Growth kinetics of the compound layers: Effect of the nitriding potential

AbstractThe aim of this work is to study the effect of the nitriding potential on development of the compound layers during the gas nitriding of Armco Fe and XC38 carbon steel. The gas nitriding experiments were realized in an atmosphere of partially dissociated gas ammonia (NH3) at 520∘C under a variable nitriding potential (from 0.25 to 3.5atm−0.5) for 2 h.Using XRD analysis and SEM observations of the cross-sections of the treated samples, it was shown that the compound layer was composed of γ′ iron nitride after exceeding a critical value of the nitriding potential that depends on the substrate’s nature. A linear semi-logarithmic relationship relating the nitriding potential to the experimentally measured layer thickness for the γ′ phase was used to evaluate the critical nitriding potential giving rise to its formation on the material substrate. It was found that the required value of the critical nitriding potential for XC steel is greater than that of Armco iron

Estimation of adhesion energy of alumina scales on FeCrAl alloys: effect of the TiO

In this experimental work, the effect of sol-gel TiO2 coating on adhesion energy of alumina scales formed on FeCrAl alloys was investigated. The adhesion energy was evaluated by means of a tensile test in the SEM chamber for the samples oxidized in air at 850 and 950°C during 72 h. In addition, the spallation rate of alumina scales was studied as a function of the imposed longitudinal strain

Estimation of adhesion energy of alumina scales on FeCrAl alloys: effect of the TiO2 sol-gel coating

In this experimental work, the effect of sol-gel TiO2 coating on adhesion energy of alumina scales formed on FeCrAl alloys was investigated. The adhesion energy was evaluated by means of a tensile test in the SEM chamber for the samples oxidized in air at 850 and 950°C during 72 h. In addition, the spallation rate of alumina scales was studied as a function of the imposed longitudinal strain

Sol-gel titania films on YHfAl foils and their influence on inhibition of transition aluminas during oxidation at high temperatures.

International audienceIn this experimental work, sol-gel technique was used as surface coating of YHfAl alloys to avoid the formation of transition aluminas (delta and theta). This technique has an advantage of low cost and rapidity. The preparation conditions of TiO(2) sol-gel coatings were presented with a description of their evolution with temperature during the first stages of YHfAl oxidation. It is noted that the rutile is the only detected phase at 800 degrees C. The sol-gel thin films were prepared in order to inhibit the formation of transition aluminas. An important gain mass was recorded at a temperature of 875 degrees C and the first grains of aluminas were appeared after 0.5 h of oxidation. A sol-gel TiO(2) film of nearly 60nm thick has proven its efficiency and has allowed to reduce the presence of transition aluminas. (C) 2010 Elsevier B.V. All rights reserved

Determination of the Diffusion Coefficients of Boron in the FeB and Fe₂B Layers Formed on AISI D2 Steel

In the present work, a diffusion model was applied to estimate the boron diffusion coefficients in the FeB and Fe₂B layers during the pack-boriding of AISI D2 steel in the temperature range of 1223-1323 K during a variable exposure time between 1 and 8 h. The mass balance equations were formulated at each growing interface by considering the effect of boride incubation times. The estimated values of boron activation energies in the FeB and Fe₂B layers were compared with the literature data. Validation of the present model was made by comparing the experimental thickness of each boride layer, taken from the literature data, with the predicted values. In addition, a simple equation was suggested to estimate the required time to obtain a single Fe₂B layer by diffusion annealing

Preparation and reactivity of sol-gel titania films on FeCrAl alloys and estimation of adhesion energy of alumina scales

The sol-gel TiO2 coatings were applied in order to improve the rapid transformation of alumina scales formed on the FeCrAl alloys during oxidation at high temperatures. The titanium-containing sol-gel coatings were prepared from the precursor tetra-isopropyl-orthotitanate (TIPT). The preparation conditions such as solvent, concentration and pH were studied. The influence of pH and (solvent/precursor ratio) on gelification time was also studied. The adhesion energy was estimated using the tensile test in the SEM chamber for the samples oxidized in air at 850 and 950 °C for 72 h

On the Competitive Growth of Alpha and Transient Aluminas During the First Stages of Thermal Oxidation of FeCrAl Alloys at Intermediate Temperatures

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