Endogenous carbide in-situ reinforced refractory high-entropy alloy and preparation method thereof

Abstract

The invention relates to the technical field of high-entropy alloy and powder metallurgy, in particular to an endogenous carbide in-situ reinforced refractory high-entropy alloy and a preparation method thereof. The refractory high-entropy alloy comprises the following chemical components: nano graphite powder and metal powder of Nb, Ta, Mo and W with equal molar ratio; the grain size of the Nb, Ta, Mo and W metal powder is 1-4 microns; the particle size of the nano graphite powder is 0.01 to 0.02 mu m; the atomic ratio of the nano graphite powder to the Nb, Ta, Mo and W metal powder is 0.05 to 0.75. According to the invention, mechanical alloying and spark plasma sintering technologies are adopted, so that alloying of high-melting-point Nb, Ta, Mo and W in a solid state is realized, and a multi-phase structure of a carbide phase and a metal alloy phase is formed under the spark plasma sintering technology. The carbide in-situ reinforced refractory high-entropy alloy not only has relatively high fracture toughness and relatively high hardness, but also has high wear resistance, in addition, the sintering time is short, the sintering temperature is low, and energy consumption is reduced.

Description

Technical Field

[0001] The present invention relates to the technical fields of high-entropy alloys and powder metallurgy, and particularly relates to a refractory high-entropy alloy with in-situ enhanced carbide and a preparation method thereof. Background Art

[0002] The high-degree mixing of multi-principal metal elements results in a high-entropy effect in the microstructure where various metal atoms are mixed with each other. The extremely high degree of disorder of various metal atoms generated by the high-entropy effect directly leads to a decrease in the Gibbs free energy of the atomic system in the microstructure, enabling the mutual diffusion of metal atoms and effectively preventing the formation of other phases in the alloy, thus forming a solid solution with a single simple crystal structure. The solid solution strengthening effect contained in a large number of reaction-generated saturated and supersaturated solid solutions, as well as the combined action of its various constituent alloy elements, can multiply the performance of the alloy. Nowadays, the performance of such high-entropy alloys has been deeply studied and it has been fully proven that their various performances far exceed those of ordinary alloys.

[0003] With the development of various advanced industrial technologies, traditional alloys have become difficult to meet more stringent working environments, especially in ultra-high temperature fields with service temperatures exceeding 1800°C. Refractory high-entropy alloys have attracted extensive attention from researchers due to their outstanding properties such as high strength at room temperature, high wear resistance, high corrosion resistance, and high temperature resistance (high melting point, high temperature strength, high temperature thermal stability, etc.), exceeding the service temperature limit of currently studied high-performance nickel-based superalloys. Moreover, such refractory high-entropy alloys have extensive applications in ultra-high temperature fields such as aerospace, nuclear energy, and metallurgy. NbTaMoW with a body-centered cubic (BCC) structure is a type of widely studied high-entropy alloy, which still has high strength at 1600°C and is an excellent high-temperature resistant material. However, its low hardness and high brittleness limit its development and application, and its room temperature hardness is only 445HV.

[0004] Currently, in the literature, it is mainly prepared by arc melting. However, due to the high melting point of the alloy (2904°C), the preparation conditions are high, and the alloy material needs to be remelted repeatedly, resulting in high energy consumption, large grain size of the obtained grain structure, and low performance. The authorized patent CN112831709 B uses metal Ni element as a solid solution atom to improve the performance of NbMoTaW refractory high-entropy alloy. However, only using metal elements as strengthening elements and preparing alloy materials by melting method has the disadvantages of high energy consumption and limited performance improvement. Some are prepared by powder metallurgy technology. For example, the authorized patent CN114774717 B uses nano-zirconia ceramic phase to strengthen NbMoTaW refractory high-entropy alloy. However, only through the simple combination of ceramic strengthening phase and metal phase, the performance improvement is limited (hardness: 593.5 - 719.3HV).

[0005] The above content is only used to assist in understanding the technical solution of the present invention, and does not represent an admission that the above content is the closest prior art. Summary of the Invention

[0006] In order to solve the problems of high energy consumption and limited performance improvement in the preparation process of NbTaMoW refractory high-entropy alloys, the present invention provides a refractory high-entropy alloy with in-situ enhanced carbide and its preparation method.

[0007] To achieve the above object, the technical solution of the present invention is realized as follows. A refractory high-entropy alloy with in-situ enhanced carbide and its preparation method. The chemical composition of the refractory high-entropy alloy includes: nano-graphite powder and Nb, Ta, Mo, W metal powders with equimolar ratios; the atomic ratio of the nano-graphite powder to the Nb, Ta, Mo, W metal powders is 0.05 - 0.75.

[0008] Preferably, the purity of the Nb, Ta, Mo, W metal powders is greater than 99.9%, and the particle size of the Nb, Ta, Mo, W metal powders is 1 - 4 μm; the particle size of the nano-graphite powder is 0.01 - 0.02 μm;

[0009] Preferably, the preparation method of the refractory high-entropy alloy includes the following steps:

[0010] S1. Put the prepared Nb, Ta, Mo, W metal powders and nano-graphite powder into the ball mill pot of a ball mill, and carry out ball milling for at least 70 h;

[0011] S2. After the ball milling is completed, place the powder in a vacuum drying oven for drying. After the drying is completed, screen it through a 200-mesh sieve to obtain high-entropy alloy powder;

[0012] S3. Use the high-entropy alloy powder as the sintering raw material, and use the controlled discharge plasma sintering method to prepare the high-entropy alloy powder into a refractory high-entropy alloy block.

[0013] Preferably, in step S3, the sintering temperature used in the controlled discharge plasma sintering is 1400 °C, the sintering pressure is 30 MPa, the sintering holding time is 1 h, the sintering heating rate is 10 °C / min, and the protective gas during sintering is argon.

[0014] Preferably, the hardness of the high-entropy alloy block in step S3 is 1458 - 1631 HV.

[0015] Preferably, the particle size radius of the refractory high-entropy alloy powder in step S2 is 100 - 300 nm.

[0016] Preferably, in step S1, the ball-to-material ratio of the ball milling is 8:1, the operation rule of the ball milling is unidirectional rotation, it stops for 10 minutes every 50 minutes of rotation, and it works in an alternating cycle mode with a rotation speed of 350 r / min. The process control agent for the ball milling is anhydrous ethanol.

[0017] The beneficial effects of the present invention are embodied in:

[0018] The present invention subjects nano-graphite powder and Nb, Ta, Mo, and W metal powders with an equimolar ratio to long-term ball milling treatment. The synthesized high-entropy alloy powder has finer grain size, high solid solution degree of the alloy, realizes the solid-phase diffusion reaction of metals at a temperature far lower than the melting point of the metal, forms a solid solution with a body-centered cubic structure, and then through spark plasma sintering, a refractory high-entropy alloy bulk with self-generated carbide reinforcement is obtained. Utilizing the prepared nano-alloy powder with a high specific surface area effectively reduces the processing temperature, and an alloy bulk with excellent properties can be obtained only at a sintering temperature of 1400 °C (the alloy melting point is as high as 2904 °C). There is no need to additionally add ceramic reinforcing phases such as oxides / carbides, and the hardness, toughness, and wear resistance are improved by relying on the self-generated carbides; the hardness is 1458 - 1631 HV, the fracture toughness is 4.6 - 5.2 MPa·m 1 / 2 , and the wear rate is 1.8 - 4.4×10 -7 mm 3 / (N·m). Compared with the alloy bulk without nano-graphite, the hardness, fracture toughness, and wear resistance of the refractory high-entropy alloy bulk with self-generated carbide reinforcement provided by the present invention are all improved. Description of the Drawings

[0019] Figure 1 It is the SEM morphology diagram of the alloy powders in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention;

[0020] Figure 2 It is the energy spectrum diagram of the elements of the alloy powder in Example 1 of the present invention;

[0021] Figure 3 It is the XRD diagram of the high-entropy alloy bulk in Example 2 of the present invention;

[0022] Figure 4 It is the SEM diagram and EDS diagram of the high-entropy alloy bulk in Example 3 of the present invention;

[0023] Figure 5 It is the SEM diagram and EDS diagram of the high-entropy alloy bulk in Comparative Example 1 of the present invention;

[0024] Figure 6 It is the optical morphology diagram of the worn surface of the high-entropy alloy bulk in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention;

[0025] Figure 7 Raman spectra of the worn surfaces of the bulk high-entropy alloys in Example 2, Example 3 and Comparative Example 1 of the present invention. Detailed implementation manners

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments and comparative examples of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Without conflict, the embodiments and features in the embodiments of this application can be combined with each other. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Example 1

[0028] A refractory high-entropy alloy reinforced by in-situ carbide and its preparation method. The chemical composition of the refractory high-entropy alloy includes: nano-graphite powder and equimolar amounts of Nb, Ta, Mo, and W metal powders; the purity of the Nb, Ta, Mo, and W metal powders is greater than 99.9%, and the particle size of the Nb, Ta, Mo, and W metal powders is 1-4 μm; the particle size of the nano-graphite powder is 0.01-0.02 μm; the atomic ratio of the nano-graphite powder to the Nb, Ta, Mo, and W metal powders is 0.05.

[0029] The preparation method of the refractory high-entropy alloy includes the following steps:

[0030] S1. Put the prepared Nb, Ta, Mo, and W metal powders and nano-graphite powder into the ball milling tank of a ball mill and perform ball milling for at least 70 h. In step S1, the ball-to-powder ratio of ball milling is 8:1, the operation rule of ball milling is one-way rotation, stop for 10 min every 50 min, and work in an alternating cycle with a rotation speed of 350 r / min. The process control agent for ball milling is anhydrous ethanol.

[0031] S2. After ball milling, place the powder in a vacuum drying oven for drying. After drying, pass it through a 200-mesh sieve to obtain refractory high-entropy alloy powder; the particle size radius of the refractory high-entropy alloy powder is 100-300 nm.

[0032] S3. Use the alloy powder after ball milling for 70 h as the sintering raw material and prepare an alloy block by SPS sintering method. Take Φ20 mm×10 mm as the designed size of the block, and place the mechanically alloyed powder in a graphite mold with an inner diameter of 20 mm. Place a graphite paper about 0.2 mm thick between the inner wall of the mold and the discharge punch to make it more convenient to sample after sintering. After loading the alloy powder, put the mold in a sintering furnace with an asbestos sleeve and use the controlled discharge plasma sintering method to prepare the refractory high-entropy alloy powder into a refractory high-entropy alloy block.

[0033] In step S3, the sintering temperature used for controlling spark plasma sintering is 1400 °C, the sintering pressure is 30 MPa, the sintering holding time is 1 h, the sintering heating rate is 10 °C / min, and the protective gas during sintering is argon.

[0034] In the experiment of this application, the Vickers hardness indentation method is used to calculate the hardness of the high-entropy alloy bulk sample and judge the fracture toughness of the sample, and the test load is 5000 gf.

[0035] The wear resistance of the high-entropy alloy bulk is measured using an HT-1000 type friction and wear testing machine. The test environment is air and room temperature, and Si 3 N 4 ceramic balls (Φ6 mm, Ra = 50 nm, hardness 21.2 ± 2 GPa) are used for friction. The test loading load is 300 gf, the rotation speed is 300 r / min, and the friction time is 30 min. The specimens before and after friction are cleaned with anhydrous ethanol and dried, and the worn form of the specimens after friction is characterized by optical morphology and Raman spectroscopy.

[0036] Figure 1 (b) is the microscopic morphology diagram of the alloy powder after mechanical alloying treatment. Alloy powders with a particle size less than 200 nm agglomerate together and pass through Figure 2 From the distribution of each element, it can be seen that the element distribution of the powder composition is relatively uniform, and there is no obvious element enrichment. The structure of the high-entropy alloy bulk after spark plasma sintering is a BCC matrix phase (rich in more Mo, W, Nb) with a second-phase carbide (TaC) dispersed in it; the Vickers hardness measured under 5000 gf is 1458 HV, and the fracture toughness measured by the indentation method is 4.67 ± 0.11 MPa·m 1 / 2 , the friction coefficient is 0.54, and the wear rate is 9.8×10 -7 mm 3 / (N·mm).

[0037] Example 2

[0038] The experimental requirements, process parameters, experimental steps, and detection methods in Example 2 are the same as those in Example 1, except that the composition is changed to the atomic ratio of nano-graphite content in the metal powder being 0.25.

[0039] Figure 1 (c) The particle size of the alloy powder after mechanical alloying treatment will be refined due to the increase in nano-graphite content; Figure 3XRD pattern of the high-entropy alloy bulk after spark plasma sintering. The structure is a BCC matrix phase (rich in Mo, W, Nb) with a second-phase carbide (TaC) dispersed in it. The Vickers hardness measured at 5000 gf is 1463 HV, and the fracture toughness measured by the indentation method is 5.00 ± 0.05 MPa·m 1 / 2 , the friction coefficient is 0.41, and the wear rate is 2.7×10 -7 mm 3 / (N·mm).

[0040] Example 3

[0041] The experimental requirements, process parameters, experimental procedures, and detection methods in Example 3 are the same as those in Example 1, except that the composition is changed to the atomic ratio of nano-graphite content in the metal powder being 0.75.

[0042] Figure 1 (d) The alloy powder after mechanical alloying treatment. The particle size of the alloy powder will be further refined due to the increase in nano-graphite content; Figure 4 Microscopic morphology and element distribution map of the high-entropy alloy bulk after spark plasma sintering. The structure is an FCC carbide phase (rich in Ta element) and a BCC metal phase (rich in Mo, W, Nb). The grain size ranges from 0.1 to 0.5 μm.

[0043] The Vickers hardness measured at 5000 gf is 1631 HV, and the fracture toughness measured by the indentation method is 5.51 ± 0.11 MPa·m 1 / 2 , the friction coefficient is 0.39, and the wear rate is 1.9×10 -7 mm 3 / (N·mm).

[0044] Comparative Example 1

[0045] The experimental requirements, process parameters, experimental procedures, and detection methods in Comparative Example 1 are the same as those in Example 1, except that the composition is changed to no nano-graphite powder added.

[0046] Figure 1 (a) The particle size of the alloy powder after mechanical alloying treatment is significantly larger than that in Examples 1, 2, and 3. Figure 5 Microscopic morphology map and composition element map of the alloy bulk. The composition phase is a BCC solid solution phase, and the composition elements are relatively evenly distributed. And from Figure 5 (a) The circled part, there is a small amount of element enrichment, and the grains are fine. The Vickers hardness measured at 5000 gf is 1402 HV, and the fracture toughness measured by the indentation method is 4.52 ± 0.08 MPa·m 1 / 2 , the friction coefficient is 0.72, and the wear rate is 13.5×10 -7 mm3 / (N·mm).

[0047] According to the attached Figure 1 It can be seen that through long-term mechanical alloying treatment, alloy powders with nanoscale and relatively uniform element distribution can be obtained; due to the high surface energy, the spark plasma sintering furnace can obtain a structure with fine grains and carbide phases precipitated in the high-entropy alloy matrix at 1400 °C (attached Figure 3 and attached Figure 4 ). In addition, it can be seen from the characteristics of the wear scar structure in the attached drawings (attached Figure 6 ) that in Comparative Example 1, obvious abrasive wear characteristics appear on the surface and there are more grinding particles. With the addition of nano-graphite, the wear scar becomes shallower, smooth and flat, showing higher friction resistance. The structural changes of the high-entropy alloy can be judged according to the signal changes of the Raman spectrum of the wear scar (attached Figure 7 ). When no nano-graphite is incorporated, the bonding of the high-entropy alloy is a metallic bond, there are no optical phonons, and the vibration of acoustic phonons is weak. In Examples 2 and 3, the characteristic peaks at ~110 cm -1 and ~180 cm -1 are attributed to transverse acoustic (LA) and longitudinal acoustic (TA). LA and TA are the characteristic peaks of the NaCl-type structure, indicating that the high-entropy alloy structure has formed a bonding of the FCC-MC (M is a metal element) structure. The Raman spectrum curve of the wear scar in Example 3 has D peak and G peak (attached Figure 7 ), and the precipitation of the graphite phase on the wear scar surface is beneficial to reducing the friction coefficient. Since the content of the hard carbide phase increases with the increase of the nano-graphite powder content, the hardness, toughness and wear resistance of the high-entropy alloy bulk have all been enhanced to varying degrees.

[0048] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A refractory high entropy alloy enhanced by in-situ endogenous carbides, characterized in that: The chemical composition of the refractory high entropy alloy includes: nano graphite powder and Nb, Ta, Mo, W metal powders in equal molar ratio; the atomic ratio of the nano graphite powder to the Nb, Ta, Mo, W metal powders is 0.05-0.

75.

2. The refractory high entropy alloy with in-situ enhancement of endogenous carbides according to claim 1, characterized in that: The particle size of the Nb, Ta, Mo and W metal powders is 1 to 4 μm; the particle size of the nano graphite powder is 0.01 to 0.02 μm.

3. The method for preparing a refractory high entropy alloy in-situ enhanced with endogenous carbides according to any one of claims 1 to 2, characterized in that: The preparation method comprises the following steps: S1. Put the prepared Nb, Ta, Mo, W metal powders and nano graphite powder into the ball milling tank of the ball mill and perform ball milling for at least 70 hours; S2. After the ball milling is completed, the powder is placed in a vacuum drying oven for drying. After the drying is completed, a refractory high entropy alloy powder is obtained; S3. Using high entropy alloy powder as sintering raw material, and adopting controlled spark plasma sintering method to prepare high entropy alloy powder into refractory high entropy alloy block.

4. The method for preparing a refractory high entropy alloy enhanced by in-situ endogenous carbide according to claim 3, characterized in that: In step S3, the sintering temperature used in controlling the spark plasma sintering is 1400° C., the sintering pressure is 30 MPa, the sintering holding time is 1 h, the sintering heating rate is 10° C. / min, and the protective gas during sintering is argon.

5. The method for preparing a refractory high entropy alloy enhanced by in-situ endogenous carbide according to claim 4, characterized in that: The particle size radius of the high entropy alloy powder in step S2 is 100 to 300 nm.

6. The method for preparing a refractory high entropy alloy enhanced by in-situ endogenous carbide according to claim 5, characterized in that: The ball-to-material ratio of the ball mill in step S1 is 8:1, and the operation rule of the ball mill is unidirectional rotation, each rotation is 50 minutes, and the stop is 10 minutes, and the rotation speed is 350r / min. The process control agent of the ball mill is anhydrous ethanol.

7. The endogenous carbide in-situ enhanced refractory high entropy alloy material according to claim 3, characterized in that: The hardness of the refractory high entropy alloy material obtained in step S3 is 1458-1631 HV; the fracture toughness of the refractory high entropy alloy material is 4.6-5.2 MPa·m 1 / 2 The wear rate of refractory high entropy alloy materials is 1.8~4.4×10 -7 mm 3 / (N·m).

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