Deformation behaviour and cyclic life of the alloy IN738LC under creep-fatigue loading

The deformation behaviour and cyclic life of a nickel base superalloy IN738LC, which is a widely used blade material in land based gas turbines. has been studied. The alloy was subjected to total strain controlled low cycle fatigue at 1223 K with superimposed periods of constant tensile stress. Microstructural examination of the fractured specimens as well as of those interrupted at different strain levels before fracture was carried out using optical and transmission electron microscopes. The average creep rate during the hold period showed an initial rapid increase with increase in the number of cycles, followed by a period of constant creep rate at higher hold stresses. ora period of slower increase in the creep rate at lower hold stresses. Fatigue life decreased continuously with decreasing hold stress. The deformation behaviour has been attributed to the nature of dislocation structure inherited from the preceeding compressive part of the cycle and directional coarsening/coalescence of the gamma precipitates.