Effect of Tungsten Carbide Additions on the Microstructure, Mechanical, and Tribological Properties of M2 High-Speed Steel Matrix Composites

The dense WC-M2 high-speed steel matrix composites (WC-M2 HSS MMCs) with different WC content were prepared by mechanical alloying and vacuum sintering process. Tungsten Carbide (WC) with 0, 2, 5, 8, and 10 (by weight %) were dispersed in the matrix. The effects of WC content on the densification mechanism, phase composition, microstructure, fracture morphology, and mechanical and wear properties of the sintered composites were systematically investigated. The experimental results showed that at a vacuum sintering temperature of 1260 degrees C, the composite material specimens achieved near-full densification, with predominant phases being Martensitic, M7C3, M6C, M2C, MC, WC, alpha-Fe, and gamma-Fe. Reasonable WC addition has improved grain uniformity and reduced micro-defects, which enhanced the overall mechanical properties. With an increase in WC content, the hardness and relative density of the composites showed a gradual increase, whereas transverse rupture strength and impact toughness initially improved but subsequently decreased. The friction coefficient displayed an initial increase followed by a decrease, while the wear rate showed an opposite trend. The impact fracture morphology is dominated by the interfacial separation between the WC particle phase and the binder phase, supplemented by the plastic tearing of the binder phase. The impact toughness mainly depended on the fracture of the binder phase. During crack propagation, both intergranular and transgranular fractures exist, of which the intergranular fracture prevails and coarse grains are more prone to transgranular fracture. With 5 wt.% WC, the steel matrix composites obtained peak mechanical performance, with impact toughness, bending strength, and hardness measuring 13.2 J cm-2, 1584.3 MPa, and 780.9 HV, respectively, which also yielded the highest wear resistance.