Study On Microstructure And Properties Of Ultra High Plasticity TB6 Alloy

In recent years,near-beta titanium alloy represented by TB6 has been widely used in Boeing 777 main landing gear,front landing gear control mechanism,larger flaps guide rail and some high strength forgings of fighter aircraft.As a high strength forging,the workability and plasticity of TB6 are important parameters.Transform induced plasticity(TRIP)can improve the ductility and delay the necking and cracking of materials during deformation.The transformation of beta phase into martensite occurs mainly in beta titanium alloys.TB6-nZr(n=0,3,4,5),TB6-nSn(n=0,1,2,3),TB6-nHf(n=0,0.35,0.75,1)alloys were prepared by adding neutral elements Zr,Sn and Hf on the basis of the original composition of the alloy.The effects of hot-rolled structure,mechanical properties and alloying elements on martensitic transformation were studied.The alloy was prepared by vacuum non-consumable melting equipment.The mechanical properties of the alloy were tested by INSTRON-5982 universal testing machine.The structure,morphology,phase composition and fracture morphology of the alloy were observed by optical metallographic microscope,scanning electron microscopy,transmission electron microscopy and X-ray diffraction.When Zr element is added to TB6-nZr(n=0,3,4,5),higher stress is required for martensitic transformation during tension.Compared with TB6 under the same conditions,the morphology and distribution of martensitic phase are blurred and the acicular martensite is more compact.The room temperature tensile properties of TB6-n Zr(n=0,3,4,5)series alloys after rolling at 800? and quenching by water show that the strength and plasticity of the alloys increase with the increase of Zr content compared with that of TB6 under the same conditions.Among them,TB6-4Zr has the best comprehensive properties.The tensile strength increases from 706 MPa of TB6 to 819 MPa of TB6-4Zr under the same conditions,and the elongation increases from 13.8% of TB6 to 46.6% of TB6-4Zr under the same conditions.The room temperature tensile properties of TB6-nHf(n=0,0.35,0.75,1)series alloys rolled at 800? and quenched by water show that with the addition of Hf,the tensile strength of the alloys decreases,but the elongation increases greatly,and the elongation of TB6-0.75 Hf is the highest.Tensile strength decreased from 706 MPa of TB6 to 608 MPa of TB6-0.75 Hf under the same conditions,and elongation increased from 13.8% of TB6 to 52.7% of TB6-0.75 Hf under the same conditions.Tensile mechanical properties of TB6-nSn(n=0,1,2,3)series alloys rolled at 800?and quenched at room temperature show that with the addition of Sn,the tensile strength of the alloys decreases,but the elongation increases greatly,and the elongation of TB6-2Sn is the highest.Tensile strength decreased from 706 MPa of TB6 to 645 MPa of TB6-2Sn under the same conditions,and elongation increased from 13.8% of TB6 to 45.1% of TB6-2Sn under the same conditions.