MECHANICAL-PROPERTIES OF ALUMINIZED COCRALY COATINGS IN ADVANCED GAS-TURBINE BLADES

The microstructure/composition and mechanical properties (22-950 degre es C) in aluminized CoCrAIY coatings of advanced gas turbine blades ha ve been examined using scanning Auger microprobe and a small punch (SP ) testing method. Aluminized coatings were made of layered structure d ivided into four regions; (I) Al enriched and Cr depleted region, (II) Al and Cr graded region, (III) fine grained microstructure with a mix ture of Al and Cr enriched phases and (IV) Ni/Co interdifusion zone ad jacent to the interface. Coating regions I and II with high microhardn ess showed easier formation of brittle cracks in a wide temperature ra nge, 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 a bove 730 degrees C. The integrity of aluminized coatings while in-serv ice is discussed in light of the variation in the low cycle fatigue li fe as well as the ductility in the layered structure. (C) 1997 Elsevie r Science S.A.