Deformation Behavior of SiC Whisker Reinforced Si3N4

ABSTRACTConstant compressive stress creep exp∼riments in jhe temperature and stress ranges of 1420K – 1570K and 50 MN/m2 –350 MN/m2 have been conducted on hot pressed unreinforced Si3N4 containing the densification aids of 6 wt% Y2O3 and 1.5 wt% Al2O3 and on a similarly prepared composite material reinforced with 20 vol% SiC whiskers. Steady-state creep data obtained on these materials in a N2 atmosphere gave stress exponent values of 1.2 – 1.6 and 0.4 – 1.6 for the unreinforced Si3N4 and the composite, respectively. A break in the steady-state creep rate vs. log stress observed only in the composite occurred at approximately 250 MN/m2 at the temperatures of 1520K and 1570K. This information coupled with the results of electron microscopy indicate that the temperature as well as the extensive crystallization (or lack of it) of the amorphous grain boundary phase are the principal factors controlling the deformation rate at a given stress within the limits of the small total strains achieved in this research.