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Dislocations and the Tensile Strength of Magnesium Oxide
Author(s) -
STOKES R. J.,
LI C. H.
Publication year - 1963
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.1151-2916.1963.tb11769.x
Subject(s) - materials science , dislocation , brittleness , crystallite , ultimate tensile strength , slip (aerodynamics) , grain boundary , partial dislocations , ductility (earth science) , oxide , composite material , magnesium , crystallography , condensed matter physics , metallurgy , creep , microstructure , chemistry , physics , thermodynamics
It has been shown with single crystals, bicrystals, and polycrystalline material that the strength of magnesium oxide depends on the availability of mobile dislocation sources. Mobile dislocations, introduced by mechanical contact at the surface, are responsible for the ductility normally observed in single crystals. When mobile dislocations are removed by a chemical polish, single crystals become extremely strong (>160,000 psi) and elastic. In the absence of mobile dislocations bicrystals are also extremely strong and elastic but in their presence bicrystals are relatively weak (10,000 psi) and brittle. The brittleness is due to the direct interaction of slip bands with grain boundaries to generate cracks. The strength of high‐density polycrystalline magnesia is similarly sensitive to the presence of mobile dislocations. When care is taken to eliminate surface defects and to immobilize dislocations, tensile strengths of 30,000 psi can be attained, but when mobile dislocations are present the strength drops to 15,000 to 20,000 psi. Mobile dislocations can be introduced directly by mechanical contact or indirectly through the presence of pores.