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Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering Nancy Yang1 • J. Yee1 • B. Zheng2 • K. Gaiser1 • T. Reynolds1 • L. Clemon1 W. Y. Lu1 • J. M. Schoenung2 • E. J. Lavernia2

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Submitted: 1 May 2016 / in revised form: 15 August 2016 / Published online: 8 December 2016 Ó ASM International 2016

Abstract We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. The study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. The study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. The current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.

& J. M. Schoenung [email protected] 1

Sandia National Laboratories, Livermore, CA 94551, USA

2

University of California, Irvine, Irvine, CA 92697, USA

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Keywords additive manufacturing  dendritic  LENSÒ  porosity  stainless steel

Introduction Emerging additive manufacturing (AM) technologies, such as 3-D laser engineered net shaping (LENS), a commercial direct energy deposition (DED) (Ref 1), is capable of building complex engineering components to its final shape, dimension and surface finishing (Ref 2). 3-D LENS deposition involves instantaneous metal melting, molten metal flow, and solidification; in many aspects, the LENS deposition is similar to well-understood processes including metal casting, welding, and thermal spray. However, the manufacturing algorithm for building complex net-shaped engineering components (through multi-pass deposition of molten metal) is unique, and the resultant bulk material properties of the finished component are not yet fully understood (Ref 3, 4). For instance, the metallurgical reaction induced by the systematic interpass re-melting during the successi