In Situ Neutron Diffraction Study of the Influence of Microstructure on the Mechanical Response of Additively Manufactur
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ADDITIVE manufacturing is a rapidly developing processing pathway that produces components by selectively melting and solidifying feedstock to build a desired geometry, rather than subtractive machining from cast or wrought material.[1] The difference in microstructures between additively manufactured (AM) and wrought components can be substantial, similar to the changes observed within welded microstructures.[2] This is significant because, in general, the options for altering the microstructure of AM components after fabrication are limited to thermal treatments, surface deformation (e.g., shot or laser peening), and chemical modifications (e.g., carburization). Bulk thermo-mechanical treatments such as rolling and forging which have been developed over centuries to optimize the microstructure of conventionally produced wrought materials cannot be readily applied to completed AM structures because components are generally built to D.W. BROWN, J.S. CARPENTER, B. CLAUSEN, G. KING, and S.C. VOGEL are with Los Alamos National Laboratory, Los Alamos, NM 87545. Contact e-mail: [email protected] D.P. ADAMS and B. REEDLUNN are with Sandia National Lab, Albuquerque, NM 87123. L. BALOGH is with Canadian Nuclear Laboratories, Chalk River, ON, Canada. T.A. PALMER is with Penn State University, University Park, PA, 16802. M.C. MAGUIRE is with Sandia National Lab, Livermore, CA, 94551. Manuscript submitted April 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
near-net shape to minimize the amount of material and post-build machining needed. Despite the sub-optimal weld-like microstructure, as-built and/or heat-treated AM materials often have quasi-static[3–5] and dynamic properties[6,7] that compare favorably with their traditional wrought counterparts. Although, post-mortem analysis of the dynamic failure tests on AM and wrought 316L material showed that the details of the failure were very different, the integrated response was very similar.[7] Thus, it is critical to understand both how the processing parameters control the microstructure in the as-built material and how the microstructure, in turn, controls the properties of the as-built material. AM processing parameters have a strong influence on component microstructure. Significant research is being performed to establish both empirical connections between the input parameters and the achieved microstructure and properties, as well as physics-based models to guide AM process optimization, e.g., Reference 8. The current work focuses on understanding how the unique microstructure produced by AM controls the resultant properties, in a specific case of laser-based directed energy deposition (DED) of 304L stainless steel. In situ neutron and high-energy X-ray diffraction techniques have been developed over the last two decades to monitor the microstructure of materials during deformation, as well as other external perturbations.[9–12] In particular, the development of internal strains, texture, and dislocation density can be
determined during deformation and, when coupled
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