Influence of Corrosion Resistance Coating of Thermo-Mechanical Fatigue Life of Gas Turbine Blad Material IN738LC
Takashi OGATA and Akiyoshi NOMOTO
Abstract:The purpose of this study is to clarify the effect of CoCrAlY coating on biaxial thermo-mechanical fatigue (TMF) life property of Inconel 738LC. In-phase and out-of-phase TMF tests at temperature between 450C and 850C were carried out by using a tension/torsion and compression TMF testing machine. In addition to these fundamental TMF tests, a complicated temperature and strain history tests, so called a blade waveform which simulates temperature and strain histories of actual gas turbine blade, were performed. Failure life of coated specimens under the in-phase condition is longer than that of the substrate and the main crack propagated from boundary between the coating and substrate to inside of the substrate. Therefore the coating plays a positive role for the substrate life due to suppression of crack initiation and propagation from oxidation effect. On the other hand, failure life of the coated specimens under the out-of-phase and blade waveform tests is approximately 1/2 of the substrate life indicating negative effect. It was suggested from failure surface observation that crack initiation period in the coating is shorten by the difference of deformation behavior between the substrate and coating, and that crack propagation rate in the substrate of the coated specimen is accelerated by the cracking of the coating compared with the crack propagation rate of substrate itself. Key Words:Thermo-mechanical fatigue, IN738LC, CoCrAlY coating, Crack initiation, Crack propagation