Material Properties for High Temperature Applications

Abstract

In many applications, especially in the space industry (e.g. jet engines and rockets) as well as electronic industry (e.g. superheat resistant materials for thermal protection, vehicle and personal body armour, electromagnetic sensors), structures or part of structures are exposed to high temperature, usually up to 2000K or even 3500K in some parts of rocket engines (Schulz et al. [202]), high temperature gradients, and/or cyclic temperature changes or impact loading. Conventionalmetallic materials, such as carbon steels or stainless steels: ASTM 321, ASTM 310, nickel- or aluminium-based alloys cannot resist such high temperatures (Odqvist [175]). The first method to improve the resistance of metallic structures against extreme temperature conditions consists in covering the structure (a substrate) with a ceramic layer (Thermal Barrier Coating — TBC), since ceramics are known for their high thermal resistance. For instance, in a metal-ceramic composite: Al-SiC the thermal conductivities ratio is approximately equal: λ_m/λ_c = 3.6, the thermal expansion coefficients ratio: α_m/α_c = 5, whereas the elastic moduli ratio: E_m/E_c = 0.16 (Poterasu et al. [181]). In the case of Ni-Al₂O₃ composite the corresponding ratios are: λ_m/λ_c = 2.95, α_m/α_c = 1.51 and E_m/E_c = 0.50 (Chen and Tong [44]). Hence, at the metal-ceramic interface, severe discontinuity of thermomechanical properties occurs, which results in high strain and stress mismatch at the interface; as a consequence, delamination or failure of the coating is rapidly observed.