Composition control in the direct laser-deposition process
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14/7/03
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Composition Control in the Direct Laser-Deposition Process R.R. UNOCIC and J.N. DuPONT Laser-engineered net shaping (LENS) is a solid freeform fabrication process that has the capability of producing functionally graded material (FGM) components by selectively depositing different powder materials in the melt pool at specific locations in the structure during part buildup. The composition in each layer of an FGM is dependent upon the degree of dilution between the substrate (or previous layer) and powder material. A study on the effects of LENS processing parameters (laser power, travel speed, and powder mass flow rate) on dilution was conducted for deposits of H-13 tool steel and copper powder on H-13 tool steel substrates. When varying a single processing parameter while holding all others constant, the dilution was found to increase with increasing laser input power and travel speed and decrease with increasing powder mass additions into the melt pool. A method for estimating dilution in LENS deposits was developed from knowledge of LENS process efficiencies and material thermophysical properties. A reasonable correlation was shown to exist between the experimentally measured dilution and the dilution calculated from the model.
I. INTRODUCTION THE fabrication of functionally graded materials (FGMs) for industry-related applications has been one aspect of solid freeform fabrication research.[1,2,3] Various solid freeform fabrication processes have the ability to fabricate intricately shaped components with local compositional control, resulting in unique mechanical properties throughout the graded structure. The laser-engineered net shaping (LENS) process is one such solid freeform fabrication method that has the ability to produce functionally graded structures by selectively depositing different elemental powders or premixed blends into the molten pool at discrete locations. The adaptation of multiple powder feeders in the LENS system makes this feasible. Dissimilar powder materials can be placed into separate powder hoppers. Computer software, which is integrated into the powder feed system, enables the user to vary the deposit composition as a function of position. Although the ability to produce FGMs with the LENS process is advantageous, this advantage can only be fully exploited when methods are available for controlling the composition within each layer deposit. Previous work in the closely related process of fusion welding has demonstrated[4] that the chemical composition of the deposit can be determined through knowledge of the geometric dilution (D) between the melted substrate and deposited powder, where D is given by D
As As AP
[1]
where As is the cross-sectional area of melted substrate and Ap is the cross-sectional area of deposited powder. It has
R.R. UNOCIC, Research Assistant, is with the Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210. J.N. DuPONT, Associate Professor, is with the Department of Materials Science and
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