Abstract
The effects of grain size and second phase on moisture-induced embrittlement of L12-type Co3Ti and Ni3(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 Co3Ti and the Ni3(Si, Ti)-Nb alloys, respectively, when their second phases are incoherent with the L12 matrix. Contrarily, finely precipitated Co solid solution phase that is coherent with the L12 matrix has the effect of enhancing moisture-induced embrittlement of the Co3Ti alloys. Mechanisms responsible for the microstructural effect on the moisture-induced embrittlement of the L12 intermetallic alloys were presented and discussed.
