Weibull statistical analysis of sapphire strength improvement through chemomechanical polishing

Significant enhancements of the flexural strength of a, and c- plane sapphire by means of "super polishing" was first reported by McHargue and Snyder [Proc. SPIE 2013, 135 (1993)). The improvement was attributed to the removal of residual mechanical polishing damage. More recently, a comprehensive series of experiments was carried out by Crystal Systems for the specific purpose of assessing the effects of various polishing procedures on the high-temperature strength of c-plane sapphire. Subsequent testing at room temperature confirmed that chemomechanical polishing improves both the effective strength and the strength distribution. In this contribution we take advantage of the methodology previously used by Klein et al. [Opt. Eng. 41, 3151 (2002)] to perform a correct Weibull statistical analysis of biaxial flexure-strength data generated in the course of Crystal Systems' investigations. We demonstrate that chemomechanical polishing procedures can improve the high-temperature characteristic strength of c-plane sapphire by 150 % and the room-temperature Weibull modulus by 100 %.