Evolution of a martensitic structure in a Cu–Al alloy during processing by high-pressure torsion

A Cu-11.8 wt% Al alloy was quenched in iced water from a high temperature (850 °C) to introduce a martensitic phase and then the alloy was processed using quasi-constrained high-pressure torsion (HPT). The micro-hardness and the microstructures of the unprocessed and severely deformed materials were investigated using a wide range of experimental techniques (X-ray diffraction, optical microscopy, scanning electron microscopy, transmission electron microscopy, and high- resolution TEM). During HPT, a stress-induced martensite–martensite transformation occurs and an \( \alpha^{\prime}_{1} \) martensite phase is formed. In the deformed material, there are nanoscale deformation bands having high densities of defects and twins in the \( \alpha^{\prime}_{1} \) martensite. It was observed that a high density of dislocations became pinned and accumulated in the vicinity of twin boundaries, thereby demonstrating a strong interaction between twin boundaries and dislocations during the HPT process.