Modeling of the mechanical effects induced by the tungsten inert-gas welding of the IN718 superalloy

Abstract

The distortion and residual stresses arising during the tungsten inert-gas (TIG) welding of the nickel-based superalloy IN718 are modeled using sequentially coupled thermal-mechanical analyses. Processing trials have been carried out for validation purposes, and, for a number of rectilinear testpieces, the distortion has been quantified. The residual stresses in one of the welds have been characterized using the neutron diffraction technique. For the same weld, the thermal cycles induced in the heat-affected zone have been measured; this information, along with the observed shape of the weld pool, enables a suitable description of the weld torch to be made. The modeling is used to rationalize the state of residual stress induced, the distortion that occurs, and its evolution as processing proceeds. It is shown that good predictions can be made of the distortion induced by processing. The residual stresses predicted are reasonable, particularly the longitudinal stresses vary through the thickness, and, since the testpieces are thin, some uncertainties are introduced. Studies are made of the sensitivity of the predictions to the materials data and model formulation.