Composition Design And Research On Microstructure And Properties Of Multi-component β Titanium Alloys

In this paper,three β-type titanium alloys of Ti-5V-4Mo-3Cr-3Zr-3Al（1#alloy）,Ti-4V-6Mo-3Cr-3Zr-3Al（2#alloy）and Ti-5V-7.5 Mo-3Cr-3Zr-3Al（3#alloy）were designed by the design criteria of alloy composition combined with molybdenum equivalent[Mo]eq,Kβ stability coefficient,valence electron concentration e/a,（Bo,Md）and other parameters.The Kp stability coefficients of the three alloys were 1.16,1.30 and 1.65,respectively.Molybdenum equivalent[Mo]eq were 9.25,10.48,14.25.The theoretical α/β phase transition points were 810℃,786℃ and 741℃,respectively.The volume fractions of a phase in annealed alloy were 55.45%,51.24%and 36.96%,respectively.（Bo,Md）were（2.7807,2.3766）,（2.7883,2.3765）and（2.7854,2.3572）,respectively.It is predicted that twins will occur during the deformation of the three alloys,and martensite transition may take place in the 1#alloy and 2#alloy,while martensite transition will not take place in the 3#alloy.Optical microscope（OM）,scanning electron microscope（SEM）and X-ray diffractometer（XRD）were used to observe and analyze the microstructure of the samples in the as-cast state and under different processess of solid solution treatment and aging treatment,and the compression test was carried out by RG3050 universal testing machine.The cold rolling deformation and post-rolling heat treatment of three kinds of alloy samples with different deformations were carried out,and the tensile mechanical properties were tested.The experimental results show that the actual α/β phase transition points of the three alloys were 830℃,810℃ and 770℃,respectively,which are not different from the theoretical calculation values,indicating that the theoretical calculation has certain guiding significance.Among the three experimental alloys,the effect of precipitated a phase of 1#alloy was stronger,while that of 3#alloy was weaker.1#alloy has the best compressive mechanical properties at 520℃/2h,with the compressive strength up to 1800MPa;2#alloy and 3#alloy have the best compressive mechanical properties at 520℃/5h,with the compressive strength above 1500MPa and 1700MPa,respectively.Twins were produced in all the three alloys during the deformation,and martensite transformation occurred in both the 1#alloy and 2#alloy,which was consistent with the theoretical prediction.1#alloy after two times of 50%cold rolling+annealing,then aging treatment,the tensile strengthσb=1360MPa,δ=5.8%.2#alloy after 72%cold rolling+annealing,then aging treatment,the tensile strength σb=1313MPa,δ=6%.3#alloy after 75%cold rolling+annealing,δ=23%,the tensile strength σb=1260MPa,δ=7.5%.