Change of electrical resistivity with martensite transformation of Ti-42 mass%Nb alloy

The behavior of the martensite transformation of Ti42 mass％Nb alloy was investigated by electrical resistivity measurement. The β phase was fully retained upon quenching from 1050℃. In the cooling and heating process below room temperature, hysteresis due to the martensite transformation was clearly observed, in contrast to previously reported behavior. The M_S and A_f temperatures of the sample prepared from the outer layer of a quenched plate were lower than those of the inner layer. Treatment of the solution under a low vacuum condition also lowered these temperatures and the hysteresis loop became much smaller. The effect of the solution temperature above βtransus on the transformation behavior was negligible. By heating to 400℃, the whole resistivity curve shifted upward, and the ω_S temperature increased, but the hysteresis loop still appeared at a low temperature. In situ TEM observation revealed that acicular martensite was formed at a low temperature and disappeared with heating, and that the reflection intensities of ω and α＂ in the β matrix increased with cooling. However, such behavior was hardly observed in a region irradiated by an electron beam during cooling.