Microstructure and Microtexture Evolution of Pure Titanium during Single Direction Torsion and Alternating Cyclic Torsio
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PURE titanium is firstly prepared from TiCl using sodium and magnesium, and then the industrial production level of titanium sponge is not realized by American until 1948. Pure titanium (GR1, GR2, GR3, and GR4) is considered as one of the potential materials to be used in aircraft, biomedical fields, and other lightweight structures due to its good mechanical properties, high chemical stability, excellent corrosion resistance, and biocompatibility.[1–3] Pure titanium is used for bulk forming where the material is subjected to very large plastic deformation. In addition to obtaining billets with desired shape, large plastic deformation can be used to tailor an optical microstructure and crystallographic texture. As a result, the properties of used metal materials can be improved. Therefore, it is necessary to explore the deformation behavior of pure titanium up to very large strain. It is known that large plastic deformation can be obtained through simple shear deformation, and torsion test is an ideal means to provide large strain dominated by shear deformation.[4] Thus, it is of great significance to exploring the deformation behavior during torsion deformation. The torsion deformation can produce a higher plastic strain accumulation than tension and compression HAN CHEN, FUGUO LI, JINGHUI LI, XINKAI MA, and QIONG WAN are with the State Key Laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China. Contact e-mail: [email protected] JIE LIU, School of Aeronautics, Northwestern Polytechnical University. Manuscript submitted October 18, 2016. Article published online March 7, 2017 2396—VOLUME 48A, MAY 2017
without rupture or strain localization.[5,6] Therefore, torsion deformation is combined with other deformation modes to improve the comprehensive properties of materials by severe plastic deformation (SPD), for instance, high pressure torsion (HPT)[7,8] and twist extrusion (TE).[9] Due to its enormous contribution to SPD, the torsion deformation has been drawn extensive attention.[10,11] The microstructure, mechanical properties, and deformation behavior of materials under torsion are quite well known for cubic materials.[6,11–14] In addition, the deformation behavior of some hexagonal closed packed (HCP) metals like zirconium[15] and magnesium[10,16–18] under torsion are studied by some present authors. Most of these scientific literatures related to microstructure evolution of torsion deformation are focused on dislocation substructure (distribution and density), grain structure (size, shape, and distribution), precipitated phase (volume fraction, size, and distribution), and interface characteristics (grain boundaries and interphase boundaries), which do not provide a complete description of microstructure sufficiently. An elaborate description of microstructure of polycrystalline materials must also include the detailed analysis about crystallographic orientations of the existing grains.[19] The deformation texture leads to a
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