High-speed thermal analysis of Zr-Nb alloys

Abstract

The M_s temperature of the ω, `diffuse ω', and α phases in Zr-Nb alloys have been studied by recording the thermal arrests obtained on rapid cooling and by electrical resistance measurements. Details of the apparatus which permits heat treatment of specimens in high vacuum, followed by gas quenching, are given together with the temperature of transformation and its dependence on rate of cooling. The transformation temperature is depressed in all alloys with increasing cooling rate, this depression being 100 degC at 3000 degC sec^-1 for pure zirconium. Proof of the dependence of ω formation on cooling rate is given. Hypothetical (M_s, M_f) curves based on the experimental results are shown which account for the sequence of phases observed in as-quenched zirconium alloys.