The influence of Co and SiC on the sintering, microstructure and tribological properties of (Ti_1/3Zr_1/3V_1/3)B₂ medium-entropy diboride-based ceramics

The (Ti_1/3Zr_1/3V_1/3)B₂(MEB) composite ceramics with various Co and SiC additions were prepared by spark plasma sintering technology at 1600 °C. The influence of Co and SiC on the microstructure and mechanical properties were studied. Reciprocating sliding wear experiments of boride ceramics sliding against GCr15 ceramic were also performed at 1 N, 5 N and 10 N (Temperature: 25 °C, frequency: 3 Hz, stroke: 1 mm). The result suggest that the sintering additives not only significantly reduces the sintering temperature of boride ceramic, but also refines the microstructure and improves its mechanical properties. The hardness and fracture toughness of MEB-20SiC–10Co ceramics are 27.76 GPa and 3.9 MPa m^1/2, 30.6 % and 60 % higher than that of MEB, respectively. The increase in fracture toughness results from crack deflection and branching of the SiC particles. Tribological results indicates that MEB-20SiC–10Co also show the best tribological performance. The wear rate of MEB and MEB-20SiC–10Co at 10 N load are 2.17 × 10⁻⁶ mm³N⁻¹m⁻¹, 1.29 × 10⁻⁶ mm³N⁻¹m⁻¹, oxidative wear and adhesive wear are the main wear mechanisms. Analyzing of the wear tracks revealed a significant transfer of material from the counterpart to the tribo-interface. A friction film consisting mainly of titanium oxide and part of boron oxide was generated on the worn surface, which contributes to the improvement of tribological performance.