Luc Segers

Electrochemical boriding of iron in molten salts

Boride coatings on iron subtrates are obtained by electrodepositions in Na2B4O7 melts at various temperatures (from 900 to 1050°C). The effects on thickness and morphology of the electrolysis parameters (current density and time) are presented. In particular results at high current density(up to 112 A dm−2 are shown. Depending on current density value and duration of the electrolysis the deposits consist of Fe2B or Fe2B layers of teeth form. Thermal post-treatment of two layers deposits decreases the FeB thickness and increases the Fe2B thickness.

Viscosite de melanges de silicates fondus du systeme CaOSiO2MnO

Viscosities of melts of the ternary system CaOSiO2MnO with 0.5 to 0.35 mole% SiO2 have been measured between the liquidus temperature and 1500°C. Results are given in function of the composition and show the effect of the silica content of the melt and of the substitution of CaO by MnO.

Determination of Thermodynamic Properties of Ternary Al‐Cu‐Zn Alloys by Electromotive Force Method

The thermodynamic properties of ternary Al-Cu-Zn alloys containing 25 to 62 at% Al have been determined by electromotive force (EMF) measurements between 420 and 920 o C by an aluminum concentration cell of the type Al[AlCl 3 -LiCl-KCl] alloy. This concentration cell was evaluated via comparison with known partial free energy for Al measured in liquid Al-Cu alloys by Wilder, and several liquidus temperatures of Al-Cu phase diagram have been determined. From EMF values, activities of Al with respect to mole fraction of Al in ternary Al-Cu-Zn alloys for three quasi-binary sections (x Cu /x Zn =7/3, 1, and 3/7) at 850 o C were determined

Conductivites electriques de melanges de silicates fondus du systeme CaOSiO2MnO

Resume Les conductivites electriques specifiques des melanges fondus du systeme CaOSiO 2 MnO ont ete determinees entre la temperature du liquidus et 1550 °C pour des titres en SiO 2 compris entre 0.55 et 0.26. La connaissance du volume molaire moyen des melanges permet le calcul de la conductivite electrique equivalente. Une interpretation structurale des resultats basee sur les theories connues concernant la structure des silicates fondus est proposee.

Thermal Fatigue of Anticorrosive Coatings and Multilayer Coatings: A Performance Index Approach

A strategy is proposed to cope with combined thermal fatigue and hot corrosion resistance affecting industrial coatings. It allows comparing different materials, coatings and geometries with respect to thermal cracking and then properly selecting protective coatings. It uses a thermo-mechanical model combining the heat transfer conditions, thermal and mechanical properties of the materials and the system geometry. The model is applied to two cases: (i) borided steel, with experimental support; (ii) multilayer coating made of a thermal barrier layer, aimed at reducing thermal gradients in the system, and a corrosion layer.

Design and experimentation of an inductive r.f. plasma process for high-speed carbon coating of silica optical fibres

Abstract A plasma-enhanced chemical vapour deposition equipment20with inductive r.f. coupling was built that enables coating of static samples (silica plates or rods) and moving optical fibres. First experiments with CH 4 /H 2 and CH 4 alone as precursor gases in an Ar plasma gave homogeneous and non-porous carbon coatings but with very low deposition rate 0.03 nm s -1 ). Much higher deposition rates (up to 7 nm s -1 ) were obtained with C 2 H 2 -Ar mixtures on 1mm diameter silica rods and were increased up to 50 nm s -1 on static 0.125 mm diameter silica fibres. Other experiments were realized on moving optical fibres after modification of the coating device and growth rates up to 50 nm s -1 were obtained.

Electrochemical behaviour of a platinum electrode in SiO2CaOMnO molten slags

Abstract The electrochemical behaviour of a platinum electrode in SiO 2 CaOMnO molten slags has been studied by cyclic voltammetry. The anodic oxidation of divalent manganese ions is a diffusion controlled process which have been confirmed by electrode impedance measurements.

Shot peening treatment characterization by surface acoustic waves

Shot peening is a classical mechanical surface treatment used to improve the properties of components, principally the fatigue and stress corrosion resistance. The possibility of characterization of shot peening treatment efficacy was assessed by leaky Rayleigh SAW generated and detected by a large aperture, broadband and lens-less focused transducer. The broadband pulses propagated in the material surface were processed in order to obtain the dispersion curves, and were compared for different samples that were submitted to different treatment conditions. The results showed that the dispersion curve is sensitive to these treatment parameters. The possibility of depth profiling of the elastic properties changes due the shot peening are discussed on base of the fact that the penetration of SAW depends on the frequency and so the dispersion curve should have information of the elastic properties in different depths. The source of these elastic changes is also analyzed in terms of plastic deformation, residual stresses, roughness and microstructural changes. A comparison of the dispersion curves with a laser based SAW system was also performed showing equivalence of the methods.

Residual Stress Evolution by the ex-situ Annealing of TiN Thin Films Deposited on Steel Substrates

TiN thin films were deposited on high speed steel substrates by a PVD method at substrate temperatures of 450 °C (film A) and 200 °C (film B). Structural properties of the films were studied by X-Ray diffraction and atomic force microscopy. Residual stresses in the films are determined by a X-Ray diffraction method. It is found that film A has an average residual stress of about 8 GPa and a rougher surface. Film B has a smoother surface and a larger residual stress (12 GPa). By annealing at a temperature of 450 °C for four hours, the residual stress in film B is reduced to the same level as that in film A. The mechanisms which affect the residual stress of TiN films will be discussed.