In Situ Observation of Deformation in Semi-solid Fe-C Alloys at High Shear Rate
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SEMI-SOLID alloys are deformed by solidification shrinkage and external forces applied by several casting processes. For example, in semi-solid processing and centrifugal casting of steels, significant stress acts on the semi-solid microstructure.[1–3] A large number of researches on the mechanical properties and viscous behavior of semi-solid alloys have been reported to develop semi-solid processing.[4–8] In addition, some of the mechanical phenomena in semi-solid alloys have been shown including agglomeration/disagglomeration,[4–6] deformation of the individual solid particles[5–7] and dilatancy, which leads to volume expansion in response to shear, during rearrangement of solid particles.[1,2] Casting defects including macrosegregation, porosity, and cracking are induced by deformation of semi-solid alloys as well as the interdendritic fluid flow.[9] Gourlay et al.[2,3] reported that the segregation bands, which are formed in centrifugal castings, result from the strain localization into a shear band of decreased solid TOMOYA NAGIRA, Assistant Professor, MASATO YOSHIYA, Associate Professor, and HIROYOSHI YOKOTA, Graduate Student, are with the Department of Adaptive Machine Systems, Osaka University, 2-1 Yamadaoka Suita, Osaka, 565-0871 Japan. Contact e-mail: [email protected] SHUGO MORITA, Graduate Student, and HIDEYUKI YASUDA, Professor, are with the Department of Materials Science and Engineering, Kyoto University, YoshidaHonmachi, Sakyo-ku, Kyoto, 606-8501 Japan. CHRISTOPHER M. GOURLAY, Lecturer, is with the Department of Materials, Imperial College London, London, SW7 2AZ, U.K. AKIRA SUGIYAMA, Professor, is with the Department of Engineering, Osaka Sangyo University, 3-1-1 Nakagaito, Daitou, Osaka, 574-8530 Japan. KENTARO UESUGI, AKIHISA TAKEUCHI, and YOSHIO SUZUKI, Researchers, are with the Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198 Japan. Manuscript submitted March 7, 2014. Article published online August 14, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
fraction, induced by the deformation of partially solid alloys. However, the mechanism of casting defects has not been fully elucidated due to a lack of understanding of the microstructural evolution during shear. The various mechanical phenomena in semi-solid alloys depend on the liquid viscosity, the shear rate, and microstructural features, such as the solid fraction, solid particle size, and solid particle morphology. In order to elucidate the complex deformation phenomena, it is advantageous to observe deformation in situ at the grain scale during shear. In recent years, the techniques for in situ observation of solidification phenomena, such as a dendrite growth, fragmentation, and coarsening, have been developed using X-ray imaging at synchrotron radiation facilities.[9–17] The in situ observations of deformation at the grain scale in semi-solid Al-Cu alloys and carbon steels have been carried out using similar techniques.[18–22] Past research[18–22] showed that shear-induced d
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