Internal stresses and microstructure of layer/substrate essemblies. Analysis of TiC and TiN coatings chemically vapour deposited on various substrated

Applied Science

Effect of Y Distribution on the Oxidation Kinetics of NiCoCrAlY Bond Coat Alloys

The relation between the Y distribution in the alloy and the growth kinetics of the developing oxide scale was studied for the thermal oxidation of two Ni–20Co–19Cr–24Al–0.2Y (at.%) alloys at 1,373 K: (i) a coarse-grain cast alloy with large Ni5Y intermetallic precipitates, and (ii) a fine-grain freestanding coating with small Ni5Y precipitates. Using a combination of experiments and model calculations, it is shown that the average growth kinetics of a NiCoCrAlY alloy are dependent on the size and distribution of Y-rich oxide inclusions (pegs) in the ?-Al2O3 oxide layer. Alumina scales containing a high density of small Y-oxide inclusions grow faster than ?-Al2O3 scales containing only a few, large Y-oxide inclusions. Upon oxidation of the freestanding coating, the Y-oxide inclusions in the scale attain their maximum size after the Y in the coating is completely consumed. After this point, a decrease in the average oxidation kinetics occurs.Surfaces & InterfacesMechanical, Maritime and Materials Engineerin

Surface and Interface Research and Engineering Delft University of Technology: A Collection of Mini Posters

Delft University of Technolog

A method for the experimental determination of surface photoemission core-level shifts for 3d transition metals

A method is presented to determine the photoelectron surface core-level shift (SCLS) of 3d transition metals using x-ray photoelectron spectroscopy. The experimental difficulties arising from the relatively large broadening of photoemission lines in the 3d transition series can be overcome by the analysis of the angular dependence of photoemission spectra. The proposed method has been demonstrated using well-defined single-crystal surfaces of copper. The observed values of the SCLS for copper are compared with those predicted by both ab initio calculations and a macroscopic atom model. The experimental determination of SCLSs opens alternative routes for collecting thermochemical data for surfaces/interfaces.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin

Modelling of surface segregation for palladium alloys in vacuum and gas environments

Surface segregation of a series of forty Palladium-based binary alloys has been investigated using a thermodynamic model based on an atom exchange approach. Their surface segregation behaviour, both in vacuum and in gas environments, were comprehensively estimated. The calculated results are in good agreement with the available experimental and computational data reported in literatures. Effects of mixing enthalpy, temperature, crystal orientation on the surface, elastic strain energy, adsorption and absorption of gases like H2, O2, CO have been discussed in detail. These results can be considered as basic guidelines to design novel Pd alloys for hydrogen separation membranes, sensors or catalysts. The model itself also offers a convenient and accurate routine to predict the surface segregation of other than Pd-based binary alloys in different gas atmospheres.(OLD) MSE-

Prediction of oxide phases formed upon internal oxidation of advanced high-strength steels

The effect of Cr on the oxidation of Fe–Mn-based steels during isothermal annealing at different dew points was investigated. The Fe–Mn–Cr–(Si) phase diagrams for oxidizing environments were computed to predict the oxide phases. Various Fe–Mn steels with different concentrations of Cr and Si were annealed at 950 °C in a gas mixture of Ar or N2 with 5 vol% H2 and dew points ranging from − 45 to 10 °C. The identified oxide species after annealing match with those predicted based on the phase diagrams. (Mn,Fe)O is the only oxide phase formed during annealing of Fe–Mn binary steel alloys. Adding Cr leads to the formation of (Mn,Cr,Fe)3O4 spinel. The dissociation oxygen partial pressure of (Mn,Cr,Fe)3O4 in the Fe–Mn–Cr steels is lower than that of (Mn,Fe)O. The Si in the steels results in the formation (Mn,Fe)2SiO4, and increasing the Si concentration suppresses the formation of (Mn,Cr,Fe)3O4 and (Mn,Fe)O during annealing.(OLD) MSE-

Surface segregation of Pd–Cu alloy in various gas atmospheres

Pd–Cu alloys have been investigated as promising candidates for hydrogen separation membranes. Surface segregation influences the long-term performance of these membranes since their catalytic effect is mainly controlled by the surface composition. In the present research, surface segregation of Pd-40 at.% Cu alloy in vacuum and various gas atmospheres (H2, CO and CO2) was investigated with both XPS and LEISS probing different depths below the surface. Adsorption of H2 and CO on the surface has a significant impact and the surface segregation trend can be reversed as compared to segregation in vacuum, however, CO2 has almost no influence on the segregation behaviour. A thermodynamic model is also presented to explain these phenomena and to understand surface segregation behaviour of binary alloys in various gas atmospheres. The results can be considered as basic guidelines to design novel alloys for hydrogen separation membranes and predict their long-term performance under actual working conditions.(OLD) MSE-