Fabrication of Fe-FeAl Functionally Graded Material Using the Wire-Arc Additive Manufacturing Process
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INTRODUCTION
FUNCTIONALLY graded material (FGM) belongs to a class of advanced materials with properties that progressively vary over one or more dimensions. Since it was applied in mid-1980 as the thermal barrier coating for hypersonic space plane projects,[1–5] FGM has increasingly attracted both research and commercial interest due to its unique gradient and locally optimized material properties, which permits application in harsh environments with high-temperature gradient, wear, and corrosion. While the reproducibility of FGMs is important for its mass production in industrial applications,[6] the deterministic gradient still remains difficult to control and the dilution effect during fabrication has not been systematically explored.[7] In addition, the fabrication cost of the composition gradient material is very high using current powder processing and fabrication methods.[8] Existing methods for FGM fabrication include layer/ disk remelting,[9] chemical vapor deposition/infiltration,[10] powder-based furnace remelting,[11] laser rapid prototyping,[12] and also weld arc deposition.[13] For certain materials, powder-based processes cannot directly produce functional parts with high structural integrity[14] and often require expensive processing steps such as hot isostatic pressing to achieve the full density which is essential for highly loaded structural materials.[15] Compared to powder-based processes, the arc welding-based wire feed deposition method has significantly lower material supply cost, higher deposition rate, and
CHEN SHEN, Ph.D. Candidate, ZENGXI PAN, Senior Lecturer, DOMINIC CUIURI, Senior Research Fellow, JON ROBERTS, Undergraduate Student, and HUIJUN LI, Professor, are with the Faculty of Engineering and Information Sciences, School of Mechanical, Materials & Mechatronics, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia. Contact e-mail: zengxi@ uow.edu.au Manuscript submitted June 4, 2015. Article published online November 23, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
lower probability of oxide contamination.[16] Up to date, wire-arc-based additive manufacturing process has been preliminary investigated and applied to fabricate structures with various materials such as titanium[17,18] and aluminum alloys.[19] In this research, a wire-arc additive manufacturing (WAAM) system is utilized for in situ fabrication of iron aluminides.[20] A gas tungsten arc welding (GTAW) arc rather than gas metal arc welding (GMAW) arc is used as the heat source, due to its higher arc stability when applied to a wide range of ferrous, non-ferrous alloys, and their combinations.[21] Compared to the GMAW process, the GTAW process generates negligible spatter and produces a quiescent melt pool, which is more desirable to produce consistent material deposition with the desired chemical composition. Pure iron and aluminum wires are fed separately into the molten welding pool through a twin-wire feeding system with a specific wire feed speed ratio in order to control the material compo
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