THE INFLUENCE OF GRAIN-ORIENTATION ON A STEADY-STATE CREEP RATE IN HOT-PRESSED BETA-SI3N4 WHISKER SIALON COMPOSITE

Two kinds of compressive creep tests, in which creep-load was applied parallel and perpendicular to the hot-pressing direction, were conduct ed on hot-pressed beta-Si3N4 whisker/SiALON composites at temperatures between 1275 degrees C and 1350 degrees C under 30-100 MPa. The creep rate in the former parallel test was higher than that in the latter p erpendicular test at the apparent steady state creep regime. The value s of beta-SiAlON (101)/(210) XRD peak area ratio on the cross-sectiona l plane perpendicular to the creep-loading direction were 1.51 and 0.2 6 in the perpendicular and in the parallel testing specimens, respecti vely, After creep, they decreased to 1.1 and to 0.23 in the perpendicu lar and in the parallel tests, respectively, In addition, the microstr uctural analysis revealed that the shape of SiAlON grains changed by t he preferential grain growth through the solution/precipitation proces s. These results indicate that the enhancement of creep rate due to hi gh orientation of grains is induced by the increase in a rate of disso lution of grains during creep.