While much focus in metal additive manufacturing has been devoted to geometrical sample shape, and sample density, far less work has been done on quantifications of the as-built microstructures and their evolution during subsequent use. In this presentation, a novel laboratory X-ray diffraction method for non-destructive 3D characterization of metal AM microstructures will be presented. It is based on a scanning principle which allows the complex as-built microstructures to be resolved. The new method allows for following the microstructural evolution during exposure to strain, heat and corrosive environments.

In the second part of the talk, examples of the possibilities for microstructural engineering in laser powder bed fusion are given. It will highlight the contribution of cell boundaries on mechanical properties in 316L, the possibility for phase design in 17-4PH steel and annealing response of AlSiMg after surface shot peening . Finally, the possibilities in design of meso-structures are discussed and preliminary results on how such structures affect mechanical properties are given.

As interest in next-generation nuclear systems grows, particularly in molten salt reactors (MSRs), the need for structural materials that can withstand harsh high-temperature fluoride environments becomes increasingly critical. In this context, additive manufacturing offers new design possibilities for nuclear components, but their corrosion performance remains insufficiently understood. This study examines the corrosion behaviour of Laser Powder Bed Fusion (LPBF) processed AISI 316L stainless steel in molten FLiNaK salt at 700 °C and compares the results of those for conventionally wrought counterparts. Samples were exposed for up to 500 hours and subsequently characterized using light optical microscopy. The wrought samples exhibited intergranular attack and progressive grain detachment with increasing exposure time. In contrast, the LPBF samples showed more localized surface degradation, associated with their complex microstructure. The results indicate that additive manufacturing can alter the corrosion mechanisms of 316L stainless steel in molten fluoride salts, offering opportunities for future material development in advanced nuclear systems.