A JMAK-microhardness model for quantifying the kinetics of restoration mechanisms in inhomogeneous microstructure

The microstructure of heavily drawn wire is inhomogeneous and subsequent annealing of the material results in inhomogeneous recrystallization. Standard JMAK analysis of the kinetics of recovery and recrystallization for such microstructure is cumbersome and sometimes unreliable. This investigation was carried out on wire drawn (to true strain of 2.31) oxygen free high conducting (OFHC) copper, which was subsequently annealed at 250, 400 and 500 °C for annealing times ranging from 10 s to 1 h. The microstructural changes during the annealing were characterized by optical and scanning electron microscopy, orientation imaging microscopy (OIM) and microhardness. While standard JMAK analysis can be used to analyze the kinetics of recrystallization and grain growth, it was inadequate for quantifying the recovery kinetics. However, the modified JMAK-microhardness model developed enabled us to evaluate the kinetics of recovery, recrystallization and grain growth, using a single equation. In this approach, the JMAK model is expressed in terms of microhardness data, from which the parameters of the different restoration kinetics were determined. The values of JMAK exponent, n, the temperature-dependent constant, k, and the activation energy, Q, for recovery, recrystallization and grain growth obtained by the new method compared well with values in the literature.