Improvement in fracture toughness of Ti-4.5Al-3V-2Mo-2Fe through microstructural optimization
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ANIUM and its alloys are well known to have lightweight, excellent corrosion resistance and high specific strength. Furthermore, they have a high operating temperature,[1] good composite compatibility,[2] and excellent biocompability.[3] However, the use of titanium and titanium alloys in industry is limited, due to their expensive price as compared with their competitors such as aluminum alloys and steels. The high cost of titanium alloys is mainly due to their high manufacturing cost.[2] Many efforts have been made to lower it, such as through alloy designing[4] and process modeling.[5] Ti-4.5Al-3V-2Mo-2Fe, a  -rich ␣ ⫹  –type titanium alloy, is an example of new titanium alloy developed in order to diminish the manufacturing cost by means of alloy designing.[4] By employing small contents of ␣ -phase-stabilizing elements (i.e., 4.5 pct Al and less then 0.1 pct O, in mass pct) but high contents of  -phasestabilizing elements (i.e., 3 pct V, 2 pct Mo, and 2 pct Fe, in mass pct) in this alloy, the superplastic temperature of this alloy is reduced to around 1000 K, that is, around 100 K lower than the superplastic temperature of the most popular GUNAWARMAN, Research Associate, Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 4418580, Japan, is Lecturer with the Department of Mechanical Engineering, Engineering Faculty, Andalas University (Unand), Padang 25163, Indonesia. Contact e-mail: [email protected] MITSUO NIINOMI is Professor with the Department of Production Systems Engineering, Toyohashi University of Technology. DANIEL EYLON is Professor, Director with the Department of Graduate Materials Engineering, University of Dayton, Dayton, OH 45469-0240. SHIRO FUJISHIRO is formerly with the Asian Office of Aerospace R&D, USAFOSR, Tokyo 106-0032, Japan. CHIAKI OUCHI is Professor with the Department of Metallurgy, Tohoku University, Sendai: 980-8579, Japan. TOSHIHIKO KAZINO is Professor with the Suzuka College of Technology, Suzuka 510-0294, Japan. Manuscript submitted November 26, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
titanium alloy, Ti-6Al-4V.[4] This reduction leads to a decrease not only in the superplastic forming cost of the alloy, but also in the processing cost of the wrought alloy and the heat-treatment cost of the products, due to lowering the temperature of the  transus (temperature of formation of 100 pct  phase). Comparative studies[4,6,7] showed that the mechanical properties (in particular, fatigue strength and tensile strength) of the alloy are greater than those of Ti6Al-4V. Due to these advantages, it has been used in many applications such as golf club heads, mountaineering crampons, wristwatches, etc.[4,8,9] It is also to be used in parts for Formula 1 engines, which require extreme levels of performance and reliability, as well as in engine parts for international motorcycle Grand-Prix racing.[9] For ␣ ⫹  –type titanium alloys, it is well known that the alloys annealed in the ␣ ⫹  field have better fatigue and tensile propertie
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