A lightweight, high-strength and tough TiB2-WC-based cermet and its preparation method

Abstract

The present invention relates to a lightweight, high-hardness, high-strength and tough TiB2-WC-based cermet composite material and a preparation method thereof, belonging to the technical field of cermets. The mass percentage composition is as follows: TiB2: 55% to 80%; WC: 0 to 15%; Co: 5 to 15%; Ni: 5 to 15%; and the sum of each component is 100%. Take each raw material powder according to the designed composition, mix by planetary ball milling, vacuum dry, screen to remove agglomerates, press into shape, and adopt an integrated technology of vacuum reduction-vacuum liquid-phase sintering dissolution and precipitation to finally sinter at 1450 °C to 1500 °C to prepare a TiB2-WC-based cermet with a "core-ring" structure toughening. Its bulk density is 4.97 to 5.52 g / cm 3 , the hardness is 92.7 to 94.4 HRA, the flexural strength is 1792.3 to 2119.62 MPa, and the fracture toughness is 10.84 to 12.21 MPa·m 1 / 2 . The product obtained by the present invention has excellent performance, a simple process flow, and is suitable for large-scale production. It has a very broad application prospect in the fields of precision machining cutting tools, wear-resistant materials, conductive and heat-conductive ceramic materials, electrode materials, high-temperature oxidation-resistant materials, etc.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of cermet composites, and particularly relates to a lightweight, high-strength and tough TiB2-WC-based cermet with a "core-ring" structure strengthening and toughening and a preparation method thereof. A new technology with controllable preparation process, stable performance and capable of realizing industrial production is provided for preparing a new type of high-performance TiB2-WC-based cermet material. Background Art

[0002] Cutting machining plays a very important role in modern industrial production. With the rapid development of China's modern automotive industry, equipment manufacturing industry, aerospace, and non-ferrous metal industry, the requirements for precision machining are getting higher and higher. The key to achieving precision machining lies in producing high-end tool materials. Currently, the cutting tool materials used in industrial production are mainly divided into ceramic tools, high-speed steel tools, cemented carbide tools, and cermet tools, etc. Ceramic tools mainly include materials such as alumina, silicon nitride, and cubic boron nitride. Due to their advantages of high hardness, wear resistance, and high temperature resistance, they are suitable for the cutting machining of high-hardness materials and the field of high-speed cutting machining. However, the toughness of ceramic tool materials is low, unable to withstand large impact loads, and prone to chipping; in addition, due to their high brittleness, it is difficult to make cutting tool materials with complex shapes, which greatly limits the application range of ceramic tools. High-speed steel has excellent mechanical properties such as flexural strength and impact toughness. However, due to its poor hot hardness at high temperatures and easy wear, it cannot meet the working conditions requirements when machining high-hardness materials. Therefore, it is generally used for cutting materials with lower hardness. WC-Co cemented carbide has excellent wear resistance, relatively high hot hardness, good flexural strength, and fracture toughness at low temperatures (usually below 800°C), and is commonly used for cutting machining of non-ferrous metals, hardened steel, stainless steel and other materials. However, at high temperatures (800°C and above), the hardness, wear resistance, and oxidation resistance of cemented carbide are poor. When the cutting machining temperature reaches 800°C and above, the surface of the cemented carbide tool will soften and adhere, accelerating the tool wear and seriously reducing the machining accuracy of the material. Therefore, cemented carbide tools cannot meet the requirements of high-precision cutting machining of high-hardness materials. Compared with WC-Co cemented carbide tools, cermet tools not only have high hardness, excellent high-temperature oxidation resistance, wear resistance, and corrosion resistance, but also have high hot hardness and good anti-adhesion performance. At high temperatures of 700 - 1100°C, the cutting speed of cermet is 3 - 10 times that of cemented carbide, and the cutting life is 2 - 5 times that of cemented carbide. Cermet is an ideal alternative product to cemented carbide in high-speed cutting and high-hardness material machining, and fills the gap of cutting tools in the field of working conditions requirements that cannot be met by high-speed steel and cemented carbide tools. Currently, the research on cermet tools mainly focuses on TiC / Ti(C,N)-based cermets, and there are relatively few relevant literature reports on TiB2-based cermet tools. The industrial application of TiB2-based cermet tools still has a long way to go. Therefore, strengthening the research on TiB2-based cermets and preparing high-performance TiB2-based cermet materials have very important economic value and scientific significance for enriching the large family of cermets and promoting the application of TiB2-based cermets in the field of cutting machining.

[0003] TiB2-based cermets have good properties in terms of hardness, hot hardness, resistance to metal adhesion, and high-temperature oxidation resistance, and have very broad application prospects in the fields of cutting tools and wear-resistant components. However, the deficiencies in strength and toughness of this cermet are the key issues restricting its wider application. By optimizing the cermet components and controlling the microstructure evolution of TiB2-based cermets during liquid-phase sintering to form a beneficial "core-ring" structure, it is one of the effective methods to achieve the strengthening and toughening of TiB2-based cermets. Summary of the Invention

[0004] In view of the current situation that the strength and toughness of TiB2-based cermets reported in current research are generally low, WC is added to the TiB2-CoNi system cermet in the present invention. Through vacuum liquid-phase sintering, WC dissolves in the CoNi binder phase and precipitates on the undissolved TiB2 particles after reaching the saturation solubility, forming a beneficial "TiB2 core-(Ti,W,Co,Ni)(B,C) ring phase" "core-ring" structure, thereby realizing the strengthening and toughening of TiB2-based cermets. During the sintering process, through the precise control of the sintering process, the adsorbed water and adsorbed oxygen in the raw material powder are removed during the vacuum sintering process, and the oxides on the surface of the raw material powder are vacuum-reduced, thereby playing the role of purifying the material and purifying the grain boundaries, making the interface combination between the TiB2 core-(Ti,W,Co,Ni)(B,C) ring phase-CoNi binder phase of the TiB2-based cermet more matching and significantly improving the interface bonding strength. To achieve the above object, the specific technical solutions provided by the present invention are as follows:

[0005] The lightweight, high-strength and tough TiB2-WC-based cermet is composed of the following components by mass percentage: TiB2: 55-80%, WC: 0-15%, Co: 5-15%, Ni: 5-15%, and the sum of the mass percentages of each component is 100%.

[0006] Preferably, the mass percentage composition of a lightweight, high-strength and tough TiB2-WC-based cermet is: TiB2: 65-80%, WC: 0.5-15%, Co: 8-12%, Ni: 8-12%.

[0007] Among the raw materials used for the TiB2-WC-based cermet, the average particle size of TiB2 is 1.0-2.0 μm, the average particle size of WC is 0.3-1.0 μm, the average particle size of Ni is 2-4 μm, and the average particle size of Co is 2-4 μm.

[0008] A preparation method of a lightweight, high-strength and tough TiB2-WC-based cermet includes the following specific steps:

[0009] (1) Preparation of mixed powder: Weigh TiB2, WC, Co, and Ni powders according to the above mass percentages, mix them by planetary ball milling or drum ball milling, dry them in a vacuum drying oven at 50 - 60 °C, and then sieve through 80 - mesh to remove agglomerates to obtain a uniformly mixed TiB2-WC-based cermet powder.

[0010] (2) Compression molding: Press the mixed powder into a cuboid green body by die pressing at 100 MPa, and then use cold isostatic pressing to hold the pressure at 250 - 300 MPa for 150 - 200 s to further increase the density of the green compact.

[0011] (3) Vacuum sintering: Carry out vacuum carbothermal reduction and vacuum liquid-phase sintering on the green body obtained in step (2) in a vacuum sintering furnace. The vacuum degree is 10 -3 ~10 -1 Pa, the final sintering temperature is 1450 - 1500 °C, and keep the temperature for 0.5 - 2 h to obtain a TiB2-WC-based cermet composite with a typical "core-ring" structure.

[0012] The planetary ball milling or drum ball milling described in step (1) is characterized in that: when preparing the mixed powder, alcohol or kerosene is used as the ball milling medium, the ball-to-material ratio is (1 - 5):1, and the ball milling speed is 150 - 200 r / min. First, ball mill and mix TiB2 and WC powders for 12 h, then add Co and Ni metal powders and ball mill together for another 24 h. Use forward rotation for 1 h and reverse rotation for 1 h alternately to mix the materials to obtain a mixed powder slurry.

[0013] The vacuum sintering described in step (3) is characterized in that: it is heated from room temperature to 143°C at a rate of 1-3°C / min and held for 1 h to remove the adsorbed water vapor in the raw material powder; then it is heated to 223°C at a rate of 1-3°C / min and held for 1 h to vacuum-remove the adsorbed oxygen in the raw material powder; then it is heated to 346°C at a rate of 1-3°C / min and held for 1 h to vacuum carbothermally reduce the oxides on the surfaces of Co and Ni powders; then it is heated to 880°C at a rate of 1-3°C / min and held for 1 h; then it is heated to 1006°C at a rate of 1-2°C / min and held for 1 h; then it is heated to 1117°C at a rate of 1-2°C / min and held for 1 h to vacuum carbothermally reduce the combined oxygen TiO2 on the surface of the TiB2 raw powder; then it is heated to 1200°C at a rate of 1-2°C / min and held for 1 h to reduce TiO2 as thoroughly as possible; then it is heated to 1335°C at a rate of 1-2°C / min and held for 1 h, at this time WC begins to form a eutectic liquid phase with Co; then it is heated to 1397°C at a rate of 1-2°C / min and held for 1 h, and the metal CoNi begins to melt to form a liquid phase; then it is heated to 1440°C at a rate of 1-2°C / min and held for 1 h, and a large amount of WC dissolves in the CoNi binder phase and begins to precipitate on some TiB2 particles; then it is heated to 1465°C at a rate of 1-2°C / min and held for 0.5-3 h, and the dissolution and precipitation are in dynamic equilibrium to form a large number of "TiB2 core-(Ti, W, Co, Ni)(B, C) ring phase" "core-ring" structures. After the heating is completed, a high vacuum is maintained throughout the process, and it is cooled to room temperature with the furnace.

[0014] The lightweight, high-hardness, high-strength and high-toughness TiB2-WC-based cermet prepared by the present invention generates a large number of "core-ring" structures with TiB2 as the core and (Ti, W, Co, Ni)(B, C) as the ring phase. Among them, the TiB2 core is of HCP structure, the (Ti, W, Co, Ni)(B, C) ring phase is of FCC structure, and the CoNi binder phase is of FCC structure. A coherent two-phase interface is formed between the TiB2 core and the (Ti, W, Co, Ni)(B, C) ring phase; a non-crystallized CoNi metal thin layer is formed between the (Ti, W, Co, Ni)(B, C) ring phase and the CoNi binder phase. Both the coherent interface and the non-crystallized metal thin layer greatly improve the interfacial bonding strength, thereby enhancing the bending strength and fracture toughness of the cermet. The TiB2-WC-based cermet prepared by the present invention has a bulk density of 4.97-5.52 g / cm 3 , a hardness of 92.7-94.4 HRA, a flexural strength of 1792.3-2119.62 MPa, and a fracture toughness of 10.84-12.21 MPa·m 1 / 2。The mechanical properties are far higher than the comprehensive mechanical properties of TiB2-based cermets developed by other materials scientists. Meanwhile, the properties are superior to those of the TiC-based cermet tool with the grade of 7G produced by Ford Company in the United States. Its density, hardness, and flexural strength are 5.80 g / cm 3 , 91.0 HRA, 1900 MPa; superior to the mechanical properties of the Ti(C,N)-based cermet tool with the grade of N540 produced by Toshiba in Japan. Its density, hardness, and flexural strength are 7.0 g / cm 3 , 91.6 HRA, 1962 MPa; superior to the mechanical properties of the fine-grained WC-Co cemented carbide tool with the grade of H5M produced by Sandvik in Sweden. Its density, hardness, flexural strength, and fracture toughness are 14.95 g / cm 3 , 92.2 HRA, 2100 MPa, 10 MPa·m 1 / 2 . The lightweight, high-hardness, high-strength and high-toughness TiB2-WC-based cermet prepared by the present invention is expected to replace the TiC / Ti(C,N)-based cermets and WC-Co cemented carbide tool materials of some domestic and foreign grades in the application in the field of cutting processing.

[0015] The present invention adopts the powder metallurgy process, which is simple in operation and suitable for large-scale industrial production. The lightweight, high-hardness, high-strength and high-toughness TiB2-WC-based cermet has very broad application prospects in the fields of precision cutting tools, wear-resistant materials, grinding wheel linings, thermoelectric ceramic materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 TG-DSC thermodynamic analysis of the sintering process of the cermet mixed powder in Example 4 of the present invention

[0017] Figure 2 Gas emission during the sintering process of the cermet mixed powder in Example 4 of the present invention

[0018] Figure 3 XRD phase analysis of the TiB2-WC-based cermet in Examples 1-6 of the present invention

[0019] Figure 4 Backscattered morphology of the TiB2-12.5wt%WC-based cermet in Example 6 of the present invention

[0020] Figure 5 Comprehensive mechanical properties of the TiB2-WC-based cermet in Examples 1-6 of the present invention, (a) bulk density and relative density, (b) hardness, (c) transverse rupture strength, (d) indentation fracture toughness DETAILED IMPLEMENTATION MANNER

[0021] Example 1: The ingredients of the TiB2-WC cermet consist of powders with the following mass percentages and average particle sizes: TiB2: 80%, average particle size of 1.25 μm, WC: 0%, average particle size of 0.82 μm; Co: 10%, average particle size of 2.5 μm, Ni: 10%, average particle size of 2.5 μm. The mass ratio of the binder phase is Co:Ni = 1:1, and the sum of the mass percentages of each component is 100%.

[0022] The specific steps for preparing the cermet are as follows:

[0023] (1) Preparation of the mixed powder: Weigh the TiB2, Co, and Ni powders according to the above mass percentages, and use planetary ball milling for mixing with alcohol as the ball milling medium, a ball-to-material ratio of 3:1, and a ball milling speed of 190 r / min. Ball mill the TiB2, Co, and Ni powders for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 52°C for 15 h, and then sieve it through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-CoNi cermet mixed powder.

[0024] (2) Compression molding: First, use die pressing to compress it into a rectangular green compact of 25×8×5 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the pressure at 270 MPa for 150 s to further increase the density of the green compact.

[0025] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), maintaining a vacuum degree of 10 -1 ~10 -3 Pa throughout. The specific heating and sintering regime is as follows: Heat from room temperature to 143°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 143°C to 223°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 223°C to 346°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 346°C to 880°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 880°C to 948°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 948°C to 987°C at a rate of 1 - 3°C / min and hold for 1 h; then heat from 987°C to 1006°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1006°C to 1117°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1117°C to 1200°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1200°C to 1335°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1335°C to 1397°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1397°C to 1440°C at a rate of 1 - 2°C / min and hold for 1 h; then heat from 1440°C to 1465°C at a rate of 1 - 2°C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout and cool to room temperature with the furnace.

[0026] The bulk density of the TiB2-0% WC cermet prepared in this example is 4.97 g / cm 3 , the hardness is 94.4 HRA, the flexural strength is 1729.3 MPa, and the fracture toughness is 10.84 MPa·m 1 / 2 . Its phase composition is as shown in Figure 3 (a), including two phases of TiB2 and CoNi binder phase.

[0027] The ingredients of the TiB2-WC cermet in Example 2 are composed of powders with the following mass percentages and average particle sizes: TiB2: 77.5%, average particle size of 1.62 μm, WC: 2.5%, average particle size of 0.65 μm; Co: 9%, average particle size of 3.0 μm, Ni: 11%, average particle size of 3.0 μm, and the sum of the mass percentages of each component is 100%.

[0028] The specific steps for preparing the cermet are as follows:

[0029] (1) Preparation of mixed powder: Weigh TiB2, WC, Co, and Ni powders according to the above mass percentages, and use planetary ball milling for mixing. Alcohol is used as the ball milling medium, the ball-to-material ratio is 1.5:1, and the ball milling speed is 160 r / min. First, planetary ball mill the TiB2 and WC powders for 12 h, then add the Co and Ni powders and continue ball milling for 24 h to obtain a mixed powder slurry. Dry the above mixed powder in a vacuum drying oven at 54 °C for 15 h, and then screen it through an 80-mesh sieve to remove agglomerates to obtain the TiB2-2.5% WC cermet mixed powder.

[0030] (2) Compression molding: First, use die pressing to press into a rectangular green compact of 25×8×7 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the pressure at 290 MPa for 160 s to further increase the density of the green compact.

[0031] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and keep the vacuum degree at 10 -1 ~10 -3Pa. The specific heating and sintering regime is as follows: from room temperature, it is heated at 1 - 3 °C / min to 143 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 223 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 346 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 880 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 948 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 987 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1006 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1117 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1200 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1335 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1397 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1440 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1470 °C and held for 0.5 h. After the heating is completed, high vacuum is maintained throughout the process, and it is cooled to room temperature with the furnace.

[0032] The bulk density of the TiB2 - 2.5% WC - based cermet prepared in this example is 5.07 g / cm 3 , the hardness is 93.2 HRA, the flexural strength is 1976.72 MPa, and the fracture toughness is 11.12 MPa·m 1 / 2 . A "core - ring" structure of TiB2 core - (Ti, W, Co, Ni)(B, C) annular phase is formed in the cermet, and its phase composition is as Figure 3 (b) shows, including 4 phases: TiB2, W2CoB2, WB, and CoNi binder phase.

[0033] The ingredients of the TiB2 - WC - based cermet in Example 3 are composed of powders with the following mass percentages and average particle sizes: TiB2: 75%, average particle size is 1.51 μm, WC: 5%, average particle size is 0.54 μm; Co: 8%, average particle size is 2.5 μm, Ni: 12%, average particle size is 3.0 μm, and the sum of the mass percentages of each component is 100%.

[0034] The specific steps for preparing the cermet are as follows:

[0035] (1) Preparation of the mixed powder: Weigh the TiB2, WC, Co, and Ni powders according to the above - mentioned mass percentages, and use planetary ball milling for mixing. Alcohol is used as the ball - milling medium, the ball - to - material ratio is 2:1, and the ball - milling speed is 180 r / min. First, planetary ball - mill the TiB2 and WC powders for 12 h, then add the Co and Ni powders and continue ball - milling for 24 h to obtain a mixed - powder slurry. Dry the above - mentioned mixed powder in a vacuum drying oven at 53 °C for 20 h, and then sieve it through an 80 - mesh sieve to remove agglomerates to obtain the TiB2 - 5% WC - based cermet mixed powder.

[0036] (2) Compression molding: First, a rectangular green compact with dimensions of 25×8×6 mm is compression molded under a pressure of 80 MPa by die pressing. 3 Then, the rectangular green compact is further densified by cold isostatic pressing at a pressure of 300 MPa for 180 s.

[0037] (3) Vacuum sintering: The green compact prepared in step (2) is subjected to vacuum sintering, maintaining a vacuum degree of 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: starting from room temperature, it is heated at a rate of 1 - 3 °C / min to 143 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 223 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 346 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 880 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 948 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 987 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1006 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1117 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1200 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1335 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1397 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1440 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1460 °C and held for 1.5 h. After the heating is completed, high vacuum is maintained throughout the process, and it is cooled to room temperature with the furnace.

[0038] The bulk density of the TiB2 - 5% WC - based cermet prepared in this example is 5.20 g / cm 3 , the hardness is 93.0 HRA, the flexural strength is 2120 MPa, and the fracture toughness is 11.33 MPa·m 1 / 2 . A large number of "core - ring" structures of TiB2 cores - (Ti, W, Co, Ni)(B, C) annular phases are formed in the cermet, and the phase composition is as shown in Figure 3 (c), including 4 phases: TiB2, W2CoB2, WB, and CoNi binder phase.

[0039] Example 4 The ingredients of the TiB2 - WC - based cermet are composed of powders with the following mass percentages and average particle sizes: TiB2: 72.5%, average particle size of 1.31 μm, WC: 7.5%, average particle size of 0.4 μm; Co: 10%, average particle size of 2.0 μm, Ni: 10%, average particle size of 2.5 μm, where the mass ratio of the binder phase is Co:Ni = 1:1, and the sum of the mass percentages of each component is 100%.

[0040] The specific steps for preparing the cermet are as follows:

[0041] (1) Preparation of the mixed powder: Weigh the TiB2, WC, Co, and Ni powders according to the above mass percentages, and use a planetary ball mill for mixing. Alcohol is used as the ball milling medium, the ball-to-material ratio is 1:1, and the ball milling speed is 200 r / min. First, planetary ball mill the TiB2 and WC powders for 12 h, then add the Co and Ni powders and continue ball milling for 24 h to obtain a mixed powder slurry. Dry the above mixed powder in a vacuum drying oven at 55 °C for 15 h, and then screen it through an 80-mesh sieve to remove agglomerates to obtain the TiB2-7.5% WC-based cermet mixed powder.

[0042] (2) Compression molding: First, use die pressing to press it into a rectangular green compact with dimensions of 25×8×5 mm 3 at a pressure of 100 MPa, and then further improve the density of the green compact by cold isostatic pressing at a pressure of 250 MPa for 150 s.

[0043] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain a vacuum degree of 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: Heat from room temperature to 143 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 223 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 346 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 880 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 948 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 987 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 1006 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1117 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1200 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1335 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1397 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1440 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1465 °C at a rate of 1-2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool it to room temperature with the furnace.

[0044] The bulk density of the TiB2-7.5% WC-based cermet prepared in this example is 5.30 g / cm 3 , the hardness is 92.7 HRA, the flexural strength is 2108 MPa, and the fracture toughness is 12.21 MPa·m 1 / 2 . A large number of "core-ring" structures of TiB2 core-(Ti, W, Co, Ni)(B, C) annular phases are formed in the cermet, and the phase composition is as Figure 3As shown in (d), it contains four phases: TiB2, W2CoB2, WB, and CoNi binder phase.

[0045] Figure 1 and Figure 2 is the TG-DSC-QMS comprehensive thermal analysis curve of this example. Using a Netzsch STA449F5 synchronous thermal analyzer, the endothermic, thermogravimetric, and exhaust behaviors of TiB2-7.5% WC-20% CoNi cermet during the heating process from room temperature to 1480 °C were measured. During the measurement process, high-purity Ar protection was used, the heating rate was 10 °C / min, and the gas flow rate was 20 ml / min. Based on the test results of TG-DSC-QMS comprehensive thermal analysis, fully considering the temperature corresponding to each endothermic peak, the change of thermogravimetry of the sintering system, the dehydration temperature of adsorbed water in the mixed powder, the reduction temperature of oxide impurities in the mixed powder, the melting temperature of metallic Co and Ni in the sintering system, and the dissolution temperature of WC and TiB2 ceramic particles in the liquid metal, the sintering regime curve of this example was comprehensively set, and a sufficient holding time was set at each corresponding temperature point to ensure the full progress of each reaction. This sintering regime curve is also the sintering regime curve adopted for TiB2-WC-based cermets with different WC addition amounts prepared by the present invention, laying a solid foundation for the preparation of high-performance TiB2-WC-based cermet materials.

[0046] The ingredients of the TiB2-WC-based cermet in Example 5 are composed of powders with the following mass percentages and average particle sizes: TiB2: 70%, average particle size of 1.45 μm, WC: 10%, average particle size of 0.65 μm; Co: 11%, average particle size of 2.5 μm, Ni: 9%, average particle size of 3.5 μm, and the sum of the mass percentages of each component is 100%.

[0047] The specific steps for preparing the cermet are as follows:

[0048] (1) Preparation of the mixed powder: Weigh TiB2, WC, Co, and Ni powders according to the above mass percentages, and use planetary ball milling for mixing with alcohol as the ball milling medium, the ball-to-powder ratio is 2.5:1, and the ball milling speed is 170 r / min. First, planetary ball mill the TiB2 and WC powders for 12 h, then add the Co and Ni powders and continue ball milling for 24 h to obtain a mixed powder slurry. Dry the above mixed powder in a vacuum drying oven at 52 °C for 15 h, and then screen it through an 80-mesh sieve to remove agglomerates to obtain the TiB2-10% WC-based cermet mixed powder.

[0049] (2) Compression molding: First, use die pressing to press it into a rectangular compact of 25×8×6 mm 3 under a pressure of 100 MPa, and then further improve the density of the rectangular compact by cold isostatic pressing at a pressure of 280 MPa for 170 s.

[0050] (3) Vacuum sintering: The green compact prepared in step (2) is subjected to vacuum sintering, and the vacuum degree is maintained at 10 -1 ~10 -3 Pa throughout. The specific heating and sintering regime is as follows: from room temperature, it is heated at 1 - 3 °C / min to 143 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 223 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 346 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 880 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 948 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 987 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1006 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1117 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1200 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1335 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1397 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1440 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1480 °C and held for 1 h. After the heating is completed, high vacuum is maintained throughout, and it is cooled to room temperature with the furnace.

[0051] The bulk density of the TiB2 - 10% WC - based cermet prepared in this example is 5.40 g / cm 3 , the hardness is 92.9 HRA, the flexural strength is 1981.7 MPa, and the fracture toughness is 11.63 MPa·m 1 / 2 . A large number of "core - ring" structures of TiB2 cores - (Ti, W, Co, Ni)(B, C) annular phases are formed in the cermet, and the phase composition is as Figure 3 (e) shows, including 4 phases of TiB2, W2CoB2, WB, and CoNi binder phase.

[0052] Example 6 The ingredients of the TiB2 - WC - based cermet are composed of powders with the following mass percentages and average particle sizes: TiB2: 67.5%, average particle size of 1.12 μm, WC: 12.5%, average particle size of 0.75 μm; Co: 12%, average particle size of 3.5 μm, Ni: 8%, average particle size of 2.5 μm, and the sum of the mass percentages of each component is 100%.

[0053] The specific steps for preparing the cermet are as follows:

[0054] (1) Preparation of mixed powder: Weigh TiB2, WC, Co, and Ni powders according to the above mass percentages, and use a planetary ball mill for mixing. Alcohol is used as the ball milling medium, the ball-to-powder ratio is 3:1, and the ball milling speed is 150 r / min. First, ball mill TiB2 and WC powders for 12 h, then add Co and Ni powders and continue ball milling for 24 h to obtain a mixed powder slurry. Dry the above mixed powder in a vacuum drying oven at 54 °C for 12 h, and then screen it through an 80-mesh sieve to remove agglomerates to obtain a TiB2-12.5% WC-based cermet mixed powder.

[0055] (2) Compression molding: First, use die pressing to compress it into a cuboid green compact with dimensions of 25×8×7 mm 3 under a pressure of 100 MPa, and then further improve the density of the cuboid green compact by cold isostatic pressing at a pressure of 260 MPa for 200 s.

[0056] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain a vacuum degree of 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering system is as follows: Heat from room temperature to 143 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 223 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 346 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 880 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 948 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 987 °C at a rate of 1-3 °C / min and hold for 1 h; then heat to 1006 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1117 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1200 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1335 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1397 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1440 °C at a rate of 1-2 °C / min and hold for 1 h; then heat to 1475 °C at a rate of 1-2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool it to room temperature with the furnace.

[0057] The bulk density of the TiB2-12.5% WC-based cermet prepared in this example is 5.52 g / cm 3 , the hardness is 93.5 HRA, the flexural strength is 1961.43 MPa, and the fracture toughness is 11.58 MPa·m 1 / 2 . The phase composition is as shown in Figure 3 (f), including 4 phases: TiB2, W2CoB2, WB, and CoNi bonding phase.

[0058] Figure 4It is the backscattered morphology photo of the TiB2-WC cermet in this embodiment. A large number of "core-ring" structures with TiB2 as the core and (Ti, W, Co, Ni)(B, C) as the ring phase are observed in the cermet. At the same time, TEM transmission analysis shows that a coherent two-phase interface is formed between the TiB2 core and the (Ti, W, Co, Ni)(B, C) ring phase, and an amorphous metal thin layer is formed between the (Ti, W, Co, Ni)(B, C) ring phase and the CoNi bonding phase. Both the coherent interface and the amorphous metal thin layer effectively enhance the interfacial bonding strength of the cermet, making the fracture of ceramic particles tend to be transgranular fracture, effectively improving the transverse fracture strength of the TiB2-WC cermet; at the same time, the improvement of the interfacial bonding strength is beneficial to enhancing the energy dissipation at the crack tip during crack propagation, enhancing the ability to resist crack propagation, and improving the fracture toughness of the TiB2-WC cermet.

Claims

1. A lightweight, high-strength and tough TiB2-WC-based cermet, characterized in that: The mass percentage composition of the lightweight, high-strength and tough TiB2-WC-based cermet is as follows: TiB2: 65 - 80%, WC: 0.5 - 15%, Co: 8 - 12%, Ni: 8 - 12%, and the sum of the mass percentages of each component is 100%; the average particle size of TiB2 is 1.0 - 2.0 μm, the average particle size of WC is 0.3 - 1.0 μm, the average particle size of Ni is 2 - 4 μm, and the average particle size of Co is 2 - 4 μm; the preparation process of the lightweight, high-strength and tough TiB2-WC-based cermet is successively: mixing, pressing, vacuum reduction and vacuum liquid-phase sintering: The lightweight, high-strength and tough TiB2-WC-based cermet has formed a "core-ring" structure with TiB2 as the core and (Ti, W, Co, Ni)(B, C) as the ring phase. The TiB2 core is of HCP structure, the (Ti, W, Co, Ni)(B, C) ring phase is of FCC structure, and the CoNi bonding phase is of FCC structure; between the TiB2 core and the (Ti, W, Co, Ni)(B, C) ring phase, a coherent two-phase interface is formed; between the (Ti, W, Co, Ni)(B, C) ring phase and the CoNi bonding phase, an amorphous CoNi metal thin layer is formed; the coherent interface and the amorphous metal thin layer both greatly improve the interfacial bonding strength, thereby enhancing the bending strength and fracture toughness of the cermet; the bulk density of the TiB2-WC-based cermet is 4.97 - 5.52 g / cm 3 , the hardness is 92.7 - 94.4 HRA, the flexural strength is 1792.3 - 2119.62 MPa, and the fracture toughness is 10.84 - 12.21 MPa·m 1 / 2 .

2. The preparation method of a lightweight, high-strength and tough TiB2-WC-based cermet according to claim 1, characterized in that: It includes the following steps: (1) Preparation of mixed powder: Weigh TiB2, WC, Co, and Ni powders according to the above mass percentages, mix them by planetary ball milling or drum ball milling, dry them in a vacuum drying oven at 50 - 60 °C, and then screen them through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-WC-based cermet mixed powder; (2) Compression molding: Use cold isostatic pressing to obtain a green body by maintaining the pressure of the mixed powder at 250 - 300 MPa for 150 - 200 s; (3) Vacuum sintering: The green compact obtained in step (2) is subjected to vacuum sintering with a vacuum degree of 10 -3 ~10 -1 Pa, the sintering temperature is 1450 - 1500 °C, and the heat preservation time is 0.5 - 3 h, obtaining a TiB2-WC-based cermet with a "core-ring" structure, whose bulk density is 4.97 - 5.52 g / cm 3 , the hardness is 92.7 - 94.4 HRA, the flexural strength is 1792.3 - 2119.6 MPa, and the fracture toughness is 10.84 - 12.21 MPa·m 1 / 2 ; The vacuum sintering includes the integrated technologies of removing adsorbed water vapor and oxygen, vacuum carbothermal reduction, and vacuum liquid-phase sintering dissolution and precipitation. The heating-up steps are as follows: heating from room temperature to 143 °C at a rate of 1 - 3 °C / min and holding for 1 h to remove the water vapor adsorbed in the raw material powder; then heating to 223 °C at a rate of 1 - 3 °C / min and holding for 1 h to vacuum-reduce the oxygen adsorbed in the raw material powder; then heating to 346 °C at a rate of 1 - 3 °C / min and holding for 1 h to vacuum-carbothermally reduce the oxides on the surfaces of Co and Ni powders; then heating to 880 °C at a rate of 1 - 3 °C / min and holding for 1 h; then heating to 1006 °C at a rate of 1 - 2 °C / min and holding for 1 h; then heating to 1117 °C at a rate of 1 - 2 °C / min and holding for 1 h to vacuum-carbothermally reduce the TiO2 contained on the surface of the TiB2 raw powder; then heating to 1200 °C at a rate of 1 - 2 °C / min and holding for 1 h; then heating to 1335 °C at a rate of 1 - 2 °C / min and holding for 1 h; then heating to 1397 °C at a rate of 1 - 2 °C / min and holding for 1 h; then heating to 1440 °C at a rate of 1 - 2 °C / min and holding for 1 h; then heating to 1465 °C at a rate of 1 - 2 °C / min and holding for 0.5 - 3 h; after the heating-up is completed, keep a high vacuum throughout the process and cool to room temperature with the furnace.

3. The preparation method of a lightweight, high-strength and tough TiB2-WC-based cermet according to claim 2, characterized in that: For the TiB2-WC-based cermet with a "core-ring" structure, a "core-ring" structure with TiB2 as the core and (Ti, W, Co, Ni)(B, C) as the ring phase is formed. The TiB2 core is of HCP structure, the (Ti, W, Co, Ni)(B, C) ring phase is of FCC structure, and the CoNi bonding phase is of FCC structure; A coherent two-phase interface is formed between the TiB2 core and the (Ti, W, Co, Ni)(B, C) ring phase; An amorphous CoNi metal thin layer is formed between the (Ti, W, Co, Ni)(B, C) ring phase and the CoNi bonding phase; Both the coherent interface and the amorphous metal thin layer greatly improve the interfacial bonding strength, thereby enhancing the flexural strength and fracture toughness of the cermet.

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