Chapter 2 Coupled Anisothermal Chemomechanical Degradation Solutions in One Dimension M. Anguiano, H. Gajendran, R.B. Hall, and A. Masud Abstract This paper focuses on thermal oxidation of Silicon Carbide (SiC) – a key process of degradation in aircraft turbine components. In this work, passive oxidation is considered, which produces amorphous silica that is accumulated on top of the SiC substrate. The mathematical problem is formulated within the context of mixture theory (Gardiner G (2017) Aeroengine composites, Part 1: the CMC invasion. Composites World 31 July 2015: n. pag. Web. 06 Mar; Jacobson, J Am Ceram Soc 76(1):3–28, 1993), which allows to model multi-constituent behavior – fluid and solid in this case – within the same continuum domain, while retaining interaction terms between constituents. Preliminary isothermal results have shown that the phenomena of interest are captured: expansion due to chemical reaction, change in solid density from unreacted to fully-oxidized material, interactive force among constituents, and stress variation across reaction zone. The method presented considers the anisothermal evolution of the problem. Keywords Anisothermal • Ceramic matrix composite • Passive oxidation • Silicon Carbide For numerous applications, modern and forthcoming engineering materials must be designed to perform in harsh thermal and/or chemical environments and numerical methods capable of simulating those conditions are required. In the case of aeronautical applications, one such group of materials is ceramic matrix composites (CMCs). Due to their thermo- mechanical properties [1] that allow them to perform stably at high temperatures, CMCs are making their way from into more areas of the turbine, replacing metallic alloy materials, which require coolant flow to be kept at working performance temperatures [2]. Some manufactures expect a tenfold increase on the use of CMCs in their engines over the next decade [2], as improvements in manufacturing and analysis techniques permit production of components of more complex geometry. However, CMCs are subjected to chemical degradation through oxidation at high temperatures [2–5]. This paper focuses on thermal oxidation of silicon carbide (SiC) – a key process of degradation in aircraft turbine components. It is also a process of interest in the electronics industry as it is one of the techniques involved in the manufacturing of semiconductors, where thermal oxidation is performed deliberately to create an insulating oxide layer [6–8]. The mechanisms of thermal oxidation of SiC have been categorized as either active or passive [3–5]. In the former, the products of reaction include volatile silicon oxide species that are lost to the surrounding environment and leave more of the SiC exposed. In contrast, passive thermal oxidation produces amorphous silica that is accumulated on top of the SiC substrate. Temperature and pressure determine which regime of thermal oxidation will occur [4]. In this work, the passive oxidation is considered. A schematic description of passive oxidation process of SiC is presented in Fig. 2.1: oxygen (O 2 ) in-diffuses through the solid, reaches substrate material (SiC), and reacts to form solid silicon dioxide (SiO 2 ) and gaseous carbon monoxide (CO). The chemical reaction that occurs between the O 2 and the SiC is described by the following chemical equation: SiC s ðÞ þ 3 2 O 2 g ðÞ ! SiO 2 s ðÞ þ CO g ðÞ ð2:1Þ M. Anguiano • H. Gajendran • A. Masud University of Illinois Urbana-Champaign, Champaign, IL, USA e-mail: manguin2@illinois.edu; amasud@illinois.edu R.B. Hall (*) Air Force Research Laboratory, Wright-Patterson AFB, OH, USA e-mail: richard.hall.16@us.af.mil # The Society for Experimental Mechanics, Inc. 2018 A. Arzoumanidis et al. (eds.), Challenges in Mechanics of Time Dependent Materials, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-63393-0_2 5