Effect of microstructure on moisture-induced embrittlement of L12 intermetallic compounds

The effects of grain size and second phase on moisture-induced embrittlement of L1(2)-type Co3Ti 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 Cc solid solution phase and Nb-containing second phase has the effect of reducing moisture-induced embrittlement of the Co3Ti and the Ni-3(Si, T)-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 CoTi alloys. Mechanisms responsible for the microstructural effect on the moisture-induced embrittlement of the L1(2) intermetallic alloys were presented and discussed.