阅读说明：本技术 一种制备高致密度超细晶稀土氧化物掺杂钨合金的方法 (Method for preparing high-density ultrafine-grained rare earth oxide doped tungsten alloy ) 是由 秦明礼 杨军军 章雨峰 陈铮 王倩玉 于瀛 母晓东 贾宝瑞 曲选辉 于 2019-09-30 设计创作，主要内容包括：一种制备高致密度超细晶稀土氧化物掺杂钨合金的方法,属于粉末冶金领域。制备方法为：以偏钨酸铵、稀土硝酸盐、燃料、硝酸铵为原料,采用低温溶液燃烧合成法制备氧化物复合粉末前驱体,然后使用H<Sub>2</Sub>还原制得纳米稀土氧化物掺杂钨合金粉末；采用多步放电等离子烧结制备高致密度超细晶稀土氧化物掺杂钨合金。本发明采用的低温溶液燃烧合成法可达到分子级别的混合,得到的前驱体中氧化钨、稀土氧化物均匀混合,还原产物为合金粉末,无需后续特殊处理；SPS适用于难熔金属及难烧结材料的快速烧结,采用多步SPS可获得高致密度超细晶稀土氧化物掺杂钨合金,相对致密度可达96％～99％,平均晶粒尺寸≤300nm。本方法的原料简单易得,设备简单,工艺快捷,适合进行大规模生产。(A method for preparing high-density ultrafine-grained rare earth oxide doped tungsten alloy belongs to the field of powder metallurgy. The preparation method comprises the following steps: preparing composite oxide powder precursor by using ammonium metatungstate, rare earth nitrate, fuel and ammonium nitrate as raw materials and adopting low-temperature solution combustion synthesis method, and then using H 2 Reducing to obtain nanometer rare earth oxide doped tungsten alloy powder; and preparing the high-density ultrafine-grained rare earth oxide doped tungsten alloy by adopting multi-step discharge plasma sintering. The low-temperature solution combustion synthesis method adopted by the invention can achieve the mixing of molecular level, and the obtained precursorThe medium tungsten oxide and the rare earth oxide are uniformly mixed, and the reduction product is alloy powder without subsequent special treatment; the SPS is suitable for rapid sintering of refractory metals and materials difficult to sinter, and the high-density ultrafine-grained rare earth oxide doped tungsten alloy can be obtained by adopting multi-step SPS, the relative density can reach 96-99%, and the average grain size is less than or equal to 300 nm. The method has the advantages of simple and easily obtained raw materials, simple equipment and quick process, and is suitable for large-scale production.)

1. A method for preparing high-density ultrafine-grained rare earth oxide doped tungsten alloy is characterized by comprising the following preparation steps:

1) The precursor is prepared by adopting a low-temperature solution combustion synthesis method, and the specific process comprises the following steps: dissolving ammonium metatungstate, rare earth nitrate, fuel and ammonium nitrate in deionized water according to a certain molar ratio to prepare an aqueous solution, and heating the solution until combustion reaction occurs to obtain fluffy tungsten oxide rare earth oxide precursor powder;

2) The precursor powder obtained is ground and then H is used₂Reducing to obtain nanometer rare earth oxide doped tungsten alloy powder, and adding N into the obtained nanometer powder₂Or storing under the protection of Ar atmosphere;

3) The high-density ultrafine-grained rare earth oxide doped tungsten alloy can be obtained by rapidly sintering nano rare earth oxide doped tungsten alloy powder by adopting multi-step discharge plasma sintering (SPS).

2. The method for preparing the high-density ultrafine grained rare earth oxide doped tungsten alloy according to claim 1, wherein the rare earth nitrate in the step (1) is at least one of lanthanum nitrate, yttrium nitrate, lutetium nitrate and cerium nitrate.

3. The method for preparing the high-density ultra-fine grained rare earth oxide doped tungsten alloy according to claim 1, wherein the fuel in step (1) is at least one of glycine, urea, EDTA and thiourea.

4. The method for preparing the high-density ultrafine grained rare earth oxide doped tungsten alloy according to claim 1, wherein the mass ratio of the ammonium metatungstate, the rare earth nitrate, the fuel and the ammonium nitrate in the step (1) is 1: (0.005-0.12): (0.38-0.42) and (0.9-1.5).

5. the method for preparing the high-density ultrafine grained rare earth oxide doped tungsten alloy according to claim 1, wherein the reduction temperature in the step (2) is 600-800 ℃, the heating rate is 1-10 ℃/min, the heat preservation time is 1-3 h, the introduction of hydrogen is kept during the reduction process, and the hydrogen flow is more than 1L/min.

6. The method for preparing high-density ultra-fine grained rare earth oxide doped tungsten alloy according to claim 1, wherein the multi-step SPS sintering process in step (3) is as follows: firstly, heating to 600-700 ℃, and preserving heat for 3-5 min; then heating to 900-1100 ℃, and preserving heat for 3-5 min; heating to 1200-1500 ℃, and preserving heat for 0.5-5 min for carrying out the third sintering step; the heating rate is 100 ℃/min; the pressure applied in the sintering process is 40-60 Mpa, and the sintering atmosphere is high vacuum.

7. The method according to claim 1, wherein the relative density of the rare earth oxide doped tungsten alloy obtained in the step (3) is 96-99%, and the average grain size is less than or equal to 300 nm.

Technical Field

The invention belongs to the field of powder metallurgy, and relates to a method for preparing high-density ultrafine-grained rare earth oxide doped tungsten alloy.

Background

Tungsten (W) has high melting point, high hardness, good high-temperature strength, heat conductivity and electric conductivity, and low thermal expansion coefficient, and is widely applied to the fields of national defense and military industry, nuclear industry and high temperature. However, the sintering temperature of W is typically above 2000 ℃, which makes it difficult to densify and causes grain growth. The particle size of the W powder is thinned to the nanometer size, so that the sintering temperature of W can be effectively reduced, but the nanometer W powder can grow rapidly in the sintering process, and the mechanical property of the W alloy is reduced. Adding rare earth oxide (La) to W alloy₂O₃、Y₂O₃、Lu₂O₃、Ce₂O₃Etc.) the grains can prevent the movement of the grain boundary in the sintering process, thereby achieving the purpose of refining the grain size.

The preparation method of the rare earth oxide doped W alloy generally adopts a powder metallurgy method, and the first step is the preparation of nano rare earth oxide doped tungsten alloy powder. At present, the common methods for preparing the nano rare earth oxide doped tungsten alloy powder include mechanical alloying, coprecipitation method, sol-gel method, hydrothermal synthesis method and the like. The mechanical alloying is to carry out high-energy ball milling on commercial W powder and rare earth oxide particles to obtain nano rare earth oxide doped tungsten alloy nano powder. The patent CN 101880808A takes micron-sized tungsten powder and nano yttrium oxide particles to prepare the ultra-fine grain tungsten-based composite material through batching, mechanical alloying and discharge plasma sintering. However, the grain diameter of the mechanical alloying powder is bimodal distribution, so that impurities are easily introduced, the sintering activity is influenced, and embrittlement is caused; distortion energy is stored in the particles, so that grains grow abnormally in the sintering process. The coprecipitation method is a wet chemical method and mainly comprises the working procedures of aqueous solution preparation, coprecipitation, filtration, washing, calcination, reduction and the like. Patent CN 106564927 a uses a coprecipitation method to prepare ultrafine yttria-doped tungsten composite precursor powder. Although this method can achieve uniform mixing between molecules, it takes a long time, and the process is complicated and energy-consuming. The low-temperature solution combustion synthesis method belongs to a wet chemical method, is a quick and energy-saving preparation method, utilizes self-propagating exothermic reaction generated among reactants to synthesize materials, can realize uniform mixing among molecules, uniformly mixes tungsten oxide and rare earth oxide in the obtained precursor, reduces the product to alloy powder, does not need subsequent special treatment, has simple process and is suitable for large-scale production.

W belongs to a difficult-to-sinter material, high density is difficult to obtain by using a traditional sintering method, and long-time sintering is needed at high temperature, which inevitably causes the growth of crystal grains and is not beneficial to preparing high-density ultrafine-grain W-based alloy. Spark Plasma Sintering (SPS) is an electric current and mechanical pressure assisted sintering technique, applicable to materials difficult to sinter; the effective heating rate, the lower sintering temperature and the heat preservation time are achieved, the grain growth can be effectively inhibited, and the W-based material with ultra-fine grains can be obtained. The multi-step discharge plasma sintering can effectively reduce the generation of internal pores of crystal grains, further inhibit the growth of the crystal grains and improve the density.

In summary, we need to find an efficient, energy-saving and environment-friendly method for preparing rare earth oxide doped tungsten alloy, and the combination of the low-temperature solution combustion synthesis method and the multi-step Spark Plasma Sintering (SPS) can meet the above requirements, and can prepare high-density ultrafine-grained rare earth oxide doped tungsten alloy.

Disclosure of Invention

The invention aims to provide a method for simply and rapidly preparing high-density ultrafine-grained rare earth oxide doped tungsten alloy according to the defects of high energy consumption, long consumption time or complicated preparation method in the prior art, wherein the mass fraction of rare earth oxide is 0.5-5%.

The invention comprises the following specific steps:

(1) The precursor powder is prepared by adopting a low-temperature solution combustion synthesis method, and the specific process comprises the following steps: dissolving ammonium metatungstate, rare earth nitrate, fuel and ammonium nitrate in deionized water according to a certain molar ratio to prepare aqueous solution, and heating the solution until combustion reaction occurs to obtain fluffy tungsten oxide rare earth oxide precursor powder.

(2) The precursor powder obtained is ground and then H is used₂Reducing to obtain nanometer rare earth oxide doped tungsten alloy powder, and adding N into the obtained nanometer alloy powder₂Or storing under the protection of Ar atmosphere.

(3) The high-density ultrafine-grained rare earth oxide doped tungsten alloy can be obtained by rapidly sintering nano rare earth oxide doped tungsten alloy powder by adopting multi-step discharge plasma sintering (SPS).

Further, the rare earth nitrate in the step (1) is at least one of lanthanum nitrate, yttrium nitrate, lutetium nitrate and cerium nitrate.

Further, the fuel in the step (1) is at least one of glycine, urea, EDTA and thiourea.

Further, the mass ratio of the ammonium metatungstate, the rare earth nitrate, the fuel and the ammonium nitrate in the step (1) is 1: (0.005-0.12): (0.38-0.42) and (0.9-1.5).

Further, the reduction temperature in the step (2) is 600-800 ℃, the heating rate is 1-10 ℃/min, the heat preservation time is 1-3 h, the introduction of hydrogen is kept in the reduction process, and the hydrogen flow is more than 1L/min.

Further, the multi-step SPS sintering procedure in step (3) is: firstly, heating to 600-700 ℃, and preserving heat for 3-5 min; then heating to 900-1100 ℃, and preserving heat for 3-5 min; heating to 1200-1500 ℃, and preserving heat for 0.5-5 min for carrying out the third sintering step; the heating rate is 100 ℃/min; the pressure applied in the sintering process is 40-60 Mpa, and the sintering atmosphere is high vacuum.

furthermore, the high-density ultrafine-grained rare earth oxide doped tungsten alloy in the step (3) has relative density of 96-99% and average grain size of less than or equal to 300 nm.

The technique of the invention has the following advantages:

(1) The method for preparing the precursor powder adopts a low-temperature solution combustion synthesis method, and tungsten oxide and rare earth oxide in the obtained precursor can be uniformly mixed at a molecular level; the finally prepared nano rare earth oxide doped tungsten alloy powder has fine particles, high sintering activity, low sintering temperature and short sintering time.

(2) the composition of the rare earth oxide doped tungsten alloy can be accurately controlled by adjusting the adding amount of the raw materials.

(3) The density can be improved by properly prolonging the heat preservation time in the low-temperature stage and inhibiting the growth of crystal grains by properly shortening the heat preservation time in the high-temperature stage by multi-step discharge plasma sintering, and the comprehensive mechanical property of the tungsten-based material can be improved.

Detailed Description