Comparison of conventional and active screen plasma nitriding of hard chromium electroplated steel

This paper considers the nitriding behavior of hard chromium electroplated steel by conventional plasma nitriding (CPN) and active screen plasma nitriding (ASPN) methods. Indentation test along the cross-section of the treated samples reveals that duplex treatment performed by two methods exhibits almost the same hardnesses. Furthermore, an increase in the time of plasma nitriding from 5 h to 10 h restores 30% of the hardness decline. Morphological studies show that surface particles formed on active screen plasma nitrided samples have orderly formed geometrical shapes while in conventional plasma nitriding they are in cauliflower shape. The reason for reaction between chromium and nitrogen seems to be the difference between thermal expansion coefficient of chromium oxide, chromium and steel substrate which results in partial breakdown of the oxide film. Moreover, the reducing of chromium oxide by hydrogen promotes the process. It looks as if nitriding treatment changes the corrosion behavior of the chromium coating from severe localized to uniform corrosion. Also active screen plasma nitriding treatment lowers the anodic dissolution 50-100 orders of magnitude which would be the result of full closure of surface microcracks.     

Effects of bovine serum albumin on the corrosion behaviour of AISI 316L, Co–28Cr–6Mo, and Ti–6Al–4V alloys in phosphate buffered saline solutions

The corrosion behaviour of AISI 316L, wrought Co–28Cr–6Mo and Ti–6Al–4V was studied in aerated solutions of phosphate buffered saline (PBS) at various concentrations of bovine serum albumin (BSA) at 37 °C. Open circuit potential, potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) experiments along with X-ray photoelectron spectroscopy (XPS) on Co–28Cr–6Mo oxide layer were conducted to study the interaction of BSA and passive layers and to measure the corrosion rates. Ti–6Al–4V alloy had the lowest corrosion rate and the highest breakdown potential. It was shown that BSA has enhanced the alloy passive film stability at higher concentrations.     

Fabrication of low friction bronze–graphite nano-composite coatings

This paper addresses the fabrication of bronze–nano-graphite coatings containing 30 nm sized graphite particles. Addition of Poly Vinyl Pyrrolidone (PVP) and dispersing the suspension by ultrasound was utilized to stabilize the electroplating solution. Pulsed current electrodeposition was used and the deposits were characterized in terms of graphite content, particle dispersion in coating and morphology. The wear behavior of the coating was compared to bronze–micro-graphite coatings prepared with the same experimental conditions. The present coating showed improved wear resistance in comparison to bronze–micro-graphite coatings at the same graphite content.     

Electrochemical corrosion behaviour of Incoloy 800 in sulphate solutions containing hydrogen peroxide

The aim of this study is to evaluate the electrochemical corrosion behaviour of Incoloy 800 in sulphate solutions containing H₂O₂ in the temperature range of 25–80 °C. The open circuit potential measurements, cathodic and anodic polarization and electrochemical impedance spectroscopy (EIS) were used to characterize the corrosion behaviour. The results provide kinetic data for reduction of hydrogen peroxide on Pt surface. The anodic polarization curves for Incoloy at different pH, temperature and H₂O₂ concentration are presented. EIS data generally confirm the polarization interpretations about the effects of various parameters. An equivalent circuit was used to fit all the acquired data.     

EIS study of potentiostatically formed passive film on 304 stainless steel

Passive film was potentiostatically grown on Type 304 stainless steel at potentials between −0.4 and 0.3 V vs. Hg/HgSO₄ in 50 mV intervals. Electrochemical impedance spectroscopy was used to study properties of the grown passive films. Relevant circuit analogs were selected to fit the electrochemical impedance data obtained at each potential. The resultant parameters were used to calculate film thickness through both film capacitance and resistance. The calculated thicknesses were compared with ellipsometry thickness measurement results. An overestimation occurred when the film resistance was used to calculate the film thickness. On the other hand, when the CPE parameter Q was used, the film thickness was underestimated. Available approaches were employed to calculate the effective capacitance of the film. A comparison between the film thickness calculated from the effective capacitance and ellipsometry measurements suggested a surface distribution of time constants on the surface.