Iron oxidation at low temperature (260–500 C) in air and the effect of water vapor

The oxidation of iron has been studied at low temperatures (between 260 and 500 C) in dry air or air with 2 vol% H2O, in the framework of research on dry corrosion of nuclear waste containers during long-term interim storage. Pure iron is regarded as a model material for low-alloyed steel. Oxidation tests were performed in a thermobalance (up to 250 h) or in a laboratory furnace (up to 1000 h). The oxide scales formed were characterized using SEM-EDX, TEM, XRD, SIMS and EBSD techniques. The parabolic rate constants deduced from microbalance experiments were found to be in good agreement with the few existing values of the literature. The presence of water vapor in air was found to strongly influence the transitory stages of the kinetics. The entire structure of the oxide scale was composed of an internal duplex magnetite scale made of columnar grains and an external hematite scale made of equiaxed grains. 18O tracer experiments performed at 400 C allowed to propose a growth mechanism of the scale

Oxidation and oxygen diffusion in Ti-6al-4V alloy: improving measurements during sims analysis by rotating the sample

Titanium alloys are attractive to the industrial world, as they offer the benefits of low density, great corrosion resistance, and relatively good strength, making them viable candidates for a multitude of applications. However, above 500 °C, oxidation and oxygen diffusion in titanium alloys need to be taken into account as they change their microstructure and then their mechanical properties. Oxidations were carried out between 600 and 750 °C on a specific titanium alloy: an a-b annealed Ti-6Al-4V. Oxidation kinetics and oxygen diffusion in the matrix were studied. SIMS analyses were realized on rotating specimens of this two-phase polycrystalline alloy in order to reduce roughness. Composition profiles along the sample thickness were compared to microhardness measurements. SIMS mappings were realized on the smooth slopes of the crater

Water Vapour Effects on Chromia Formaion and Scale Adhesion,

International audienc

Water Vapor Effects in Low- and High-pO2 Environments

International audienc

Kinetic and morphologic study of the pack-aluminization of a series of refractory alloys

Five refractory alloys, Fe-20Cr-20Ni, Fe-20Cr-36Ni, Fe-20Cr-45Ni, Fe-20Cr-60Ni and Ni-20Cr, were submitted to pack aluminization at 850 °C for different durations in a NaF-activated pack. After a short period to achieve steady state, the coating kinetics were shown to be linear. The rate of aluminization was the same for the four alloys containing iron (about 1 mg.cm-2.h-1) and notably higher (1.8 mg.cm-2.h-1) in the case of the Ni-20Cr alloy. The nature of the formed products and the morphology of the layers were shown to depend on the alloy composition. The most important feature was the presence of external FeA13 on the four Fe-containing alloys, whereas a mixture of Ni2Al3 +NiAl was observed on the Ni-20Cr alloy. Kinetic experiments and thermodynamic calculations allowed a derivation of the value of the Al-activity at the gas-substrate interface. The mechanisms involved in the aluminization were shown to depend on the Al-concentration in the pack, on gaseous diffusion for low Al concentration and on interface reaction for high Al concentration

HIGH TEMPERATURE PROPERTIES OF LASER ALLOYED TITANIUM

Surface alloys are of great interest for improving the mechanical and/or chemical properties of the near surface region of metallic materials. Surface alloy formation by laser melting involves the base metal and one or several foreign elements, introduced either in a predeposited slurry or directly in the melt pool by the means of a power feeder. Surface alloys were produced on titanium by laser irradiation of predeposited aluminium and silicon powders. It was observed that hardness increased with silicon content and carbon dissolution. The maximum value achieved was as high as 1100 Hv without the presence of carbon. It was also observed that laser aluminization improved isothermal as well as cyclic oxidation resistance while the presence of carbon was detrimental. The addition of silicon led to a decrease of the minimum concentration of aluminium necessary to form a continous and protective layer of Al2O3

High Temperature Coatings

International audienc

The photoelectrochemical technique, an innovative tool for assessing the nature of semiconductor phases present in thin oxide films

International audienc