Machining, Surface Work Hardening, and Strength of MgO

Abstract

Machining of MgO by sawing, grinding, sanding, and polishing introduces a surface layer of dense slip whose depth depends on material (e.g. yield stress and grain size) and machining parameters. Cracks, which were always more shallow than the depth of slip, extended from sawn and, to a lesser extent, from ground surfaces into single crystals and some large grains. Annealing removed the slip and decreased surface grain growth in fine‐grained bodies but in general did not result in recrystallization. Surface work hardening increases hardness; it also increases bend strengths of some single crystal orientations and of larger‐grained bodies, especially those with limited intragranular porosity. Fine‐grained bodies were weakened by machining.