Abstract
In order to investigate the characteristics of low cycle fatigue strength of a forged Ni-base superalloy IN 718 at elevated temperatures, strain-controlled fatigue tests were carried out on the smooth specimens and load-controlled fatigue crack propagation tests on the notched specimens. As a result, the failure life for the smooth specimen was found to be sensitive to the fracture mode and to decrease by changing from transgranular to intergranular fracture. It was also found that the failure life was independent of the type of straining in compression. The crack propagation rate in the intergranular fracture mode as well as in the transgranular fracture mode was correlated well with the stress intensity factor, which implied the creep fracture under a small scale creep condition.
