Phase stability, oxidation, and interdiffusion of a novel Ni?Cr?Al?Ti?Si bond-coating alloy between 900 and 1100�C

Abstract

A novel, low-expansion experimental Ni−Cr−Al−Ti−Si bond-coating alloy was investigated in the as-cast state concerning its phase stability, oxidation resistance in air, and interdiffusion with single-crystal IN-100 at 900, 1000, and 1100°C. Isothermal oxidative thermogravimetry was employed up to 500 hr. Interdiffusion was compared to a commercial Ni−Co−Cr−Al−Y alloy on IN-100. Oxidized Ni−Cr−Al−Ti−Si specimens and diffusion couples were characterized by metallography, SEM, EDX, XRD, and XRF. The Ni−Cr−Al−Ti−Si alloy provides good oxidation resistance in air at least up to 1000°C. The alloy is an alumina former. Due to its coarse microstructure, other oxides (e.g., rutile) may form and considerably dominate the oxidation behavior. The kinetics of oxidation were correlated with temperature, formation of phases, and morphology of oxides. Interdiffusion fluxes between Ni−Cr−Al−Ti−Si and IN-100 were mainly directed to the superalloy. They were faster than in Ni−Co−Cr−Al−Y/IN-100 diffusion couples.