[0058] Example 4

[0059] Step 1: Prepare raw materials: Using ammonium rhenate, yttrium nitrate, ammonium nitrate, stearic acid, and glycine as raw materials, calculate the ratio of ammonium rhenate to yttrium nitrate so that the total volume of yttrium oxide generated by the metallic rhenium in the ammonium rhenate and the yttrium in the yttrium nitrate is 100%, and the volume of yttrium oxide generated by the yttrium in the yttrium nitrate accounts for 10.0% of the total volume; the ratio of ammonium rhenate, ammonium nitrate, and glycine is calculated according to a molar ratio of 1:2.5:5.4, and the ratio of stearic acid is calculated according to 0.2% of the mass of the metallic rhenium in the ammonium rhenate.

[0060] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 800°C to obtain rhenium-coated nano-yttrium oxide core-shell alloy powder with a powder size of 35 nm.

[0061] Step 3: Forming and Sintering: After compaction, the formed body undergoes spark plasma pre-sintering in a vacuum at 1670°C for 1 minute. The temperature is then lowered to the densification sintering temperature of 1450°C and held for 5 minutes. This results in a nano-yttria coherent-reinforced rhenium alloy with a relative density of 98.9%, an average grain size of 0.7 μm, and a compressive strength exceeding 1000 MPa at 600°C.

[0062] Example 5

[0063] Step 1: Prepare raw materials: Using ammonium rhenate, lutetium nitrate, ammonium nitrate, stearic acid, and glycine as raw materials, calculate the ratio of ammonium rhenate to lutetium nitrate so that the total volume of lutetium oxide generated by metallic rhenium in the ammonium rhenate and lutetium in the lutetium nitrate is 100%, and the volume of lutetium oxide generated by lutetium in the lutetium nitrate accounts for 10.0% of the total volume; the ratio of ammonium rhenate, ammonium nitrate, and glycine is calculated according to a molar ratio of 1:2.5:5.4, and the ratio of stearic acid is calculated according to 0.2% of the mass of metallic rhenium in the ammonium rhenate.

[0064] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 800°C to obtain rhenium-coated nano-lutetium oxide core-shell alloy powder with a powder size of 35 nm.

[0065] Step 3: Forming and Sintering: After compaction, the formed body undergoes spark plasma pre-sintering in a vacuum at 1670°C for 1 minute. The temperature is then lowered to the densification sintering temperature of 1450°C and held for 5 minutes. This results in a nano-lutetium oxide coherent-reinforced rhenium alloy with a relative density of 98.9%, an average grain size of 0.7 μm, and a compressive strength exceeding 1000 MPa at 600°C.

[0066] Example 6

[0067] Step 1: Prepare raw materials: ammonium metatungstate, cerium nitrate, ammonium nitrate, stearic acid and glycine are used as raw materials, and the ratio of ammonium metatungstate and cerium nitrate is calculated so that the total volume of cerium oxide generated from the metal tungsten in the ammonium metatungstate and the cerium in the cerium nitrate is 100%, and the volume of cerium oxide generated from the cerium in the cerium nitrate is 15.0%; the ratio of ammonium metatungstate, ammonium nitrate and glycine is calculated according to a molar ratio of 1:1.5:3.2, and the amount of stearic acid is 0.2% of the mass of the metal tungsten in the ammonium metatungstate.

[0068] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent and uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 750°C to obtain a tungsten-coated nano-cerium oxide core-shell alloy powder with a powder size of 27nm and a compressive strength of more than 1000MPa at 600°C.

[0069] Step 3: Molding and sintering: The tungsten-coated nano-cerium oxide core-shell alloy powder obtained in step 2 is pressed to form a formed body, and the formed body is pre-sintered by spark plasma in a vacuum at a pre-sintering temperature of 1600°C for 1 minute, and then cooled to a densification sintering temperature of 1400°C and kept for 5 minutes to prepare a nano-cerium oxide coherent reinforced tungsten alloy.

[0070] The obtained nano-cerium oxide coherent reinforced tungsten alloy has a relative density of 99.7%, an average grain size of 0.5 μm, and a compressive strength of more than 1000 MPa at 600°C.

[0071] Example 7

[0072] Step 1: Prepare raw materials: ammonium metatungstate, hafnium nitrate, ammonium nitrate, stearic acid and glycine are used as raw materials, and the ratio of ammonium metatungstate and hafnium nitrate is calculated so that the total volume of the metal tungsten in the ammonium metatungstate and the hafnium oxide generated from the hafnium in the hafnium nitrate is 100%, and the volume of the hafnium oxide generated from the hafnium in the hafnium nitrate is 15.0%; the ratio of ammonium metatungstate, ammonium nitrate and glycine is calculated according to a molar ratio of 1:1.5:3.2, and the amount of stearic acid is 0.2% of the mass of the metal tungsten in the ammonium metatungstate.

[0073] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent uniform gel, increase the temperature to 500°C to cause a combustion reaction to obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 750°C to obtain a tungsten-coated nano-hafnium oxide core-shell alloy powder with a powder size of 27 nm.

[0074] Step 3: Molding and sintering: The tungsten-coated nano-hafnium oxide core-shell alloy powder obtained in step 2 is pressed to form a formed body, and the formed body is pre-sintered by spark plasma in a vacuum at a pre-sintering temperature of 1600°C for 1 minute, and then cooled to a densification sintering temperature of 1400°C and kept for 5 minutes to prepare a nano-hafnium oxide coherent reinforced tungsten alloy.

[0075] The obtained nano-hafnium oxide coherent reinforced tungsten alloy has a relative density of 99.7%, an average grain size of 0.5 μm, and a compressive strength of more than 1000 MPa at 600°C.

[0076] Example 8

[0077] Step 1: Prepare raw materials: ammonium metatungstate, thorium nitrate, ammonium nitrate, stearic acid and glycine are used as raw materials, and the ratio of ammonium metatungstate and thorium nitrate is calculated so that the total volume of thorium oxide generated from the metal tungsten in the ammonium metatungstate and the thorium in the thorium nitrate is 100%, and the volume of thorium oxide generated from the thorium in the thorium nitrate is 15.0%; the ratio of ammonium metatungstate, ammonium nitrate and glycine is calculated according to the molar ratio of 1:1.5:3.2, and the amount of stearic acid is 0.2% of the mass of the metal tungsten in the ammonium metatungstate.

[0078] Step 2: Prepare alloy powder: Dissolve various raw materials in water to prepare a solution, heat the solution at 200°C, volatilize and concentrate the solution to form a transparent uniform gel, increase the temperature to 500°C to cause a combustion reaction, and obtain a precursor powder; reduce the precursor powder in hydrogen at a reduction temperature of 750°C to obtain a tungsten-coated nano-thorium oxide core-shell alloy powder with a powder size of 27 nm.

[0079] Step 3: Molding and sintering: The tungsten-coated nano-thorium oxide core-shell alloy powder obtained in step 2 is pressed to form a formed body. The formed body is pre-sintered by spark plasma in a vacuum at a pre-sintering temperature of 1600°C for 1 minute. The temperature is then lowered to a densification sintering temperature of 1400°C and held for 5 minutes to prepare a nano-thorium oxide coherent reinforced tungsten alloy.

[0080] The obtained nano-thorium oxide coherent reinforced tungsten alloy has a relative density of 99.7%, an average grain size of 0.5 μm, and a compressive strength of more than 1000 MPa at 600°C.

[0081] Comparative Example 1

[0082] The same method as in Example 1 was used except that the modifier stearic acid was not used.

[0083] See the results Figure 3-4 .

[0084] By observing the alloy prepared by the present invention through transmission electron microscopy and high-resolution transmission electron microscopy, it can be observed that the second phase of high melting point metal oxide is dispersed in the refractory metal, for example Figure 1 The TEM image of the alloy of Example 1 is shown, which shows the dispersed distribution of aluminum oxide in the tungsten matrix. It can also be observed that the oxide of the second phase high melting point metal forms a coherent phase interface with the refractory metal, for example Figure 2 This is a HRTEM photograph of the nano-alumina coherent reinforced tungsten alloy prepared in Example 1 of the present invention, showing the coherent interface formed by the alumina and the tungsten matrix; Figure 3 This is a TEM photograph of an alumina reinforced tungsten alloy prepared without applying the method provided by the present invention. The second phase particles appear as huge agglomerates. Figure 4 This is a HRTEM photo of an alumina reinforced tungsten alloy that was not prepared using the method provided by the present invention. It is difficult for the two to form a coherent interface.

[0085] It is explained that the method of the present invention can obtain a phase boundary coherent refractory alloy, in which the oxide of the second phase high melting point metal forms a coherent phase interface with the refractory metal, and the oxide of the second phase high melting point metal is dispersed in the refractory metal.

[0086] The present invention proves the feasibility of the method of the present invention through multiple embodiments. At the same time, the second phase high melting point metal can be used in the present invention as long as it can generate an oxide at 500°C to 800°C and maintain the oxide form at 600°C to 1200°C under hydrogen conditions without decomposing into a metal element, such as one of lutetium, cerium, hafnium, thorium, and lanthanum.

[0087] The product prepared by the method of the present invention can be used as a material for turbine blades and combustion chambers that require high temperature resistance and excellent mechanical properties.

[0088] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a phase boundary coherent refractory alloy, characterized in that: The oxide of the second phase high melting point metal in the phase boundary coherent refractory alloy forms a coherent phase interface with the refractory metal, and the oxide of the second phase high melting point metal is dispersed in the refractory metal; The refractory metal is selected from one of tungsten, molybdenum or rhenium; the second phase high melting point metal is selected from one of zirconium, yttrium, aluminum, lutetium, cerium, hafnium, thorium and lanthanum; The volume fraction of the second phase high melting point metal oxide in the phase boundary coherent refractory alloy is 3%-30%; The preparation method comprises the following steps: Step 1. Prepare raw materials: use a water-soluble salt of a refractory metal, a water-soluble salt of a second-phase high-melting-point metal, a modifier, ammonium nitrate, and glycine as raw materials; wherein the ratio of the water-soluble salt of the refractory metal to the water-soluble salt of the second-phase high-melting-point metal is such that, based on the sum of the volume of the refractory metal in the water-soluble salt of the refractory metal and the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal being 100%, the volume of the corresponding oxide generated by the second-phase high-melting-point metal in the water-soluble salt of the second-phase high-melting-point metal is 3%-30%; the modifier is stearic acid; Step 2: Preparing alloy powder: The raw materials are mixed and formulated into a uniform aqueous solution, and in situ compounded under heating conditions to form a core-shell complex gel; then, the mixture is heated to 500°C to 700°C to cause a combustion reaction to prepare a coated core-shell precursor powder comprising a refractory metal oxide and a second-phase high-melting-point metal oxide; the coated core-shell precursor powder is further reduced in a reducing gas at a temperature of 600°C to 1200°C to prepare an alloy powder with a core-shell structure in which the refractory metal is coated with the second-phase high-melting-point metal oxide; Step 3, forming and sintering: The alloy powder obtained in step 2 is pressed and formed, and a two-step spark plasma sintering method is adopted. The temperature is first raised to the pre-sintering temperature by spark plasma sintering and kept at this temperature for 1 min to 2 min, and then the temperature is lowered to the densification sintering temperature and kept at this temperature for 3 min to 6 min to obtain a phase boundary coherent refractory alloy; wherein the pre-sintering temperature is 1500 ° C to 1800 ° C, and the densification sintering temperature is 120 ° C to 350 ° C lower than the pre-sintering temperature.

2. The preparation method according to claim 1, characterized in that In step 1, the water-soluble salt of the refractory metal is selected from ammonium metatungstate, sodium tungstate, ammonium tungstate, ammonium molybdate, sodium molybdate, potassium molybdate, ammonium rhenate, sodium rhenate, and potassium rhenate; In step 1, the water-soluble salt of the second phase high melting point metal is selected from aluminum nitrate, zirconium nitrate, yttrium nitrate, lutetium nitrate, cerium nitrate, hafnium nitrate, thorium nitrate, lanthanum nitrate, zirconium chloride, yttrium chloride, aluminum chloride, lutetium chloride, cerium chloride, hafnium chloride, thorium chloride, and lanthanum chloride.

3. The preparation method according to claim 1, characterized in that In step 1, based on the sum of the volume of the refractory metal in the water-soluble salt of the refractory metal and the volume of the corresponding oxide generated by the second-phase refractory metal in the water-soluble salt of the second-phase refractory metal being 100%, the volume of the corresponding oxide generated by the second-phase refractory metal in the water-soluble salt of the second-phase refractory metal is 5.0% to 15.0%.

4. The preparation method according to claim 1, characterized in that The amount of modifier added is 0.1% to 0.5% of the mass of the refractory metal in the water-soluble salt of the refractory metal; The molar ratio of the water-soluble salt of the refractory metal, ammonium nitrate and glycine is 1:1.3-2.6:3-6.

5. The preparation method according to claim 1, characterized in that In step 2, the temperature used for in-situ composite formation of the core-shell complex gel under heating conditions is 150°C to 300°C; In step 2, the solvent in the aqueous solution is evaporated and concentrated under heating conditions to obtain an in-situ composite core-shell complex gel.

6. The preparation method according to claim 1, characterized in that In step 2, the temperature of the combustion reaction is 500°C-650°C; the temperature range of the reduction is 700°C-800°C.

7. The preparation method according to claim 1, characterized in that In step 3, the pre-sintering temperature is 1550°C to 1650°C; In step 3, the densification sintering temperature is 150°C to 300°C lower than the pre-sintering temperature, and is kept warm for 4 min to 5 min.

8. The preparation method according to claim 1, characterized in that The relative density of the phase boundary coherent refractory alloy is not less than 98.0%, and the grain size is less than 1.0 μm.

Images