TEM and SANS investigation of age hardened nimonic PE16 after cyclic loading at room temperature

A nickelbase superalloy Nimonic PE16 shows softening when subjected to low cycle fatigue (LCF) at room temperature. Controversy exists in literature over the mechanisms of such softening observed in many precipitation hardened alloys. Small angle neutron scattering (SANS) and transmission electron microscopy (TEM) have been used to study the morphology of γ′-precipitates in the Nimonic PE16 after LCF at room temperature. In TEM dark field images using superlattice reflections, deformation bands free of γ′-precipitates are observed. SANS measurements allowed the characterization of the disappeared precipitates with regard to their average size, size distribution and volume fraction by comparing the scattered intensities of loaded and unloaded specimens. An analysis of the results shows that the γ′-precipitates within the deformation bands have completely dissolved and not just disordered or cut to sizes smaller than the TEM resolution limit.