Research On The Hot Forming Properties Of Hydrogenated TC2 Titanium Alloy Sheet

TC2 titanium is a near α phase alloy with good plasticity and its strength is about 700 MPa. The TC2 titanium with good thermal form ability is mainly used for sheet metal structure, welding parts and a variety of catheters. TC2 titanium alloy sheet metal stampings has been widely used in the aviation industry. In a certain extent, TC2 titanium with hot forming alloy forming will restricts its wider application. Titanium with hydrogen induced plasticity can reduce the flow stress of titanium alloy and improve its elongation. Also it can reduce the thermoforming temperature of the alloy to achieve lower manufacturing costs. This is an effective way to promote TC2 titanium alloy can be more widely applied.In this paper, heat treatment is used to obtain alloy with 0wt.% hydrogen and hydrogen is absorbed by solid state TC2 alloys to obtain alloys with 0.06 wt.%,0.13 wt.%, 0.18 wt.%, 0.3wt.% and 0.44 wt.% hydrogen addition. The mechanical properties of the alloys with different hydrogen contents are investigated in temperature range of 450℃~600℃, with strain rate range of 0.001/s~0.03/s. The results show that the TC2 alloys with 0.18 wt.% hydrogen, with forming temperature is 600℃, with strain rate is 0.001/s, exhibits a max increase of the plasticity.Compared with the unhydrogenated TC2 alloys, the yield strength is decreased by31 MPa, and the tensile strength is decreased by 28 MPa, and the elongation is increased 41.5 percent, and the activation energy is decreased by 19.65 percent.After hydrogenation, the reason of the increase of the plastic deformation of the TC2 titanium alloy is as follows.(1) As β stabilizing element, hydrogen can reduce the phase transition point of the TC2 titanium alloy The phase transition point is reduced from 0H of 950℃ to 0.18 H of 910℃, and the the content of the βphase is increased.(2) The rapid movement of the hydrogen atoms can promote the movement of the dislocation, thus contributing to the deformation process of dynamic recovery.(3) Hydrogen-induced weak bond action. After hydrogenation,the elastic modulus of the TC2 titanium alloy is reduced.This will reduce the binding force between the atoms inside the TC2 titanium alloy, which reduces the dislocation start of the critical shear stress, resulting in the reduce of the flow stress.In this paper,we also studied the thermoforming properties of the 0H TC2 alloys and the 0.18 H alloys at 600℃. The bulging experiment is carried out on the bulging die based on electronic universal testing machine in order to get the hot forming limit diagram. The simulation and experimental results are similar, the TC2 alloys with 0.18 wt.% hydrogen exhibits lager forming limit. The FLD0 value of the0 wt.% hydrogen TC2 alloys is 0.199, and the FLD0 value of the 0.18 wt.% hydrogen TC2 alloys is 0.23, increased by 16%. For 45 mm wide TC2 titanium alloy sheet, 0H titanium plate bulging height is 5.8mm, and the thinning rate is 52.8%, while the0.18 H titanium alloy sheet bulging height is 7.14 mm, and the thinning rate is71.8%.