Comparison of Neutron Bragg edge imaging and diffraction for measurement of residual stresses in pure W welds for nuclear fusion applications

The weldability of tungsten (W) is a very sought after process because this will expand the scope of material science in reactors, especially with tokamak reactors. Being able to measure the residual stresses, caused by welding is vital to the integrity of the W welds, and can be important depending on the regions in which the welds will be utilised. Neutron diffraction (ND) measurements in all 3 strain orientations were done on novel pure W butt-welds that were created through electron beam welding (EBW). The same experiment was repeated using novel Bragg edge peak imaging (BEPI) technique, for the normal strain orientation. A comparison between the 2 techniques found there were similarities in the compressive and tensile behaviour of the normal strain component. The normal strain profiles are seen to be similar in all 3 main weld regions, with the parent region showing the best agreement and the heat affected zone (HAZ), giving the biggest difference in strain values. Additional measurements from both techniques are needed to compare all 3 strain components, which will be used to measure the overall residual stress across the W welds.