Mechanical behavior and electrochemical stability of gas-nitrided FeMnAlC alloy in simulated body fluid

The mechanical performance and electrochemical stability in simulated body fluid (SBF) of a lightweight Fe-30Mn-10Al-1C (in wt.%) alloy after gas nitridation were investigated. The gas nitriding process was performed at 550 °C for 5 h under pure NH₃ atmosphere. The nitrided layer was ∼45 μm-thick and consisted predominantly of fine AlN. The surface microhardness, ultimate tensile strength, yield strength, and elongation of the present gas-nitrided alloy are 1814 Hv, 1078 MPa, 1024 MPa, and 77%, respectively. The corrosion tests in SBF showed that the gas-nitrided alloy exhibited a corrosion current density (I_corr) of 5.0 × 10⁻⁹ A/cm², a pitting corrosion current density (I_pit) of 5.1 × 10⁻⁷ A/cm², and a passivation region with ΔE (≡E_p − E_corr) ≈ +1804 mV, respectively, which are substantially better than those obtained in the plasma-nitrided and hydroxyapatite-coated 316L stainless steel. The results demonstrated that the present gas-nitrided alloy having an excellent combination of strength, ductility and corrosion resistance is a promising candidate to replace 316L stainless steel for medical implants.