Effect of platinum on the growth rate of the oxide scale formed on cast nickel aluminide intermetallic alloys

Abstract

Thermo-Gravimetric Analysis ( TGA) and Scanning Electron M icroscopy ( SEM ) data of the initial stages of oxidation of Ni50Al50 and Ni40Pt10Al50 alloys of low and high sulfur content at 900◦ C and 1100◦ C are reported. The results show that the addition of Pt promotes the growth of the transient θ- Al2O3 oxide scale. This effect is particularly sensitive in the initial stages of oxidation at 1100◦ C where Pt considerably increases the total mass gain. It is attenuated in the presence of a high sulfur content in the alloy, indicating a competitive effect of Pt and S on the segregation of Al. The slower θ-to- α transition observed in the presence of Pt leads to an extended lifetime of the θ phase layer, which is proposed to be benecial to the relaxation of the stresses created by the growth of α-Al2O3.