Effect of La, Y and Al Additions on the High-Temperature Oxidation of Ni–20Cr Alloy

Abstract

The isothermal oxidation of Ni–20Cr alloys with a simultaneous addition of rare earths (La and Y) and Al was investigated in air at 1273, 1373 and 1473 K. The simultaneous addition of rare earths and Al significantly reduced the oxidation rate of the Ni–20Cr alloy especially at higher temperatures, while singular additions of La and Y lost their improvement effect. The simultaneous addition completely suppressed the spalling of the scale even at 1473 K, where severe spalling was observed in the Ni–20Cr alloys with a singular addition of La, Y and Al. The density of the internal oxide formed beneath the scale was markedly increased by the simultaneous addition, but internal oxidation experiments revealed that the simultaneous addition of rare earths and Al did not accelerate the Al diffusion. There was no apparent correlation between the mass of the spalled scale and the density of the internal oxide. This result suggested that effects other than the “keying” or “pegging” effect might contribute to the scale adhesion.