Failure mechanisms of coating systems applied to advanced turbine components

Abstract

The maintenance period of critical gas turbine components operating in advanced D, E and F technology industrial turbines is often determined by the ilfe of the coating system applied to protect the base alloy substrate. The progressively higher firing temperatures used in ail of the advanced engine designs results not only in very high metal surface temperatures but also in very high temperature gradients and concomitant thermal stresses Induced in part by the complex cooling systems. In order to develop optimum component life strategies, it is important to establish the actual operating conditions of each component, and, to define the predominant degradation modes. Metallurgical life assessment of these advanced component designs has identified several distinct coating/base metal failure mechanisms not generally encountered in earlier generation turbines, in addition to the mora usual degradation modes, accelerated by the increases in temperature. A review and examples of these degradation mechanisms encountered on service exposed coating systems currently used by some of today's major manufactures are presented.