Twin boundary energetics in pure aluminium

Abstract

The energetics of annealing twins in pure aluminium were investigated by thin film transmission electron microscopy techniques. Coherent {111} twin boundaries were rigorously analyzed, and found to have a frequency of less than 10 −3/grain as compared with approximately 1–10/grain for other f.c.c. metals and alloys at 0.8 T m . The formation of grain-corner twins was observed for the first time, indicating that corner twin formation is energetically favorable in pure aluminium. While twin bands (two parallel twin boundaries) intersecting grain boundaries were not observed, the analysis of nearly symmetrical twin boundary-grain boundary intersections allowed a mean ratio of twin boundary/grain boundary free energy to be measured as 0.23 at 450°C. The temperature coefficient for twin boundary free energy was found to be approximately −0.07 ergs/cm 2°C; and the twin boundary and stackingfault free energies were estimated to be 105 and 210 ergs/cm 2 respectively at room temperature (25°C).