Preparation method of high-hardness wc / covtib high-entropy alloy composite material

Abstract

The application discloses a preparation method of high-hardness WC / CoVTiB high-entropy alloy composite material and belongs to the technical field of alloy materials. The composite material is composed of WC reinforcing phase and CoVTiB high-entropy alloy, the WC reinforcing phase is dispersedly distributed in the CoVTiB high-entropy alloy matrix, and the components in the composite material are as follows: WC 60-70%, Co 10-15%, V 3-5%, Ti 4-7% and B 13-17%. The WC content in the composite material can reach 60-70%, through twice discharge plasma sintering processes and parameter control, part of W and C in the WC enters into the alloy melt, the reinforcing phase WC is metallurgically combined with the alloy matrix, and the hardness, wear resistance and other performances of the material are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, specifically to a method for preparing a high-hardness WC / CoVTiB high-entropy alloy composite material. Background Technology

[0002] High-entropy alloys, as a new research hotspot in the field of materials science, offer significant improvements in mechanical, chemical, and physical properties compared to traditional alloys. These improvements include high strength, high hardness, and excellent wear and corrosion resistance, making them a focus of research in powder metallurgy. High-entropy alloys, also known as multi-principal-element alloys, are composed of four or more elements, and their final properties are determined by the combined effects of these multiple principal elements. Although high-entropy alloys have a large number of constituent elements, they often form relatively simple phase structures after solidification. Randomly miscible solid solutions are typical microstructures of high-entropy alloys, including face-centered cubic (FCC), body-centered cubic (BCC), or hexagonal close-packed (HCP) structures, such as... Figure 1 As shown, due to the different atomic sizes added, severe distortion occurs in the crystal lattice, resulting in a strong solid solution strengthening effect, which brings advantages such as high strength and excellent wear resistance. However, compared with wear-resistant steel, wear-resistant ceramics, and other materials, there is still considerable room for improvement in terms of hardness and wear resistance.

[0003] In recent years, metal matrix composites have received considerable attention and development, and their combination with multi-principal-element high-entropy alloys has become a new research direction. High-entropy alloy matrix composites have simple crystal structures and do not contain other complex phases in their microstructure. They combine the excellent properties of reinforcing phases and high-entropy alloy matrices, making them highly valuable for scientific research and widely used in cutting tools, grinding wheels, and other fields.

[0004] Currently reported bulk high-entropy alloy composites are mainly prepared using arc melting technology. However, high-entropy alloys prepared using this technology typically have non-equilibrium structures and suffer from defects such as shrinkage cavities, porosity, and compositional segregation. These require lengthy homogenization annealing and subsequent thermomechanical treatments, resulting in high costs. Furthermore, the low-melting-point Al element is easily burned off during the melting process, making precise control of the alloy composition difficult.

[0005] There are also reports of using the self-propagating high-temperature synthesis (SHS) method to prepare bulk high-entropy alloy composites. The basic principle is to thoroughly mix the reinforcing phase components with metal powder in a certain proportion, press them into a compact, and ignite them in a vacuum or inert atmosphere using a tungsten wire preheating process. This ignites the mixture, causing a chemical reaction between the components. The released heat spreads, causing unreacted adjacent parts to continue burning until the reaction is complete, thus obtaining the bulk high-entropy alloy composite. This method is simple to produce, reacts rapidly, consumes little heat, and produces high-purity products. However, due to the fast reaction rate and large temperature gradient during synthesis, the reaction is difficult to control, resulting in high porosity and low density in the product. It is also prone to defect concentration and non-equilibrium transition phases, which increase the product's activity.

[0006] In summary, there is an urgent need to develop a low-cost, high-density, high-hardness, and wear-resistant high-entropy alloy composite material. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a high-hardness WC / CoVTiB high-entropy alloy composite material, the prepared composite material having excellent hardness and wear resistance.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A high-hardness WC / CoVTiB high-entropy alloy composite material is prepared using spark plasma sintering (SPS) technology, specifically including the following steps:

[0010] (1) Weigh each raw material according to the composition of the composite material. The raw materials are WC powder, Co powder, V powder, Ti powder and B powder. After mixing the raw materials, place them in a planetary ball mill for ball milling to obtain a mixed reaction material.

[0011] (2) The mixed reactants are fed into a graphite mold and pre-pressed into a block blank;

[0012] (3) Place the graphite mold containing the block blank into the heating cavity of the discharge plasma sintering furnace, then add the upper and lower heating punches, pass current through the blank in the cavity to perform plasma discharge, the current flows through the sintered powder and generates instantaneous high temperature at the contact part of the powder particles, until the blank powder reaches a semi-molten state (paste-like) and the discharge stops, take it out and cool (air cool) to obtain the material ingot.

[0013] (4) The material ingot is put back into the heating cavity of the discharge plasma sintering furnace, and current is passed through to perform plasma discharge to make it reach the melting state. The heating is continued until the temperature is 2850-2950℃, then the discharge is stopped, and the ingot is taken out and cooled (air cooling) to obtain the ingot of the WC / CoVTiB high entropy alloy composite material.

[0014] (5) The sample obtained in step (4) is cooled (air-cooled) after solution treatment to obtain the ingot of the WC / CoVTiB high-entropy alloy composite material; the ingot of the WC / CoVTiB high-entropy alloy composite material is then machined to obtain the composite material product required by the design.

[0015] In step (1) above, the components (raw materials) in the composite material are as follows by atomic percentage: WC 60-70%, Co 10-15%, V 3-5%, Ti 4-7%, B 13-17%.

[0016] The ball milling process in step (1) above is carried out in a planetary ball mill for 10-12 hours. The abrasive used in the ball mill is alumina ceramic balls. The ball-to-material ratio is (2-3):1. The rotation speed of the planetary ball mill is 50-65 r / min.

[0017] In step (3) above, the applied pressure is 35-50 MPa, the sintering atmosphere is argon, and the heating rate is 60-80 °C / min.

[0018] In step (4) above, the applied pressure is 15-25 MPa, the sintering atmosphere is argon, and the heating rate is 10-20 °C / min.

[0019] The solution treatment temperature in step (5) above is 2650-2700℃, and the treatment time is 45-50min.

[0020] The prepared WC / CoVTiB high-entropy alloy composite material is composed of WC reinforcing phase and CoVTiB high-entropy alloy, with the WC reinforcing phase dispersed in the CoVTiB high-entropy alloy matrix.

[0021] The CoVTiB high-entropy alloy matrix of this composite material includes a BCC phase solid solution, a Co3Ti phase, a TiC phase, and an in-situ generated TiB2 phase.

[0022] The advantages and beneficial effects of this invention are as follows:

[0023] 1. This invention adds element B to a high-entropy alloy matrix and optimizes the proportion of each component so that the addition of element B can greatly improve the high temperature resistance and corrosion resistance of the alloy, especially improve the density of the high-entropy alloy.

[0024] 2. The alloy matrix of the WC / CoVTiB high-entropy alloy composite material of this invention mainly consists of BCC phase solid solution, Co3Ti phase, and in-situ generated TiB2 phase. This phase composition improves the oxidation resistance, corrosion resistance, microhardness, and wear resistance of the composite material.

[0025] 3. In the WC / CoVTiB high-entropy alloy composite material of the present invention, as the WC content increases, the BCC phase solid solution content in the matrix increases, the microstructure is refined, the average microhardness of the composite material increases, and the wear resistance is improved.

[0026] 4. When the WC / CoVTiB high-entropy alloy composite material of this invention is prepared using conventional processes such as electric arc melting and laser cladding, cracks and cracking tendencies appear after the WC content increases to 15%, which in turn affects the overall hardness improvement of the material. However, in this invention, the WC content can reach 60-70%. Through two discharge plasma sintering processes and parameter control, some W and C in the WC enter the alloy melt, so that the reinforcing phase WC forms a metallurgical bond with the alloy matrix, and greatly improves the hardness, wear resistance and other properties of the material. Attached Figure Description

[0027] Figure 1 It is a phase structure of a high-entropy alloy.

[0028] Figure 2 The image shows the XRD pattern of the bulk composite material prepared in Example 1.

[0029] Figure 3 Metallographic photograph of the blocky composite material prepared in Example 1.

[0030] Figure 4 The dry sliding wear surface morphology of the blocky composite material prepared in Example 1. Detailed Implementation

[0031] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0032] Example 1:

[0033] The specific process for preparing the WC / CoVTiB high-entropy alloy composite material in this embodiment is as follows:

[0034] 1. The components of this composite material are designed as follows, in atomic percentage: WC 65%, Co 12%, V 4%, Ti 5%, B 15%.

[0035] 2. The composite material is prepared using spark plasma sintering (SPS) technology. The raw materials are weighed according to the composition of the composite material. The raw materials are WC powder, Co powder, V powder, Ti powder, and B powder. After mixing, the raw materials are placed in a planetary ball mill for ball milling to obtain a mixed reaction material. The ball milling process is carried out in a planetary ball mill for 12 hours. The abrasive used in the ball mill is alumina ceramic balls. The ball-to-material ratio is 2.5:1, and the planetary ball mill speed is 60 r / min.

[0036] 3. The mixed reactants are fed into a graphite mold and pre-pressed into a block-shaped blank;

[0037] 4. Place the graphite mold containing the block-shaped blank into the heating cavity of the discharge plasma sintering furnace, then add upper and lower heating punches to pass current through the blank in the cavity for plasma discharge. During discharge plasma sintering, the applied pressure is 40 MPa, the sintering atmosphere is argon, and the heating rate is 75℃ / min. The current flowing through the sintering powder generates instantaneous high temperatures at the contact points between the powder particles. Discharge is stopped when the blank powder reaches a semi-molten, paste-like state. After removal, air cooling is performed to obtain the material ingot.

[0038] 5. The material ingot is placed back into the heating cavity of the discharge plasma sintering furnace, and current is passed through it to perform plasma discharge until it reaches a molten state. Heating continues until the temperature reaches 2900℃, then the discharge is stopped, and the ingot is removed and air-cooled. During discharge plasma sintering, the applied pressure is 20MPa, the sintering atmosphere is argon, and the heating rate is 15℃ / min. After cooling, the ingot of the WC / CoVTiB high-entropy alloy composite material is obtained and removed.

[0039] 6. The obtained sample is subjected to solution treatment at a temperature of 2680℃ for 45-50 minutes. After air cooling, the ingot of the WC / CoVTiB high-entropy alloy composite material is obtained.

[0040] The blocky composite material sample prepared in this embodiment was polished after being cut by electrical discharge machining. Its phase composition was analyzed by X-ray diffraction (XRD). After the sample surface was etched with aqua regia, its microstructure was analyzed by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS).

[0041] In the preparation process of the block composite material in this embodiment, the block blank is first sintered by spark plasma to reach a semi-molten state. At this time, the raw material powders are wetted, and under the pressure applied to the block blank, the gaps between the powders are reduced, thereby increasing its density.

[0042] During the second sintering process using spark plasma to reach the molten state, the WC particles partially melt in the alloy melt, and some carbon and tungsten elements enter the alloy solution. After solidification, they form an alloy composite material reinforced with WC particles. At the same time, some of the carbon and tungsten elements that entered the melt combine with other elements in the alloy. Figure 2 The XRD pattern of the composite material sample is shown below. Figure 2 It can be seen that, in addition to the diffraction peaks of β-Ti (BCC) and WC, the sample also shows TiC, Co3Ti (FCC) phases, and in-situ generated TiB2 phase. The FCC and BCC phases are typical equilibrium-stable phase compositions, while high-entropy alloy composites prepared using conventional arc melting technology are generally metastable phases and exhibit compositional segregation. Furthermore, when preparing the composite material of this embodiment using conventional arc melting technology, the material cracked due to the large amount of WC added.

[0043] The Co3Ti phase exhibits high oxidation and corrosion resistance, as well as good toughness. The addition of boron refines the dendritic structure and induces in-situ, dispersed TiB2 formation in the alloy matrix. Simultaneously, the appropriate amount of boron gradually increases the proportions of the BCC and TiB2 phases, thus improving the microhardness and wear resistance of the composite material. The Vickers hardness of the alloy was tested using an HV-1000 Vickers hardness tester. The test load was 300 N, the holding time was 15 s, and five tests were performed, with the average value taken. The test results show that the average microhardness of the composite material in this embodiment reaches 950 HV.

[0044] Figure 3 The microstructure of the composite material in this embodiment shows that the WC and TiB2 phases are uniformly distributed in the matrix.

[0045] Tests showed that the wear rate of this composite material was less than 10% within a temperature range from room temperature to 800°C. -6 mm 3 / Nm. The wear mechanism was studied. Figure 4 The wear track morphology of the composite material after a friction test at 600℃ is shown in photographs. It can be seen that the worn surface is relatively smooth without obvious grooves. This is because the hard WC particles prevent wear on the matrix, and because the WC particles are firmly bonded to the matrix, under high contact stress, the matrix transfers the carrier to the wear-resistant WC particles, thus avoiding wear and effectively preventing brittle detachment. Observation of the wear tracks after friction tests at 200, 400, and 800℃ shows that temperature has little effect on wear. That is, the strong bond between the high-hardness WC particles and the tough matrix plays a crucial role in improving resistance to cutting and adhesive wear.

[0046] In addition, the FCC phase in the composite material gives the alloy good plasticity and toughness, while the large amount of BCC phase endows the material with excellent strength. The combined effect of the FCC phase and BCC phase makes the composite material exhibit good comprehensive mechanical properties.

Claims

1. A method for preparing a high-hardness WC / CoVTiB high-entropy alloy composite material, characterized in that: This method involves preparing the WC / CoVTiB high-entropy alloy composite material using spark plasma sintering (SPS) technology, and includes the following steps: (1) Weigh each raw material according to the composition of the composite material. The raw materials are WC powder, Co powder, V powder, Ti powder and B powder. After mixing the raw materials, place them in a planetary ball mill for ball milling to obtain mixed reaction material. The raw materials for preparing the composite material are: WC 60-70%, Co 10-15%, V 3-5%, Ti 4-7%, B 13-17% by atomic percentage. (2) The mixed reactants are fed into a graphite mold and pre-pressed into a block-shaped blank; (3) Place the graphite mold containing the block blank into the heating cavity of the discharge plasma sintering furnace, and then add the upper and lower heating punches to pass current through the blank in the cavity to perform plasma discharge. The current flows through the sintering powder and generates instantaneous high temperature at the contact part of the powder particles. Stop the discharge when the blank powder reaches a semi-molten state. After taking it out, air cool to obtain the material ingot. In the discharge plasma sintering, the applied pressure is 35-50MPa, the sintering atmosphere is argon, and the heating rate is 60-80℃ / min. (4) The material ingot is put back into the heating mold cavity of the discharge plasma sintering furnace, and current is passed through to perform plasma discharge to make it reach the melting state. The heating is continued until the temperature is 2850-2950℃, then the discharge is stopped and the ingot is taken out. In the discharge plasma sintering, the pressure applied is 15-25MPa, the sintering atmosphere is argon, and the heating rate is 10-20℃ / min. (5) The sample obtained in step (4) is subjected to solution treatment and then air-cooled to obtain the ingot of the WC / CoVTiB high-entropy alloy composite material; the ingot of the WC / CoVTiB high-entropy alloy composite material is then machined to obtain the composite material product required by the design.

2. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 1, characterized in that: Step (1) The ball milling process is carried out in a planetary ball mill for 10-12 hours. The abrasive used in the ball mill is alumina ceramic balls. The ball-to-material ratio is (2-3):

1. The rotation speed of the planetary ball mill is 50-65 r / min.

3. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 1, characterized in that: The solution treatment temperature in step (5) is 2650-2700℃, and the treatment time is 45-50 min.

4. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 1, characterized in that: The composite material is composed of a WC reinforcing phase and an CoVTiB high-entropy alloy, with the WC reinforcing phase dispersed in the CoVTiB high-entropy alloy matrix.

5. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 4, characterized in that: The CoVTiB high-entropy alloy matrix of this composite material includes a BCC phase solid solution, a Co3Ti phase, and an in-situ generated TiB2 phase.

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