Development of Sintered MCrAlY Alloys for Aeronautical Applications

Thermal barrier coatings (TBCs) are widely used in turbines for propulsion and power generation (Bose & DeMasi-Marcin ,1995; Choi et al., 1998; Cruse et al. 1988; DeMasi-Marcin & Gupta, 1994; DeMasi-Marcin et al., 1990; Eaton & Novak, 1987; Golightly et al., 1976; Hillery, 1996; Lee & Sisson, 1994; Mariochocchi et al., 1995; Meier et al. ,1991 & Gupta, 1994; Miller, 1984; Kingery et al., 1976; Rigney et al., 1995; Strangman, 1985; Stiger et al., 199;, 1999 & Evans, 1999). They comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. The benefit of these coatings results from their ability to sustain high thermal gradients in the presence of adequate back-side cooling. Lowering the temperature of the metal substrate prologs the life of the component: whether from environmental attack, creep rupture, or fatigue. In addition, by reducing the thermal gradients in the metal, the coating diminishes the driving force for thermal fatigue. Both of these benefits can be traded off in design for greater component durability, or for reduced cooling air or for higher gas temperature/improved system efficiency. As a result, TBCs have been increasingly used in turbine engines. Successful implementation has required comprehensive testing protocols, facilitated by engineering models (Cruse et al. 1988; Eaton & Novak, 1987; Meier et al. ,1991; Wright, 1998). Expanded application to more demanding scenarios (Fig. 1) requires that their basic thermo-mechanical characteristic be understood and quantified. This need provides the opportunities and challenges discussed in this article.