The effect of heat treatment on corrosion behavior of selective laser melted Ti-5Al-5Mo-5V-3Cr-1Zr alloy.

Recently, additive manufacturing (AM) of titanium alloys has become favored by manufacturing industries. However, the obvious anisotropy of microstructure during the process of AM will be caused by the complex solidification mechanism, which will cause uncertainties in determining corrosion behavior. Two heat treatment techniques are developed to tune the microstructure of selective laser melted Ti-5Al-5Mo-5V-3Cr-1Zr (Ti-55531) alloy, i.e. , αβ phase region (αβ-STA) and supertransus triplex heat treatment (Triplex-HT). Bimodal and bi-lamellar microstructure are obtained after certain heat treatments and the corresponding corrosion resistance is systematically investigated. The columnar β grains in the vertical planes (VP) are eliminated by conducting Triplex-HT, and the corresponding corrosion anisotropy between the horizontal planes (HP) and VP is significantly reduced. While the Ti-55531 treated by αβ-STA possesses significant refinement of primary α precipitates (α p) within β grains. The size of α grains relates to the Al-rich active region, where the corrosion pits are mainly concentrated. Further immersion experiments indicate that the generation and development of pits on the passive film are determined by the occupation of oxygen vacancies by chlorine ions. The results are expected to provide a reference for the selective laser melting (SLM) Ti-55531 alloy to eliminate anisotropy and improve corrosion resistance by the adjustment of the micromorphology. • The anisotropy of the corrosion behavior of Ti-55531 is caused by columnar β. • The isotropy of Ti-55531 alloy is achieved by supertransus triplex heat treatment. • The formation of oxygen vacancies is influenced by elemental segregation. • Oxygen vacancy plays a decisive role in pitting resistance of passive film. [ABSTRACT FROM AUTHOR]