Niobium coating effects on the tensile strength of sapphire fibres

Using a modified Weibull analysis to incorporate censored fracture data from fibres containing multiple flaw populations, this study has examined the effect of niobium coatings on the room temperature tensile strength of sapphire fibres. Fibre strengths were limited by failures which occurred predominantly from a combination of surface flaws, which are abrasion-induced, and internal voids, which form during the fibre growth process. Heat treatment of as-sputtered coated fibres at 1375°C caused a significant (∼36%) strength degradation. Unexpectedly, the cause of the strength degradation was traced to internal void growth which occurred only in the coated specimens.