Plastic Deformation of MgO Single Crystals up to 1600°C

Abstract

Stress-strain curves are presented for MgO single crystals, compressed with (100) and (111) stress axes, for temperatures from 1000' to 1600OC. The yield stress of (100) specimens decreases slightly in this temperature range. The strain-hardening rate passes through a maximum at about ll0O'C and decreases by a factor of about 8 at 1600°C. Above about llOO°C, the strain rate of (100) specimens is considerably less sensitive to changes in stress and the shape of t h e stress-strain curves changes. The yield stress of (1 11) specimens decreases rapidly with increasing temperature without a change of slope up to 1600'C. T h e ratio of the yield stresses for (111) and (100) specimens decreases continually from 1200' to 16OOOC. Various stress rates were used to obtain a measure of strain hardening at 13OO0C.Static recovery experiments were carried out at 1000' and 1400'C. At lO0O'C static pinning occurred during t h e unloaded period; at 1400°C orthorecovery occurred. Stress-strain curves were analyzed by a dynamic approach based on the length of moving dislocation line in the crystal and the average dislocation velocity.

Dislocations and Plastic Deformation in MgO Crystals: A Review

“…In the study of Day et al [7], dislocation slip is confined in a single slip system between room temperature and 1000 K. From 1000 K to 1400 K, two conjugate 1 ⁄2<110>{110} slip systems (with orthogonal slip planes) interpenetrate and produce the strain. This configuration is also mentioned in the work of Copley [8]. In both temperature regimes, the initial distribution of dislocations plays a key role on the primary slip plane activity.…”

“…Schmid factors for {110}, {100} and {111} modes and <100>, <110> and <111> compression axis (CA) are shown Table 2. Etched surface analyses were also performed to characterize slip localization [6][7][8]. In the study of Day et al [7], dislocation slip is confined in a single slip system between room temperature and 1000 K. From 1000 K to 1400 K, two conjugate 1 ⁄2<110>{110} slip systems (with orthogonal slip planes) interpenetrate and produce the strain.…”

“…Hulse, Copley and Pask performed a set of compression tests on single crystals investigating the CRSS and deformation processes in both slip modes [5,8,14]. Temperatures investigated range from 100 K up to 1400 K for the 1 ⁄2<110>{110} slip systems.…”

A Critical Review of the Peierls Mechanism

“…Thomson and Roberts (1960), May and Kronberg (1963), Hulse et al (1963) and Copley and Pask (1965) Several data., however, seem to diss.ualify the Peie1·ls mechanism;…”

Creep of lithium fluoride single crystals at elevated temperatures

“…-28- It should be noted that this particular trend in stress-strain behavior is the reverse of that observed previously for MgO by Copley 20 and Pask. The strain hardening rate for <111> oriented MgO crystals in compression was there found to be considerably greater than that for <100> crystals for all temperatures up to 1600°C (~.61 T ), the limit m of test temperatures employed in that investigation.…”