Recrystallization behavior of boron-doped Ni76Al24

Abstract

Considerable hardness recovery and almost complete restoration of order were observed during annealing of 85 pct cold-rolled boron-doped Ni76Al24 prior to recrystallization. Recrystallization kinetics were investigated over a wide range of temperatures at small intervals of transformed volume fraction. The variation of transformed volume fraction with time showed two unusual distinct regions characterized by separate Avrami exponents and activation energies. The exponent decreased from 2.2 at 800 °C to 0.7 at 950 °C for X > 0.6 and had a temperature-insensitive value of 3 for X > 0.6. The activation energy below 900 °C was 145 kJ/g atom for X < 0.6 and 110 kJ/g atom for X > 0.6, and that above 900 °C was about 435 kJ/g atom. Equations for the kinetics have been derived based on concurrent recovery in the untransformed regions during recrystallization. The predictions of the equations agree exceedingly well with the experimental results and yield separate values of the activation energies for interface migration and recovery.