Quantification of recrystallization kinetics in heavily drawn OFHC copper wires by microhardness technique

Mechanical properties of materials are inherently dependent on the micro structures that evolve during processing. The microstructure of heavily drawn and annealed OFHC copper is inhomogeneous, and as such it is difficult to assess its recrystallization kinetics by conventional methods. In this article, restoration kinetics of static recrystallization of heavily drawn oxygen free high conducting (OFHC) copper wires has been investigated by microhardness technique. The investigation was carried out on two cold drawn wires deformed to a true strain of 2.31 and 3.10 and annealed at 250°C for annealing times ranging from 10 s to 1 hr. The physical phenomena during annealing were characterized and analyzed using optical microscopy and measurement of microhardness. A unified approach, through the use of microhardness data, for the analysis of the restoration kinetics of recovery, recrystallization, and grain growth has been proposed. In this approach, a JMAK (Johnson-Mehl-Avrami- Kolmogrov) model was expressed in terms of microhardness data, and the results showed that the modified model linked the different restoration kinetics and provided the critical time for the transition from recovery to recrystallization, and to grain growth. The model compared favorably with conventional models, which treat the different restoration kinetics separately. Exponents of about 0.4 for recovery, 4.0 for recrystallization, and 0.5 for grain growth, were obtained. The results also showed that the JMAK exponent, n, is of the same order of magnitude as the grain growth exponent, 1/p.