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Procedia Engineering 207 (2017) 2340–2345
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, International Conference on theCambridge, TechnologyUnited of Plasticity, ICTP 2017, 17-22 September 2017, Kingdom Cambridge, United Kingdom
Approach to Enhance Gas Bulging Formability of TA15 Titanium Approach to Enhance Gas Bulging Formability of TA15 Titanium Alloy Tube Based on Dynamic Recrystallization Alloy Tube Based on Dynamic Recrystallization Kehuan Wangb,c , Gang Liua,b *, Ke Huangdd b,c a,b Kehuan Wang , Gang Liu *, Ke Huang
State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, 150001, China b of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, ChinaChina State School Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, 150001, c b Department Mechanical Engineering, ImperialHarbin CollegeInstitute London,ofExhibition Road, London SW7 2AZ, School of of Materials Science and Engineering, Technology, Harbin, 150001, ChinaUK d c Thermomechanical Metallurgy LaboratoryEngineering, - PX Group Imperial Chair, Ecole Polytechnique Fédérale Road, de Lausanne CH-2002 Neuchâtel, Department of Mechanical College London, Exhibition London(EPFL), SW7 2AZ, UK d Thermomechanical Metallurgy Laboratory - PX Group Chair,Switzerland Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-2002 Neuchâtel, Switzerland a a
Abstract Abstract In order to further improve the gas bulging formability of laser-welded TA15 titanium alloy tube, studies about the effects of initial In order to further the gas bulging formability laser-welded titanium alloy tube, studies about the of initial microstructures onimprove the formability were carried out atof 800 ℃.VacuumTA15 annealing procedures were performed to effects obtain different microstructures formability out at 800 ℃.Vacuum annealing were was performed to obtain different microstructures. on Thethe formability of were these carried TA15 titanium alloy sheets with differentprocedures microstructures subsequently investigated by hot tensile testThe andformability hot gas free Thetitanium results show after thedifferent recrystallization annealing the two phases field, the microstructures. ofbulging. these TA15 alloy that sheets with microstructures wasinsubsequently investigated by hot dislocation tensile test and hot of gasthe freematerial bulging.was Thereduced results greatly show that the recrystallization the twocoarser. phases After field, the initial density dueafter to recrystallization and annealing the grains inbecame initial dislocation of βthe material reduced greatly due and the grains became double annealing atdensity the near phase field,was phase transformation of αtotorecrystallization β happened, secondary α formed in thecoarser. β matrixAfter and the equiaxed α grew coarser. Theβstrength of material elevated temperature and the ductility decreased after the annealing. double annealing at the near phase field, phase at transformation of α to βincreased happened, secondary α formed in the β matrix and the equiaxed grew coarser. strength ofthe material at elevated temperature increased and the ductility decreased the annealing. Under theαuniaxial tensileThe deformation, material consisting of equiaxed α microstructure with high initial after dislocation density Under the the uniaxial tensile deformation, thedeformation, material consisting of equiaxed α microstructure withhappened high initial exhibited best formability. During its lots of dynamic recrystallization (DRX) duedislocation to its highdensity initial dislocation density at the earlyDuring stage ofitsdeformation, fraction of high angle grain boundaries, refined the exhibited the best formability. deformation,which lots ofincreased dynamic the recrystallization (DRX) happened due to its high initial dislocation density at thethe early stage ofofdeformation, which increased the fraction of high angle boundaries, refined the microstructure, promoted occurrence grain boundary sliding and enhanced the formability of thegrain material. The bulging results microstructure, promoted the occurrence grain boundary sliding and enhanced ofstrength the material. The bulging results are consistent with the tensile results. Theofannealed tubes deformed more slowly the dueformability to the higher at elevated temperature. Theconsistent tube consisting of equiaxed α microstructure with high initial dislocation density also the bestatformability. Therefore are with the tensile results. The annealed tubes deformed more slowly due to theexhibited higher strength elevated temperature. The tube consisting of equiaxed α microstructure withofhigh initial dislocation density exhibited the best formability. Therefore increasing the occurrence of DRX at the early stage deformation by increasing thealso initial dislocation density in the material is increasing occurrence of DRXtheatgas thebulging early stage of deformation by increasing the initial dislocation density in the material is an efficientthe approach to improve formability. an efficient approach to improve the gas bulging formability. © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. © 2017 The Authors. Published by Elsevier Ltd.
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[email protected] 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. the scientific of the Peer-review 1877-7058 ©under 2017responsibility The Authors. of Published by Elseviercommittee Ltd. Plasticityunder . Peer-review responsibility of the scientific committee of the Plasticity.
International Conference on the Technology of International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.1005
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Kehuan Wang et al. / Procedia Engineering 207 (2017) 2340–2345 2341 scientific committee of the International Conference on the Technology
Peer-review under responsibility of the of Plasticity.
Keywords: Titanium alloy; dynamic recrystallization; hot gas forming; formability
1. Introduction Titanium alloys are advanced materials with superior strength-to-weight ratio and excellent corrosion resistance, which are widely applied in the aerospace, marine, chemical, energy and transportation industries [1]. In recent years, in order to further improve the performance of aircrafts, the requirement of working pressure for the fuel and hydraulic pipe system is greatly increased, therefore fabricating tubular products made of high strength titanium alloy is becoming urgent [2]. However, currently most of the titanium and titanium alloy tubular products are made of pure titanium or low strength titanium alloy [3]. Studies about the formability of the high strength titanium alloy tubes for hot gas forming are still limited. It is well known that microstructure has a substantial influence on the properties of titanium alloys. Titanium alloys have three typical microstructure morphologies: equiaxed, bimodal and fully lamellar [1]. It has been demonstrated by lots of studies that titanium alloys with equiaxed microstructure have better formability than other microstructures [4]. During the thermomechanical processing of titanium alloys, three types of dynamic recrystallization (DRX) phenomena are reported for near α titanium alloy: discontinuous dynamic recrystallization [5], continuous dynamic recrystallization [6], and geometric dynamic recrystallization [7]. Most of the studies focused on the DRX mechanisms during the deformation, while the effect of DRX, which has been summarized in a recent review papers [8], on the formability of titanium alloy tube with equiaxed microstructure during hot deformation is also still unclear. Therefore, in order to investigate the effect of DRX on the formability of titanium alloy tubes for hot gas forming, a TA15 titanium alloy with yield strength of 983.1 MPa at room temperature was selected. The different microstructures were acquired by vacuum annealing. The formability of the sheet and tube before and after heat treatments was tested by tensile test and hot gas free bulging, respectively. The microstructure evolution was systematically studied by optical microscopy (OM) and electron backscattered diffraction (EBSD). An approach to enhance the gas bulging formability of TA15 titanium alloy tube was proposed based on DRX. 2. Materials and experimental methods 2.1. Material and annealing process A near-α titanium alloy (TA15) with a chemical composition of Ti–6.5Al–2Zr–1Mo-1V (in wt.%) was employed in the present study. The initial thickness of the sheet is 2 mm. The initial microstructure of the sheet is shown in Fig. 1, in which the black lines represent high angle grain boundaries (HAGBs, θ>15o), the blue lines represent low angle grain boundaries (LAGBs, 2 o
