Multiscale plasticity behavior and fatigue performance of laser melting multi-layer nickel-based superalloys upon heat treatments

The present work focuses on heat treatment effects on cyclic plasticity behavior, multiscale strengthening mechanisms and low cycle fatigue performance of laser melting nickel-based su-peralloys. Microscopic indentation analysis, mesoscopic DIC analysis and macroscopic material testing were conducted to identify multiscale mechanical properties. A DIC-aided indentation method was developed to identify the constitutive parameters of the laser melting material by introducing the reference material. The dendritic-cellular microstructures in the remelting zone (RZ) significantly decrease the effects of the grain size and morphology. Heat treatments can improve the strength but decrease the ductility of RZ and do not affect the macroscopic stress-strain responses of the multilayered material. Moreover, the strengthening mechanisms in the laser melting material were verified to reveal size-and plasticity-dependent effects. The strengthening contributed by grain boundaries and twin boundaries yields little effect on the strength at micro scales and the influences increase with plastic deformations. Furthermore, the aging treatment increases the fatigue life of RZ by factor 2 and, however, decreases the low cycle fatigue performance of the multilayered material, meaning that the under-matched material can be stronger than the base material in certain configurations. The stabilized fatigue load of the laser melting material has strong correlations with the mismatching and loading levels. The present study provides a deep insight into the strengthening mechanisms and cyclic plasticity behaviors of laser-manufactured materials.