STRENGTHENING SAPPHIRE BY COMPRESSIVE SURFACE LAYERS

Compressive surface layers were formed on sapphire rods. The methods included glazing and quenching, formation of Al2O3Single Bond signCr2O3 solid solution surface layers, and formation of mullite and calcium aluminate surface layers. The presence of the compressive stresses was demonstrated by slotted rod tests. Substantial improvements in flexural strength and thermal shock resistance were observed. The highest average flexural strength was obtained by glazing and quenching and was 340 000 psi. The strengths were measured in the as-treated" and "as-treated and abraded" conditions. The abraded samples retain a substantial portion of the improved strength. © 1969 The American Institute of Physics."