Resistivity study and computer modelling of the isothermal transformation kinetics of Ti-8Al-1Mo-1V alloy

The kinetics of the betadouble right arrowalpha+beta phase transformation in Ti-8Al-1Mo-1V alloy under isothermal conditions have been studied using electrical resistivity technique. The kinetics have been modeled in the theoretical frame of the Johnson-Mehl-Avrami (JMA) theory. Different mechanisms of the betadouble right arrowalpha+beta phase transformation have been observed at different temperatures of isothermal exposure. At temperatures below 900 C homogeneous nucleation and plate-like grown alpha-phase has been observed. At temperatures above 900 C two mechanisms of the transformation have been suggested. First primary alpha-phase is formed in grain boundaries followed by alpha-phase volume fraction increase in conditions of decreasing nucleation rate and a plates nucleated and grown from the grain boundaries. The JMA kinetic parameters have been derived for the different temperatures and mechanisms of the transformation. A good agreement between the calculated and the experimental transformed fractions has been demonstrated. Time-temperature-transformation diagram with iso-lines tracing the amounts of the alpha-phase has been designed for the betadouble right arrowalpha+beta transformation in the Ti-8Al-1Mo-1V alloy. Disagreement between calculated and experimental phase equilibria for the alloy studied has been shown. (C) 2002 Elsevier Science B.V. All rights reserved.