The high temperature tensile and compressive deformation characteristics of magnesia doped alumina

The mechanical characteristics of alumina have not yet been characterized c ompletely in tension due in part to strain hardening accompanying grain,gro wth and premature cavitation failure. Tensile tests were conducted on fine grained magnesia doped alumina over a range of strain rates, grain sizes an d temperatures to evaluate the stress exponent. inverse grain size exponent and activation energy. Constant stress compression creep tests were also c arried out under a similar range of experimental conditions. Extensive micr ostructural characterization after deformation indicated that there was con siderable grain growth during deformation; however, the grains retained the ir initially equiaxed structure after significant deformation. Although a s tandard plot of strain rate versus stress indicated a stress exponent of si milar to 2, a complete analysis including the compensation of data for conc urrent grain growth revealed that true stress exponent was similar to I, co nsistent with diffusion creep. It is argued that grain rearrangement proces ses accompanying grain growth will tend to mask the development of an elong ated grain structure predicted by diffusion creep processes. In contrast to several ceramics with a significant amount of glassy phase, there is no si gnificant difference between the elevated temperature tensile and compressi ve behavior of alumina. (C) 2000 Acta Metallurgica Inc. Published by Elsevi er Science Ltd. All rights reserved.