Grain-boundary sliding measurements in Al[sub 2]O[sub 3] by machine vision photogrammetry

The nucleation, growth and coalescence of grain-boundary cavities is the primary damage mechanism observed during creep of structural ceramics. Furthermore, grain-boundary sliding (GBS) has been identified as the driving force process. Although the creep characteristics of structural ceramics have been extensively studied, very little is known about the details of GBS during creep and how GBS relates to cavitation kinetics. This paper presents the results of a study using a machine vision system to measure Mode 2 GBS displacements in a Lucalox Al[sub 2]O[sub 3]. Specifically, sliding displacements as large as 0.4 [mu]m were measured. The measured displacements indicate that some grain boundaries experienced shear strains and strain rates of 4,200% and 2.3 [times] 10[sup [minus]2]s[sup [minus]1], respectively. The techniques utilized for these measurements are described in detail, and data gathered during a 2 1/2 h compressive creep test under a stress of 138 MPa at 1,600 C are presented and discussed.