Oxidation of Ultra-High Temperature Transition Metal Diboride Ceramics
The oxidation behaviour of transition metal diboride ceramics is reviewed with emphasis on the performance of zirconium diboride and hafnium diboride. First, the oxidation behaviour of nominally pure diborides is discussed, focusing on the transition to linear mass gain kinetics at temperatures above 1100⁰C. Next, the use of SiC and other additives that produce silica based scales when oxidised is reviewed. These additives improve oxidation protection due to the formation/stability of the outer layer of borosilicate glass that acts as a barrier to diffusion of oxygen to the substrate. However, elevated temperatures (>1650⁰C) and/or the combination of aerodynamic flow, high heat flux and reactive atmosphere associated with hypersonic flight destabilises the outer oxide and decreases oxidation protection. Other additives that affect the composition and structure of the crystalline oxide scale without forming an outer glassy layer are a promising approach to improving oxidation behaviour of diborides. These additives require further research to understand the mechanisms of improved protection and further optimise the protective behaviour. While the oxidation of ultra-high temperature diborides has been studied for many years, several possible areas for future research are identified.
W. Fahrenholtz and G. Hilmas, "Oxidation of Ultra-High Temperature Transition Metal Diboride Ceramics," International Materials Reviews, vol. 57, no. 1, pp. 61-72, Maney Publishing, Jan 2012.
The definitive version is available at http://dx.doi.org/10.1179/1743280411Y.0000000012
Materials Science and Engineering
Keywords and Phrases
Hafnium diboride; Oxidation; Review; Zirconium diboride; Crystalline oxides; Diborides; Elevated temperature; Glassy layers; High heat flux; Hypersonic flights; Mass gain; Outer layer; Oxidation behaviours; Oxidation protection; Reactive atmospheres; Ultrahigh temperature
International Standard Serial Number (ISSN)
Article - Journal
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