Role of shrinkage pores, carbides on cyclic deformation behaviour of conventionally cast nickel base superalloy CM247LC® at 870 °C

Abstract

Cyclic deformation behaviour of conventionally cast and equiaxed grained nickel base superalloy CM247LC® has been studied at various strain amplitudes ranging from 0.3% to 0.9% at 870°C. Two features typical of cast materials viz., shrinkage pores and carbide particles were seen to influence the crack initiation and propagation process during strain controlled LCF testing in the alloy. While low overall dislocation density marked the deformation substructures of specimens cycled at low strain amplitudes, dislocation density levels were higher at higher strain amplitudes and were also seen to increase with cycling especially in gamma channels and around carbide particles. Cyclic stress response and dual slope behaviour in Coffin–Manson plots exhibited by the alloy have been analysed in light of deformation substructures and fractographic observations to gain insight into the fatigue deformation process and fracture mechanisms operating in the alloy.