Premium
Thermal‐Mechanical History and the Strength of Magnesium Oxide Single Crystals: II, Etch Pit and Electron Transmission Studies
Author(s) -
STOKES R. J.
Publication year - 1966
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1966.tb13146.x
Subject(s) - materials science , dislocation , transmission electron microscopy , crystallographic defect , impurity , dislocation creep , oxide , magnesium , composite material , condensed matter physics , metallurgy , crystallography , chemistry , nanotechnology , organic chemistry , physics
Mechanical tests show that the room‐temperature flow strength of magnesia single crystals varies with heat treatment. Flow strength depends on the size, density, and distribution of precipitate particles which inhibit the motion of dislocations. The present paper describes optical and electron transmission microscope evidence for a precipitation reaction in magnesium oxide. The observations correlate fairly well with mechanical test data. Mechanical tests also show that mobile dislocations are locked by heating above 600°C. The room‐temperature yield strength increases with time and temperature particularly when the aging temperature exceeds 1000°C. Studies to determine the nature of this locking mechanism are described. Etch pit studies show that dislocations aged above 600°C etch at a slower rate than fresh dislocations. This corresponds precisely with the change in mechanical behavior and both effects are attributed to impurity diffusion to dislocation lines. Electron transmission studies indicate a redistribution of point defects, left by moving dislocations, above 600°C. Eventually these result in a change in dislocation configuration which is considered responsible for the strong locking observed above 1000°C.