Creep behavior of a superplastic Y-TZP/Al2O3 composite:: An examination of the possibility for diffusion creep

The creep characteristics of a high purity superplastic Y-TZP/Al2O3 composite were studied. The test samples had a uniform initial grain size of essentially equiaxed grains and the phase distribution was also uniform. Creep tests were conducted at elevated temperatures in tension and measurements were taken after testing to determine the average size and shape of the grains. The creep curves showed the existence of a primary stage of creep and then a transition into a steady-state region where the strain rate remained reasonably constant. Observations by scanning electron microscopy revealed an elongation of the alumina grains with the grain strain essentially matching the overall strain within the sample. There was some grain growth after testing at the lower stresses. Preliminary observations using an atomic force microscope revealed direct evidence for the occurrence of some grain boundary sliding within the samples. The results are compared with earlier data reported for Y-TZP/Al2O3 composites and they are analyzed using the interface reaction-controlled diffusion creep model.