Anormal Temperature Dependence of Resistivity in Ti-Mo Binary Alloys

The composition and temperature dependence of resistivity ρ was studied for Ti-2∼25 mass%Mo alloys quenched from 1173 K. The retained β phase after water quenching from 1173 K was observed in the alloys containing more than 9 mass%Mo. The anormal, so-called “negative”, temperature dependence (NTD), characterized by a larger ρ value at liquid nitrogen temperature than that at room temperature, appeared in the composition range between 10 and 23 mass%Mo. The observed anormal NTD was completely reversible and could be classified into three types at elevating measurement temperature by the behavior of the temperature coefficient of ρ, δρ⁄δT:(i) In the lower NTD composition range (10 and 12 mass%Mo), δρ⁄δT changed from positive to negative after passing through a maximum in ρ.(ii) δρ⁄δT was always negative over the whole temperature range of measurement in the medium part of the NTD composition range (12-15 mass%Mo) and(iii) In the higher NTD composition range (20 and 23 mass%Mo), δρ⁄δT changed from negative to positive after passing through a minimum in ρ.Because of the complete reversibility, the NTD was related to a diffusionless phase transformation, e.g. athermal ω formation, without any hystereses and not to aging phenomena with diffusion. The NTD with a maximum and minimum in ρ can be explained qualitatively from summation of a normal temperature dependence of stable β phase and an increase in ρ due to the formation of the athermal ω phase with decreasing temperature.