The high-temperature deformation mechanisms of O-free high-conductivity material were evaluated at 300 to 950C, using strain rates of 0.001 to 100/s. The stress-strain behavior during hot-compression was typical of the occurrence of dynamic recrystallization: with an initial peak in the flow stress, followed by a steady state, and preceded by oscillations at lower strain rates and higher temperatures. The results were analyzed by using the kinetic rate equation; involving a hyperbolic sine relationship of the steady-state flow stress to the strain rate. At 500 to 950C, and strain-rates of 0.001 to 10/s, a stress exponent of 5 and an apparent activation energy of 145kJ/mol were deduced. The power-law relationship also yielded similar values (5.18 and 152kJ/mol). On the basis of these parameters, the rate-controlling mechanism was suggested to be dislocation-core diffusion. The flow stress for O-free high-conductivity Cu data, reported by earlier investigators for different O contents, was consistent with the present analysis. It revealed that an O content of less than about 40ppm did not have any significant effect upon core diffusion since it was too low to clog the dislocation pipes. At strain-rates greater than 10/s, and at 750 to 950C, the stress exponent was equal to about 3.5 and the apparent activation energy was 78kJ/mol. This suggested that the plastic flow was controlled by grain-boundary diffusion.

Kinetics of High-Temperature Deformation of Polycrystalline OFHC Copper and the Role of Dislocation Core Diffusion. Y.V.R.K.Prasad, K.P.Rao: Philosophical Magazine, 2004, 84[28], 3039-50