Assessment of the actual operation temperature of a GTD-111 1st stage bucket by microstructure evaluation and simulation approach

GTD-111 is a widely used Ni-based superalloy to manufacture the first stage bucket of Industrial Gas Turbines (IGT) due to its excellent high temperature properties. It is well known that superalloys degraded when they are exposed to high temperature and stress during service. The main microstructural changes include coarsening and coalescence of gamma-prime phase, intergranular decomposition of the primary carbides (MC) to secondary carbides (M23C6), and topological close-packed (TCP) phases formation. These changes have a strong detrimental effect on the thermomechanical performance of the turbine component.

The aim of this study is to understand the effect of temperature on the service-induced degradation of a GTD-111-DS first stage bucket of a GE7FA IGT. In order to identify the critical temperature zones in the blade, a combined finite element and computational fluid dynamics modeling-numerical analysis were calculated. These results were correlated with microstructural and chemical characterization of different cross section along the bucket.