The effect of reactive elements on the segregation behavior and microstructure of α-Al2O3 scales on β-NiAl

Abstract

In order to improve oxidation resistance, small quantities of certain oxygen-active or “reactive” elements (RE) such as Y, Zr, Hf, or Ce are added to chromia- and alumina-forming high temperature alloys. Many theories have been proposed to explain the effects of RE additions, with a number of these theories including some aspect of the observed segregation of RE ions to oxide scale grain boundaries and the metalscale interface. The RE-ion segregation to the scale grain boundaries has been proposed to affect the oxidation behavior by suppressing cation transport along grain boundaries. It has been demonstrated that the quantity of RE segregation at α-Al2O3 scale grain boundaries varies with oxidation time and temperature and is greatly affected by the formation of RE-rich oxide particles in the scale (particularly at the gas interface). A previous study of scale formation on Y-implanted β-NiAl found that the Y implant had only a short-term (<1 h) effect at high temperatures.