Microstructure and creep behavior of an Y-alpha-beta sialon composite

Flexural creep behavior of a Y-alpha-beta sialon composite was studied in a ir at temperatures of 1250-1350 degreesC and stresses of 110-290 MPa. The c omposite in which YAG was designed as intergranular phase has an original a lpha/beta ratio of 65/35. The stress exponents in Norton equation were dete rmined to br 1.31 +/-0.12, 1.49 +/-0.15 and 1.62 +/-0.10 at 1250, 1300 and 1350 degreesC, respectively, and creep activation energy was 677 +/- 25 kJ mol(-1). Combining the microstructure observations, grain boundary diffusio n accommodated by grain boundary sliding was identified as the rate-control ling creep mechanism for the composite. The creep rate exponent p in Monkma n-Grant relation was found to be 1.6, and the nucleation and growth of cavi ties in triple grain pockets was responsible for the creep rupture. (C) 200 1 Elsevier Science Ltd. All rights reserved.