This paper describes examination of the microstructure/composition and mechanical properties (22–950 °C) in over aluminized CoCrAlY coatings of advanced gas turbine blades using scanning Auger microprobe and a small punch (SP) testing method. Aluminized coatings consisted of layered structure divided into four regions; (I) Al enriched and Cr depleted region, (II) Al and Cr graded region, (III) fine grained microstructure with a mixture of Al and Cr enriched phases and (IV) Ni/Co interdifusion zone adjacent to the interface. SP specimens were prepared in order that the specimen surface would be located in the various coating regions. SP tests indicated a strong dependence of the fracture properties on the various coatings regions. Coating zones I and II with high micro hardness showed much easier formation of brittle cracks in a wide temperature range, compared to regions III and IV The coating region III had lower room temperature ductility than the zone IV. However, the ductility in the coating zone III exceeded that in the region IV above 730 °C due to a precipitous ductility increase. The integrity of aluminized coatings while in-service is discussed in light of the variation of the low cycle fatigue life as well as the ductility in the layered structure.

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