Temperature Dependent Residual Stress Models for Ultra-High-Temperature Ceramics on High Temperature Oxidation
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Temperature Dependent Residual Stress Models for Ultra-High-Temperature Ceramics on High Temperature Oxidation Ruzhuan Wang 1 & Weiguo Li 1
Received: 23 October 2016 / Accepted: 24 October 2016 # Springer Science+Business Media Dordrecht 2016
Abstract The strength of SiC-depleted layer of ultra-high-temperature ceramics on high temperature oxidation degrades seriously. The research for residual stresses developed within the SiC-depleted layer is important and necessary. In this work, the residual stress evolutions in the SiC-depleted layer and the unoxidized substrate in various stages of oxidation are studied by using the characterization models. The temperature and oxidation time dependent mechanical/thermal properties of each phase in SiC-depleted layer are considered in the models. The study shows that the SiC-depleted layer would suffer from large tensile stresses due to the great temperature changes and the formation of pores on high temperature oxidation. The stresses may lead to the cracking and even the delamination of the oxidation layer. Keywords Ultra-high-temperature ceramics . High temperature oxidation . SiC-depleted layer . Residual stresses . Models Abbreviations λ Volume fraction of each phase during oxidation Volume fraction of each phase before oxidation λ0 Pre-exponential constant ko ρ Density m Molar mass Gasification coefficient η(T1) Migration coefficient ξ(T1) μ Pilling-Bedworth ratio Activation energy not associated with temperature EA R Gas constant
* Weiguo Li [email protected]
1
State Key Laboratory of Coal Mine Disaster Dynamics and Control, College of Aerospace Engineering, Chongqing University, Chongqing 400030, China
Appl Compos Mater
T1 t1 σ E t α ΔT E(T) α(T) E(T,t1) α(T,t1) σ(T,t1)
oxidation temperature Oxidation time Residual stress Young’s modulus Thickness Thermal expansion Temperature difference Temperature-dependent Young’s modulus Temperature-dependent thermal expansion Temperature-time-dependent Young’s modulus Temperature-time-dependent thermal expansion Temperature-time-dependent residual stress
1 Introduction Ultra-high-temperature ceramics (UHTCs) are a family of transition-metal composites that are widely used as thermal protection materials in aerospace applications. Those materials have melting points higher than 3000 °C, and have good high temperature chemical and physical stability [1–5]. Many experimental studies have been conducted to understand and improve the oxidation resistance of UHTCs. The studies showed that at temperatures above 1200 °C the oxidation resistance of single-phase UHTCs is poor [6]. This provided the motivation for the current work which aims to improve the oxidation resistance above 1200 °C for these materials. The addition of SiC is found to be the most promising approach to improve the oxidation resistance of UHTCs in the temperature range of 1200–1650 °C [5, 7]. However, at temperatures above 1650 °C the oxidation resistance of SiC particulate reinforced UHTCs becomes poor owing to the destruction of the outer borosilicate glass
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