Prismatic Slip of A1₂O₃ Single Crystals Below 1000°C in Compression Under Hydrostatic Pressure

Abstract

Alumina single crystals were compressed perpendicular to the [0001] axis at a constant strain rate between 20° and 950°C. At r>200°C, failure was suppressed by_hydrostatic pressures of 500 to 1500 MPa. Prismatic slip {1120}〈1100〉 was deduced from optical observations of the lateral surfaces and from stress‐optical features in thin sections cut from the specimens. The critical resolved shear stress (CRSS) decreased rapidly with increasing temperature, from a maximum of ∼3000 MPa at 200°C (strain rate 2±10‐−5 s−1). A simple linear law can be fitted with the logarithm of the CRSS as a function of temperature, up to 1800°C. The rate‐controlling mechanism for dislocation glide is likely to be either the Peierls barrier or barriers due to dissociation out of the glide plane.

Damage evolution in dynamic deformation of silicon carbide

“…This equation shows that the fragment size increases with the material resist- ance to cracking (K IC ). SiC-II had a higher fracture toughness, and a concomitantly larger fragment size than SiC-I, in accordance with equation (3). However, as shown in Fig.…”

“…It was modi®ed by McClintock and Walsh [2] to include the eect of friction of crack surfaces. Castaing et al [3] demonstrated that, under superimposed hydrostatic stresses, Al 2 O 3 can undergo signi®cant plastic deformation by dislocation motion at ambient temperature. Mitchell, Pletka, Heuer and co-workers [4±6] developed a work-hardening theory for Al 2 O 3 , based on the interaction of prismatic dislocation loops with gliding dislocations.…”

“…3(b), the minimum gives d G . If additional work terms are involved in the energy balance, the predicted fragment size would be dierent than the size calculated from equation (3). Two terms should be added to the energy E: a plastic work term (W ) and an internal damage term (D ).…”

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

“…The similarity in bounds for slip and twinning thus points to rate and pressure independence of initial yield at low to room temperatures. The pressure independence of yield at confining pressures of the order of 1.5 GPa has been confirmed experimentally for prism slip (Castaing et al 1981). However, in shock experiments, plastic strain rates are not constant, but ramp up from small values at the onset of yielding at the front of the plastic wave to values estimated in excess of 10 5 s K1 in the wake of the plastic wavefront (Munson & Lawrence 1979), with the maximum rate depending on the material and the severity of the impact loading.…”

“…Owing to sapphire's brittle nature at low temperatures, measurements of the yield mechanisms corresponding to (4.1)-(4.3) must occur at high pressures that suppress tensile fracture, e.g. indentation (Tymiak & Gerberich 2007) or confined compression (Graham & Brooks 1971;Castaing et al 1981;Scott & Orr 1983;Lankford et al 1998). Graham & Brooks (1971) suggested that shear failure via attainment of the theoretical strength (4.3) could occur in shock-loaded sapphire.…”