Exploring the impact of laser surface oxidation parameters on surface chemistry and corrosion behaviour of AISI 316L stainless steel

Abstract

This study delves into the corrosion resistance enhancement of stainless steel through laser processing, focusing on the interplay between surface chemistry, morphology, and electrochemical properties. Two sets of 3 × 3 full factorial design of experiment (DoE) designs were employed to explore the influence of laser process parameters, including power, scan speed, frequency, and hatching distance. The findings underscore the superiority of reduced areal energy in producing optimal corrosion resistance 10 times better then unprocessed stainless steel, demonstrating the best results under optimized conditions of a 15 µm hatching distance, 250 mm/s scan speed, 100 kHz frequency, and 80 % power. X-ray Photoelectron Spectroscopy (XPS) analysis reveals the predominant surface composition of iron and chromium oxides, with variations in the oxide combinations correlating closely with areal energy. Depth profiling revealed the transformation of oxide layers and highlights the importance of chromium-to-iron ratio in surface corrosion behaviour. Cyclic polarisation results demonstrate the formation of passive, transpassive, and pitting domains, with metastable pitting observed in some samples. The direct positive correlation recorded between corrosion current and Cr/Fe ratio underscores the significance of oxide composition in corrosion resistance. Electrochemical impedance spectroscopy (EIS) further confirmed the superior corrosion resistance of laser-processed samples to non-laser processed samples, with lower areal energy exhibiting higher resistance compared to higher areal energy. SEM morphology analysis revealed the removal of surface defects and the formation of a protective oxide layer in laser-processed samples, with lower areal energy samples exhibiting the lowest level of surface defects. The 3D optical profilometer measurements of corrosion pits corroborate these findings, with lower areal energy samples demonstrating the lowest pit depth and area, indicating superior corrosion resistance. Overall, this study provides comprehensive insights into optimizing laser processing parameters to enhance the corrosion resistance of stainless steel, offering valuable understanding and strategy for improving the metal surface corrosion resistance.