Microstructure and thermostability of a W-Cu nanocomposite produced via high-pressure torsion

A coarse-grained W-25% Cu alloy is subjected to high-pressure torsion (HPT) at room temperature to different strains. Evolution of the microstructure during HPT processing is studied using X-ray diffraction analysis, scanning and transmission electron microscopy. It is demonstrated that HPT processing results in fragmentation of the tungsten particles and the formation of a 5-15 nm grain size nanostructure at equivalent strains of >= 256 (saturation). It is shown that the nanostructured W-25% Cu is thermostable up to 500 degrees C, with grain growth up to 50nm at 720 degrees C. During HPT processing, the lattice parameter of the copper and tungsten was found to increase and decrease, respectively, with increased level of equivalent strain. This is proposed to occur through the interdiffusion of copper atoms into tungsten grains and tungsten atoms into copper grains, as suggested by energy-dispersive X-ray analysis of the individual grains. The formation of a limited solid solution is considered and possible mechanisms for this effect discussed.