Deformation mechanisms and defect tolerance in the microstructure of 3D-printed alloys
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ADDITIVE MANUFACTURING OF METALS: COMPLEX MICROSTRUCTURES AND ARCHITECTURE DESIGN
Deformation mechanisms and defect tolerance in the microstructure of 3D-printed alloys Matthew Moneghan1, Christopher Williams1, Reza Mirzaeifar1,a) 1
Department of Mechanical Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA Address all correspondence to this author. e-mail: [email protected]
a)
Received: 3 December 2019; accepted: 27 February 2020
A novel approach is utilized to investigate the deformation mechanisms at the microstructural level in 3Dprinted alloys. The complex formation methods leave a unique and complicated microstructure in the as-built 3D-printed alloys. The microstructure is three leveled, composed of meltpools, grains, and cells. Deformation mechanisms in this microstructure are still highly unexplored due to the complexities of analysis at this scale. To understand these, we establish an image processing framework that converts scanning electron microscope (SEM) images directly into models that are scaled up and 3D printed with representative stiff and soft materials for the proposed material types within the body. These bodies are loaded in uniaxial tension with digital image correlation to study the strain gradient and stress delocalization as a result of the microstructure. The same models were tested through Finite Element Analysis (FEA) with materials similar to reality. Our testing shows the hierarchical material distribution leads to an increased damage tolerance.
Introduction In response to the opportunities and challenges of the 21st century, additive manufacturing (AM) is rapidly replacing conventional manufacturing methods. After years of extensive development in AM methods for polymeric systems, 3D printing of metals, particularly by the selective laser melting (SLM) technique, is now being extensively adopted by multiple industry subsectors. Investigating different aspects of the mechanical properties of SLM parts has been attracting growing attention in the past few years [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. Parts printed in this manner have many advantages over traditionally manufactured parts, including graded material compositions, complex geometries that are unobtainable through subtractive manufacturing, and less material usage [14]. These parts are currently in use across multiple fields such as the automotive industry in performance vehicles, the aerospace industry as manifolds and rocket engines, and the medical field as joint replacements and prosthetics [15, 16, 17]. As these parts are produced more for research and commercial use, more studies are being carried out on the complex substructures of the materials. Compared to polycrystalline metals, in which grains are the major microstructural feature of the material, SML parts have two unique extra microstructures: cells and meltpools.
ª Materials Research Society 2020
Meltpools are roughly semicircular shapes that form as the laser melts a section of the powder, which then solidifies [18, 19, 20]. These meltpools
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