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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.

The report presents a summary of the following research efforts: (1) a major effort was devoted to studying the synergetic effect of the gamma to alpha alumina phase transformation on pressure-sintering kinetics of high- density alumina ceramics. (2) An extensive program was also initiated with the purpose of relating diffusion coefficients observed for ceramics subjected to pressure-sintering or press-forging operations with interdiffusion coefficients observed in diffusion experiments. (3) In addition to the studies on basic mechanisms in the densification kinetics of ceramics, considerable attention was also devoted to studies of the mechanical behavior of ceramic materials. (4) Additional studies of the mechanical behavior of ceramic materials involved an analysis of fracture energies.