Effect Of V Element On The Microstructure And Properties Of TC4 Alloy By Laser Additive Manufacturing

TC4 alloys are widely used in the aerospace industry due to their high specific strength,good corrosion resistance and thermal stability.In recent years,with the rapid development of process manufacturing,laser additive manufacturing(LAM)technology has been rapidly emerging,and although the mechanical properties of LAM TC4 alloys can basically meet the standard requirements of forgings,they often require subsequent heat treatment to achieve.The subsequent heat treatment increases the cost of manufacturing LAM TC4 alloys and,to a certain extent,limits the industrial application of large structural parts.For this reason,it is particularly important to further optimise the composition of TC4 alloys so that their LAM integrated mechanical properties meet the performance requirements.Test specimens of TC4 alloy with different vanadium(V)content(mass fraction)were prepared using the LAM technique.The effects of V on the organisation and properties of TC4alloy were investigated using optical microscopy,scanning electron microscopy,X-ray diffractometer,universal tensile tester and pin-disk friction wear tester.The results of the tissue studies showed that the tissues of TC4 alloys with different V additions were composed of a large number of dense hexagonal structureα-Ti(α)phases and a small number of body-centred cubic structureβ-Ti(β)phases.As element V is a stableβ-phase element,the volume fraction ofβ-phase in the alloy at room temperature gradually increases with the addition of element V.The macrostructure of TC4 alloys with different additions of element V shows equiaxed crystal structure in the cross-section perpendicular to the deposition direction(XY direction)and columnar crystal structure in the cross-section parallel to the deposition direction(Z direction);with the increase of the addition of element V,the macroscopic grain size in both directions gradually decreases.The macroscopic grain size gradually decreases in both directions with the increase of V addition;the microstructure shows the primaryαphase in different directions,and the size of the primaryαphase gradually decreases with the increase of V content,and there is a trend of gradual transformation to equiaxial crystal;theβphase exists in the(α+β)organization between the primaryαphase.The results of the mechanical properties tests show that in both the XY and Z directions,the microhardness increases with the addition of element V,but the increase is not significant;in the XY direction,the tensile strength increases first and then decreases with the addition of element V.The tensile strength reaches a maximum value of about1122 MPa(elongation of about 9.2%)when the addition amount is 6%V;in the XY direction,the elongation decreases first and then increases with the addition of element V.The tensile strength and elongation in the Z-direction change in the same trend as the XY-direction with the increase of element V.The tensile strength reaches the maximum value of about 1018 MPa(elongation of about 11.2%)when the addition amount is 6%V,and the elongation reaches the minimum value of about 11.2%when the addition amount is 8%V.The tensile strength and elongation in the Z-direction change in the same trend as the XY-direction with the increase of element V.The tensile strength reaches the maximum value of about 1018 MPa(elongation of about 11.2%)when the addition amount is 8%V.The elongation reaches a minimum value of about 7.6%(tensile strength of about 980 MPa).Friction and wear test results show that TC4alloys with 2%V,4%V and 6%V additions have better friction coefficients(0.56,0.58,0.58)and Wear volume(48.26mm~3,50.17mm~3,48.74mm~3)than TC4 alloys(friction coefficient 0.63and Wear volume 70.71mm~3).The comparative analysis shows that the TC4 alloy has the best overall performance when 6%V is added.