Basal Slip and Twinning in Sapphire (α-Al₂O₃)

Abstract

Dislocation slip is an important mode of plastic deformation in sapphire (α-Al₂O₃) above its brittle to ductile transition temperature (≈ 1100°C). Three dislocation slip system have been identified, (0001) 1/3 $\left\langle {2\bar 1\bar 10} \right\rangle$ † basal slip, $\left\{ {\bar 12\bar 10} \right\}\left\langle {10\bar 10} \right\rangle$ prism plane slip, and $\left\{ {\overline 1 101} \right\}\frac{1}{3}\left\langle {101\overline 1 } \right\rangle$ (and/or $\left\{ {\overline 1 012} \right\}\frac{1}{3}\left\langle {10\overline 1 1} \right\rangle$ and/or $\left\{ {\overline 1 \overline 1 23} \right\}\frac{1}{3}\left\langle {10\overline 1 1} \right\rangle$ ) pyramidal slip.^1–15 It has further been shown that at elevated temperatures basal slip (|b _B| = 0.476nm) is the easy slip system, whereas prism plane slip (|b _Pr| = 0.822nm) is the secondary slip system and pyramidal slip (|b _py | = 0.513nm) is the most difficult slip system to activate at all temperatures. At low temperatures, however, prism plane slip is preferred over basal slip,^12–14 and both basal^{2, 16, 21} and rhombohedral twinning,^22–26 become important deformation mechanisms. Thus, it is important to understand how the different deformation mechanisms are related to each other, and of particular interest in this paper is the relationship between basal slip and basal twinning