A previous investigation revealed that the addition of Cr to the Mo2NiB2 complex boride base cermet changed the boride phase structure from orthorhombic to tetragonal and resulted in the remarkable improvement of mechanical properties and microstructural refinement. In this investigation, the effects of eight alloying elements, such as V, Fe, Co, Ti, Mn, Zr, Nb, and W, on the mechanical properties and microstructure of the cermets were studied by using model cermets with composition of N-6 masss% B-58, 6 mass% Mo-10 mass% X (X = additional elements), From these elements V showed the same effects as Cr showed on the mechanical properties and microstructure associated with a simultaneous phase transformation of the complex boride, Addition of other alloying elements (Fe, Co, Ti, Mn, Zr, Nb, and W) did not exhibit the structural change and strengthening, These elements tended to form coarse grained orthorhombic complex boride, as well as coarse grained carbide or intermetallic compounds which degraded the strength of the cermets. The phase transformation of the Mo2NiB2-type complex boride from orthorhombic to tetragonal with optimal addition of Cr and V was essential for the improvement of the mechanical properties and microstructural refinement of the cermet. (C) 1997 Academic Press. [References: 4]
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