MICROSTRUCTURE STUDIES OF POLYCRYSTALLINE REFRACTORY OXIDES
Quarterly progress rept. no. 2,
AVCO CORP WILMINGTON MA RESEARCH AND ADVANCED DEVELOPMENT DIV
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Transverse bend strength and elastic modulus determinations made of fine-grained 1 to 2 micron, dense, pure Al2O3 and MgO specimens as a function of temperature up to 1350 C revealed values higher than those obtained by other investigators for these oxides in more porous form and of larger grain sizes. Studies of the grain growth kinetics of alumina and magnesia were conducted in order to obtain information to enable preparation of specimens with desired larger grain sizes for subsequent thermomechanical testing. Based on observations of the fracture modes exhibited by alumina and magnesia as a function of temperature, it was suggested that an elastic deformation or possible plastic flow in the so-called equicohesive temperature range may influence the mode of fracture. By analogy with findings in metals systems, it was hypothesized that the apparent transition from transgranular to intergranular fracture might occur below some critical stress rather than above some critical temperature.
- Inorganic Chemistry