The determination of the residual strains and stresses in a tungsten inertgas welded sheet of IN718 superalloy using neutron diffraction

The residual stress state in a tungsten inert gas (TIG) welded sheet of IN7 18, a high-strength nickel-based superalloy, has been characterized using n eutron diffraction. The measurements were performed using a time-of-flight diffractometer, which allowed lattice strains from the gamma-gamma' {111} a nd gamma-gamma' {311} composite peaks to be compared with the Reitveld-refi ned spectra. Residual stresses were estimated using plane-specific values o f Young's modulus and Poisson's ratio for the {311} and {111} peaks, and th e macroscopic material response for the Reitveld-refined data. These values were obtained from a theoretical analysis of existing data after Kroner. The weld considered was an autogenous TIG weld 180 mm long placed centrally on to a 2 mm x 100 mm x 200 mm solution heat-treated sheet of IN718. The s train was mapped over the central 140 mm of the plate; within this region, the measured strains were almost constant along the length, with the peak b ulk longitudinal strain of 1700 x 10(-6) detected 4 mm from the weld centre , in the heat-affected zone. The corresponding peak longitudinal stress was 270 MPa, and the tensile region 11 mm wide, with the longitudinal residual stresses typically up to 2.5 times greater than those in the transverse di rection. It was also found that, while in-weld stresses derived from analys is of single peaks may be incorrect due to textural and compositional effec ts, those derived from Reitveld refinement of the entire spectrum showed re asonable. agreement with those obtained from incremental hole drilling meas urements made with the Matthar-Soete method.