The ductile-brittle transition in ionic solids

Abstract
Polished monocrystals of silver chloride, sodium chloridc, lithium fluorido and magnesium oxide have been shown to exhibit ductility transitions when loaded by impact bending. The behaviour of silver chloride stood apart from that of the other solids in that the temperature below which it cleaved without macroscopic deformation was less than 0.1 Tm (where Tm is the melting point in degrees Kelvin) whereas the corresponding temperatures for sodium chloride, lithium fluoride and magnesium oxide were in the range 0.6–0.7 Tm . Notched monocrystals of silver chloride exhibited a change in fracture mode from cleavage to shear at a temperature of the order of 0.4 Tm . It is emphasized that the ductility of ionic solids is extremely sensitive to strain rate and the presence of a notch.

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