阅读说明：本技术 一种提升微波烧结铁磁性高熵合金致密度与性能的方法 (Method for improving density and performance of microwave sintered ferromagnetic high-entropy alloy ) 是由 李桂荣 刘明 王宏明 高立鹏 于 2020-04-22 设计创作，主要内容包括：本发明提供了一种提升微波烧结铁磁性高熵合金致密度与性能的方法,采用静磁场冷等静压技术制备高熵合金压胚,在磁场作用下进行微波烧结。该方法适用于任何含有铁、钴、镍等铁磁元素系列高熵合金的微波烧结制备,有效解决了微波烧结高熵合金致密度较低的应用问题,同时促进高熵合金软磁性能与力学性能的同步提升,是一种十分有发展潜力的新型高熵合金制备技术。(The invention provides a method for improving the density and performance of a microwave sintered ferromagnetic high-entropy alloy. The method is suitable for microwave sintering preparation of any series of high-entropy alloys containing iron, cobalt, nickel and other ferromagnetic elements, effectively solves the application problem of low density of the microwave sintered high-entropy alloys, promotes synchronous promotion of soft magnetic performance and mechanical performance of the high-entropy alloys, and is a novel high-entropy alloy preparation technology with great development potential.)

1. A method for improving the density and performance of microwave sintered ferromagnetic high-entropy alloy is characterized by comprising the following steps: and (3) carrying out cold isostatic pressing on the high-entropy alloy powder in a magnetic field environment to obtain an alloy pressed blank, and carrying out microwave sintering on the pressed blank under the condition of a magnetic field with the same magnetic field direction in the cold isostatic pressing.

2. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 1, wherein the ferromagnetic high-entropy alloy is a high-entropy alloy containing ferromagnetic elements of iron, cobalt and/or nickel.

3. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 1, wherein the average particle size of the high-entropy alloy powder is in a range of 1-20 μm.

4. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 3, which is characterized in that: the high-entropy alloy powder for the cold isostatic pressing blank is prepared by an atomization method, an electrolytic deposition method or a grinding method.

5. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 3, characterized in that: the high-entropy alloy powder for the cold isostatic pressing blank is as follows: the high-entropy alloy is prepared by mixing the metal powder of the high-entropy alloy components, and performing ball milling in protective gas to perform mechanical alloying treatment.

6. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 5, wherein the purity of the metal powder is 99.99 wt%, and the average particle size is 10 μm to 50 μm.

7. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 5, characterized in that: before ball milling, firstly, a vacuum machine is used for vacuumizing to 0.01MPa, then, argon gas with the pressure of 0.5MPa is filled as protective gas, and the ball milling parameters are as follows: the mass ratio of the ball to the powder is 5:1, the mass ratio of grinding balls with different diameters is 5mm:10mm:15 mm: 4:2:1, absolute ethyl alcohol with the mass fraction of 15% is added for wet grinding for 60 hours, the wet grinding rotating speed is 300r/min, a positive and negative alternative ball grinding mode is adopted, and the powder is cooled after stopping 15min every 1 hour; the particle size range of the powder after ball milling is 0.5-15 mu m, the powder is placed in a vacuum drying oven after ball milling is finished, and the powder is taken out after 20 hours.

8. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 1, which is characterized in that: the microwave sintering is carried out under the protection atmosphere of inert gas.

9. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 1, characterized in that: the parameters of cold isostatic pressing in a magnetic field environment are as follows: maintaining the pressure for 3min, and forming at 300 Mpa; (ii) a The magnetic field is a static magnetic field and is provided by strong magnets fixed at two ends of the rubber mold, and the surface magnetic field intensity of the strong magnets is 0.1-2T.

10. The method for improving the compactness and the performance of the microwave sintered ferromagnetic high-entropy alloy according to claim 1 or 8, characterized in that: the intensity of the applied magnetic field during microwave sintering is 0.1-5T, the application form is static magnetic field or pulse magnetic field, and the frequency of the pulse magnetic field is 0-100 Hz.

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a preparation process of a high-entropy alloy, in particular to a method for preparing the high-entropy alloy by microwave sintering.

Background

The high-entropy alloy is a multi-component alloy material, and is a solid solution alloy formed by mixing five or more than five elements in an equimolar ratio or a nearly equimolar ratio. At present, the main constituent elements of the high-entropy alloy are still more formed by ferromagnetic elements such as iron, cobalt, nickel and the like, and the high-entropy alloy formed by the ferromagnetic elements is more mature in research, more stable in performance and higher in strength. In a plurality of methods for preparing the high-entropy alloy, the powder metallurgy has wider application and more mature technology, and is more suitable for alloy components which are difficult to prepare by other processes such as refractory high-entropy alloy and the like.

The microwave sintering technology is a novel powder metallurgy rapid sintering technology and is mainly used for preparing structural ceramics, polymers and composite materials. The conventional concept considers that microwave is a high frequency electromagnetic wave, and metal reflects most energy and has limited absorption, so that it cannot be used for heating metal materials. Until 1999, american academics have first applied microwave sintering technology to the powder metallurgy field and have produced a large number of metal and alloy products. Compared with the conventional sintering, the microwave sintering has the following characteristics: (1) the sintering temperature is greatly reduced, and compared with the conventional sintering, the maximum temperature reduction amplitude can reach about 500 ℃. (2) Compared with the conventional sintering, the energy is saved by 60-80%, and the sintering energy consumption cost is greatly reduced. (3) The temperature is quickly raised, the growth of crystal grains can be effectively inhibited, and the sintering time is reduced. (4) Is safe and pollution-free, and is a green and environment-friendly metallurgical technology. However, microwave sintering also has the biggest problem that the sintering process has no sintering pressure. Therefore, although the microwave sintering method can fully utilize microwave energy to realize rapid sintering, the performance of the prepared part is often not up to the standard due to low density. The invention provides a microwave sintering technology under a magnetic field strengthening environment aiming at the problem, can well solve the problem of lower density of the high-entropy alloy in the microwave sintering process, and simultaneously greatly improves the strength and the magnetic property of the alloy, thereby being a very effective processing method.

Disclosure of Invention

In order to solve the problem of low density of the microwave sintered high-entropy alloy, the invention provides a preparation process under the condition of magnetic field enhancement, wherein the cold isostatic pressing process and the sintering process are both carried out under the magnetic field environment, so that the flowability of powder in the pressing process can be effectively improved, and the formation and growth of a sintering neck in the sintering process can be accelerated, thereby improving the density of the microwave sintered high-entropy alloy and obviously improving the structure and performance of a sintered workpiece.

The specific technical scheme of the invention is as follows:

a method for improving the density and performance of microwave sintered ferromagnetic high-entropy alloy is characterized by comprising the following steps: and (3) carrying out cold isostatic pressing on the high-entropy alloy powder in a magnetic field environment to obtain an alloy pressed blank, and carrying out microwave sintering on the pressed blank under the condition of a magnetic field with the same magnetic field direction in the cold isostatic pressing.

A method for improving the density and performance of microwave sintered ferromagnetic high-entropy alloy is characterized by comprising the following steps: and (3) carrying out cold isostatic pressing on the high-entropy alloy powder in a magnetic field environment to obtain an alloy pressed blank, and carrying out microwave sintering on the pressed blank under the condition of a magnetic field with the same magnetic field direction in the cold isostatic pressing.

Further, the ferromagnetic high-entropy alloy is a high-entropy alloy of ferromagnetic elements containing iron, cobalt and/or nickel.

Further, the average particle size of the high-entropy alloy powder is in a range of 1 μm to 20 μm.

Further, the high-entropy alloy powder for the cold isostatic pressing blank is prepared by an atomization method, an electrolytic deposition method or a grinding method.

Further, the high-entropy alloy powder for cold isostatic pressing is as follows: the high-entropy alloy is prepared by mixing the metal powder of the high-entropy alloy components, and performing ball milling in protective gas to perform mechanical alloying treatment.

Further, the purity of the metal powder is 99.99 wt%, and the average particle size ranges from 10 μm to 50 μm.

Further, before ball milling, a vacuum machine is firstly used for vacuumizing to 0.01MPa, then 0.5MPa argon is filled as protective gas, and the ball milling parameters are as follows: the mass ratio of the ball to the powder is 5:1, the mass ratio of grinding balls with different diameters is 5mm:10mm:15 mm: 4:2:1, absolute ethyl alcohol with the mass fraction of 15% is added for wet grinding for 60 hours, the wet grinding rotating speed is 300r/min, a positive and negative alternative ball grinding mode is adopted, and the powder is cooled after stopping 15min every 1 hour; the particle size range of the powder after ball milling is 0.5-15 mu m, the powder is placed in a vacuum drying oven after ball milling is finished, and the powder is taken out after 20 hours.

Further, the microwave sintering is carried out under the inert gas protection atmosphere.

Further, the parameters of cold isostatic pressing in a magnetic field environment are as follows: maintaining the pressure for 3min, and forming at 300 Mpa; (ii) a The magnetic field is a static magnetic field and is provided by strong magnets fixed at two ends of the rubber mold, and the surface magnetic field intensity of the strong magnets is 0.1-2T.

Furthermore, the intensity of the applied magnetic field during microwave sintering is 0.1-5T, the applied form is static magnetic field or pulse magnetic field, and the frequency of the pulse magnetic field is 0-100 Hz.

The invention respectively applies magnetic field action to a cold isostatic pressing link and a microwave sintering link in the preparation process of the high-entropy alloy, and the principle is as follows: the action of the magnetic field on ferromagnetic elements in the high-entropy alloy is utilized to enhance the flowability of powder in the cold isostatic pressing process, so that the compactness of the pressed blank is improved. The high-density pressing blank is beneficial to the rapid sintering process; meanwhile, the magnetic field plays a significant role in the microwave sintering process, and the magnetic force generated by the magnetic field on the ferromagnetic element is beneficial to the formation and growth of a sintering neck in the sintering process, so that the acceleration of the sintering process is promoted. In addition, the magnetic field is applied to the cold isostatic pressing and microwave sintering process, the magnetic domain parallel to the direction of the external magnetic field in the alloy can be increased, the magnetic domain perpendicular to the external magnetic field is reduced, and the uniaxial anisotropy along the direction of the external magnetic field is induced, so that the soft magnetic performance of the alloy is improved.

Compared with the existing microwave sintering technology, the uniqueness of the invention lies in the application of the magnetic field, and the invention has obvious improvement on the microwave sintering technology of the ferromagnetic high-entropy alloy. In addition, the invention mainly has the following three effects:

(1) the invention is suitable for the microwave sintering preparation of any high-entropy alloy containing ferromagnetic elements, and has wide application range;

(2) the improvement provided by the invention has the advantages of low cost, obvious effect and strong economy.

(3) The improvement method provided by the invention does not affect the physical health of personnel, does not increase an additional operation process, has high safety and does not pollute the environment.

The invention aims at the problem that the utilization of a magnetic field needs to simultaneously act on a cold isostatic pressing process and a microwave sintering process, and the utilization of the magnetic field is not necessary. This is because the cold isostatic pressing process without magnetic field enhancement cannot obtain an alloy compact with good density, and more importantly, the magnetic domains in the powder are disordered, which is not favorable for the oriented growth of magnetic particles in the sintering process. Although the mechanical property of the alloy can be improved due to the improvement of the compaction density of the blank in the microwave sintering without magnetic field enhancement, the original consistent magnetic domain becomes disordered again in the sintering process, so that the soft magnetic property of the alloy cannot be improved.

The invention uses static magnetic field in cold isostatic pressing process, and uses static magnetic field or pulse magnetic field in microwave sintering process. Under the same condition, the density of the cold isostatic pressing under magnetic field enhancement is generally about 7-18% higher than that of an alloy pressing blank without the enhancement effect, the comprehensive sintering effect under magnetic field enhancement is about 20% better than that of a non-magnetic field sintering, the magnetic performance can be improved by 34% at most, and the mechanical performance can be improved by 29% at most. Under the same magnetic field intensity, the microwave sintering process enhanced by the pulse magnetic field is more obvious than the microwave sintering process enhanced by the static magnetic field.

Drawings

FIG. 1 is a distribution diagram of the average particle size of the high-entropy alloy powder obtained by a ball milling process in the method of the invention.

Fig. 2 is a schematic diagram of the field enhanced cold isostatic pressing of the present invention.

FIG. 3 is a schematic diagram of the magnetic field enhanced microwave sintering of the present invention.

FIG. 4 is a scanning structure diagram of FeCoNiCrCu high entropy alloy when the magnetic field strength of both microwave sintering and cold isostatic pressing is 0.1T.

FIG. 5 is a scanning structure diagram of FeCoNiCrCu high entropy alloy when the cold isostatic pressing magnetic field strength is 0.6T and the microwave sintering magnetic field strength is 2T.

FIG. 6 is a structural scan of FeCoNiCuAl high entropy alloy obtained by cold isostatic pressing at a magnetic field strength of 0.3T and microwave sintering at a magnetic field strength of 1T.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.

The method for improving the density and performance of the microwave sintered ferromagnetic high-entropy alloy comprises the steps of carrying out cold isostatic pressing on high-entropy alloy powder in a magnetic field environment to obtain an alloy pressing blank, and carrying out microwave sintering on the pressing blank in a magnetic field condition with the same magnetic field direction in the cold isostatic pressing. The magnetic field used in the cold isostatic pressing process is a static magnetic field, and the magnetic field used in the microwave sintering process is a static magnetic field or a pulse magnetic field.

The high-entropy alloy powder for the cold isostatic pressing blank is as follows: metal powder of the high-entropy alloy composition is prepared by mixing, ball-milling in protective gas and carrying out mechanical alloying treatment; or is prepared by powder preparation processes such as an atomization method, an electrolytic deposition method or a grinding method. The average particle size range of the high-entropy alloy powder is 1-20 mu m, and the excessive particle size can influence the efficiency of microwave sintering. If the alloy powder is prepared by adopting a ball milling process, the powder purity of various metal elements of the high-entropy alloy components is 99.99 wt%, and the particle size is not more than 50 mu m. The excessively small particle size of the powder is expensive, which greatly increases the production cost, and therefore, the powder of the alloying element has an average particle size in the range of 10 μm to 50 μm is suitable.

The following examples used a mechanical alloying process, i.e., a high energy mechanical ball milling process, to prepare high entropy alloy powders. In the actual production, high-entropy alloy powder can be prepared by powder production technologies such as an atomization method, an electrolytic deposition method, a grinding method and the like, and in order to obtain a good sintering effect, the alloying degree of the alloy powder used for magnetic field cold isostatic pressing and magnetic field microwave sintering is ensured to be as high as possible, and the particle size is as small as possible and is not more than 20 μm at most. The technical scheme of the mechanical high-energy ball milling process adopted by the embodiment is as follows: selecting high-purity metal powder with the granularity not more than 45 mu m, proportioning the high-purity metal powder according to design components, and mixing the powder and grinding balls according to the weight ratio of 1: 5, putting the mixture into a ball milling tank, pouring absolute ethyl alcohol with the mass fraction of 15%, vacuumizing the ball milling tank, and introducing argon with the pressure of 0.5MPa as protective gas. Setting ball milling technological parameters of ball milling for 60h at a rotating speed of 300r/min, and adopting a positive and negative alternative ball milling mode. In order to avoid high energy in the ball milling process, the powder is stopped for 15min every 1h, and is cooled. And (3) putting the ball-milled powder into a vacuum drying box for drying at the temperature of 70 ℃ for 40 h. And (4) cooling the dried powder to room temperature, then carrying out vacuum sealing storage, and waiting for subsequent pressing. The particle size distribution of the high-entropy alloy powder prepared by the process is shown in figure 1, and the average particle size of the powder is 5.36 mu m.