Martensitic Transformation And Strain Recovery Properties Of Ti-V-Al Alloy With Sc Addition

Ti-N i alloys is widely used in the aerospace field for its good shape memory effect and superelastic. But the high density of Ti-N i is above 6.7g/cm³ is not suitable for the demand of weight reduction of aircraft materials.Thus,developing excellent shape memory effect and high martensitic transformation te mperature lightweight shape memory al oy is meaningful.Ti-V-Al shape memory alloys as a great candicate for aerospace industry,for its relatively low density,about 4.5g/cm³,and a great cold workability.The research about addition of Sc in Ti-V-Al alloy and its influence has not been reported.In this paper,the influence rules and mechanisms that how Sc content and themal- mechanical treatment effect the consist of phase,microstructure,martensitic transformation, mechanical properties and shape memory effect of（Ti-13V-3Al）_100-xSc_x（X=0,0.01,0.025,0.04） al oys are systematacially investigated by XRD,OM,SEM,DSC,TEM and tensile test.After solution treated, Ti-V-Al-Sc alloys consists of singal α " martensitic phase,which is orthorhombic. The addition of Sc cannot change its phase at room temperature. Martensite variants are major self-accommodation morphology. With the addition of rare earth Sc, the relationship of twins’ self-accommodation is mainly（111） α" Ⅰtype twin.The recrystallization temperature of Ti-V-Al-Sc alloys range from 700℃ to 750℃, which will raise with the increase of Sc.In solution-treated Ti-V-Al-Sc alloys,the martensitic reverse transformation temperatures（As,Ap,Af） increase with the increase of Sc. And the martensitic reverse transformation peak temperature（Ap） ranges from 343℃ to 369℃. When the number of cyclic increases,the martensitic transformation temperature of（Ti-13V-3Al）_100-x Sc_x（X=0.025） gradually increase, especially the number reaches 5, the transformation temperature greatfully increases.With the increase of Sc content, the elongation of both solution-treated and cast Ti-V-Al-Sc alloys first increase and then decrease, when the Sc content is 0.025 at.%, it has the largest elongation, and all of the alloys are ductile fracture. With the increase of Sc content, the shape memory effect of Ti-V-Al-Sc alloys firstly increases and then decreases. When the Sc content is 0.025 at.%, the alloy exhibits the maximum recovery strain with 6% pre-strain at room temperature. The maximum recovery strain can be as large as 5.2%. After annealing at 750℃, the alloy shows the maximum recovery strain of 4.7% with 7% pre-strain at room temperature. With the increase of cold rolling deformation, the shape memory effects of（Ti-13V-3Al）_100-x Sc_x（X=0.025） alloys gradually decrease.