阅读说明：本技术 VNbMoTaW高熵合金的制备方法 (Preparation method of VNbMoTaW high-entropy alloy ) 是由 唐宇 李顺 白书欣 乔娅婷 叶益聪 朱利安 刘希月 王震 于 2020-04-30 设计创作，主要内容包括：本发明公开了一种VNbMoTaW高熵合金的制备方法,包括先采用机械合金化法,将W、Mo、V、Nb、Ta单质粉末混合,不添加球磨介质进行球磨,得到单相或双相单一体心立方结构的VNbMoTaW高熵合金粉末,然后采用热压烧结,压力为30MPa～50MPa,升温速率为5℃/min～15℃/min,保温温度为1700℃～1900℃,得到具有单相单一体心立方结构且致密度>99.5％的VNbMoTaW高熵合金块体。本发明的方法工艺简单,不需要加热到熔点温度就可获得性能较好的块体材料,有效地降低了加工温度,且制备成本较低,具有很高的工业应用价值。(The invention discloses a preparation method of VNbMoTaW high-entropy alloy, which comprises the steps of firstly mixing single substance powder of W, Mo, V, Nb and Ta by adopting a mechanical alloying method, carrying out ball milling without adding a ball milling medium to obtain the VNbMoTaW high-entropy alloy powder with a single-phase or double-phase single-body-center cubic structure, and then carrying out hot-pressing sintering at the pressure of 30-50 MPa, the heating rate of 5-15 ℃/min and the heat preservation temperature of 1700-1900 ℃ to obtain a VNbMoTaW high-entropy alloy block with the single-phase single-body-center cubic structure and the density of 99.5%. The method has simple process, can obtain block materials with better performance without heating to the melting point temperature, effectively reduces the processing temperature, has lower preparation cost and has higher industrial application value.)

1. A preparation method of VNbMoTaW high-entropy alloy is characterized by comprising the following steps:

(1) mechanical alloying method: mixing W, Mo, V, Nb and Ta elementary substance powder, performing ball milling without adding a ball milling medium, wherein the adopted ball milling tank and the grinding balls are made of WC hard alloy to obtain VNbMoTaW high-entropy alloy powder which is in a single-phase or two-phase single-body-centered cubic structure;

(2) vacuum hot pressing sintering method: carrying out hot-pressing sintering on the VNbMoTaW high-entropy alloy powder under the protection of inert atmosphere, wherein the pressure is 30-50 MPa, the heating rate is 5-15 ℃/min, the heat preservation temperature is 1700-1900 ℃, and a VNbMoTaW high-entropy alloy block is obtained and has a single-phase single-body-centered cubic structure and the density is more than 99.5%.

2. The preparation method of the VNbMoTaW high-entropy alloy according to claim 1, wherein in the step (1), the ball-to-material ratio of the ball mill is 10: 1, the rotation speed of the ball mill is 300r/min, and the ball milling time is 15-55 h.

3. The method for preparing VNbMoTaW high-entropy alloy according to claim 1, wherein in the step (1), the amounts of W, Mo, V, Nb and Ta are equal to or unequal to equal atomic ratio, and the molar ratio of each element is W: Mo: V: Nb: Ta ═ a: b: c: d: e, wherein a, b, c, d and e are all independently any value in [0.98,1.02 ].

4. The method for preparing the VNbMoTaW high-entropy alloy according to any one of claims 1 to 3, wherein in the step (1), the ball milling process is carried out under the protection of inert gas.

5. The method for preparing the VNbMoTaW high-entropy alloy according to any one of claims 1 to 3, wherein in the step (2), the material of a mould used for hot-pressing sintering is isostatic three-high graphite, the heat preservation time of the hot-pressing sintering is 1-2 h, and the cooling mode is furnace cooling.

Technical Field

The invention belongs to the technical field of high-entropy alloys, relates to a preparation method of a VNbMoTaW high-entropy alloy, and particularly relates to a preparation method of a high-melting-point VNbMoTaW high-entropy alloy.

Background

High-entropy alloys (High-entropy alloys) are a novel multi-principal-element alloy which is discovered by Cantor team in 2004 first in experiments and named by leaves in the same year according to the characteristic that the alloy has High mixing entropy. Unlike conventional alloys, which consist of one main element and a plurality of trace elements, high entropy alloys are solid solutions of a plurality of elements (usually more than 4) mixed at equal or near equal ratios. Under the action of high thermodynamic entropy, atoms with different properties occupy disordered positions in solid solution, so that serious lattice distortion is caused. The special crystal structure enables the high-entropy alloy to have excellent characteristics of high strength, strong corrosion resistance, radiation resistance and the like.

Refractory high-entropy alloys (Refractory high-entropy alloys) are a new high-entropy alloy system proposed by Senkov in 2010 based on the development of high-temperature structural metals by the us air force research laboratory. The refractory high-entropy alloy mainly comprises refractory metals including Cr, Hf, Mo, Nb, Ta, Ti, V, W, Zr and the like. Because the characteristics of high melting point, high strength and high hardness of refractory metal are inherited, the refractory high-entropy alloy generally has excellent high-temperature mechanical property and can keep high strength in a wide temperature range. Among them, the as-cast VNbMoTaW alloy prepared by arc melting can still maintain the strength of 477MPa at 1600 ℃ because of having high melting point higher than 2700 ℃. This is not only a corollary to the reported refractory high entropy alloys, but it is also far superior to the nickel-based superalloys currently in use.

At present, the preparation of refractory high-entropy alloys including VNbMoTaW is mainly based on a vacuum arc melting method, however, the melting points of the components of the refractory high-entropy alloys are greatly different, for example, the melting point of V is 1890 ℃, the melting point of W reaches 3620 ℃, the difference is 1530 ℃ and is higher than the boiling point of V (3000 ℃), therefore, during the melting preparation process of the refractory high-entropy alloys, volatilization of low-melting-point substances is easily caused, and further the composition of the formed alloy deviates from the initial setting, meanwhile, the huge melting point difference enables the refractory metals to form a very wide liquid-solid two-phase temperature zone when being mixed two by two, further, a remarkable solidification time difference is caused, a large number of casting defects such as shrinkage cavities, dendrites and the like are formed, and the performance and large-size forming of the refractory high-entropy alloys are influenced, therefore, the maximum size of the existing cast and formed refractory high-entropy alloys is only 10mm × mm × mm, which is far from meeting the practical application, and even difficult to meet the requirement of the.

Powder metallurgy is a technique for converting a powder material having a certain specific particle size, shape and apparent density into a material having high strength, high precision and high performance, and its key steps include preparation of powder, shaping and subsequent sintering and heat treatment. Since the powder metallurgy technology has the advantages of low energy consumption, high material utilization rate, low cost, unique shape, high product performance and the like, the powder metallurgy technology is widely used for scientific research and industrial production of various metal materials at present. In recent years, scholars at home and abroad also try to prepare high-melting-point refractory high-entropy alloy by a powder metallurgy method. However, researchers have adopted methods such as "pre-ball milling to coat the grinding balls and the tank walls with powder" to improve the quality of the alloy. But overall, the constituent metal contamination from the grinding balls and the tank walls (especially stainless steel tanks), and O, N or C contamination from environmental and process control agents, are almost unavoidable. On the other hand, most of the solid-phase sintering methods of high-entropy alloy powders currently used in research are Spark Plasma Sintering (SPS). As a new solid phase sintering technology, SPS is superior to the traditional hot pressing sintering method in the sintering quality of samples. However, the high equipment price and the not yet completely understood mechanism make SPS technology currently used in laboratory research rather than in widespread industrial applications. For example, Hong et al, high scientific and technical college, korea, 2018, although successfully prepared a material with macroscopic single body-centered cubic (BCC) junction by "alloying powder mechanically + presintering powder + Spark Plasma Sintering (SPS)"The structural VNbMoTaW high-entropy alloy. However, considerable Ta still appears in the formed alloy₂VO₆The mechanical properties of the alloy are deteriorated. Even there is the research that adopts the hot pressing sintering method, but too big pressure can cause the harm of equipment, and in addition, conventional hot pressing sintering furnace can't all carry out cooling rate's regulation, if carry out rapid cooling through modes such as opening furnace at the cooling in-process, can increase the danger that personnel are injured and equipment damages undoubtedly. Therefore, it is necessary to continue to develop a new method for producing a VNbMoTaW high-entropy alloy.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a preparation method of VNbMoTaW high-entropy alloy, which has the advantages of obviously reduced procedures, reduced cost and excellent density compared with the prior art, and the preparation method can obtain multi-element alloy with a single Body Centered Cubic (BCC) structure and the density of more than 99.5% by utilizing the traditional process of mechanical alloying and hot pressing sintering.

In order to solve the technical problems, the invention adopts the following technical scheme.

A preparation method of VNbMoTaW high-entropy alloy comprises the following steps:

(1) mechanical alloying method: mixing W, Mo, V, Nb and Ta elementary substance powder, performing ball milling without adding a ball milling medium (without a process control agent), wherein the adopted ball milling tank and the grinding balls are made of WC hard alloy to obtain VNbMoTaW high-entropy alloy powder which is in a single-phase or double-phase single-body-centered cubic structure;

(2) vacuum hot pressing sintering method: carrying out hot-pressing sintering on the VNbMoTaW high-entropy alloy powder under the protection of inert atmosphere, wherein the pressure is 30-50 MPa, the heating rate is 5-15 ℃/min, the heat preservation temperature is 1700-1900 ℃, and a VNbMoTaW high-entropy alloy block is obtained and has a single-phase single-body-centered cubic structure and the density is more than 99.5%.

Preferably, in the step (1), the ball-to-material ratio of the ball mill is 10: 1, the rotation speed of the ball mill is 300r/min, and the ball milling time is 15-55 h.

In the above VNbMoTaW high-entropy alloy production method, preferably, in the step (1), the amounts of the W, Mo, V, Nb, and Ta single substance powders are equal atomic ratios or non-equal atomic ratios close to equal atomic ratios, and the molar ratio of each element is W: Mo: V: Nb: Ta: a: b: c: d: e, where a, b, c, d, and e each independently take any value of [0.98,1.02 ].

In the above method for preparing the VNbMoTaW high-entropy alloy, preferably, in the step (1), the ball milling process is performed under the protection of an inert gas.

Preferably, in the step (2), the material of the die used for hot-pressing sintering is isostatic pressing three-high graphite, the heat preservation time of the hot-pressing sintering is 1-2 h, and the cooling mode is furnace cooling.

In the invention, the mixed powder in the step (1) is gradually alloyed in the high-energy ball milling process, and finally alloy powder with a single/double-phase BCC structure is formed.

Compared with the prior art, the invention has the advantages that:

the invention develops a technology of preparing alloy powder by mechanical alloying and hot-pressing sintering, which comprises two parts of preparing VNbMoTaW alloy powder by mechanical alloying and sintering the alloy powder into a VNbMoTaW high-entropy alloy block by adopting a hot-pressing sintering furnace, and the technical scheme has important significance for simplifying the preparation process of the alloy, reducing the oxidation probability of active alloy and preparing high-melting-point VNbMoTaW high-entropy refractory alloy by utilizing general industrial equipment:

(1) compared with the existing report of mechanical alloying and hot-pressing sintering, the technology reduces the use of a crucible while maintaining the high density of the prepared alloy, greatly reduces the pressure during sintering, and does not require a faster cooling speed any more. On the other hand, the use of the conventional crucible made of boron nitride or the like increases the cost for preparing the material. On the other hand, the limit pressure which can be applied by the hot-pressing sintering furnace which is generally used industrially is less than 100MPa, and the damage of the equipment can be caused by the excessive pressure. Moreover, conventional hot pressing fritting furnace all can't just carry out cooling speed's regulation, if carry out rapid cooling through modes such as opening furnace at the cooling in-process, can increase the danger that personnel are injured and equipment damages undoubtedly.

(2) Because W, Mo, V, Nb and Ta are high-melting point metals, the traditional melting method can melt the W, Mo, V, Nb and Ta only by heating to a high temperature of more than 3422 ℃, and simultaneously remelting is needed for multiple times to eliminate component segregation.

(3) Compared with the existing ' mechanical alloying powder + alloy powder presintering + Spark Plasma Sintering (SPS) ' mechanical alloying powder + high-pressure hot-pressing sintering ' process flow is simpler and equipment is more common and more practical, only two steps of ball milling and hot-pressing sintering are needed, so that the two simple steps can be used for preparing the material which can be prepared by multiple steps in the past, the oxidation probability of the active alloy and the preparation cost of the alloy are reduced, the density is obviously improved, and the mechanical property is excellent.

(4) As the refractory high-entropy alloy generally has the characteristics of stable structure at high temperature and room temperature and metastable structure in a medium temperature region (800-₂VO₆And the mechanical properties of the alloy are seriously deteriorated. The obtained VNbMoTaW has excellent thermodynamic stability through the design of the process and process details, and the structural transformation of the VNbMoTaW high-entropy alloy cannot be caused by furnace cooling in the hot-pressing sintering process, so that the final experimental result also confirms the point.

Drawings

FIG. 1 is an X-ray diffraction pattern of a VNbMoTaW high-entropy alloy prepared in example 1 of the invention.

FIG. 2 is an X-ray diffraction pattern of the VNbMoTaW high-entropy alloy prepared in example 2 of the invention.

FIG. 3 is an X-ray diffraction pattern of a VNbMoTaW high-entropy alloy prepared in example 3 of the invention.

FIG. 4 is an X-ray diffraction pattern of a VNbMoTaW high-entropy alloy prepared in example 4 of the invention.

FIG. 5 is an X-ray diffraction pattern of the VNbMoTaW high-entropy alloy prepared in example 5 of the invention.

FIG. 6 is an X-ray diffraction pattern of the VNbMoTaW high-entropy alloy prepared in example 6 of the invention.

FIG. 7 is a graph showing the die and hearth damage when VNbMoTaW high-entropy alloy is prepared according to comparative example 1 of the present invention.

FIG. 8 is a graph showing die damage when a VNbMoTaW high-entropy alloy is prepared according to comparative example 2 of the present invention.

FIG. 9 is a metallographic micrograph of a VNbMoTaW high entropy alloy prepared according to comparative example 3 of the present invention.

Detailed Description

The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.

The materials and equipment used in the following examples are commercially available.