TEM investigation of γ′ free bands in nimonic PE16 under LCF loading at room temperature

Abstract

The cyclic stress strain behavior of nickel base alloy Nimonic PE16 has been studied at room temperature under constant strain rate of 4 × 10-3s-1 and at a strain amplitude of 0.57% for different γ′ particle sizes. Fatigue softening is observed for all microstructures. Detailed TEM investigations reveal γ′ free bands in all specimens. Evolution of these bands is studied as a function of cumulative deformation the specimen has bee subjected to γ′ particles within deformation bands are initially sliced by movement of dislocations and on further deformation slices are fragmented by cross slip of dislocations within bands. A conceptual model for reduction in size of γ′ particles during fatigue is proposed on the basis of these results. Reaging studies of deformed samples reveal nucleation of very fine γ′ particles within bands. Comparison of γ′ particle size within these bands with those formed after ageing in specimens deformed in solution treated condition indicates that γ′ particles have completely dissolved in the specimen containing smallest γ′ precipitates. These results are explained on the basis of the concept of particle fragmentation under cyclic loading. © 1990.