In-Situ High-Energy X-ray Diffraction During a Linear Deposition of 308 Stainless Steel via Wire Arc Additive Manufactur
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AN obstacle to wide-spread adoption of metal additive manufacturing (AM) components in property-critical applications is the currently limited understanding of the process-structure-property-performance (PSPP) relationship of metal AM components. This limits the ability of process models to predict the in-service behavior of such components.[2,3] Solidification at the cooling rates appropriate for AM has not been extensively studied, leading to a gap in existing data in the literature that would potentially validate process models that seek to predict microstructures. Pathways to filling this gap can make use of in-situ process diagnostics, material diagnostics, or heat source [1]
D.W. BROWN, J.S. CARPENTER, B. CLAUSEN, J.C. COOLEY, V. LIVESCU, and T.J. STOCKMAN are with the Los Alamos National Laboratory, Los Alamos, NM, 87545. Contact e-mail: [email protected] A. LOSKO is with the Technical University Munich, 85748 Garching b. Mu¨nchen, Germany. P. KENESEI and J.-S. PARK are with the Argonne National Laboratory, Lemont, IL, 60439. M. STRANTZA is with the Lawrence Livermore National Laboratory, Livermore, CA, 94550. Manuscript submitted July 1, 2019. Article published online January 6, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
diagnostics coupled with ex-situ measurements of microstructure or mechanical properties that provide data to models and theories and tie the diagnostic data to the process variables. The high solidification and cooling rates experienced during AM result in metastable microstructures that are significantly different from traditional material processing techniques.[4] This is important because, in general, the options for post-build manipulation of the microstructure of AM components after fabrication are limited. Also, AM frequently results in large residual stresses on multiple length scales[1] in the component due to the rapid cooling and associated thermal gradients as well as complex build patterns. Residual stresses frequently drive distortion that can lead to build failure, components out of geometrical specification, or premature fracture. Thus, monitoring the development of the microstructure and residual stress during AM becomes of primary importance to understanding and developing the relationships between PSPP at these rapid cooling rates. Commercial alloys, such as stainless steels, have complex phase diagrams and their composition has been chosen largely through an optimization process for traditional manufacturing conducted at relatively slow
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cooling rates. In stainless steels, in particular, the formation of ferrite or austenite on solidification and evolution of the solid-state phase transformation during cooling can lead to mechanical instability of weldments and/or AM deposit.[5,6] Elmer et al. provide an overview of microstructural development during solidification of stainless steel alloys,[7] showing that cooling rates and the chemical composition of the alloy influence the primary solicitation mode that establishes the microstructure at t
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