Fabrication and Evaluation of the High-Temperature Bending Strength for Mo2NiB2-Ni Cermets

Mo2NiB2-Ni cermets, a type of boride-based cermet, exhibit attractive mechanical properties such as high hardness and good wear resistance. However, the mechanical properties of these cermets have predominantly been evaluated at room temperature. In this study, three-point bending tests were conducted at high temperatures to investigate the mechanical properties and fractography of Mo2NiB2-Ni cermets. A ternary Mo2NiB2-Ni cermet was prepared using a calcination process to synthesize Mo2NiB2 before sintering. The calcination process resulted in finer and more uniform Mo2NiB2 particles, enhancing the microstructure. Consequently, hardness and transverse rupture strength (TRS) were improved. Three-point bending strengths were measured for samples measuring 4.0 × 3.0 × 24 mm at temperatures up to 800°C in an argon environment, using silicon carbide jigs with a 16 mm span. The results indicated that TRS remained approximately constant at about 1.6 GPa up to 500°C but decreased sharply above 600°C, reaching about 0.12 GPa at 800°C. This decrease was attributed to the softening of the nickel binder phase, which adversely affected the TRS.