The microbiologically influenced corrosion of SLM 3D printed TC4 by Geobacter sulfurreducens

This work investigates the microbiologically influenced corrosion (MIC) behavior of TC4 titanium alloy fabricated via selective laser melting (SLM-TC4) and conventional forging (Forged-TC4), with Geobacter sulfurreducens as the model electroactive bacterium. Microstructural characterization revealed that SLM-TC4 features finer grains (≈ 4 μm), martensite-like α‘ phases, and denser intragranular dislocations, whereas Forged-TC4 exhibits a basket-weave microstructure with larger grains (≈ 900 μm) and grain-boundary dislocations. Electrochemical tests, surface analysis, and biofilm characterization were employed to evaluate the corrosion performance and MIC mechanisms. Forged-TC4 was found to outperform SLM-TC4 in corrosion resistance, due to its higher content (84.1%) of TiO 2 in the passive film. In the presence of G. sulfurreducens , SLM-TC4 suffered more severe corrosion, with a corrosion current density (19.5 nA/cm²) about 2 times higher than Forged-TC4. G. sulfurreducens accelerated corrosion via extracellular electron transfer (EET), reducing TiO₂ content in the passive film and increasing metastable Ti₂O₃. CLSM observations confirmed deeper pitting (6.5 μm) on SLM-TC4 in the bacterial system than on Forged-TC4. This work demonstrates that SLM-induced microstructural characteristics weaken the passive film stability, rendering SLM-TC4 more susceptible to MIC by G. sulfurreducens . Optimizing the SLM process to improve passive film stability is proposed as an effective strategy for mitigating MIC of TC4.