CRACK HEALING OF ALUMINA WITH A RESIDUAL GLASSY PHASE - STRENGTH, FRACTURE-TOUGHNESS AND FATIGUE

The crack-healing behavior of identation cracks and large precracks in 96 wt.% alumina was studied as a function of annealing temperature in air and inert environments. Crack healing occurred at annealing tempe ratures of 800-degrees-C and above in both air and inert (argon) envir onments, indicating its cause as transport of existing material to the crack plane, and resulted in increased strength and fracture toughnes s. However, the resulting phase assemblage in the crack plane was susc eptible to fatigue at room temperature in distilled water, as evidence d by a somewhat low fatigue parameter of N = 68. Furthermore, polished -and-annealed samples were more susceptible to fatigue at room tempera ture in air than as-polished samples.