Effects of Mo/B Atomic Ratio on the Mechanical Properties and Structure of Mo2NiB2 Boride Base Cermets with Cr and V Additions

The effects of Mo/B atomic ratio ranging from 0.8 to 1.5 (Mo contents) on mechanical properties and phase formation were studied for cermets with the composition of Ni–5.0B–xMo– 3.5Cr–11.5V (wt%). A strong correlation between mechanical properties and phase formation was observed in the cermets. The cermets with somewhat higher stoichiometric Mo content, i.e., Mo/B ratios of 1.1 and 1.2, showed a very fine ideal two-phase microstructure with a homogeneous distribution of a tetragonal Mo2NiB2 (M3B2)-type complex boride in a solution-strengthened Ni base binder and hence exhibited an excellent transverse rupture strength (TRS) of more than 2.7 GPa and hardness of about 88 RA. In the cermets with low and high Mo/B ratios, another type of a complex boride, which was an orthorhombic M3B2 or a tetragonal M5B3 boride, was detected and was considered to deteriorate TRS due to a coarse-grained microstructure.