Effect of Zr on microstructure and properties of TC4 alloy fabricated by laser additive manufacturing

In this paper, the effect of Zr on the microstructure of laser additive manufactured Ti–6Al–4V (TC4) alloy is studied by adding different contents of Zr (0%, 15%, 30%, 45%), and the mechanisms of strengthening and corrosion passivation are also discussed. The results show that the stability of β phase increases with increasing Zr content, when Zr content reaches 45%, the β phase is completely retained to room temperature. The microstructure of TC4 can be refined by Zr (when the content of Zr is less than or equal to 30%), and the ultra-fine martensite with twinning substructure can be formed. With the increase of Zr content to 45%, the strength of the alloy increases from 1044 MPa to 1360 MPa. The elongation decreases from 10.8% to 7.7% with the increase of Zr content to 30%. However, as the content of Zr increases to 45%, the elongation increases to 12.5%. The abnormal phenomenon of elongation is mainly due to the change of deformation mechanism from dislocation slip to stress-induced martensite transformation with the content of Zr increasing to 45%. The corrosion resistance of TC4-Zr alloys increases significantly with the increase of Zr content, which is mainly attributed to the better corrosion resistance of Zr and the better protection of ZrO2 formed in passivation film.