Characterization of In-Situ Alloyed and Additively Manufactured Titanium Aluminides
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INTRODUCTION
IT is generally recognized that gamma titanium aluminides are promising structural materials for high temperature aero engine and automotive applications, including turbine wheels, compressor blades, and pistons for reciprocating engines.[1–3] Central to such applications is the attractive combination of low density, unique mechanical properties, and resistance to oxidation.[4] Despite the desirable characteristics of c-TiAlbased alloys, one of the major barriers to their widespread use has been associated with difficulties in processing and the subsequent high costs.[5] Many improvements have been made in the production of c-TiAl-based alloys using conventional casting, ingot forging, powder processing, and also new advanced techniques such as sheet production by hotrolling, laser forming, and sintering. Although each of these processes is capable of producing material with acceptable properties, processing costs are still prohibitive for many commercial applications.[6,7] For conventional metals, additive layer manufacturing (ALM)[5,8] has been established as an economic alternative to conventional manufacturing methods such as casting and machining from billet. Additive layer manufacturing is used to produce complex, near net shape components through deposition of many consecutive layers in the form of powder or wire, offering high geometrical flexibility and major savings in time, material, and hence cost.[9] Significant effort has been devoted to developing ALM processes for alloys such as Ti-6Al-4V, while limited work has been done on intermetallics such as titanium aluminides. Murr et al.[10] and Biamino et al.[11] have recently succeeded in producing c-TiAl-based alloy YAN MA and NICHOLAS HOYE, Ph.D. Candidates, DOMINIC CUIURI and ZENGXI PAN, Senior Research Fellows, and HUIJUN LI, Associate Professor, are with the Faculty of Engineering and Information Sciences, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia. Contact e-mail: [email protected] Manuscript submitted December 20, 2013. Article published online August 5, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
by powder-based additive manufacturing technology using electron beam melting (EBM) of c-TiAl-based alloy powder, however, no information is available on the use of other heat sources or material feeding methods. This paper evaluates the feasibility of producing c-TiAl-based alloy components via additive layer manufacturing, using the gas tungsten arc welding (GTAW) process to deposit the intermetallic alloy in-situ from separate commercially pure titanium and aluminum wire feed stocks. Microstructural characterization and hardness properties of the as-fabricated alloy are presented.
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EXPERIMENTAL METHOD
Several test ‘‘walls’’ measuring approximately 100 mm in length, 11 mm in height, and 10 mm in thickness were produced on a pure titanium substrate by multilayer deposition. A schematic drawing of the process is shown in Figure 1. The deposition process was protected from oxidation using an appropr
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