Wc / covtib high-entropy alloy composite material and preparation method thereof

Abstract

The application discloses a WC / CoVTiB high-entropy alloy composite material and a preparation method thereof, and belongs to the technical field of alloy materials.The composite material is composed of a WC reinforcing phase and a CoVTiB high-entropy alloy, the WC reinforcing phase is dispersedly distributed in the CoVTiB high-entropy alloy matrix, and the composite material comprises the following components: 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 a twice-discharge plasma sintering process and parameter control, part of W and C in the WC enters into an 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 WC / CoVTiB high-entropy alloy composite material and its preparation method. 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] Therefore, there is an urgent need to develop a high-entropy alloy composite material with low cost, high density, excellent hardness and wear resistance. SUMMARY

[0007] The application aims to provide a WC / CoVTiB high-entropy alloy composite material and a preparation method thereof.

[0008] To achieve the above-mentioned purpose, the technical solution adopted by the application is as follows:

[0009] A WC / CoVTiB high-entropy alloy composite material is composed of a WC reinforcing phase and a CoVTiB high-entropy alloy, and the WC reinforcing phase is dispersedly distributed in the CoVTiB high-entropy alloy matrix.

[0010] In the composite material, the components are as follows in terms of atomic percentage: WC 60-70%, Co 10-15%, V 3-5%, Ti 4-7%, and B 13-17%.

[0011] In the CoVTiB high-entropy alloy matrix of the composite material, there are a BCC phase solid solution, a Co3Ti phase, a TiC phase, and an in-situ generated TiB2 phase.

[0012] The WC / CoVTiB high-entropy alloy composite material is prepared by using a spark plasma sintering (SPS) technology, and the preparation method specifically includes the following steps:

[0013] (1) The raw materials are weighed according to the component composition of the composite material, and the raw materials are WC powder, Co powder, V powder, Ti powder, and B powder; the raw materials are mixed and then placed in a planetary ball mill for ball milling to obtain a mixed reaction material;

[0014] (2) The mixed reaction material is put into a graphite mold to be pre-pressed into a block-shaped blank;

[0015] (3) The graphite mold containing the block-shaped blank is placed in a heating mold cavity of a spark plasma sintering furnace, and upper and lower heating punches are added; an electric current is passed to the blank in the cavity to perform plasma discharge; the current flows through the sintering powder to generate a momentary high temperature at the contact part of the powder particles; when the blank powder reaches a semi-melted state (paste-like), the discharge is stopped, and the material ingot is obtained after cooling (air cooling);

[0016] (4) The material ingot is put into the heating mold cavity of the spark plasma sintering furnace again, an electric current is passed to perform plasma discharge to make it reach a molten state; the heating is continued until the temperature reaches 2850-2950℃, then the discharge is stopped, and the WC / CoVTiB high-entropy alloy composite material ingot is obtained after cooling (air cooling);

[0017] (5) the sample obtained in step (4) is subjected to solid solution treatment and then cooled (air cooling) to obtain a WC / CoVTiB high-entropy alloy composite ingot; the WC / CoVTiB high-entropy alloy composite ingot is subjected to mechanical processing to obtain a composite product required by design.

[0018] The ball milling process in step (1) is carried out in a planetary ball mill, the ball milling time is 10-12 h, the abrasive in the ball milling is an alumina ceramic ball, the ball-to-material ratio is 2-3:1, and the rotation speed of the planetary ball mill is 50-65 r / min.

[0019] In the spark plasma sintering in step (3), the applied pressure is 35-50 MPa, the sintering atmosphere is argon, and the heating rate is 60-80 ℃ / min.

[0020] In the spark plasma sintering in step (4), the applied pressure is 15-25 MPa, the sintering atmosphere is argon, and the heating rate is 10-20 ℃ / min.

[0021] In the solid solution treatment in step (5), the temperature is 2650-2700 ℃, and the treatment time is 45-50 min.

[0022] The advantages and beneficial effects of the present application are as follows:

[0023] 1. In the present application, B element is added to the high-entropy alloy matrix, and the proportion of each component is optimized, so that the addition of B element can greatly improve the high-temperature resistance and corrosion resistance of the alloy, especially the compactness of the high-entropy alloy.

[0024] 2. The alloy matrix of the WC / CoVTiB high-entropy alloy composite material in the present application mainly has a BCC phase solid solution, a Co3Ti phase and an 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 in the present application, as the content of WC increases, the content of the BCC phase solid solution 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 in the present application is prepared by conventional arc melting and laser cladding processes, cracks and cracking tendency occur when the content of WC increases to 15%, which further affects the improvement of the overall hardness of the material; in the present application, the content of WC can reach 60-70%, and through the two processes of spark plasma sintering and parameter control, part of W and C in WC enters the alloy melt, so that the reinforcing phase WC and the alloy matrix form a metallurgical bond, and the hardness, wear resistance and other properties of the material are greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The phase structure of the high-entropy alloy.

[0028] Figure 2 XRD spectrum of the bulk composite prepared in Example 1.

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

[0030] Figure 4 Dry sliding wear surface morphology of the bulk composite prepared in Example 1. DETAILED DESCRIPTION

[0031] In order to further understand the present application, the present application is described below in conjunction with examples, but the examples are only for further elaboration of the features and advantages of the present application, and are not a limitation on the claims of the present application.

[0032] Example 1:

[0033] The process of preparing the WC / CoVTiB high-entropy alloy composite in this example is as follows:

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

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

[0036] 3. The mixed reaction material is put into a graphite mold to be pre-pressed into a bulk blank.

[0037] 4. The graphite mold containing the bulk blank is placed in the heating cavity of the spark plasma sintering furnace, and upper and lower heating punches are added. The blank in the cavity is connected to an electric current, and plasma discharge is carried out. In the spark plasma sintering process, the applied pressure is 40 MPa, the sintering atmosphere is argon, and the heating rate is 75℃ / min. The current flows through the sintered powder to generate a high temperature at the contact points of the powder particles. When the blank powder reaches a semi-melted state like a paste, the discharge is stopped, and the blank is taken out for air cooling to obtain the material ingot.

[0038] 5, the material ingot is put into the heating mold cavity of the discharge plasma sintering furnace again, current is passed to make it reach the molten state, and then heating is continued until the temperature is 2900 DEG C, the discharge is stopped, and the ingot is taken out and air-cooled; in the discharge plasma sintering, the applied pressure is 20 MPa, the sintering atmosphere is argon, and the temperature rising rate is 15 DEG C / min. The ingot of the WC / CoVTiB high-entropy alloy composite material is obtained after being taken out and cooled;

[0039] 6, the obtained sample is subjected to solid solution treatment, the solid solution treatment temperature is 2680 DEG C, the treatment time is 45-50 min, and after air cooling, the ingot of the WC / CoVTiB high-entropy alloy composite material is obtained.

[0040] The blocky composite material sample prepared in the embodiment is polished after being cut by electric spark, the phase composition is analyzed by X-ray diffractometer (XRD), and the microstructure is analyzed by scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) after the sample surface is etched by aqua regia.

[0041] In the preparation process of the blocky composite material in the embodiment, the blocky blank is first subjected to discharge plasma sintering to reach a semi-molten state, at this time, the powders are in a wet state, and under the condition of applying pressure to the blocky blank, the gaps between the powders are reduced, and the density is increased.

[0042] When the discharge plasma sintering is used for the second time to reach the molten state, the WC particles partially dissolve in the alloy melt, part of the carbon and tungsten elements enter the alloy solution, and after solidification, the alloy composite material reinforced by WC particles is formed, and part of the carbon and tungsten elements in the melt combine with other elements in the alloy. Figure 2 The XRD spectrum of the composite material sample is shown in the following figure: Figure 2 As can be seen, in addition to the diffraction peaks of β-Ti (BCC) and WC, TiC, Co3Ti phase (FCC) and in-situ generated TiB2 phase also appear in the sample. The composition of the FCC phase and the BCC phase is a typical equilibrium stable phase composition, while the high-entropy alloy composite material prepared by conventional arc melting technology is generally a metastable phase and has composition segregation. In addition, when the composite material in the embodiment is prepared by conventional arc melting technology, the prepared material cracks due to the large amount of WC added.

[0043] Co3Ti phase has high oxidation resistance and corrosion resistance, and has good toughness. The addition of B refines the dendritic structure and generates TiB2 dispersedly in the alloy matrix. The addition of proper amount of B makes the BCC phase and TiB2 phase gradually increase, and the microhardness and wear resistance of the composite material are also improved. The Vickers hardness of the alloy is tested by HV-1000 Vickers hardness tester, the load is 300N, the pressure holding time is 15s, and the test is repeated 5 times to take the average value. The test results show that the average microhardness of the composite material in this embodiment reaches 950HV.

[0044] Figure 3 For the microstructure of the composite material in this embodiment, it can be seen that WC and TiB2 phases are uniformly distributed in the matrix.

[0045] The test shows that the wear rate of the composite material is less than 10 -6 mm 3 / N.m in the range of room temperature to 800℃. Figure 4 The wear scar morphology photo of the composite material after friction test at 600℃ is given, it can be seen that the wear surface is relatively flat and there is no obvious groove. This is because the WC hard particles block the wear of the matrix, and at the same time, the WC particles and the matrix are firmly combined as a whole, so that the matrix is transferred to the wear-resistant WC particles under high contact stress to avoid wear and effectively avoid brittle falling. The observation of wear scar after friction test at 200, 400 and 800℃ shows that the temperature has little effect on wear. That is, the firm combination between high hardness WC particles and ductile matrix plays a key role in improving the cutting resistance and anti-adhesive wear.

[0046] In addition, the FCC phase in the composite material makes the alloy have good plasticity and toughness, and a large amount of BCC phase endows the material with excellent strength, and the comprehensive action of FCC phase and BCC phase makes the composite material exhibit good comprehensive mechanical properties.

Claims

1. A WC / CoVTiB high-entropy alloy composite material, characterized in that: The composite material is composed of WC reinforcing phase and CoVTiB high-entropy alloy, and the WC reinforcing phase is dispersedly distributed in the CoVTiB high-entropy alloy matrix. In the composite material, the components are as follows in terms of atomic percentage: WC 60-70%, Co 10-15%, V 3-5%, Ti 4-7%, and B 13-17%. In the CoVTiB high-entropy alloy matrix of the composite material, there are a BCC phase solid solution, a Co3Ti phase, and an in-situ generated TiB2 phase.

2. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 1, characterized in that: The method is for preparing the WC / CoVTiB high-entropy alloy composite material by using a spark plasma sintering technology, and the method comprises the following steps: (1) The raw materials are weighed according to the component composition of the composite material, and the raw materials are WC powder, Co powder, V powder, Ti powder, and B powder; the raw materials are mixed and then placed in a planetary ball mill for ball milling to obtain mixed reaction materials; (2) The mixed reaction materials are put into a graphite mold to be pre-pressed into a block-shaped blank; (3) The graphite mold containing the block-shaped blank is placed in a heating mold cavity of a spark plasma sintering furnace, and then upper and lower heating punches are added; the blank in the cavity is connected to a current to generate plasma discharge; the current flows through the sintering powder to generate a transient high temperature at the contact position of the powder particles; the discharge is stopped when the blank powder reaches a semi-melted state, and the blank is taken out and air-cooled to obtain a material ingot; (4) The material ingot is put into the heating mold cavity of the spark plasma sintering furnace again, and a current is connected to generate plasma discharge to reach a molten state; the heating is continued until the temperature reaches 2850-2950℃, and then the discharge is stopped; (5) The sample obtained in step (4) is subjected to solid solution treatment and then air-cooled to obtain a WC / CoVTiB high-entropy alloy composite material ingot; the WC / CoVTiB high-entropy alloy composite material ingot is machined to obtain a composite material product that meets the design requirements.

3. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 2, characterized in that: The ball milling process in step (1) is carried out in a planetary ball mill, and the ball milling time is 10-12h; the abrasive in the ball milling is alumina ceramic beads; the bead-to-material ratio is 2-3:1; and the rotation speed of the planetary ball mill is 50-65r / min.

4. The preparation method of the WC / CoVTiB high-entropy alloy composite material according to claim 2, characterized in that: In the spark plasma sintering in step (3), the applied pressure is 35-50MPa, the sintering atmosphere is argon, and the heating rate is 60-80℃ / min.

5. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 2, characterized in that: In the spark plasma sintering in step (4), the applied pressure is 15-25MPa, the sintering atmosphere is argon, and the heating rate is 10-20℃ / min.

6. The method for preparing the WC / CoVTiB high-entropy alloy composite material according to claim 2, characterized in that: In step (5), the solid solution treatment temperature is 2650-2700℃, and the treatment time is 45-50min.

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