Yueh-Lien Lee

This study investigates the tribocorrosion behavior of 304 stainless steel (304SS), S31254 super austenitic stainless steel (S31254 SASS), and a medium-entropy austenitic stainless steel (MEASS) in 3.5 wt.% NaCl solution under sliding conditions. The objective is to clarify the performance differences among these alloys when exposed to simultaneous mechanical wear and corrosion. Electrochemical techniques, including potentiodynamic polarization and potentiostatic sliding tests, were used to evaluate corrosion resistance and repassivation behavior. Quantitative analysis based on ASTM G119 revealed that MEASS showed a 68% lower total material loss compared to 304SS and a 55% lower loss compared to S31254. MEASS also exhibited the lowest corrosion current density (1.46 μA/cm²) under tribocorrosion conditions, representing an 83% reduction compared to 304SS. These improvements are attributed to the higher chromium and nickel contents of MEASS, which enhance passive film stability and reduce susceptibility to localized corrosion. The results demonstrate that MEASS offers superior resistance to combined mechanical and corrosive degradation in chloride-containing environments.

Although extensive studies have examined the tribocorrosion behavior of stainless steels, the performance of medium-entropy austenitic super stainless steels (MEASS) under severe combined corrosion and mechanical wear conditions has not been fully established. This study systematically compares the tribocorrosion behavior of a newly developed MEASS with conventional S31254 super austenitic stainless steel (SASS) in a 1 M H₂SO₄ solution, aiming to explore innovative material designs for enhanced performance under these demanding conditions. Electrochemical tests were conducted under both open-circuit potential (OCP) and cathodic potential, with and without sliding wear, to assess the corrosion, wear, and synergistic effects influencing the tribocorrosion performance. Worn surface morphologies and hardness were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and hardness measurements, respectively. The experimental results revealed that MEASS exhibits a superior repassivation capability compared to S31254, with a 34.3% lower total material loss after 24 h of tribocorrosion test, primarily attributed to enhanced strain hardening and improved wear resistance. These findings emphasize the strong potential of MEASS for use in corrosive environments, particularly in chemical processing industries, where high resistance to wear and corrosion is critically required.

This study characterizes and determines the corrosion resistance of Mn-Ce conversion coated LZ91 magnesium alloy that undergoes pretreatments. It is challenging to process large and curved workpieces in the industry because the geometric shapes are complex if they are mechanically ground. This study uses acid pickling instead of mechanical grinding, and a nitric acid solution is used for pickling. After pretreatments, the samples are immersed for 30 s in a conversion coating solution containing 0.1 M KMnO₄ and 0.025 M Ce(NO₃)₃ with a pH of 1.5, as demonstrated in previous studies by the authors. The microstructure of the coating layer and electrochemical behavior of conversion coated samples exposed to 3.5 wt.% NaCl solution are studied. The corrosion behavior of Mn-Ce conversion coating specimens is determined using a salt spray test (SST). Scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS) are used to analyze the interface between the coating layer and the underlying magnesium substrate and to investigate the microstructure of the specimens. The roughness of the coatings is measured using 3D white light interferometry. The results show that the deteriorated area ratio for conversion coated LZ91 decreases to less than 5% after 72 h of SST exposure, and the corrosion resistance is improved 2.25 times with the Mn-Ce conversion coating on LZ91 magnesium alloy.

This study proposes coating impedance detector 3.0 (CID 3.0), an improved version of our previously developed CID 2.0. The new circuit design in CID 3.0 has lower power consumption because it has fewer components, and it affords better accuracy through the modification of the analog part of CID 2.0 and the use of oversampling. This approach successfully afforded CID 3.0 with higher measurement stability for evaluating a high-performance coating with impedance values exceeding 109 Ω. Furthermore, CID 3.0 could detect impedance decreases associated with coating delamination when the coating suffers an attack.