Texture and Crystal Orientation in Ti-6Al-4V Builds Fabricated by Shaped Metal Deposition
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RODUCTION
DUE to their excellent strength to weight ratio, superior biocompatibility, low elastic modulus, and exceptional corrosion resistance, Ti alloys are widely used in aeronautical and prosthesis applications. Yet, material and traditional machining are very costly. Therefore, innovative manufacturing routes are required. Shaped metal deposition (SMD) is a novel manufacturing route, patented by Rolls-Royce (Derby, UK), in which fully dense metallic components are fabricated by successively welding layer upon layer. The advantages of this additive layer manufacturing technique are the following: near-net-shape production of fully dense parts, no or very limited tooling and finishing required, reduction in lead times and cost, the ease with which design changes can be incorporated, little or no scrap, and reduced environmental impact. The mechanical properties are competitive to cast material with a low amount of oxygen and nitrogen contamination.[1–3] Ultimate tensile strengths between 929 and 1014 MPa are reported. The strain at failure significantly depends on the orientation relative to the SMD layers. A strong dependence of the strain at failure on the tensile orientation relative to the SMD layers was found. Maximum values of about 19 pct for tension perpendicular and only one third of that for tension parallel to the layers are stated. This particular production route involves the transition from liquid to solid state, and the successive BERND BAUFELD and STEVEN DILLIEN, Researchers, and OMER VAN DER BIEST, Professor, are with Katholieke Universiteit Leuven, MTM, 3001 Leuven, Belgium. Contact e-mail: [email protected] Manuscript submitted May 19, 2009. Article published online June 10, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
welding acts effectively as subsequent heat treatments for the already deposited layers. This complex fabrication scheme results in a particular microstructure and crystallographic texture, which determines the properties of the component. The aim of the present article is to investigate the texture and the crystalline correlations of the microstructure for a component made out of Ti-6Al-4V, one of the most commonly used a/b alloys. In other publications, the microstructure[2,4] and the mechanical properties[1–3] of these SMD components are discussed in detail.
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EXPERIMENTAL SETUP
A. Shaped Metal Deposition The SMD component was fabricated by AMRC (Sheffield). The SMD cell consists of a tungsten inert gas (TIG) welding torch attached to a six-axis Kuka robot (Augsburg, Germany) linked to a two-axis table, all of which are enclosed in an airtight chamber ensuring an inert gas atmosphere. The TIG welding is performed with a Ti-6Al-4V wire with a diameter of 1.2 mm. The atmosphere consists of argon controlled to 99.999 pct purity. More details about the cell can be found elsewhere.[4] Wall thickness and surface finish in particular are controlled by the welding parameters. For the component discussed in this article, an electrical current of 140 A, a travel speed of
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