Coating degradation of first and second stage gas turbine blades

Degradation study of over-aluminized CoCrAlY coatings (GT-29+) on conventionally cast (CC) GTD11 Ni based super alloy substrates was investigated by evaluating first and second stage turbine blades after their 48,000 h of original services. The degradation evidences such as enlargement of the inter-diffusion zone, aluminum depletion from both top aluminide and CoCrAlY coating and related phase formations were observed by using an EPMA. The elemental mapping and quantitative analysis of the phases were also performed using WDS device attached to EPMA. Microhardness changes along the duplex coating thickness for both blades were determined by a Vickers microhardness tester.