Slip and Twinning in Polycrystalline Alumina (α‐Al₂O₃) Deformed under Hydrostatic Pressure between 600° and 1000°C

Abstract

The microstructure of polycrystalline alumina deformed under hydrostatic pressure and at low temperature is investigated by transmission electron microscopy. Deformation occurs mainly by prism plane slip and rhombohedral twinning. Introduction of hydrogen leads to a significant decrease in the yield stress. In large grain size alumina deformed with hydrogen, accommodation of twinning involves dislocation reactions in the twin boundary and in the grains rather than by cracking. Prism plane dislocations decompose into basal dislocations by cross slip probably due to a decrease of Peierls stress for basal slip in the presence of hydrogen.

Processing of Alumina and Corresponding Composites

“…In particular, it experiences practically no deformation under compressive loads at temperatures up to 1200 C, above which sapphire can deform by dislocation motion (Kronenberg, 1957;Lagerlof, Heuer, Castaing, Rivière, & Mitchell, 1994;Scott & Orr, 1983;Snow & Heuer, 1973). Only under extremely high hydrostatic stresses, which prevent crack propagation, plasticity may be extended at low temperatures such as 200 C; deformation is further enhanced in hydrogen atmosphere (Korinek & Castaing, 2003). Due to its high refractoriness, one of the most successful applications of alumina is in cutting tools for high-speed machining of metals.…”

ECCI, EBSD and EPSC characterization of rhombohedral twinning in polycrystalline α-alumina deformed in a D-DIA apparatus

“…In addition, they have been found at temperatures in the range of 623-1973 K [examples are reported by Stofel & Conrad (1963), Bertolotti & Scott (1971) and Scott & Orr (1983)]. Rhombohedral twin systems can also be activated at ambient pressures up to 1.5 GPa (Castaing et al, 2002(Castaing et al, , 2004Korinek & Castaing, 2003;Geipel et al, 1994;. Furthermore, rhombohedral twins have been reported at higher pressures in shock-loaded alumina samples [examples are given by Luo et al (2007) and Zhang et al (2008)].…”

“…Microstructural characterization of rhombohedral twins in deformed alumina has been primarily performed using transmission electron microscopy (TEM) (Hockey, 1971;Kim et al, 1973;Grimmer et al, 1990;Korinek & Castaing, 2003;Lartigue-Korinek et al, 2008;Barber & Tighe, 1965;Castaing et al, 2000). Deformation twins can also be characterized quantitatively in a SEM using electron channeling contrast imaging (ECCI) coupled with electron backscatter diffraction (EBSD).…”

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

“…3 On the other hand in ruby deformed at 10001C again under basal slip, dislocations are further aligned with h 2110i (Burgers vector at 601 from the line). 21 Mostly screw and edge dislocations have been observed in sapphire deformed under prism slip at 4001C (Cadoz et al 22 ) as well as in polycrystals deformed at 6301C (Lartigues Korinek and Castaing 26 ). The following discussion is focused on these dislocation characters.…”