Microtopographic evolution and damage characteristics of sapphire fiber under high temperatures

Sapphire fibers exposed to air exhibit performance degradation during high-temperature in-situ testing. Therefore, analyzing the damage characteristics of sapphire fibers under high-temperature conditions and developing effective protective measures are essential. This study investigates the damage characteristics and microtopographic evolution of sapphire fibers annealed at temperatures ranging from 1400°C to 1600°C, with 100°C intervals. The high-temperature damage characteristics of the sapphire fibers were analyzed using a size threshold filtering method combined with thresholding and connected component labeling techniques. The results indicate that both the size and density of bubble-like damage on the sapphire fiber increase with higher annealing temperatures. Furthermore, the O: Al (oxygen: aluminum) ratio was calculated to study the high-temperature damage products of the sapphire fibers. The findings suggest that the damaged products exist as a mixture of hydrated alumina. Additionally, transverse etched lines, initially present on the pristine sapphire fiber surface, transform into longitudinal etched lines during annealing due to the release of internal stress. The width of these longitudinal etched lines increases progressively with higher annealing temperatures. To prevent damage at high temperatures, a vacuum annealing method was employed, and gradient annealing effectively suppressed the expansion of etched lines. This study provides further insight into the damage mechanisms and microtopography evolution of sapphire fibers under high-temperature conditions while also providing a theoretical foundation for the packaging and protective technologies used in high-temperature applications of sapphire fibers.