On the residual stress relaxation in Inconel 718 superalloys at high temperature by real-time neutron diffraction

[Display omitted] •In-situ neutron diffraction was used to study the residual stress relaxation kinetics and the mechanisms of a large-size bulk sample.•The multi-stage kinetics of relaxation were found to be correlated to the competing stress relaxation mechanisms in the atomic scale.•The residual stresses were largely relieved after annealing for 14 ∼ 20 h at 718 °C.•The deviatoric stress components were accurately determined even when the samples have heterogeneous chemistry. Residual stresses in nickel-based superalloy engineering structure develop during various manufacturing stages, which can result in component distortion or reduction of performance reliability during high temperature service. Experimental quantification of residual stress built-up and its relaxation at high temperatures provides the time-dependent evolution and model validation for residual stress predictions. Via in situ time-of-flight neutron diffraction, a real-time study of residual stress relaxation is carried out on Inconel 718 (IN 718) blocks with different initial residual states after oil or water quenching and annealing processes. The residual stresses are largely relieved after 14 ∼ 20 h at 718 °C, and multi-stage kinetics of relaxation are observed. The staged feature is correlated to the competing stress relaxation mechanisms in the atomic scale that are clued from the evolution of neutron diffraction data. Although with large initial discrepancy in samples due to different thermal treatments, the final residual stresses tend to be within small variations after the relaxation.