Characterization of residual stresses in IN 718 turbine discs by neutron diffraction and finite element modeling


Residual stresses in a commercially produced forged and water-quenched turbine disc made of the nickel-based superalloy IN 718 have been studied using neutron diffraction. The aim of this experimental study was to verify the residual stress predictions of a finite element simulation that is used to model forging and cooling of the discs. In addition to the disc, a thin plate of the same material was also studied. The residual stress predictions of the simulation for the disc agree quite well with the residual stress results obtained from neutron diffraction measurements. However, the heat transfer rate during water quenching was found to be a crucial parameter in the simulation. The stress distributions in the thin plate could only be predicted satisfactorily by using a temperature dependent heat transfer coefficient that was derived from temperature measurements in a disc during quenching.
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