Effect of chemical composition on the microstructure and mechanical properties of MoCoB based cermets

Abstract

MoCoB–Co cermets with varying Mo/B atomic ratios (ARMo/B) and Co contents were fabricated, and their microstructure, mechanical properties, and corrosion behavior were investigated. The MoCoB hard phase exhibited the maximum grain size and anisotropy when the ARMo/B was 0.84, which degraded the mechanical properties. For ARMo/B ≥ 1.08, a third phase, Co7Mo6, and dense three-dimensional networks composed of stacking faults and ε-martensite plates were observed. These three-dimensional networks limited the dislocation slip in face-centered cubic γ-Co and ε-martensite, improving the hardness of the cermet and decreasing the transverse fracture strength (TRS). The corrosion resistance of the cermets was influenced by the MoCoB particle size, the Mo content of the binder phase, and the ε-martensite content. With an increase in the ARMo/B, the corrosion resistance of cermets initially decreased and then increased. Additionally, as the Co content increased, the hardness gradually increased, whereas the TRS and fracture toughness steadily decreased. For ARMo/B = 0.92 and a Co content of 45 at.%, the cermet displayed the best overall performance, with hardness, TRS, and fracture toughness values of HRA 89, 1720 MPa, and 13.2 MPa m1/2, respectively.