The Development of High Performance Ti-6Al-4V Alloy via a Unique Microstructural Design with Bimodal Grain Size Distribu
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TI-6AL-4V is one of the most widely used commercial titanium alloys for structural applications, ranging from bio-implants to airframes, due to its impeccable performance owing to the exceptional combination of mechanical and chemical properties.[1–3] However, intense research efforts are being continuously made to achieve better performance via improving mechanical properties. It is envisaged that the improved mechanical properties will also reduce the cost by not only reducing the usage of the alloy by providing high strength small-sized components but also avoiding the frequent replacements of the components due to improved performance. Therefore, extensive research activities are being carried out to achieve further improvement in the mechanical properties of the Ti-6Al-4V alloys. In general, the microstructural refinement has proved to be a very attractive and efficient way SANJAY KUMAR VAJPAI, Senior Researcher, and MIE OTA, Researcher, are with the Research Organization of Science and Technology, Ritsumeikan University, Kusatsu, Japan. Contact e-mail: [email protected] TOMOYUKI WATANABE and RYO MAEDA, Graduate Students, are with the Graduate School, Ritsumeikan University, Kusatsu, Japan. TATSUYA SEKIGUCHI, Former Graduate Student, is with the Graduate School, Ritsumeikan University, and also with the IHI Corporation, Tokyo, Japan. TAKAYUKI KUSAKA and KEI AMEYAMA, Professors, are with the Department of Mechanical Engineering, Ritsumeikan University, Kusatsu, Japan. Manuscript submitted January 31, 2014. Article published online November 11, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
of strengthening metals and alloys wherein the metals and alloys with fine-grained microstructure demonstrated a considerably higher strength as compared to their coarse-grained (CG) counter parts.[4–6] In particular, it has been demonstrated that an ultra-high strength can be achieved in metals and alloys via creating an ultrafine-grained (UFG) microstructure. In the case of Ti-6Al-4V alloys, most of the strengthening attempts involved microstructural manipulations in terms of obtaining either different phases with a particular topological distributions or microstructural refinements.[7–13] The intended microstructural characteristics were achieved via a combination of different processing approaches involving quaternary alloying additions, thermal treatment, and different variants of thermo-mechanical treatment. In recent years, several efforts have been made to improve the mechanical properties via grain refinements, wherein UFG Ti-6Al4V alloys were prepared by ingot metallurgy as well as powder metallurgy routes.[14–24] The UFG Ti-6Al-4V alloys, thus produced, exhibited remarkably higher yield and fracture strengths as compared to the CG Ti-6Al-4V alloys with similar compositions. However, it would be worth emphasize that UFG Ti-6Al-4V alloys, similar to the most of the materials with UFG microstructure, exhibited considerably inferior ductility as compared to their CG counterparts. Therefore, it is extremely important to co
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