Process-Defect-Structure-Property Correlations During Laser Powder Bed Fusion of Alloy 718: Role of In Situ and Ex Situ
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TRODUCTION
ONE of the obstacles critical to the adoption of additive manufacturing (AM) is the need for rapid qualification[1,2] of components that includes geometrical conformity, minimal defect density, ideal microstructure, as well as targeted performance requirements
S.J. FOSTER is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN and also with Oerlikon AM US, Charlotte, NC. K. CARVER, R.B. DINWIDDIE, and F. LIST III are with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN and also with the Manufacturing Demonstration Facility, Oak Ridge National Laboratory, Oak Ridge, TN. K.A. UNOCIC is with the Materials Science and Technology Division, Oak Ridge National Laboratory. A. CHAUDHARY is with Applied Optimization Inc., Dayton, OH. S.S. BABU is with the Department of Materials Science and Engineering, The University of Tennessee and with the Department of Mechanical and Aerospace and Biomedical Engineering, The University of Tennessee, Knoxville, TN 37934 and also the Manufacturing Demonstration Facility, Oak Ridge National Laboratory. Contact e-mail: [email protected] Manuscript submitted May 6, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
through many pathways. First, during the development of AM process parameters, extensive mechanical property (e.g., tensile or fatigue) testing can be performed on standard samples with a given alloy powder and machine. Using the above data and Weibull statistics, the risks of using the same parameters for complex geometry can be forecasted.[3] Second, while manufacturing each and every complex geometry, sacrificial samples with standard geometries for mechanical testing can be made around that component. If the tensile samples meet the target properties, one may assume that the printed component is also qualified in conjunction with existing non-destructive evaluations. Third, extensive amounts of in situ measurements[4,5] of thermal signatures,[6–14] geometry,[15,16] and chemistry[17,18] can be performed during the additive manufacturing of components. These in situ data can be used in conjunction with selective ex situ measurements and integrated computational materials engineering (ICME) principles to predict the expected performance of individual components.[19] The current paper pertains to the validity of this third approach for structural metals and alloys processed by powder bed fusion using laser and/or electron beam energy source. In this paper, we
evaluated this third approach using Inconel 718 powders and a laser powder bed fusion (L-PBF) process.[20] To define the specific scope of the current paper, the existing process flow followed by additive manufacturing practitioners is briefly reviewed. (i) The first step involves, the identification of optimum processing parameters (e.g., laser power, spot size, velocity, hatch distance, and layer thickness) using single track,[21] multiple tracks, and finally followed by layer melting experiments.[22] (ii) Once the layer melting is o
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