Effects of wet oxidation on residual stress variation of SiCf/SiC composites

Abstract

Continuous silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites, used as thermal structures for gas turbines, are prone to degrade under the gas stream (mainly composed of O2 and H2O). Here, the degradation of the composites in wet oxygen environment was investigated by Raman spectroscopy. Results show that the composites exhibit significant residual stress as the oxidation proceeds. SiC matrix in the as-received condition exhibits average hydrostatic tensile stresses of approximately 1350 MPa, while SiC fiber exhibits compression stress of approximately 1450 MPa. Both the residual stresses in matrix and fiber decrease with the increasing oxidation temperature. Moreover, the residual stress evolution is found to be related to the formation of cristobalite and the volatilization of Si(OH)4, CO, H2. This work can open new alternatives for understanding the degradation mechanism of SiCf/SiC composites in gas turbine environment, and for developing mathematical model to predict their service life.