Correlation between domain size obtained by X-ray Bragg profile analysis and macroscopic flow stress in severely plastically deformed copper

The deformation-dependent evolutions of microstructure and of strength characteristics of pure copper processed by high-pressure torsion (HPT) have been studied under different values of the hydrostatic pressure. Multiple X-ray Bragg profile analysis (MXPA) and microhardness measurements were performed to analyze the structural and mechanical features of the samples deformed by HPT within wide ranges of true equivalent strains (0.5–100) and of applied pressures p = 4 to 8 GPa. A definite reciprocal correlation between the size of coherently scattering domains and the macroscopic flow stress has been revealed. This kind of domains represents that area of crystal which has been distorted less than 2° with respect to neighbouring areas of the grain. The data at best fit to a Hall–Petch like relation with an exponent of n = 1 which confirms that the macroscopic hardening is governed by subboundaries rather than by the boundaries of highly misoriented grains which size dependence on strain does not correlate at all with that one of the microhardness.