Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions
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er Engineered Net Shaping (LENS™) Process is an additive manufacturing (AM) technique for the fabrication of metallic parts, originally developed at Sandia National Laboratories in the 1990s. Parts are built in a layer-by-layer fashion as powder is injected into a melt pool created by a focused laser beam, which is moved in a specific pattern to build the desired part. LENS™ and other energy deposition-based AM processes have gathered interest because of their potential for producing parts with advantageous microstructural features,[1] unique structures,[2] and/or improved mechanical properties.[3] Additional abilities of such deposition processes include building of compositionally or functionally graded parts,[4] fully dense parts, and use in part repair.[5] Parts made from titanium alloys in particular, owing to its low density, high strength, and corrosion resistance, have the potential to be produced MATTHEW R. ROLCHIGO, MICHAEL Y. MENDOZA, DAVID A. BRICE, and BRIAN MARTIN are with the Department of Materials Science and Engineering, Iowa State University, 2220N Hoover Hall, Ames, IA, 50011. PEYMAN SAMIMI, PETER C. COLLINS, and RICHARD LESAR are with the Department of Materials Science and Engineering, Iowa State University and also with the Center for Advanced Non-Ferrous Structural Alloys (CANFSA), Iowa State University, 2220N Hoover Hall, Ames, IA, 50011. Contact e-mail: [email protected] Manuscript submitted January 15, 2017. Article published online May 15, 2017 3606—VOLUME 48A, JULY 2017
via LENS™ for applications ranging from biomedical to aerospace.[6] One of the biggest challenges in the use of AM processes is, however, the details of the relationships between processing parameters and the properties of the final part. While extensive research has been done in modeling of the molten pool and microstructure produced in welding operations, different process parameters, material properties, and forces acting on the molten pool in laser and electron beam-based deposition processes necessitate model extensions for AM conditions. The development of such a model for a given additive process is aided by a detailed understanding of similarities and differences between welding and AM conditions, and how the conditions affect development of the microstructure in the solidified material. The purpose of this paper is to present the first step in the development of a multiscale computational model of AM processes, with the goal of predicting details of the as-solidified microstructures and properties in metallic alloys. We focus on the LENS™ process for a specific alloy system. There is a wide range of physical phenomena occurring during the deposition and rapid solidification of alloys created via LENS™ and similar beam-based deposition processes. As the laser is moved across the sample, a melt pool is created that involves not only the melted powder feedstock but also previously deposited layers. Heat transport through various modes in solid, liquid, and gas are important in determining the METALLURGICAL AND MATERIALS TRANS
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