Microstructure and corrosion behavior of Ti-6Al-4V alloy using selective laser melting

To reveal the feasibility of applying selective laser melting (SLM) to titanium alloy-made underwater equipment components, the corrosion resistance of SLM-prepared Ti64 alloy in a simulated seawater environment was explored. The research finds that the SLM-prepared Ti64 alloy primarily consists of needle-like α' martensite, with a β-phase content of approximately 0.3%. Comparison through electrochemical tests reveals that in a NaCl solution with a mass fraction of 3.5%, the open-circuit potential of SLM-prepared Ti64 is −119.3 mV, significantly lower than that of wrought Ti64 (234.12 mV). The analysis of the potentiodynamic polarization curves using the extrapolation method shows that the corrosion potential (E_corr) of the SLM-prepared Ti64 is −237.3 mV, also lower than that of wrought Ti64 (118.4 mV). By fitting the impedance spectra with an equivalent circuit model, the passive film resistance (R_f) and charge transfer resistance (R_ct) of the SLM-prepared Ti64 alloy are 192.4 kΩ·cm² and 2.69 MΩ·cm², respectively, both lower than those of wrought Ti64 (235 kΩ·cm² and 4.34 MΩ·cm²). The slow stress and strain corrosion results at different strain rates are analyzed. At strain rates of 10⁻⁵ s⁻¹, 5 × 10^–6 s⁻¹, and 10^–6 s⁻¹, the stress corrosion susceptibility of the SLM-prepared Ti64 alloy is 20.2%, 17.2%, and 14.4%, respectively, all higher than that of wrought Ti64 under the same conditions (−1.4%, 12.9%, and 10.8%).