Thermally treated FeCrAl alloy as potential biomaterial: surface characterization, corrosion resistance and cytotoxicity studies.

Metal alloys are widely used in implantology due to their excellent mechanical properties. However, their biocompatibility can be compromised by corrosion, which releases toxic metal ions that may provoke adverse biological reactions and contribute to implant failure. This study introduces a novel metal-ceramic composite based on a high-chromium FeCrAl alloy, specifically engineered to form a thermally grown α-Al₂O₃ surface layer. This design aims to significantly enhance biocompatibility and corrosion resistance for potential biomedical implant applications. Samples of the Fe-44Cr-5Al alloy were produced using an arc melting process. The mechanically polished alloy coupons were given a mirror-like finish and underwent high-temperature oxidation at 1050 °C for 20 h in laboratory air to develop a dense and adherent α-Al₂O₃ layer. Both bare and oxidized samples were immersed in artificial saliva at 37 °C for two months to assess their corrosion resistance under simulated oral conditions. Biocompatibility was evaluated through cytotoxicity and mitotic activity tests using primary human gingival fibroblasts cultured on both the bare and oxidized samples. The results showed that thermal oxidation effectively produced a uniform, adherent, and stable α-Al₂O₃ layer on the surface of the FeCrAl alloy. The oxidized samples demonstrated superior corrosion resistance, with negligible metal ion release and no formation of corrosion products. In contrast, the bare (unoxidized) alloy exhibited extensive corrosion and significant ion release. Cytotoxicity tests indicated that the oxidized alloy supported normal cell adhesion, proliferation, and morphology comparable to control samples. Although a slight reduction in cell proliferation was noted on the oxidized metal surface, overall bioactivity remained high. Structural and morphological analyses were performed using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Grazing Incidence X-ray Diffraction (GIXRD) to confirm the formation and integrity of the oxide layer. Post-immersion corrosion tests in artificial saliva and detailed microscopy further validated the favorable biological responses to the oxidized alloy.