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Insufficient corrosion resistance, electrical conductivity and wettability of bipolar plates are some of the important issues affecting the performance of hydrogen fuel cells. To address these issues, an amorphous Al–Cr–Mo–N coating is deposited on type 316L stainless steel using direct current (DC) magnetron sputtering. The electrochemical corrosion behaviour is investigated under simulated fuel cell anode (H 2 -purging) and cathode (air-purging) environment consisting of 0.5 M H 2 SO 4 + 2 ppm NaF at 70 ± 2 °C. The corrosion current density is reduced to 0.02 μA cm−2 comparable to the commercially used Ta/TaN coatings. The polarization resistance increases by two orders of magnitude and the interfacial contact resistance (ICR) reduces significantly due to the application of the coating. Further, the coating shows better water management due to high hydrophobicity than the bare stainless steel. • Amorphous Al–25Cr–5Mo–40N alloy coating is developed on type 316L SS. • Corrosion resistance of the present coating is comparable to Ta/TaN coating. • ICR of the coating is significantly lower than that of the bare substrate. • High hydrophobicity of the coating can lower water flooding within PEMFC stacks. [ABSTRACT FROM AUTHOR]

A286 (AISI 660), an austenitic precipitation hardening stainless steel has good strength and corrosion resistance, but its low hardness restricts their use in applications involving abrasive wear. In order to improve the hardness without loss of corrosion resistance properties of A286 stainless steel, plasma nitrocarburizing process was carried out at temperatures ranging from 350 °C to 500 °C for 4 and 8 h. The gas mixture composition employed during the process was 78% nitrogen, 20% hydrogen and 2% acetylene gas. Plasma was generated using a pulse DC power supply having a frequency of 30 kHz. After plasma nitrocarburizing, a dual layer was formed consisting of nitrogen and carbon in the top layer followed by carbon in the bottom layer. Compared with the untreated A286 stainless steel specimens, the microhardness values measured from the plasma nitrocarburized specimens treated at 400 and 450 °C increased by a factor of two and three respectively. The electrochemical corrosion behavior of the plasma nitrocarburized A286 specimens has been studied in 3.5 wt.% NaCl solution. The results show that specimens treated at 400 °C for 4 h has better pitting corrosion resistance and higher surface hardness compared with that of the untreated A286 stainless steel. This is mainly attributed to the presence of carbon and nitrogen in the modified layer existing as a solid solution. [ABSTRACT FROM AUTHOR]

Abstract: Low energy plasma immersion ion implantation (PIII) of nitrogen ions on vacuum arc melted 316L (316LVM) austenitic stainless steel has been carried out at three different temperatures namely, 250 °C, 380 °C and 500 °C. X-ray diffraction analysis indicated that PIII results in the formation mixed iron-nitrides along with expanded austenite phase at all temperatures. Microhardness measurements revealed a significant increase in hardness after PIII treatment. Corrosion resistance in 3.5% NaCl increases when implanted for 3 h. The passive current density seems to increase with treatment temperature. Wear measurements carried out using a pin-on-disc machine show an increase in wear resistance with rise in treatment temperature. [Copyright &y& Elsevier]

Abstract: This paper concerns with the effect of nitrogen addition to 904L stainless steel (SS) welds on their stress corrosion cracking (SCC) behavior in high temperature (288°C) and high pressure (1050psi) water of high oxygen content (100ppb) and high conductivity (2.5μS/cm). For this study, 316L SS base plate TIG welded with 904L SS filler wire and with nitrogen contents of 0.027, 0.058 and 0.095wt.% were used. Flat pin-loaded tensile specimens were fabricated from transverse welds, with the weld in the gauge length. Slow strain rate tests (SSRT) were carried out at a strain rate of 2.2×10−6 s−1. The study shows that the samples, when tested in air, failed at the weld fusion zone for 0.027 and 0.058wt.% N and at the base metal for 0.095wt.% N. In the environment, the samples failed in the base metal except the one with least nitrogen content (0.027wt.%). With nitrogen addition, as the failure location shifted to the base alloy, the weld seemed to acquire SCC resistance and became even more resistant than the base alloy. [Copyright &y& Elsevier]

Effect of shot-peening on the oxidation behaviour of alloy 304HCu in controlled advanced ultra-supercritical (AUSC) steam at 650 ◦C, 31 MPa for 600 h was investigated. Non-shot peened surfaces form thick Fe-rich oxides, undergo internal oxidation, and suffer oxide spallation sooner than those reported in literature. Shot-peened surfaces form a thin, external chromia scale with Mn(Cr,Fe) 2 O 4 and MnCr 2 O 4 spinels growing above and below it respectively. Shot-peening enhances Cr and Mn diffusivity through grain refinement and increased dislocation density, which aids in resisting chromia scale breakdown, eliminating iron oxides, and preventing oxide spallation. Oxide growth mechanism in AUSC steam is discussed. [Display omitted] • Alloy 304HCu was oxidized in AUSC steam at 650 ℃, 31 MPa for 600 hours. • Non-shot peened surfaces form thick Fe-rich oxides and undergo internal oxidation. • AUSC steam causes severe oxidation and early onset of oxide spallation. • Shot-peening resulted in grain refinement and high dislocation density. • Shot-peened surfaces resist Cr 2 O 3 breakdown, form thin, external Cr & Mn-rich oxides. [ABSTRACT FROM AUTHOR]

Abstract: Stainless steels usually contain some amounts of sulfide type of inclusions which are known to affect their corrosion behavior in mild aqueous chloride solutions. The life of the stainless steel components is severely affected as the manganese sulfide inclusions dissolve and the reaction products at the site of inclusions lead to pitting corrosion. The pits so formed as well as manganese sulfide inclusions, being local heterogeneities were studied by a microprobing technique called scanning electrochemical microscopy. In order to demonstrate how this local probing technique can be optimally used to investigate the corrosion behavior of inclusion containing austenitic stainless steels, different experimental parameters were varied one by one. The effect of different factors such as substrate potential, rate of scanning and concentration of chloride was studied in detail. The study shows that a scan rate of 0.32μm/s (3.2μm step distance for 10s hold time) for 50μm by 50μm scans and a scan rate of 0.1μm/s (1μm step distance for 10s hold time) for 20μm by 20μm scans produced optimum results throughout the study. [Copyright &y& Elsevier]

Abstract: Precipitation hardenable 17-4 stainless steel has been subjected to a solution annealing treatment followed by ageing treatment at 580°C for durations upto 6h. Microstructural characterization of the solution annealed and the aged specimens has been done using optical microscopy, X-ray diffraction and electron backscattered diffraction. Mechanical characterization was done using tensile testing and charpy impact toughness testing at room temperature. Microstructural characterization indicated that the reverted austenite formation started in the initial stages of the ageing treatment itself and it continuously increased with duration of ageing. Results of mechanical testing indicated that the austenite content did not correlate with the strength of the material therefore, nature of the copper precipitates, which form along with the reverted austenite, is the dominant factor controlling the strength and the impact properties. [Copyright &y& Elsevier]