Basal slip in sapphire (α-Al2O3)

Chromium hardening and Peierls mechanism for basal slip in sapphire (α-Al2O3) at temperatures between 900 and 1500°C

“…They are not significantly higher than for undoped sapphire. 2,7 For all Cr concentrations and temperatures, we did not observed any serrated flow that is typical of dynamic strain ageing due to mobile dislocations interacting with diffusing impurities.…”

“…Athermal Cr solution hardening is observed essentially because plastic deformation can be achieved only at high temperature (above 0.6 times the melting temperature) in sapphire [2][3][4][5] which is brittle below 900 • C. This explains the impossibility to observe in sapphire thermally-activated Cr hardening below 0.2-0.3 times the melting temperature, contrary to observations in metals. 23 Although the analysis of work-hardening is beyond the scope of the present investigation, one can make the following remarks.…”

“…They were cut in the form of parallelepipeds of 2 mm × 2 mm × 4 mm. The compression direction is at 57 • from the [0 0 0 1] axis of sapphire, toward the [0 11 0] direction (orientation "aa" in Castaing et al 2 ) contained in the (211 0) plane parallel to two lateral faces. The orientation of the compression load favours the 1/3[11 2 0] and 1/3[1 21 0] basal slip with a Schmid factor of about 0.4 and it prevents 1 1 0 1 {11 0 2} rhombohedral twinning from being activated.…”

“…(0 0 0 1)1/3 2 1 1 0 basal slip is the primary deformation system for temperatures above 700 • C. [1][2][3][4][5][6][7] Prism plane slip along {12 1 0} 1 0 1 0 is the easiest slip system below 700 • C. 3,4 The 1 0 1 0 Burgers vector for prism plane slip, which is the fourth in length in sapphire, is dissociated into three partial dislocations with collinear 1/3 1 0 1 0 Burgers vector. 8 The Peierls mechanism has been frequently invoked to explain the movement of dislocations in sapphire, as much in the basal plane as in the prismatic plane, at intermediate temperatures.…”

Directionally Solidified Eutectic Ceramics; In-Situ Composites for High Temperature Structural Applications

“…Dislocation-assisted medianisms can be also ruled out. Given the orientation of the fibers, and the experimental conditions, if plastic deformation was in^rtant at the crack tips twinning should be observed [33]. Nfirror surfaces are flat and smooth and no striations are observed in the exterior of the fibers.…”