Analysis of a Kink Pair Model Applied to a Peierls Mechanism in Basal and Prism Plane Slips in Sapphire (α‐Al₂O₃) Deformed Between 200° and 1800°C

Abstract

A model based on dislocation glide controlled by the nucleation and propagation of kink pairs in a high Peierls stress crystal is revisited and modified to account for changes in dislocation densities and segment lengths with temperature and stress. It is applied to the critical-resolved shear stress (CRSS) for basal and prism plane slip in sapphire (a-Al 2 O 3 ). According to agreedupon knowledge on dislocations in sapphire, basal slip and prism plane slip are modeled with undissociated and dissociated dislocations, respectively. In the latter case, partial dislocations move independently. Among a number of sets of fitting parameters, good fits between experimental and modeled CRSS's are obtained in the long segment limit over the whole range of temperatures by making use of physically sound parameters, including a stress dependence of the dislocation density.

A continuum description of nonlinear elasticity, slip and twinning, with application to sapphire

“…Experimental data quantifying the mechanical response of sapphire single crystals of various orientations and spanning a wide range of temperatures and strain rates are available (Graham & Brooks 1971;Tymiak & Gerberich 2007). While various kinetic relationships for slip (Lagerlof et al 1994;Rodriguez et al 2008) and twinning (Scott & Orr 1983) have been postulated to describe individual experiments, a more general model is needed to collectively explain the material's behaviour over a broad range of loading conditions encountered in practical applications.…”

Creep behavior and related structural defects in Al2O3–Ln2O3 (ZrO2) directionally solidified eutectics (Ln=Gd, Er, Y)

“…A non-extensive list of works on sapphire deformation may be found in Refs. [21][22][23] Basal slip has the lowest critical resolved shear stress at all temperatures above 700 • C. [23][24][25] Prism plane slip is preferred at lower temperature; at high temperature it occurs for much higher stresses than those required for basal glide 22 and prism plane dislocations are found to decompose into basal dislocations; prism plane dislocations are no more found after some percents of deformation. 22 Pyramidal slip {0 11 2}1/3 01 1 1 , or {1 01 1}1/3 01 1 1 , requires such high stresses that is rarely a dominant deformation mechanism.…”

Superplastic deformation of directionally solidified nanofibrillar Al2O3–Y3Al5O12–ZrO2 eutectics

“…Although pyramidal and rhombohedral slip have also been reported in AI2O3, the stresses required are too high to be active in the ternary eutectic rods. 27 ' 28 Finally, it should be noticed that dislocation slip is far easier in YSZ than in either AI2O3 or YAG 29 but the small thickness of YSZ domains (<50 nm) leads to very high stresses for dislocation nucleation 30 and hinders the dislocation activity in this phase.…”