Densification characteristics, microstructure, and mechanical properties of h-BN@Al₂O₃/WC-based cemented carbides prepared by spark plasma sintering

To improve h-BN dispersion and the local interfacial environment in WC-based cemented carbides, an h-BN@Al₂O₃ composite powder was prepared by heterogeneous nucleation and calcination, with h-BN as the designed core phase and Al₂O₃ as the designed outer-layer component. The composite powder was incorporated into WC-based cemented carbides consolidated by spark plasma sintering (SPS), and the effects of powder content and sintering temperature on phase composition, microstructure, mechanical properties, and densification characteristics were examined. The h-BN@Al₂O₃ content was closely related to WC grain size, microstructural uniformity, and porosity. At 1300 °C, the specimen containing 5 vol% h-BN@Al₂O₃ had a fine, relatively homogeneous microstructure with few visible pores; higher additions increased porosity and local particle agglomeration. For the 5 vol% composition, raising the sintering temperature from 1100 to 1400 °C increased the relative density and reduced visible porosity. At 1500 °C, local WC grain coarsening, microstructural inhomogeneity, and residual porosity increased, accompanied by lower mechanical properties. The best overall performance was obtained with 5 vol% h-BN@Al₂O₃ at 1400 °C: a relative density of 99.1 ± 0.4%, flexural strength of 871.3 ± 26 MPa, Vickers hardness of 1912.1 ± 38 HV, and fracture toughness of 9.86 ± 0.2 MPa·m 1/2 .