The role of copper twin boundaries in cryogenic indentation-induced grain growth

Nanostructured Cu films with and without a high density of twins were indented at approximately 77 K with a load of 0.5 N. Utilizing precession-enhanced electron diffraction in the transmission electron microscope, the crystallographic texture, grain size, and grain-to-grain misorientation were quantified. In both orientations, the nanotwinned Cu underwent grain growth in the pile-up region of the indent, with the < 100 > oriented nanotwinned Cu having marked increases in the Sigma 3 and Sigma 5 boundary fractions as compared to the < 111 > orientated nanotwinned Cu. The Cu film without twin boundaries predominately experienced grain distortion and refinement. The twinned grain structure seems to facilitate the observed grain growth, either as a result of the increased mobility of the twin boundaries through a complex mechanically-induced detwinning mechanism and/or microstructure dependent dynamic recrystallization. (C) 2013 Elsevier B.V. All rights reserved.