Sintering of Titanium in Vacuum by Microwave Radiation
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MICROWAVE (MW) sintering has been actively explored over the last three decades, motivated by several attributes not attainable by conventional means, such as rapid volumetric heating, selective heating, and nonthermal effects.[1–4] These distinctive features make it possible to fabricate materials with novel microstructures and properties.[5,6] To date, MW radiation has proven to be effective in sintering a large number of ceramic systems and some metallic and metallic-ceramic composites, where the MW-sintered microstructure is often denser and finer than that obtained from conventional sintering.[7,8] In addition, the significantly reduced sintering cycle time implies much improved productivity and energy consumption efficiency. In many cases reported so far, MW sintering was shown to be energy efficient.[1,9] Another merit is that the reduced consumption of protective gases resulting from the significantly reduced sintering cycle is environmentally beneficial. Titanium and its alloys are advanced metallic materials, which possess an outstanding array of properties. However, cost remains the largest impediment to the wider take up of titanium components. As a result, structural applications of titanium alloys have been largely limited to the aerospace, power generation, chemical processing, and offshore petroleum industries. S.D. LUO and M. YAN, Postdoctoral Research Fellows, G.B. SCHAFFER, Professor, and M. QIAN, Reader in Materials, are with The University of Queensland, School of Mechanical and Mining Engineering, ARC Centre of Excellence for Design in Light Metals, Brisbane, QLD 4072, Australia. Contact e-mail: [email protected] Manuscript submitted July 22, 2010. Article published online March 26, 2011 2466—VOLUME 42A, AUGUST 2011
The high cost of a titanium part arises from the titanium metal as well as from the manufacturing process, which, in many cases, determines the actual consumption of the titanium material needed for a finished part. Clearly, there are economic advantages to producing near-netshape titanium parts, but there are also sound processing advantages as titanium is difficult to machine and not easy to recycle through conventional remelting processes.[10] In this regard, powder metallurgy (PM) offers an attractive means of near-net-shape manufacturing for Ti for a wide range of applications.[10,11] Additionally, there are mechanical property advantages of finer grain size and greater chemical homogeneity for Ti parts made from powders.[12] Sintering techniques that are energy effective or cost effective, thus, are particularly attractive for the fabrication of PM Ti products. The effectiveness of MW sintering of other systems suggests that MW radiation may be one such option for the fabrication of PM Ti parts. However, there is little information available on the sintering of Ti by MW radiation. This is likely due to the following reasons. Fundamentally, Ti is a paramagnetic metal, which couples weakly with the magnetic field of MWs.[13] It has been established experimentally that the magnetic component of
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