Abstract
To apply to plastic injection molding parts, the effects of Cr and Mo contents on mechanical properties and corrosion resistance in a molten fluoropolymer were studied in two series of Mo2NiB2 base cermets with the composition of Ni-5.0mass%B-Xmass%Cr-51.0mass%Mo (X: 12.5∼20.0) and Ni-5.0mass%B-15.0mass%Cr-Ymass%Mo (Y: 46.6∼55.4 (Mo/B atomic ratio: 1.05∼1.25)).
In Ni-5.0mass%B-Xmass%Cr-51.0mass%Mo cermets, transverse rupture strength (TRS) increased with increasing Cr content and showed a maximum value of 2.2GPa at 17.5mass%Cr, and then decreased at 20.0mass%Cr. Hardness increased monotonically with increasing Cr content and showed a maximum value of 86.5HRA at 20.0mass%Cr. In Ni-5.0mass%B-15.0mass%Cr-Ymass%Mo cermets, TRS increased with increasing Mo content and showed a maximum value of 2.3GPa at 53.2mass%Mo (Mo/B atomic ratio: 1.20), and then decreased at 55.4mass%Mo (Mo/B atomic ratio: 1.25). Hardness increased monotonically with increasing Mo content and showed a maximum value of 87.5HRA at 55.4mass%Mo. In both series of cermets, improvements of TRS and hardness were mainly attributed to refinement of tetragonal M3B2 (M: Mo, Ni, Cr) complex boride particles. Lowering of TRS seems to be due to embrittlement caused by aggregation of tetragonal M3B2 complex boride particles and precipitation of tetragonal M5B3 complex boride particles.
The excellent corrosion resistance equivalent to Hastelloy C in a molten fluoropolymer was obtained in Ni-5.0mass%B-15.0∼17.5mass%Cr-51.0mass%Mo and Ni-5.0mass%B-15.0mass%Cr-48.8∼53.2mass%Mo (Mo/B atomic ratio: 1.10∼1.20) cermets.
