Improved Refractory Oxides for Structural Applications. Part I. Slip Systems in Aluminum Oxide (Al2O3). Part II. On the Yield Point in Sapphire

摘要

Two reports are presented. In the first, crystallographic notation for Al2O3 is reviewed, with particular reference to the correct basis to be used in describing slip systems. Electron microscopical analysis of an alumina polycrystal deformed about 5% at 1150C under a hydrostatic confining pressure confirmed that pyramidal slip occurred. The second discusses yielding in sapphire undergoing basal slip. This appears to occur by a dislocation multiplication mechanism and thus depends on the initial density of dislocation sources. Thermal treatments employed--annealing and flame polishing--raised the lower yield stress. This hardening appears to be caused by precipitation of gaseous or solid precipitates. In addition, a yield drop can be induced in sapphire by strain aging.