Effects of Environment On Creep Behavior of Nextel720/Alumina-Mullite Ceramic Composite With 45 Deg. Fiber Orientation at 1200 Deg. C

摘要

The present effort will investigate the off-axis creep behavior of the Nexte720/Alumina-Mullite CMC, a material system which relies on a porous alumina/mullite matrix for damage tolerance as compared to the pure alumina matrix in earlier studies. This research evaluated the creep behavior of N720/AM with a +/- 45 degree fiber orientation at 1200 degrees C in: laboratory air, steam, and argon environments. Creep-rupture tests at the creep stress levels of: 32, 30, 26, and 20 MPa were conducted in each environment. Additionally 35 MPa stress level examined in air and 13 MPa stress level examined both in air and steam. The N720/AM with a +/- 45 degree fiber orientation survived creep run-out (100 h of creep stress) for stress levels smaller or equal to 20 MPa in all environments. Retained tensile strength was evaluated for all specimens achieving run-out. The creep-rupture results showed a decrease in creep life with increasing creep stress. The presence of steam had negative effect on the creep rates. Following the tests Optical and Scanning Electron Microscope (SEM) micrographs were used to examine damage zones.