CN108060322A - The preparation method of hard high-entropy alloy composite material - Google Patents

Abstract

The invention discloses a method for preparing a hard high-entropy alloy composite material, which comprises the following steps: (1) selecting superhard material powder and alloy element powder as raw materials, wherein the alloy element powder is selected from Fe powder and Co powder , Cr powder, Ni powder, Mn powder, and alloy powders composed of any three or more elements mentioned above; the superhard material powder is selected from one or more of WC alloy powder, BN powder, and diamond powder; ( 2) ball milling the raw materials selected in step (1) to obtain fine-grained powder; (3) subjecting the fine-grained powder to discharge plasma sintering and cooling with the furnace, and the resulting sintered block is a hard high-entropy alloy composite Material. The present invention uses high-entropy alloys with excellent plasticity such as FeCoCrNiMn as the matrix, and adds superhard particles such as WC and cubic BN as the reinforcing phase, which can make the product obtain high hardness while reducing the cost of hard high-entropy raw materials, and the density and density of the product. Difficulty of preparation.

Description

Preparation method of hard high-entropy alloy composite material

technical field

The invention belongs to the field of alloy materials, and in particular relates to a method for preparing hard high-entropy alloy composite materials by using a powder metallurgy method.

Background technique

Powder metallurgy tool steel has the advantages of high strength, high hardness and wear resistance, and is widely used in molds, cutting tools, rolls and other fields. However, because this type of material contains many types of alloying elements and the structure of carbides is complex, it is difficult to control the microstructure, phase structure and morphology of carbide particles. At the same time, due to the low plasticity and poor toughness of powder metallurgy tool steel, it is difficult to prepare and process tools and molds. By changing the matrix composition of tool steel, it is possible to improve its plasticity. High-entropy alloys also have high content of alloying elements, but relatively few types, simple phase structure and good toughness, so they can be used as potential matrix materials for tool steels. In addition, high-entropy alloys generally have the characteristics of high-temperature oxidation resistance. On the basis of high-entropy alloy components, by adding or in-situ precipitation of hard carbides, the development of tool and mold materials with high wear resistance, high toughness and high temperature oxidation resistance has very important engineering significance.

Hard high-entropy alloys in the prior art are mainly prepared from refractory metal elements, such as MoTaWNbV, WMoNbZr, TaNbVZr and the like. Although this type of high-entropy alloy also has high hardness, the cost of raw materials used is high, the material density is high, the material has a high melting point, and the preparation energy consumption is large, which poses challenges to the preparation equipment.

At present, the preparation of multi-principal high-entropy alloy bulk mainly adopts the method of vacuum melting. However, the melting point of hard materials is generally very high, and the melting method is difficult to melt, such as hard phases such as WC, and the energy consumption of the melting process is also large. In addition, thermal expansion and condensation will occur during the casting process, resulting in large internal stress in the as-cast high-entropy alloy block; moreover, the as-cast high-entropy alloy has a large grain size, significant internal composition segregation, and many defects such as voids and shrinkage cavities , which also affects the performance of cast high-entropy alloys; in addition, most of the cast high-entropy alloys are brittle, which limits the further application of the alloy. The powder metallurgy process has the advantages of short process flow, small equipment investment, and low energy consumption. Powder metallurgy process can prepare hard composite materials such as cemented carbide. Therefore, powder metallurgy technology is also one of the potential technologies for preparing hard high-entropy alloys. In the conventional powder metallurgy process, the molding process usually adopts the molding method, but there is friction between the powder and the mold wall during the molding process, and the hard particles have high hardness, so that the green body made by molding has a high porosity. However, the mechanical properties of the finished product are low; moreover, the sintering time after grinding and pressing is usually longer, and the structure growth phenomenon in the material is obvious, thereby reducing the mechanical properties of the material.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing hard high-entropy alloy composite materials by using powder metallurgy to overcome the deficiencies and defects mentioned in the above background technology.

In order to solve the problems of the technologies described above, the technical solution proposed by the present invention is:

A method for preparing a hard high-entropy alloy composite material, comprising the following steps:

(1) Superhard material powder and alloy element powder are selected as raw materials, wherein the alloy element powder is selected from Fe powder, Co powder, Cr powder, Ni powder, Mn powder and alloy powder composed of any three or more aforementioned elements; The superhard material powder is selected from one or more of WC alloy powder, BN powder, and diamond powder;

(2) ball milling the raw materials selected in step (1) to obtain fine-grained powder;

(3) The fine-grained powder is subjected to spark plasma sintering and cooled with the furnace, and the obtained sintered block is a hard high-entropy alloy composite material.

In the above preparation method, preferably, in the raw materials, the atomic content of the superhard material powder is not higher than 70%.

In the above preparation method, preferably, the particle size of the superhard material powder is -200 mesh to -600 mesh, and the particle size of the alloy element powder is -200 mesh to -300 mesh.

The above preparation method, preferably, in step (2), the ball milling process is carried out under the protection of an inert gas, the ball milling speed is 240-280r/min, the ball milling time is 5-10h, and the particle size of the matrix powder after ball milling is 30-40 μm.

In the above preparation method, preferably, in step (3), the pressure during the spark plasma sintering process is controlled to be 30MPa-40MPa, the sintering temperature is 900°C-1200°C, and the sintering holding time is 15min-30min.

In the above preparation method, preferably, in step (3), the spark plasma sintering is sintered with a graphite mold; the aspect ratio of the graphite mold is 1:8-1:1.

Compared with the prior art, the present invention has the advantages of:

(1) In the preparation method of the present invention, spark plasma sintering can be used to obtain high-density products, the sintering time is short, and the fine microstructure caused by the ball milling process can be retained, so that the material has higher mechanical properties; in addition, sintering The speed is fast, the degree of element diffusion in this process is low, and the added superhard material particles can be better retained in the matrix, thereby greatly improving the hardness of the material.

(2) The present invention adopts FeCoCrNiMn and other high-entropy alloys with excellent plasticity as the matrix, and adds superhard particles such as WC and cubic BN as the reinforcing phase, which can reduce the cost of hard high-entropy raw materials and products while obtaining very high hardness. Density and preparation difficulty.

(3) The present invention adopts substrates such as FeCoCrNiMn to have good plasticity, toughness and better high-temperature oxidation resistance, and the hard high-entropy alloy prepared has inherited the excellent characteristics of the substrate; the added superhard particles have significantly improved the material The hardness makes it have better overall performance than die steel.

Description of drawings

Fig. 1 is a process flow chart of the present invention for preparing hard high-entropy alloy composite materials.

Fig. 2 is the relationship curve of the change of hardness with the amount of carbide added in the high-entropy alloy composite material prepared in Example 1 of the present invention.

Fig. 3 is a SEM photo of the high-entropy alloy composite material prepared in Example 1 of the present invention.

Detailed ways

In order to facilitate the understanding of the present invention, the invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

Unless otherwise defined, all technical terms used hereinafter have the same meanings as commonly understood by those skilled in the art. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the protection scope of the present invention.

Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

Example 1:

A kind of preparation method of hard high entropy alloy composite material of the present invention, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Choose WC powder with a particle size of -280 mesh and alloy element powder (oxygen content less than 0.3%) with a particle size of -300 mesh as raw materials, the atomic ratio of WC powder and metal element powder is 3: 7, Fe in the metal element powder The atomic ratio of Cr powder, Ni powder, and Co powder is 1:1:1:1; among them, the alloy element powder does not contain other impurities except a small amount of unavoidable impurity oxygen, and the raw materials do not contain WC powder, Elemental components other than Fe powder, Cr powder, Ni powder, and Co powder;

(2) The raw material powder that step (1) is obtained is packed in the ball mill jar, adopts planetary ball mill and cemented carbide ball mill jar, ball mills at the speed of 250r/s 5 hours, obtains fine-grained powder, and ball mill process is in argon gas Carried out under the protection of the environment, the fine-grained powder with a particle size of about 3540 μm is obtained;

(3) The fine-grained powder obtained in step (2) is carried out to spark plasma sintering (using graphite mold sintering, the aspect ratio of graphite mold is 1:2), the pressure control in the spark plasma sintering process is 30MPa, and the sintering temperature is 1000℃, the heating rate is 100℃/min, the holding time is 15min, the sintering process is carried out under the protection of nitrogen atmosphere; the sintered block obtained after sintering is completed and cooled in the furnace is a hard high-entropy alloy composite material. Hard high-entropy alloy composite materials are processed by wire cutting to obtain hard powder metallurgy workpieces of various shapes to meet the needs of different products.

The product of this embodiment was tested by the drainage method, and the density of the hard high-entropy alloy composite material was measured to be 98%, and the hardness (Vickers) was 760HV (the test results are shown in Figure 2).

The SEM photo of the powder metallurgy hard high-entropy alloy composite material prepared in this embodiment is shown in Figure 3 (A in Figure 3 is a high-entropy phase; B is a tungsten carbide phase; C1 and C2 are chromium carbide phases), as shown in Figure 3 , the hard high-entropy alloy composite material prepared in this example has good compactness, relatively fine structure, uniform phase distribution, and superhard WC particles are well retained in the high-entropy matrix.

The tensile test elongation of the hard high-entropy alloy composite material is 9%, and the fracture toughness is 1324kJ/m ^{2 ;} after the sample is oxidized in air atmosphere at 973K for 4 hours, the mass of the sample increases to 0.0013mg/mm ² .

Example 2:

A kind of preparation method of hard high entropy alloy composite material of the present invention, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) choose particle size as -600 mesh cubic BN powder and particle size as -300 mesh alloy element powder (oxygen content is lower than 0.3%) as raw material, the atomic ratio of BN powder and metal element powder is 4: 6, in the metal element powder The atomic ratio of Fe powder, Cr powder, Ni powder and Co powder is 1:1:1:1; Among them, the alloy element powder does not contain other impurities except a small amount of unavoidable impurity oxygen, and the raw materials do not contain BN powder , Fe powder, Cr powder, Ni powder, Co powder other elemental components;

(2) The raw material powder that step (1) is obtained is packed in the ball mill jar, adopts planetary ball mill and cemented carbide ball mill jar, ball mills 7 hours under the speed of 240r/s, obtains fine-grained powder, and ball mill process is in argon gas Carried out under the protection of the environment to obtain a fine-grained powder with a particle size of about 35 μm;

(3) the fine-grained powder that step (2) makes is carried out spark plasma sintering (adopting graphite mold sintering, and the aspect ratio of graphite mold is 2:3), the pressure control in spark plasma sintering process is 40MPa, and sintering temperature is 1100°C, the heating rate is 130°C/min, the holding time is 20min, the sintering process is carried out under the protection of nitrogen atmosphere; the sintered block obtained after sintering is completed and cooled in the furnace is a hard high-entropy alloy composite material. Hard high-entropy alloy composite materials are processed by wire cutting to obtain hard powder metallurgy workpieces of various shapes to meet the needs of different products.

The product of this embodiment is tested by the drainage method, and the density of the hard high-entropy alloy composite material measured is 98%, the hardness (Vickers) 960HV, the elongation of the tensile test is 8%, and the fracture toughness is 1203kJ/m ^2. After the sample is oxidized in air atmosphere at 973K for 4 hours, the mass of the sample increases to 0.0017 mg/mm ² .

The hard high-entropy alloy composite material prepared in this example has good compactness, relatively fine structure, uniform phase distribution, and superhard BN particles are well retained in the high-entropy matrix.

Example 3:

A kind of preparation method of hard high entropy alloy composite material of the present invention, its process flow diagram as shown in Figure 1, comprises the following steps:

(1) Choose diamond powder with a particle size of -400 mesh and alloy element powder (oxygen content lower than 0.3%) as raw materials with a particle size of -300 mesh, the atomic ratio of diamond powder and metal element powder is 2: 8, Fe in the metal element powder The atomic ratio of Cr powder, Ni powder, and Co powder is 1:1:1:1; among them, the alloy element powder does not contain other impurities except a small amount of unavoidable impurity oxygen, and the raw materials do not contain diamond powder, Elemental components other than Fe powder, Cr powder, Ni powder, and Co powder;

(2) The raw material powder obtained in step (1) is packed into a ball mill jar, and ball milled at a speed of 260r/s for 6 hours by using a planetary ball mill and a cemented carbide ball mill jar to obtain a fine-grained powder. Carried out under the protection of the environment to obtain a fine-grained powder with a particle size of about 35 μm;

(3) The fine-grained powder obtained in step (2) is subjected to spark plasma sintering (sintering with a graphite mold, and the aspect ratio of the graphite mold is 1:2). The pressure during the spark plasma sintering process is controlled to 35MPa, and the sintering temperature is 1050°C, the heating rate is 150°C/min, the holding time is 25min, the sintering process is carried out under the protection of nitrogen atmosphere; the sintered block obtained after sintering is completed and cooled in the furnace is a hard high-entropy alloy composite material. Hard high-entropy alloy composite materials are processed by wire cutting to obtain hard powder metallurgy workpieces of various shapes to meet the needs of different products.

The product of this embodiment is tested by the drainage method, and the density of the hard high-entropy alloy composite material measured is 98%, the hardness (Vickers) 830HV, the elongation of the tensile test is 11%, and the fracture toughness is 1456kJ/m ² ; after the sample was oxidized in an air atmosphere at 973K for 4 hours, the mass increase of the sample was 0.0011 mg/mm ² .

The hard high-entropy alloy composite material prepared in this example has good compactness, relatively fine structure, uniform phase distribution, and superhard diamond particles are well retained in the high-entropy matrix.

Claims (6)

1. a preparation method of hard high-entropy alloy composite material, is characterized in that, comprises the following steps: (1) Superhard material powder and alloy element powder are selected as raw materials, wherein the alloy element powder is selected from Fe powder, Co powder, Cr powder, Ni powder, Mn powder and alloy powder composed of any three or more aforementioned elements; The superhard material powder is selected from one or more of WC alloy powder, BN powder, and diamond powder; (2) ball milling the raw materials selected in step (1) to obtain fine-grained powder; (3) The fine-grained powder is subjected to spark plasma sintering and cooled with the furnace, and the obtained sintered block is a hard high-entropy alloy composite material. 2. The preparation method according to claim 1, characterized in that, in the raw materials, the molar content of superhard material powder is not higher than 70%. 3. The preparation method according to claim 1, wherein the particle size of the superhard material powder is -200 mesh to -600 mesh, and the particle size of the alloy element powder is -200 mesh to -300 mesh. 4. The preparation method according to claim 1, characterized in that, in step (2), the ball milling process is carried out under the protection of an inert gas, the ball milling speed is 240～280r/min, the ball milling time is 5～10h, the matrix after ball milling The particle size of the powder is 30-40 μm. 5. The preparation method according to any one of claims 1 to 4, characterized in that, in step (3), the pressure in the spark plasma sintering process is controlled to be 30MPa to 40MPa, the sintering temperature is 900°C to 1200°C, and the sintering The holding time is 15min to 30min. 6. The preparation method according to any one of claims 1 to 4, characterized in that, in step (3), spark plasma sintering adopts graphite mold sintering; the aspect ratio of the graphite mold is 1:8～1: 1.