EXAGGERATED TEXTURE AND GRAIN-GROWTH IN A SUPERPLASTIC SIAION

A fine-grained superplastic beta'-silicon nitride solid solution (SiAlON) was found to develop elongated grains and a pronounced texture during tensile deformation at 1550-degrees-C. The texture development is well-described by a geometrical model of grain rotation in accordance with the strain field. Once aligned, grains can then grow with little constraint due to impingement and often coalesce into each other. With the above microstructural development, the stress-strain curve displayed unusually strong strain hardening characteristics due to a fiber-reinforcement effect of the aligned silicon nitride grains on the glass-containing matrix. By extending the rheological model of Chen and Yoon and considering these microstructural evolutions, we are able to simulate the deformation behavior.