Mo2NiB2系硬質合金の機械的性質と硼化物相の結晶構造

駒井 正雄, 山崎 裕司, 小崎 信也, 高木 研一

doi:10.2320/jinstmet1952.58.8_959

Effects of alloying elements on the mechanical properties and boride crystal structure of Mo₂NiB₂ base hard alloys were studied using the alloys whose compositions were Ni-6 mass%B-58.6 mass%Mo-(0-20)mass%Cr and Ni-6 mass%B-58.6 mass%Mo-10 mass%X (X: V, Fe, Co, Ti, Mn, Zr, Nb and W). The alloys consist of a Mo₂NiB₂ type ternary boride as a hard phase and a nickel base binder alloyed with Mo and other elements, both of which are formed by reaction boronizing sintering. The transverse-rupture strength (TRS) of the Cr containing alloys depended strongly on the microstructure, which varied significantly with Cr content. The maximum TRS of 2.3 GPa and a hardness of HRA87 were obtained at 10 mass%Cr content. A crystal structural change from the orthorhombic M₃B₂ (M: Metal) to the tetragonal M₃B₂ was observed with increasing Cr content. The highest TRS value at 10 mass%Cr was attributed to the formation of fine M₃B₂ particles with a tetragonal structure. In the eight additional elements, vanadium showed the same effects as chromium on the mechanical properties associated with the crystal structural change of M₃B₂ from the orthorhombic to the tetragonal. Additions of the other alloying elements did not lead to the crystal structural change of M₃B₂ and the improvement of the mechanical properties of the Mo₂NiB₂ base hard alloys. The Rietveld analysis method successfully revealed the atomic configurations as well as the lattice parameters of the unit cells of the orthorhombic M₃B₂ at non-Cr and the tetragonal M₃B₂ at 10 mass%Cr.

Mo<SUB>2</SUB>NiB<SUB>2</SUB>系硬質合金の機械的性質と硼化物相の結晶構造

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