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Non-destructive testing techniques based on neutron imaging and diffraction can provide information on the internal structure of relatively thick metal samples (up to several cm), which are opaque to other conventional non-destructive methods. Spatially resolved neutron transmission spectroscopy is an extension of traditional neutron radiography, where multiple images are acquired simultaneously, each corresponding to a narrow range of energy. The analysis of transmission spectra enables studies of bulk microstructures at the spatial resolution comparable to the detector pixel. In this study we demonstrate the possibility of imaging (with ~100 μm resolution) distribution of some microstructure properties, such as residual strain, texture, voids and impurities in Inconel 625 samples manufactured with an additive manufacturing method called direct metal laser melting (DMLM). Although this imaging technique can be implemented only in a few large-scale facilities, it can be a valuable tool for optimization of additive manufacturing techniques and materials and for correlating bulk microstructure properties to manufacturing process parameters. In addition, the experimental strain distribution can help validate finite element models which many industries use to predict the residual stress distributions in additive manufactured components.

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Investigations of the production of thin-walled steel alloys through the gas carburization of structures made from reduced and sintered metal oxide powders were performed. Extrusions with low-alloy steel composition were produced successfully without the occurrence of metal dusting, yielding a novel technique for the production of thin-walled steel structures. Thin strip geometries (~200 to 300 lm final thickness) of samples with the composition of 4140 steel, without carbon, were produced through the extrusion of a paste of metal-oxide powders. Full reduction and sintering in a 10 pct H 2 /90 pct Ar atmosphere yielded a metal part containing all necessary alloying elements except carbon. Gas carburization in a controlled CO/CO 2 atmosphere was then used to introduce carbon through the thickness of the structure while carburization parameters were controlled such that metal dusting was not observed. It has been shown in this study, through heat treatment and microstructural investigations, that structures with 4140 composition displaying microstructures and mechanical properties comparable with conventionally made steels can be reached in approximately 30 minutes during gas carburization. The research shows that carbon contents above the eutectoid composition can be reached in less than 30 minutes. As a result, a novel alloy development tool has been introduced.