Synthesis, microstructure evolution, and phase transformation of novel MoCoB–Co cermets.

To develop tungsten-free cermets, a novel MoCoB–Co cermet composed of MoCoB as a hard phase and Co as a binder phase was synthesized by the reaction sintering of Mo, Co, and B powders. The microstructure evolution, phase transformation, and mechanical properties of the cermet were investigated. We demonstrated that the mixed powders experienced three solid-phase reactions, Co + B → Co 2 B, 11Mo + 15Co 2 B → Mo 2 Co 21 B 6 + 9MoCoB, and 4Mo + Mo 2 Co 21 B 6 → 6MoCoB +15Co, and underwent two liquid-phase reactions. Nanosized, tremella-like Co structures were formed on the surface of the particles between 1100 and 1200 °C. The formation of these structures may be due to the Kirkendall effect. Further, the first liquid, L 1 , was formed at 1242 °C by a eutectic reaction between the tremella-like Co structures and MoCoB. This led to an increase in the relative density of the sample from 43% to 71.7%. At 1268 °C, the second liquid, L 2 , was formed as a result of a eutectic reaction between Co and MoCoB that further increased the relative density of the sample to 95%. At 1300 °C, the cermet exhibited the highest hardness and transverse rupture strength of 83.9 HRA and 1700 MPa, respectively. [ABSTRACT FROM AUTHOR]