Improved Corrosion and Long-Term Immersion Behavior in 3.5 wt% NaCl Solution of Laser Powder Bed Fusion Produced Ti5Cu After Heat Treatment

This work investigates the corrosion behavior and mechanism of laser powder bed fusion produced (LPBFed) Ti5Cu and its heat-treated counterparts in 3.5 wt% NaCl solution. The results indicate that heat treatment can enhance the corrosion resistance of LPBFed Ti5Cu by generating Ti₂Cu phase, and heat treatment at higher temperature enhances corrosion resistance by forming a stable oxide film with a lower electron diffusion rate. The existence of Ti₂Cu phase in the heat-treated sample acts as the microanode that decelerates the corrosion on α-Ti phase (prior dissolution of Ti₂Cu phase). The long-term immersion test results also confirm that the Ti₂Cu phase present in HT900 (at higher heat-treatment temperature) provides a better protective effect against corrosion compared to the one in HT740 and as-LPBFed samples. Compared with the heat-treated counterparts, the worst corrosion resistance of the as-LPBFed Ti5Cu is attributed to that the acidic environment (e.g., Cl⁻) increases the electron diffusion rate in the film/solution interface, which makes the thermodynamically unstable α'-Ti phase be preferentially corroded.