Laser cladding and wear testing of nickel base hardfacing materials: Influence of process parameters

In fast neutron reactors, some parts can be subjected to displacements between each other (as movable parts for example). On these parts, the contact areas usually need a hardfacing coating. The standard hardfacing alloy is a cobalt-base alloy (for example Stellite®6). Unfortunately, in the primary coolant circuit and on wear conditions, cobalt can be released. Under neutron flux, the stable59Co can be transmuted into60Co by radioactive capture of neutrons and, therefore, can contaminate the primary circuit. Therefore, it is desired to replace this cobalt based hardfacing alloy by a cobalt-free one. Previous presentations have shown the potential interest of some nickel base materials as Colmonoy® alloy. In parallel, laser cladding has been identified as a deposition process that could increase the performances of the hardfacing materials compared to the standard process (Plasma Transferred Arc Welding). In all the study, the base material is the stainless steel 316LN. In the first section of this article, the authors present previous results related to the selection of hardfacing materials and their evaluation in comparable tribology conditions. Then, Tribaloy® 700, another nickel based alloy that has been poorly investigated, is presented and evaluated. This nickel base has a completely different microstructure, and its tribological behavior related to the variation of the microstructure is not well known. First, the authors present the features of the selected materials. Then, the authors present various property characterization results obtained by changing several process parameters. The quality of the clad is considered, and the process window providing a good clad is determined (no crack, only a few porosities, etc.). The variation of the microstructure is analyzed, and solidification paths are proposed regarding the process parameters. Wear tests are performed on typical wear conditions. The movement is linear. Argon is used for the protection of the sample against oxidation. Tests are carried out at 200 °C. Wear tests are analyzed, and wear mechanisms are correlated with the microstructure of the material

Accuracy Assessment of the ESA CCI 20M Land Cover Map: Kenya, Gabon, Ivory Coast and South Africa

This working paper presents the overall and spatial accuracy assessment of the European Space Agency (ESA) 20 m prototype land cover map for Africa for four countries: Kenya, Gabon, Ivory Coast and South Africa. This accuracy assessment was undertaken as part of the ESA-funded CrowdVal project. The results varied from 44% (for South Africa) to 91% (for Gabon). In the case of Kenya (56% overall accuracy) and South Africa, these values are largely caused by the confusion between grassland and shrubland. However, if a weighted confusion matrix is used, which diminishes the importance of the confusion between grassland and shrubs, the overall accuracy for Kenya increases to 79% and for South Africa, 75%. The overall accuracy for Ivory Coast (47%) is a result of a highly fragmented land cover, which makes it a difficult country to map with remote sensing. The exception was Gabon with a high overall accuracy of 91%, but this can be explained by the high amount of tree cover across the country, which is a relatively easy class to map

Encapsulation of Crude Oil Emulsions

The formation of crude oil emulsions is unavoidable during crude oil production. The characterisation of such emulsions on-site is an important challenge in order to identify problems that can occur in separation processes. On-line characterisation by classical techniques (light diffusion, acoustic attenuation) is particularly difficult because of the opacity, high volume fraction of dispersed phase and presence of gas bubbles. Consequently, one of the best way to measure on-site droplets size in crude oil emulsions is to sample a representative part of the flow and to lock the system, in order to avoid any coalescence of the droplets before analysis in the laboratory. Prevention of coalescence can be easily performed by encapsulation of the droplets by formation of a polymer film at the oil/water interface. Within this interfacial stabilisation, the emulsion droplets size distribution can be determined in the laboratory by classical techniques such as optical microscopy and image analysis. This technique was applied on-site to characterise actual crude oil emulsions but also in the laboratory. The additives were selected according to the nature of the organic phase (crude oil). Concentrations were optimised in order to obtain a resistant film of polymer, even for very high volume fractions of dispersed phase

On laser welding of thin steel sheets

International audienceThis paper presents a process-structure-property relationship study of laser welds as a continuous consolidation method for joining thin monophased steel foils, thereby providing a more effective, less costly method to construct automotive catalytic converters. A body centred cubic (bcc) iron-chromium-aluminium alloy doped with Mischmetal was utilised in this study. Both pulsed and continuous wave modes were used to establish the limit welding diagrams for lap joint configuration. Actual laser welding parameters were selected using several testing conditions. The laser welds behaved substantially different from the base material under creep and high temperature oxidation. The difference was mainly attributed to the changes in grain morphology, precipitation of aluminium nitrides and carbides, and relocalisation of the reactive elements during liquid metal flow upon keyhole formation, solidification and cooling