Solute Composition and Cryogenic Temperature Effects on the Stability of Nano-Twins Under Load

A series of Cu(Al) films were sputter-deposited with a high density of twins. These films were then subjected to indentation and compression loading under liquid nitrogen (-196 deg. C), dry-ice (-79 deg. C) and ambient temperature (23 deg. C) conditions after which the indent crater was characterized post-mortem. The ambient temperature indentation caused the film’s columnar morphology to undergo significant bending that tracked with the indent angle of penetration. For columnar grains that experienced this deformation, de-twinning occurred evident by a loss of twin content within the grain; however, the initial and final columnar grain morphology was retained. In contrast, the liquid nitrogen indent samples revealed very minor columnar bending with indent depth but the contact surface of the film against the indent resulted in a dramatic coalesce of the upper-most portions of the columnar grains into equiaxed grains with no evident twins. Through computational modeling, we reveal the higher mobility of twins as a function of reducing temperature. Using this information, we address how this temperature dependent mobility, under load and temperature, evolves the observed granular morphology. Furthermore, the influence of the solute on the twin behavior under these conditions is addressed.