Thierry Schweitzer

Kinetic and metallographic study of oxidation at high temperature of cast Ni 25Cr alloy in water vapour rich air

Abstract The high temperature oxidation behaviour of a Ni–25 wt-%Cr alloy in air enriched with water vapour (180 mbars H2O) was studied at 1000, 1100, 1200 and 1300°C. The oxidised samples were characterised by X-ray diffraction, electron microscopy and wavelength dispersion spectroscopy. The obtained data were compared to the ones earlier obtained for the same alloy oxidised in dry air. Water vapour globally induced at all temperatures a decrease of the parabolic constant Kp and an increase in the chromia volatilisation constant Kv. The oxide scales do not present morphologic difference between the two atmospheres. After oxidation in humidified air the scale thickness is thinner and the Cr depleted depth is lower than in dry air.

Comparaison du joint de colle entre les attaches préencollées APC™ PLUS et les attaches APC™ Flash-Free

INTRODUCTION Does the new adhesive-coated APC™ Flash-Free bracket from the 3M Unitek® group simplify the bonding protocol without compromising precision? OBJECTIVES The aim of this study was to compare the morphology of the adhesive joint between the classic APC™ PLUS adhesive-coated brackets and APC™ Flash-Free brackets. MATERIALS AND METHODS In vitro bonding of esthetic brackets in the CLARITY™ ADVANCED range was performed to compare the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets. RESULTS No statistically significant difference was found concerning the morphology of the excess flash between APC™ PLUS and APC™ Flash-Free brackets. A statistically significant difference was found regarding the thickness of the adhesive between the two types of bracket. The adhesive used for the APC™ Flash-Free brackets was significantly thicker than for the APC™ PLUS brackets (P=0.0001). Adhesive thickness was also more homogeneous on the APC™ Flash-Free brackets (P=0.001 for the relative difference). CONCLUSION The adhesive is thicker but adhesive homogeneity is greater with APC™ Flash-Free brackets than with APC™ PLUS brackets.

Correlation Between the Pitting Potential Evolution and \(\varvec\sigma\) Phase Precipitation Kinetics in the 2205 Duplex Stainless Steel

The aim of this work is to correlate the pitting potential (Epit) evolution with the kinetics of σ phase precipitation in the 2205 duplex stainless steel aged at 850 °C after solution treatment at 1150 °C. The potentiodynamic polarization curves indicate a reduction of the pitting corrosion resistance with the aging time, which is revealed by a decrease in the Epit values from 0.65 to 0.40 VSCE. Thus, Epit values are used to determine the kinetics parameters of the σ phase precipitation. The experimental transformed fraction agrees well with the one calculated by using the modified Kolmogorov–Johnson–Mehl–Avrami equation with an impingement parameter c = 0.6.

Corrosion Behavior in a Neutral ArtificialSaliva of Several Binary Co-Cr Alloys withVarious Chromium Contents

Substitution of too expensive alloys rich in noble metals by alloys based on nickel or chromium is often considered in prosthetic dentistry. When containing chromium in quantities high enough the corrosion performances of the “predominantly base” alloys very interesting, as well as their mechanical properties. Such alloys are generally rather complex because of the presence of other elements such as molybdenum, tungsten, silicon and other, which may be active during corrosion and mask the importance of the chromium content. In this work it was chosen to look for a critical chromium content over which the corrosion behaviour is acceptable or very good, by working with simple binary Co-xCr alloys (x varying from 0 to 30 wt.% by slices of 5 wt.%) especially prepared by casting, by avoiding any interference of other elements classically present (Mo, W, Si…). Electrochemical investigations were carried out in a neutral 37°C-heated 9 g/L NaCl solution, classically used in such studies. Follow-up of open circuit potential, application of the Stern-Geary and Tafel methods, and cyclic polarizations allowed identifying 25 wt.% as being a threshold to respect for being certain to benefit from the highest corrosion resistance.