629 高強度Mo_2NiB_2複硼化物系硬質合金の開発(新技術開発レポート)

抄録

Borides are promising candidates for wear resistant materials. But poor sinterability and extreme brittleness of borides retarded the fabrication of bulk materials. This paper gives criteria for the development of boride base cermets. Reaction boronizing sintering technique has successfully brought development of Mo_2NiB_2 type ternary boride base cermets. The addition of Cr and V to the cermets changed the boride structure from orthorhombic to tetragonal and resulted in the improvement of mechanical properties and microstructural rifinment. Ni-4.5B-47.9Mo-12.5V-xMn (mass%) model alloys with five levels of Mn content from 0 to 10mass% were prepared to investigate the effects of Mn on the mechanical properties and microstructure of Mo_2NiB_2 base cermets. The transverse rupture strength (TRS) of the cermets depended strongly on the microstructure, which varied significantly with Mn content. The maxmum TRS obtained at 2.5mass%Mn were 3.5GPa with hardness of 87HRA.