Temperature Range of Formation of Athermal ω Phase in Quenched β Ti-Nb Alloys

Abstract

Negative temperature dependence (NTD) of electrical resistivity (ρ) was investigated on several Ti-Nb alloys quenched from 1073 K in relation to α″ martensite and athermal ω phases.The estimation of starting and ending temperatures of the athermal ω formation, ωs and ωf, respectively, was attempted with special care to avoid the reverse transformation of the α″ phase and the decomposition of the retained β phase.The α″ was observed in the 20∼35%Nb alloys, and in the alloys with more than 40%Nb only the retained β was observed. The NTD was observed only in the 40%Nb alloy, and both a maximum and a minimum of ρ appeared in the temperature range of 77∼350 K. This supports the previously proposed model for the resistivity change during the athermal ω formation.The values of ωs and ωf estimated from resistivity temperature curves decreased with Nb content. The composition range of alloys, in which the so-called quenched ω phase was observed, coincided with that of the alloys which was intermediate between ωs and ωf at room temperature.Therefore, the “quenched ω” may be the athermal ω with a large volume fraction at room temperature.