Potential of IrAl base alloys as ultrahigh-temperature smart coatings

For developing ultrahigh-temperature oxidation-resistant coatings, phase constitution and stability, fabrication methods, mechanical properties, thermal expansion and oxidation behavior are discussed for B2 IrAl alloys. Effects of ternary additions (Ni, Co and Fe) on oxidation behavior are also described. For practical use of ultrahigh-temperature coatings, an effective oxygen diffusion barrier (ODB) is required for the heart of multilayered ultrahigh-temperature coatings and Ir has promise to be ODB. A problem in using Ir is a formation of gaseous oxide, IrO3, over 1395K. This can be overcome by alloying with Al. Recently we have found that, by oxidation, IrAl-base alloys form smart and self-healing multifunctional layered structures composed of (1) continuous Ir layer as ODB and (2) continuous Al2O3 layer to protect ODB. In this paper, several characteristics of IrAl alloys are described and potential of IrAl as smart oxidation resistant coatings is discussed.