Results of a Japanese round robin on creep crack growth evaluation methods for Ni-base superalloys

Creep crack growth (CCG) tests on Ni-base superalloys were carried out in the Japanese VAMAS group as part of a round-robin program in order to assist the standardization of the CCG test method for creep-brittle alloys. The effect of temperature, load, specimen thickness and material microstructure on CCG behavior was investigated. The applicable range of fracture mechanical parameters to evaluate the CCG rate was evaluated. The CCG rate was characterized by the C∗ parameter independent of testing conditions in the range where the CCG rate accelerated. However, the acceleration stage occupied only a small portion of life time for the creep-brittle superalloys. In the range where the CCG rate was constant, the CCG rate and the fracture life could be predicted approximately by the Q∗ method based on the thermally activated process.