Strength of Synthetic Single Crystal Sapphire and Ruby as a Function of Temperature and Orientation

The modulus of rupture of sapphire single crystals was determined as a function of temperature for specimens with orientations favoring plastic deformation and for specimens with unfavorable orientations. From 600°C. to l000°C., the strength of both types increased with increasing temperature, but the increase was more pronounced for the former. Ruby specimens oriented favorably for plastic deformation also showed a large increase in strength. It is conjectured that the increase in strength results from stress relief by microscopic plastic deformation.