ABSTRACT: In order to achieve long thermal barrier coating lifetimes, underlying metallic bond coats need to form adherent, slow-growing Al2O3 layers. A set of guidelines for developing aluminide bond coat compositions is proposed in order to maximize oxidation performance, i.e. forming a slow-growing adherent alumina scale. These criteria are based on results from cast, model alloy compositions and coatings made in a laboratory-scale chemical vapor deposition facility. Aluminide coatings are thought to have more long-range potential because of their lower coefficient of thermal expansion compared to MCrAlYs. The role of Pt in improving alumina scale adhesion and countering the detrimental role of indigenous sulfur is discussed. However, the improvements associated with Pt are minimal compared to reactive element doping. One strategy which has great promise for improvement is to incorporate Hf into the coating. From an oxidation standpoint, this would preclude the need for Pt in the coating and also reduce the scale growth rate. While excellent oxidation performance was observed for cast Hf-doped NiAl, its benefits can be compromised and even eliminated by co-doping with elements such as Cr, Ti, Ta and Re. Creating a pure Hf-doped NiAl is one promising approach for improving the oxidation performance of bond coats.

Read Article

B. A. Pint, J. A. Haynes, K. L. More, I. G. Wright and C. Leyens. “Compositional Effects on Aluminide Oxidation Performance: Objectives for Improved Bond Coats. T. M. Pollock, R. D. Kissinger, R. R. Bowman, K. A. Green, M. McLean, S. Olson and J. J. Shirra eds. Superalloys 2000. Warrendale, PA: TMS. 2000. Pp. 629-638.