Influence of Weld Process Parameters on Residual Stress in 70/30 Copper-Nickel Alloys

Copper-nickel alloys exhibit a drastic dip in their ductility at intermediate temperatures. During processes such as welding or additive manufacturing, the intermediate temperature ductility drop often results in cracking--referred to as ductility dip cracking (DDC). Such cracking is more likely during multi-pass solidification processes, such as Gas Tungsten Arc Welding (GTAW), because the localized cyclic heating and cooling imparts considerable stresses in the fusion zone and heat affected zone. While several mechanisms have been considered for DDC susceptibility in a wide range of welded FCC alloys, the compounding influence of weld parameters and residual stress evolution on the loss of ductility and crack formation has remained unclear. The current study considers the effect of weld process parameters including heat input, plate thickness, interpass temperature, and weld fixturing on residual stress in welds. Samples of wrought copper-nickel (C71500) were welded using the mechanized GTAW process, and residual stresses were measured using neutron diffraction at the High Flux Isotope Reactor on the HIDRA beamline at Oak Ridge National Laboratory. Results indicate that interpass temperature, plate thickness, and welded assembly fit-up (specifically tack welding of the backing bar) each have significant impact on residual stress distribution and magnitude in the welds.