Effect of platinum addition on oxidation behaviour of γ/γ′ nickel aluminide

Bulk gamma/gamma' nickel aluminide alloys of composition (in at.%) Ni-20Al with the addition of 0, 5, 10 and 15Pt were fabricated using arc melting, and the microstructure of the alloys was characterized. The oxidation behaviours of the alloys at 1150 degrees C were studied and compared in terms of oxide spallation, oxide microstructure and growth, residual stress in the alpha-Al2O3 scale and oxide/alloy interface morphology. Progressively increased platinum addition into the alloys results in (1) improvement in the resistance to oxide spallation, (2) reduction in oxidation of nickel, (3) lower stresses in the alpha-Al2O3 scale and (4) more planar oxide/alloy interfaces. In addition, for short-time oxidation (<= 1 h), the stresses in the alpha-Al2O3 scale on the gamma' phase region of the alloy are lower than those on the gamma/gamma' mixed phase region. Discussion on the platinum effect has been focused on selective oxidation of the alloy and stress development in the oxide scale. It is concluded that the selective oxidation of aluminium promoted by platinum plays a crucial role in the evolution of the oxidation behaviour with the platinum addition. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.