Neutron diffraction stress determination in W-laminates for structural divertor applications

• An innovative multi-layer W–Cu model sample for divertor applications has been non-destructively characterized by means of neutron diffraction measurements.
• The average strains and stresses present in the two materials, in the as-brazed state, have been determined with strain accuracies of approximately ±100 µm/m.
• Average stress values as low as −17 ± 32 MPa are found through the sample, with some inhomogeneity in the two materials and in the different positions inside the investigated sample.
• The experimental procedure developed for this study can be applied to more complex samples, designed for mono-block construction, as well as for in-situ high temperature measurements.

Neutron diffraction measurements have been carried out to develop a non-destructive experimental tool for characterizing the crystallographic structure and the internal stress field in W foil laminates for structural divertor applications in future fusion reactors. The model sample selected for this study had been prepared by brazing, at 1085 °C, 13 W foils with 12 Cu foils. A complete strain distribution measurement through the brazed multilayered specimen and determination of the corresponding stresses has been obtained, assuming zero stress in the through-thickness direction. The average stress determined from the technique across the specimen (over both ‘phases’ of W and Cu) is close to zero at −17 ± 32 MPa, in accordance with the expectations.