An integrated analysis of transport, oxidation, and creep during oxidation of interior pores in SiC

Abstract

Oxidation of SiC plays a critical role in the durability of ceramic matrix composites, as large changes in molar volume generate significant stresses that can drive cracking in adjacent features. The analysis of such phenomena requires coupling between descriptions of diffusion through the oxide, growth of the oxide domain (i.e., evolution of the oxide/SiC interface), and creep relaxation in the oxide at elevated temperatures. This paper presents a two‐dimensional finite element framework that uses a single finite element mesh to predict these behaviors; large changes in the oxide geometry are simulated by tracking the oxidation front as a discrete interface and periodically re‐meshing. The numerical performance of the framework is illustrated using an analytical description of oxidation of a flat surface and subsequent stress evolution. The framework is then used to analyze internal oxidation within a cylindrical cavity for a wide range of temperatures and water vapor concentrations pertinent to gas turbines. The results are used to discuss the roles of oxide growth rate, creep, and geometry with respect to the tensile stresses that develop in the adjacent SiC, and their implications for oxidation‐driven damage at high temperatures.

Intermediate temperature degradation of a SiC/BN/SiC (MI) composite with holes at 500–900°C in steam

“…[24][25][26] The second is the development of residual tension in the fibers by way of the large volume expansion concomitant with the reaction of SiC to SiO 2 + C(g) in the interface region. 27,28 Very recently, and particularly in this work, a fourth mechanism has become evident. 18,21,29 The primary feature of this mechanism is the extensive loss of BN fiber coatings without (before) full replacement by oxide.…”

“…The first of these is direct oxidative degradation of the fiber 24–26 . The second is the development of residual tension in the fibers by way of the large volume expansion concomitant with the reaction of SiC to SiO 2 + C(g) in the interface region 27,28 . Very recently, and particularly in this work, a fourth mechanism has become evident 18,21,29 .…”