Mechanical properties of aluminized CoCrAlY coatings in advanced gas turbine blades

The microstructure/composition and mechanical properties (22–950 °C) in aluminized CoCrAlY coatings of advanced gas turbine blades have been examined using scanning Auger microprobe and a small punch (SP) testing method. Aluminized coatings were made 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. Coating regions I and II with high microhardness showed 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 and conversely higher elevated temperature ductility than the region IV due to a precipitous ductility increase above 730 °C. The integrity of aluminized coatings while in-service is discussed in light of the variation in the low cycle fatigue life as well as the ductility in the layered structure.