Thermal stability of highly nanotwinned copper: The role of grain boundaries and texture

To study the effect of nanotwins on thermal stability, a comprehensive characterization study was performed on two types of ultrafine grained (UFG) copper samples, with and without nanotwins. The two samples were sequentially heat-treated at elevated temperatures, and the grain size, grain boundary character, and texture were characterized after each heat treatment. The as-prepared nanotwinned (nt) copper foil had an average columnar grain size of similar to 700 nm with a high density of coherent twin boundaries (CTBs) (twin thickness, similar to 40 nm), which remained stable up to 300 degrees C. In contrast, the other UFG sample had few CTBs, and rapid grain growth was observed at 200 degrees C. The thermal stability of nt copper is discussed with respect to the presence of the low energy nanotwins, triple junctions between the twins and columnar grains, texture and grain growth.