Thermomechanical behavior of different Ni-base superalloys during cyclic loading at elevated temperatures

The material behavior of three Ni-base superalloys (Inconel® 718, Allvac® 718Plus^TM and Haynes® 282®) during in-phase cyclic mechanical and thermal loading was investigated. Stress controlled thermo-mechanical tests were carried out at temperatures above 700 °C and different levels of maximum compressive stress using a Gleeble® 3800 testing system. Microstructure investigations via light optical microscopy (LOM) and field emission gun scanning electron microscopy (FEG-SEM) as well as numerical precipitation kinetics simulations were performed to interpret the obtained results. For all alloys, the predominant deformation mechanism during deformation up to low plastic strains was identified as dislocation creep. The main softening mechanism causing progressive increase of plastic strain after preceding linear behavior is suggested to be recrystallization facilitated by coarsening of grain boundary precipitates. Furthermore, coarsening and partial transformation of strengthening phases was observed. At all stress levels, Haynes® 282® showed best performance which is attributable to its stable microstructure containing a high phase fraction of small, intermetallic precipitates inside grains and different carbides evenly distributed along grain boundaries.