Corrosion resistance and thermal stability of sputtered Fe44Al34Ti7N15 and Al61Ti11N28 thin films for prospective application in oil and gas industry

Fe-and Al-based thin-film metallic glass coatings (Fe₄₄Al₃₄Ti₇N₁₅ and Al₆₁Ti₁₁N₂₈) were fabricated using magnetron co-sputtering technique, and their corrosion performances compared against wrought 316L stainless steel. The results of GI-XRD and XPS analyses demonstrated amorphous structure and oxide layer formation on the surface of the fabricated thin films, respectively. The potentiodynamic (PD) polarization test in chloride-thiosulfate (NH₄Cl ?+ ?Na₂S₂O₃) solution revealed lower corrosion current (I_corr) (0.42 ?± ?0.02 ?μA/cm² and 0.086 ?± ?0.001 ?μA/cm² Vs. 0.76 ?± ?0.05 ?μA/cm²), lower passivation current (I_pass) (1.45 ?± ?0.03 ?μA/cm² and 1.83 ?± ?0.07 ?μA/cm² Vs. 1.98 ?± ?0.04 ?μA/cm²), and approximately six-fold higher breakdown potential (E_bd) for Fe- and Al-based coatings than those of wrought 316L stainless steel. Electrochemical Impedance Spectroscopy (EIS) of both films showed 4- and 2-fold higher charge transfer resistance (R_ct), 7- and 2.5-times higher film resistance (R_f), lower film capacitance values (Q_f) (10 ?± ?2.4 ?μS-s^acm^-2, and 5.41 ?± ?0.8 ?μS-s^acm^-2 Vs. 18 ?± ?2.21 ?μS-s^acm^-2), and lower double-layer capacitance values (Q_dl) (31.33 ?± ?4.74 ?μS-s^acm^-2, and 15.3 ?± ?0.48 ?μS-s^acm^-2 Vs. 43 ?± ?4.23 ?μS-s^acm^-2), indicating higher corrosion resistance of the thin films. Cyclic Voltammetry (CV) scan exhibited that the passive films formed on the Fe- and Al-based coatings were more stable and less prone to pitting corrosion than the wrought 316L stainless steel. The surface morphology of both films via SEM endorsed the CV scan results, showing better resistance to pitting corrosion. Furthermore, the thermal analysis via TGA and DSC revealed the excellent thermal stability of the thin films over a wide temperature range typically observed in oil-gas industries.