Phase evolution in laser-deposited titanium-chromium alloys
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IN recent years, direct fabrication of metallic components using the solid freeform fabrication route has been shown to be a viable and promising manufacturing technology. United Technologies Research Center (UTRC) in 1979[1] pioneered producing bulk metallic components of near-net shape by depositing multiple thin layers using an energy beam. Fusing was carried out using a laser beam, and the deposited material was fed in the form of either a powder or a wire feedstock. This process has been referred to as the layerglaze process.[1] By marrying the concepts of stereolithography and layerglaze, a new generation of processes for laser deposition of solid freeform components has been developed. These include the laser-engineered net-shaping (LENS*)[2] and directed-light fabrication (DLF)[3] processes. *LENS is a trademark of Optomec Design Company, Albuquerque, NM.
The LENS process was developed at the Sandia National Laboratories and subsequently commercialized by the Optomec Design Company of Albuquerque, New Mexico, while the DLF process was developed at the Los Alamos National Laboratories in the early 1990s. Both processes are similar in that they used a focused laser beam as a heat source to melt metallic powder and create a solid, three-dimensional object. A variety of metals and alloys have been deposited using LENS.[2,4] The alloys deposited using this process have primarily been from prealloyed powders of the required composition. However, since the LENS process uses a powder feedstock, it allows the flexibility to deposit a blend of elemental powders and create an alloy in situ. This is a very attractive proposition, since, if successful,
R. BANERJEE, Research Scientist, Center for the Accelerated Maturation of Materials, Department of Materials Science and Engineering, P.C. COLLINS, Graduate Fellow, Department of Materials Science and Engineering, and H.L. FRASER, Ohio Regents Eminent Scholar and Professor, Department of Materials Science and Engineering, and Director, Center for the Accelerated Maturation of Materials, are with The Ohio State University, Columbus, OH 43210. Contact e-mail: [email protected] Manuscript submitted June 12, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
it could potentially reduce the costs of processing to a large extent. In addition, using elemental powder blends in a system with multiple hoppers also allows the possibility of depositing graded compositions within the same sample. There have been only a limited number of studies on the deposition of alloys from elemental powder blends.[5,6] Takeda et al.[5] and Steen et al.[6] have used this approach to study laser-deposited Fe-Cr-Ni and FeCo-Al alloys, respectively. In the case of Fe-Cr-Ni alloys, laser tracks of three different alloy compositions with varying Cr:Ni ratios were deposited on a substrate. The Cr:Ni ratios used were 13:6, 18:9, and 25:20, selected on the basis of the Schaeffler diagram, corresponding to martensitic, austenite/martensite ferrite, and austenite/ferrite microstructures, respectively.[5]
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