Production of nanotwinned copper via cryogenic milling

Abstract

Nanostructured copper powder was synthesized using high velocity cryomilling in order to induce deformation twinning and deformation twins in the refined microstructure. The powder was cold compacted and the Vickers hardness determined. A characterization of the powder evolution with increasing milling time was done using scanning electron microscopy and its microstructure was analysed with electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The mean hardness for low milling times was around 140 HV and for high milling times around 170 HV. In this final state, the microstructure was not homogeneous and showed three different grain-types: Nanostructured or ultrafine grains around 100-500 nm with nanosized twins, nanosized grains smaller than 50 nm and large equiaxed grains of 1 μm of diameter. The mean twin spacing in the nanotwinned grains was around 15 nm.