2003 / Solid Freeform Fabrication Proceedings
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Author S. Bontha and N. W. Klingbeil Department of Mechanical and Materials Engineering Wright State University Dayton, OH, 45435
Source Solid Freeform Fabrication Proceedings, 2003, pp 219-226.
Abstract The ability to predict and control microstructure in laser deposited materials requires an understanding of the thermal conditions at the onset of solidification. The focus of this work is the development of thermal process maps relating solidification cooling rate and thermal gradient (the key parameters controlling microstructure) to laser deposition process variables (laser power and velocity) . The approach employs the well-known Rosenthal solution for a moving point heat source traversing an infinite substrate. Cooling rates and thermal gradients at the onset of solidification are numerically extracted from the Rosenthal solution throughout the depth of the melt pool, and dimensionless process maps are presented for both thin-wall (2-D) and bulky (3- D) geometries. In addition, results for both small-scale (LENS TM ) and large-scale (higher power) processes are plotted on solidification maps for predicting grain morphology in Ti-6Al-4V. Although the Rosenthal results neglect temperature-depen dent properties and latent heat effects, a comparison with 2-D FEM results over a range of LENS TM process variables suggests that they can provide reasonable estimates of trends in solidification microstructure. The results of this work suggest that changes in process variables could potentially result in a grading of the microstructure (both grain size and morphology) throughout the depth of the deposit, and that the size-scale of the laser deposition process is important. (Auth abstract) [References: 12] XX
Solid Freeform Fabrication Proceedings can be obtained from: The Solid Freeform Fabrication Symposium
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The University of Texas at Austin
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Mechanical Engineering Dept.
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MC C2200
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