A transformation kinetic model and its application to CuZnAl shape memory alloys—II. Non-isothermal conditions

Abstract

It has been demonstrated that the activation energies of the solid state transformations obeying the modified Johnson-Mehl-Avrami/Austin-Rickett type kinetic equation can be determined from both the Kissinger method and the Ozawa method Q RT m is lager than 5. The errors involved in the activation energy determined from the two methods have been presented as a function of Q/ RT m is larger than 5. The errors involved in the effects of the kinetic exponents, c and n, and the heating rate θ and y m and T m have been analyzed It has shown that the fraction y m is nearly independent of the heating rate while the peak temperature T m is a very weak function of the exponents n and c. The effects of the kinetic parameters and the heating rate on the ( yvs T) and (d y/d t vs T) curves are also discussed. Moreover, procedures for the simultaneous determination of the exponents c and n from a single DSC trace are provided. This kinetic model has been applied to the analyses of the non-isothermal aging kinetics of three CuZnAl shape memory alloys. The comparison between isothermal and non-isothermal results further supports the validity of this kinetic equation for the description of heterogeneous solid state transformations.