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

Growth performances, carcasses parameters and meat fatty acid composition of lamb fed green oak acorns (Quercus ilex) based diet

The aim of this experiment is to compare the effects of diets containing green oak acorns (GO) and barley (BL) on the growth performances, carcasses parameters and the composition in fatty acids of lambs. Twogroups of five lambs each were fed, respectively, during 105 days with diets containing 50% of oaks acorns and 50% of barley. At the end of the test, the animals of the two diets expressed comparable body weights and weight gain. A significant difference (P < 0.05) was observed for the thickness of fat cover which is 3 mm for the BL group against 1.6 mm for GO group even if no significant difference was revealed concerning the output with slaughtering. The intramuscular lipids were significantly higher (P < 0.05) in the group of animals fed with GO diet compared to the BL diet (3.88 vs 2.83 g.100-1 g of muscle). Among the saturated fatty acids (SFA), the stearic acid significantly appeared in higher proportion (P <0.05) in GO diet (20.8 vs 18.1%) whereas the palmitic acid is prevalent in the group of animals fed with the BL diet (25 vs 30%). For the  polyunsaturated fatty acid (PUFA), no significant difference was observedbetween the two groups. The linoleic acid is prevalent among the PUFA of two groups without significant difference. The linolenic acid is higher in the animal fed BL. The n-6: n-3 ratio is higher in the BL group (8.9 vs 7.3). At the end, the low level of incorporation of PUFA in muscle of the lamb because of biohydrogenation, suggests us supplementing the diet by green grass

Self-healing processes in coil coated cladding studied by the scanning vibrating electrode

The ability of the zinc layer in coil-coated cladding to protect the underlying metal substrate exposed to the environment through a sub-centimetre circular defect was established by using the scanning vibrating electrode technique (SVET). The onset of electrochemical corrosion is observed through the development of local anodes and cathodes in the defective system, with the formation of soluble zinc species. The dissolution process is maintained until a sufficiently high concentration is attained by the metal ions, and their subsequent precipitation inside the holiday blocks the defect as to hinder further corrosion. A self healing effect was thus observed. The role of zinc salts was confirmed by SEM and EDX observation

Influence of normal and radial contributions of local current density on local electrochemical impedance spectroscopy.

A new tri-electrode probe is presented and applied to local electrochemical impedance spectroscopy (LEIS) measurements. As opposed to two-probe systems, the three-probe one allows measurement not only of normal, but also of radial contributions of local current densities to the local impedance values. The results concerning the cases of the blocking electrode and the electrode with faradaic reaction are discussed from the theoretical point of view for a disk electrode. Numerical simulations and experimental results are compared for the case of the ferri/ferrocyanide electrode reaction at the Pt working electrode disk. At the centre of the disk, the impedance taking into account both normal and radial contributions was in good agreement with the local impedance measured in terms of only the normal contribution. At the periphery of the electrode, the impedance taking into account both normal and radial contributions differed significantly from the local impedance measured in terms of only the normal contribution. The radial impedance results at the periphery of the electrode are in good agreement with the usual explanation that the associated larger current density is attributed to the geometry of the electrode, which exhibits a greater accessibility at the electrode edge

Investigation of Adhesion and Tribological Behavior of Borided AISI 310 Stainless Steel

In the present study, the effects of the boriding process on adhesion and tribological properties of AISI 310 steel were investigated. Boriding was performed in a solid medium consisting of Ekabor-II powders at 1123 and 1323K for 2 and 6 h. The boride layer was characterized by optical microscopy, the X-ray diffraction technique and the micro-Vickers hardness tester. The X-ray diffraction analysis of the boride layers on the surface of the steels revealed the existence of FexBy, CrxBy and NixBy compounds. Depending on the chemical composition of substrates, the boride layer thickness on the surface of the AISI 310 steel was found to be 56.74 μm. The hardness of the boride compounds formed on the surface of the AISI 310 steel ranged from 1658 to 2284 HV0,1, whereas the Vickers hardness value of the untreated steel AISI 310 was 276 HV0,1. The wear tests were carried out in a ball-disc arrangement under a dry friction condition at room temperature with an applied load of 10N and with a sliding speed of 0.3 m/s, at a sliding distance of 1000m. The wear surfaces of the steel were analyzed using an SEM microscopy and X-ray energy dispersive spectroscopy EDS. It was observed that the wear rate of unborided and borided AISI 310 steel ranged from 4.57 to 71.42 mm3/Nm

A Diffusion Model for the Fe_{2}B Layers Formed on a Ductile Cast Iron

In this work, a diffusion model was applied to estimate the boron diffusion coefficients in the $Fe_{2}B$ layers on the ASTM A-536 ductile iron in the temperature range 1173-1273 K by the powder-pack boriding. The mass balance equation at the ($Fe_{2}B$/substrate) interface was formulated considering the effect of boride incubation times. As a result, the value of activation energy for boron diffusion in the ductile iron was estimated and compared with the literature. To verify the validity of the present model, the experimental $Fe_{2}B$ layer thickness obtained at 1173 K for 10 h was compared to the predicted value. A good concordance was observed between the predicted value of $Fe_{2}B$ layer thickness and the experimental data