Creep Behavior and Grain‐Boundary Sliding in Polycrystalline A1 2 O 3

The creep properties of polycrystalline A1 2 O 3 (grain size 14 to 65 μm) were examined under compressive stresses of between 4,000 and 18,000 psi (27.6 and 124 MPa) in the range 1600° to 1700°C. Two distinct types of behavior were observed. The creep rate of medium‐grained specimens (14 to 30 μm) could be described by ασ 1.2 / d 2 where σ is the applied stress and d is the grain size. These results are consistent with the Nabarro‐Herring creep mechanism. For the coarse‐grained (65 μm) specimens, the creep rate was related to the stress by ασ 2.6 . This behavior was not related to cracking; instead, a dislocation mechanism was thought to be rate‐controlling. Considerable evidence for grain‐boundary sliding was seen, and measurements showed that grain‐boundary sliding contributed between 46 and 77% of the total strain in the 3 medium‐grained specimens examined and between 38 and 50% in the 3 coarsegrained specimens examined.