Microstructure and mechanical properties of WC ceramic particles reinforced Ni-base composites prepared by hot pressing

The preparation of WC ceramic particles reinforced Ni-based composites by hot pressing sintering was studied. The Ni-based matrix was designed to include two or more of nickel powder, Ni₆₀, and FeCr₅₅C_6.0 (high carbon ferrochrome powder). The microstructure of the WC composite was characterized by XRD and SEM. The structure of the precipitated phase Cr₇C₃ was calculated by first principles, and the hardness, fracture toughness and the bending strength of the composite were tested. The results show that at a hot-pressing sintering temperature of 950 ℃, the WC ceramic particles partially dissolved, and W and C reacted with Ni and Cr in the metal matrix, resulting in the formation of island-shaped small-sized complex mixed W-containing carbide precipitation phases. At the same time, C combined with elements such as Cr and Fe to form hard carbides such as Cr₇C₃, which were uniformly distributed in the composite material, playing a role of dispersion strengthening. The partial wave density of states (PDOS) calculated by first principles shows that the average number of C-Cr bonds in Cr₇C₃ is 0.26 at most, the bond strength is the highest, and the average bond length is 2.16 Å. From the perspective of mechanical properties, the hardness values of WC ceramic particles under different matrix compositions are not much different, while the hardness of metal matrices of different composite materials varies greatly, which is caused by the difference in microstructure formed by matrices of different compositions. The average hardness of the composite material based on Ni₆₀ and FeCr₅₅C_6.0 is the highest at 1364.42 HV. The Cr content in the matrix is high, and a large number of high-hardness Cr-containing carbides such as Cr₇C₃ are generated. The composite material based on nickel powder, Ni₆₀ and FeCr₅₅C_6.0 has a maximum fracture toughness of 4.544 MPa·m^1/2. It also has the highest bending strength and good matrix hardness, and therefore has the best mechanical properties.