Hot Forming Properties Of Hydrogen Ti₂AlNb And Sheet Based Alloy

Ti2AlNb-based alloys with excellent high temperature mechanical properties arethe new high temperature structural materials. But their excellent mechanicalproperties at high and room temperature increase the difficulty of deformation, and soseverely restrict the application of the alloys. Hydrogen-induced plasticity of titaniumalloys as a new processing technology can effectively reduce the deformationresistance and increase ductility, to reduce the cost of die materials and increase dielife. So, the technology is expected to solve the deformation difficulties of theTi2AlNb-based alloys.In this paper, hydrogen is absorbed by solid state Ti2AlNb-based alloys to obtainalloys with0.1~0.4wt.%hydrogen addition. The mechanical properties of the alloyswith different hydrogen contents are investigated in temperature range of870~990℃, with strain rate range of0.0025~0.25/s. The results show that the alloyswith0.2wt.%hydrogen exhibits a maximum reduction of deformation resistancecompared with the unhydrogenated alloys, by about25~30%, and the elongation isincreased by50~100%. In the temperature range of870~990℃, the deformationactivation energy of the hydrogenated alloys decreases from468.8kJ/mol to407.6kJ/mol compared with the unhdyrogenated alloys.Hydrogen-induced plasticity of Ti2AlNb-based alloys are attributed to thefollowing reasons:(1) H as β-stabilizing element makes α2+B2+Oâ†'α2+B2phasetransition temperature decrease from930to1020℃, increasing plastic B2phase anddecreasing tough O phase;(2) H makes the morphology of brittle α2phase changewith0.2wt.%hydrogen addition, where granular α2phase transforms to strip-like one,distributing along new B2-phase boundaries, which increases the strength andtoughness of the alloy, to avoid necking due to local softening and improve elongation;(3)0.2wt.%hydrogen addition makes grain boundary sliding and dynamicrecrystallization dominant, inducing superplastic deformation;(4) dislocations in thedeformed alloys move in a regular banding way, which greatly reduces theaccumulation of dislocations and pinning strengthening effect, and the higherdeformation temperature, the more regular arrangement of dislocations;(5)hydrogen-weakened interatomic bonding remarkably reduces the elastic modulus ofTi2AlNb-based alloys.In this paper, cylindrical deep drawing properties of the hydrogenated alloys arealso investigated using self-designed dies with variable drawing ratio based on anelectronic universal testing machine. The results show that (1) at960℃and0.025/s,winkling disappears, wall thickness becomes uniform, and drawing part with good quality are obtained, and the load (5.9kN) is decreased by about25%, with0.2wt.%hydrogen addition and a drawing ratio of0.56; when the drawing ratio reduces to0.33,the maximum drawing displacement without rupture is7.22mm, increased by about20%, and the load is decreased by12%, compared with the unhydrogenated alloys;(2) at960℃and0.0025/s, load is2.8kN, decreased by about40%; when thedrawing ratio is0.33, the maximum drawing displacement without rupture is7.9mm,increased by about30%, and the load is2.6kN, decreased by about50%.