Stress-Induced Twinning and Phase Transformations during the Compression of a Ti-10V-3Fe-3Al Alloy
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STRESS-INDUCED phase transformations occur in b-phase in titanium alloys during tensile, compression, or creep loading, which significantly govern the mechanical properties. There are four possible stress-induced products in titanium alloys: hcp a¢ martensite, orthorhombic a¢¢ martensite, hcp x phase, and deformation twins, such as {332}h113ib and {112}h111ib. The hcp a¢ martensite has been observed in dilute titanium alloys and causes the deterioration of mechanical properties especially ductility.[1] Hence, its formation does not attract much interest. On another hand, there is tremendous interest in stress-induced a¢¢ martensite as it results in high ductility, shape-memory effect, and pseudo-elastic or super-elastic behavior.[2–4] Deformation accompanied by hcp x phase formation and twinning is of particular interest as it can affect the yield stress, ductility, and strain hardening.[5–7] However, the presence of stress-induced products is dependent upon the stability of the b phase. The b phase stability is defined as the electronic characteristics of the elements present in the b phase. These characteristics are MANSUR AHMED and AHMED A. SALEH, Research Fellows, are with the School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, Wollongong, NSW 2522, Australia. Contact e-mail: [email protected] AZDIAR A. GAZDER, Senior Research Fellow, is with UOW Electron Microscopy Centre, University of Wollongong, North Wollongong, New South Wales 2500, Australia. DAVID WEXLER, Senior Research Fellow, and ELENA V. PERELOMA, Professor of Physical Metallurgy, are with the School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, and also with UOW Electron Microscopy Centre, University of Wollongong. Contact e-mail: [email protected] Manuscript submitted December 15, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
called mean d-orbital energy level (Md) and mean bond order ðBoÞ. The details about the calculation of d-orbital energy level and bond order can be found in Reference 8. Morinaga et al.[8] proposed a phasestability diagram where the location of deformation products is shown to be dependent on the b phase stability. It is obvious from the phase-stability diagram that a combination of more than one stress-induced products and slip can be obtained based on the alloy composition, i.e., b phase stability. The simultaneous operation of stress-induced transformation and deformation twinning mechanisms leading to improved plasticity in steels has attracted scientific interest for a long time.[9–11] More recently, these phenomena have gained attention in terms of their applicability to Ti alloys.[5,7] The realization of transformation-induced plasticity and/or twinning-induced plasticity effects is a promising pathway to combat the low ductility of Ti alloys. Whereas a majority of these studies have focused on operating mechanisms in single phase b-Ti alloys,[12–14] recent work assessed this behavior when a and athermal x phases were also present.[6,15,16] In
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