Small crack propagation behaviour during thermo-mechanical creep-fatigue loading of Ni based superalloy specimen under non-uniformly distributed temperature condition

摘要

A new testing system has been developed to get a basic understanding on the thermomechanical creep-fatigue (TMCF) small crack propagation behaviour around the cooling holes in high temperature Ni base superalloy used for advanced gas turbine components. By means of the test system the TMCF tests under creep-fatigue condition were carried out for a directionally solidified Ni base superalloy hollow specimen with nine cooling holes which were machined in a 363 square array within the specimen gauge length, simulating the cooling system in air cooled gas turbine blades. Special attention was paid to the early growth of creep-fatigue crack(s) around the holes. Some fracture mechanics discussions are made to interpret the experimental results and the effect of cooling system on the TMCF failure, taking account of the roles of stress concentration and the local thermal stress induced under a significant temperature gradient.