Effect of Microstructure on Moisture-induced Embrittlement of L12 Intermetallic Compounds

Abstract

The effects of grain size and second phase on moisture-induced embrittlement of L1 2 -type Co 3 Ti and Ni 3 (Si, Ti) alloys were investigated by tensile test in air and vacuum as functions of strain rate and temperature, in combination with microstructural and fractographic observation. In both the intermetallic alloys, brittle-ductile transition (BDT) strain rate defined from an elongation vs. strain rate curve decreased with decreasing grain size, meaning that fine-grained microstructure has the effect of reducing the moisture-induced embrittlement. Also, it was found that dispersion of Co solid solution phase and Nb-containing second phase has the effect of reducing moisture-induced embrittlement of the Co 3 Ti and the Ni 3 (Si, Ti)-Nb alloys, respectively, when their second phases are incoherent with the L1 2 matrix. Contrarily, finely precipitated Co solid solution phase that is coherent with the L1 2 matrix has the effect of enhancing moisture-induced embrittlement of the Co 3 Ti alloys. Mechanisms responsible for the microstructural effect on the moisture-induced embrittlement of the L1 2 intermetallic alloys were presented and discussed.