Influence of Metal Temperature on Base Material and Coating Degradation of GTD-111 Buckets

Abstract

The surface metal temperature on the first row cooled buckets varies along the height of a bucket and among the buckets in a row. Two first-row GT 29+ coated buckets, from the same turbine, have been investigated for in-service material and coating degradation variation. The results showed that the γ′ particles were coarser and the width of the interdiffusion zone below the CoCrAlY coating was wider in one bucket than the other, indicating that the former bucket had seen higher metal temperature than the latter. Fewer uncertainties are associated with interdiffusion zone width measurements, and the change in zone width can be used to develop a time-temperature correlation for the subject bucket material and coating system. The uncertainties associated with γ′ particle measurements for time temperature correlation are discussed.