Asymmetric Cracking in Mar-M247 Alloy Builds During Electron Beam Powder Bed Fusion Additive Manufacturing
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INTRODUCTION
POWDER bed fusion (PBF) either with electron beam or laser technology allows for manufacturing of metallic components with greater flexibility in geometric
Y.S. LEE, M.M. KIRKA, S. KIM, N. SRIDHARAN, A. OKELLO, and R.R. DEHOFF are with the Manufacturing Demonstration Facility, Oak Ridge National Laboratory, Knoxville, TN 37932 and also with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830. Contact e-mail: [email protected] S.S. BABU is with the Manufacturing Demonstration Facility, Oak Ridge National Laboratory and also with the Department of Mechanical, Aerospace and Biomedical Engineering, University of Tennessee, Knoxville, TN 37916. Notice of Copyright. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). Manuscript submitted February 7, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
design. However, the applications of PBF to nickelbased superalloys, especially with high volume fraction of c¢ precipitates, have been limited either to prototype evaluation or low volume production due to challenges in qualification and certification. These challenges are mainly attributed to the presence of defects (i.e., porosity, lack of fusion and cracks), surface roughness, improper dimensional tolerance, and also non-optimal c¢ precipitate distributions.[1–3] Mar-M247 has been widely used for last three decades in aerospace and gas turbine industries due to its superior mechanical strength, hot corrosion resistance, and high-temperature creep behavior.[4] However, Mar-M247 is classified as a traditionally non-weldable alloy[5] due to various cracking mechanisms[6] including solidification, liquation, strain age, and ductility-dip cracking brought about by complex thermal histories and mechanical constraints. The mechanical drivers for the cracking involve (i) thermal stresses that stem from rapid heating and cooling with thermal gradients and/or (ii) presence of residual stresses that is brought about by the gradient in accumulated plastic strains. Although physical processes during metal additive manufacturing (AM) are analogous to welding, AM involves complex and widely varying geometries that lead to complex
interactions between geometry, process, and spatial and temporal variation of cracking susceptibility.[7–9] Therefore, additive manufacturing of complex geometries requires exhaustive experimental trial and error optimization and challenges the business cas
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