Small crack growth behaviors of a polycrystalline Ni- based superalloy under temperature gradient creep condition

Abstract

The crack growth behaviors of Ni-based superalloys were studied under thermal gradient creep condition (TGC) and compared with isothermal creep condition (ITC). Special attention was paid on getting basic understandings on small crack growth behavior around cooling holes in turbine blades. It was found that the cracks under the TGC showed higher crack growth rate than that under the ITC. Also a significant difference in growth rate was observed between the crack nucleated from cooling hole and the naturally initiated crack under the TGC conditions. These behaviors were analyzed in terms of creep J-integral, J_c; a time-dependent nonlinear fracture mechanics parameter. Some mechanistic background was discussed on the characteristic behaviors of the crack advance under the TGC condition.