Kinetics of Beta-Phase Decomposition and the Precipitation of Alpha-Zirconium in Nb-25 at%Zr Superconducting Alloy

The kinetics of beta-phase decomposition and the precipitation of alpha-zirconium were investigated by mesuring the change in electrical resistivity at liquid nitrogen temperature. Studies on the reaction in the miscibility gap region were carried out by rapidly heating the specimens which were previously quenched from 1200°C or cold-worked after the quenching. The kinetics of the decomposition are conveniently described with T-T-T curves extending from 650°C to 800°C. It is evident that there is a general acceleration of the decomposition in the cold-worked specimens. For example, the 50 per cent decomposition lines in 25 to 75 per cent cold worked specimens are displaced to about 1/10 of that for the specimens quenched from 1200°C.In order to investigate the precipetation of alpha-zirconium, specimens after about 75 per cent beta-phase decomposition, heated at 750°C for 46 hr after 75 per cent cold drawing, were used and the reaction rate was measured between 400°C and 500°C. The time required to attain about 95 per cent of the transformation were about 103 min at 500°C and about 6×103 min at 400°C. The acceleration of the precipitation by cold work are also shown in the specimens cold-worked after the beta-phase decomposition treatment.