A Microstructure Evolution Model for the Processing of Single-Crystal Alloy CMSX-4 Through Scanning Laser Epitaxy for Tu
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SCANNING laser epitaxy (SLE), a laser-based additive manufacturing technology, was introduced in Part I.[1] SLE can produce dense, SX deposits of superalloys such as CMSX-4 on similar chemistry substrates. The high-resolution raster scan used in the process allows preand post-heating during each pass, thus reducing the residual stresses and resulting in crack-free deposits. The use of a stationary powder bed eliminates any undesired convection as is often formed in blown powder-based laser cladding processes and helps in reducing the RANADIP ACHARYA, Ph.D. Candidate, is with the George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Dr., Atlanta, GA 30332-0405. ROHAN BANSAL, formerly a Graduate Student with the George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, is now Ph.D. with the Chart Industries, Buffalo, NY. JUSTIN J. GAMBONE, formerly a Graduate Student with the George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, is now M.S. with GE Global Research, Niskayuna, NY. SUMAN DAS, Professor and Morris M. Bryan, Jr. Chair, is with the George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, and also with the School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Dr. NW, Atlanta, GA 30332-0405. Contact e-mail: [email protected] Manuscript submitted January 21, 2014. Article published online September 16, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
formation of stray grains in the deposit. The highresolution scan and tighter thermal control also facilitate the formation of a finer grain structure than that typically formed in investment casting, which can be beneficial for attaining superior mechanical properties. A CFD-based coupled flow-thermal model was also developed in Part I.[1] This model takes into account the temperature-dependent physical properties of CMSX-4, the complete raster scan pattern, and the effect of natural and Marangoni convection, and predicts the thermal and flow fields in the process. The model was validated with quantitative melt depth and the qualitative microstructural data. Time tracking of the solidification history was introduced to exclusively account for the effect of the trailing edge of the melt pool while coupling the microstructural model. In order to extract microstructural information from the experimentally obtained micrographs, an active contour-based graphical image-analysis technique has been developed in MATLABTM (The MathWorks, Inc., Natick, MA). Typically, the microstructural image first passes through the Canny edge detection technique which can preserve important structural data while filtering out a vast majority of the image information.[2,3] Active contours are splines (also known as snake lines) that move due to external energies being applied to them through a map, while maintaining a shape through the VOLUME 45B, DECEMBER 2014—2279
use of an internal energy. The total energy of the snake line is gi
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