Effects of crystallization of inter-granular glassy phase on the mechanical performance of alumina ceramics

Abstract

Alumina ceramics are widely used to fabricate the insulating tubes of vacuum electronic devices. The long-term stress borne by ceramics during service may lead to failure, so it is of great significance to investigate the mechanical reliability of ceramics. Annealing is a commonly used step in the processing of an alumina ceramic, which may affect its mechanical performance. Herein, the effects of inter-granular crystalline phase induced by annealing on the service reliability of a 95% alumina ceramic are studied, and the mechanisms are analyzed by material characterizations. Moreover, the service life of annealed ceramics is predicted through theoretical calculation. The crystallization of inter-granular glassy phase results in the decreased fracture strength of the alumina ceramic, but increases its long-time service reliability. The existence of inter-granular crystalline phases is responsible for the increase of flaw tolerance and corrosion-resistance of the alumina ceramic, and therefore the alleviated static fatigue can be obtained after annealing. Furthermore, the reliability of the annealed ceramic-Kovar alloy composite joints is analyzed, in which the stresses induced by brazing may lead to cracks in the alumina ceramic. In summary, this work discusses the influence of the crystallization of inter-granular glassy phase on the mechanical performance of alumina ceramics, which is of great value for developing ceramics with excellent mechanical reliability.