Neutron Bragg edge imaging for strain characterization in powder bed additive manufacturing environments

Spatially resolved studies of crystalline structures, e.g. lattice spacings, are enabled by recording the transmitted spectra in neutron Bragg edge imaging. The recorded signals are, however, a result of through-thickness averaging of the probed specimen in the beam direction. Therefore, it is challenging to extract the strain distribution when the strain varies across the thickness, which applies for studies on different materials or material states along the beam. Here we introduce the approach to disentangle contributions to the recorded signals, i.e. separating the transmission spectra of two different material states. This is particularly applicable to powder bed additive manufacturing environments where operando strain characterization of the printed specimen using neutrons is intended. In this work, Laser Powder Bed Fusion (PBF-LB/M)-built 316L and IN718 samples embedded in their corresponding powders are used, extracting the desired spectra of the printed spec-imen. The disentanglement is proven to be satisfactory by obtaining coinciding strain maps of identical specimens embedded in powder layers of different thicknesses. Furthermore, the obtained residual strain distributions of 316L samples were verified by conventional neutron diffraction with lower spatial resolution due to the gauge volume averaging.(c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

Spatially resolved studies of crystalline structures, such as lattice spacings, can be conducted using neutron Bragg edge imaging. However, extracting strain distribution becomes challenging when the strain varies across the thickness of the probed specimen. This study introduces an approach to separate the transmission spectra of two different material states, which is particularly useful for operando strain characterization in powder bed additive manufacturing environments.