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Influences of the Welding Heat Input and the Repeated RepairWelding on Ti–3Al–2.5V Titanium AlloyHui-Jun Yi • Yong-Jun Lee • Kwang-O LeeReceived: 15 August 2014/Revised: 27 December 2014/Published online: 5 March 2015? The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg 2015Abstract The primary purpose of this study was to determine the effects of gas tungsten arc welding heat input on thehigh-temperature tensile properties, toughness, and microstructural features of titanium alloy Ti–3Al–2.5V. The secondaryobjective was to examine the effect of the repeated repair welding on the properties of the alloy. It was also found that themechanical properties progressively decreased with increasing the repair welding cycles, especially in the case of theweldment after the first welding repair. It was observed that the sizes of the acicular a 0 and prior b grain boundaries as wellas the volume fraction of the acicular a 0 phases increased with increasing the welding heat input. In addition, the amountand size of the acicular a 0 phases were found to increase with increasing the repair welding cycles.KEY WORDS: Ti–3Al–2.5V; Repair welding; Heat input; Tensile properties; Microstructure1 IntroductionOwing to the high strength-to-weight ratio, exceptionalcorrosion resistance, and good fatigue resistance of titani-um, its alloys are widely used in gas turbine engines, air-craft frames, seawater coolers, and desalination and otherchemical plants [1]. The joining of titanium alloy parts isusually done by welding, especially gas tungsten arcwelding (GTAW) process. This is because of the ability ofthe process to produce high-quality welds, its mechaniza-tion, and the extensive industrial experience available.Furthermore, the relatively low conductivity and coeffi-cient of thermal expansion of titanium minimize the pos-sibility of distortion by welding. However, the welding oftitanium alloys is difficult owing to the extremely highchemical reactivity of titanium at high temperatures. Dur-ing the welding of the titanium alloy, the material easilyabsorbs oxygen and nitrogen from the atmosphere.Although the absorption of limited amounts of oxygen andnitrogen by the solid material significantly increases itsstrength, excessive amounts result in brittleness [2]. Thus,the weldability of titanium alloys is usually assessed basedon the toughness and ductility of the weld metal (WM) andthe heat-affected zone (HAZ) [3–5]. The HAZ of a–b ti-tanium alloys such as Ti–3Al–2.5V and Ti–5Al–2.5Sntends to become brittle when heat-treated to high strengthlevels, and the fusion zone (FZ) is known to exhibit poorductility relative to the base material. The mechanicalproperties of the welded zone are altered by the chemicalreactions of the WM with the filler metal, resulting in theinflux of impurities, dynamic solidification, and large in-clinations [6, 7]. Depending on the characteristics of thebase metal (BM), unexpected changes may also occur.Furthermore, a change in the chemical composition orstructure of the BM may reduce the strength or ductility ofthe BM. Particularly, growth of the grains of the materialmay be induced by the welding heat. The grains in theHAZ may become coarse, depending on the coolingAvailable online at http://link.springer.com/journal/40195H.-J. Yi (&) ? Y.-J. Lee ? K.-O. LeeSchool of Mechanical Engineering, Pusan National University,Busan 609-735, Koreae-mail: yi.h.jun@gmail.com123Acta Metall. Sin. (Engl. Lett.), 2015, 28(6), 684–691DOI 10.1007/s40195-015-0248-2