The crater wear of alumina coated WC-Co cutting tools is thought to be influenced by the chemical reactions between the coating and the workpiece material. Three different crystal orientations ((001), (012), and (100) of alpha alumina CVD coatings are examined in combination with four workpiece materials of steel to establish what reactions are present, and the extent of diffusion. The alumina coatings and workpiece materials were pressed together as diffusion couples and heat treated at 1250- 1300°C for 10-20hours. It was fond that the types of inclusions present in the workpiece were more impactful on the chemical wear of the coating than the crystal orientation of the coating. EDS measurements show significant amounts of W and Co on the surface of the coatings and on the steel surfaces after heat treatment. This is thought to be connected to the migration of Co through the coating in cooling cracks and other impurities. In the surface of the coating, areas of solidified Co-rich structure have been found, implying that Co has formed an alloy with Fe, C, Al, and W with sufficiently low melting temperature to partially melt during the heat treatment. This has been confirmed as possible by simulations in Thermo-calc. Turning tests and scratch tests were made with the same combinations of coatings and workpiece material and show differences in adhesion of workpiece material on the different coating orientations. The 100-orientation has been found to have the most adhered workpiece material, the reason for this being its higher surface roughness. Ultimately no noticeable differences in chemical reactivity between the coating crystal orientations was found. The Co diffusion though the coating occurred for all the coating orientations and further experiments in turning with the different workpiece materials are required to determine the effect of Ca-rich inclusions on the magnitude of chemical wear. / <p>Handledare på företag:</p><p>Susanne Norgren </p><p>Doc.  Ph.D,  Group Expert Materials Design</p>

La famille des matériaux semiconducteurs III-N présente des propriétés adéquates pour diversesapplications que ce soit dans le domaine de l’optique ou de l’électronique. Certaines de ces applicationsconsistent à intégrer ces matériaux dans des environnements hostiles et notamment soumis à l’actiond’ions lourds à différentes énergies. Lors de cette thèse, le travail consistait tout d’abord à comprendrel’évolution microstructurale sous irradiation du substrat alpha-Al2O3, puis du film mince GaN, afin d’établirun profil de l’évolution de l’endommagement en fonction de la profondeur. Un comportement assezsimilaire concernant l’évolution des paramètres de maille a été observé pour les deux matériaux. Dansla direction parallèle à la trajectoire du faisceau d’ions, une importante augmentation du paramètre demaille a été mise en évidence tandis que peu de variations ont été relevées perpendiculairement à latrajectoire du faisceau d’ions. Les formations de couche amorphe pour l’alpha-Al2O3 et de couche fortementendommagée pour le GaN ont été observées en surface. Les épaisseurs de ces couches augmentent enfonction de la fluence, associé à l’augmentation des contraintes résiduelles au sein du matériau. Al’aide d’hypothèses et des différents résultats obtenus, deux profils d’endommagement en profondeuront été proposés. D’autre part, la nanoindentation a montré que les paramètres de dureté et de moduled’élasticité évoluent fortement sous irradiation en fonction de la fluence. / Nitride semiconductors are attractive materials for the development of optical and electronic devices.Some of these applications can expose materials to extreme environments and especially radiation ofheavy ions at different energies. In this thesis, the study focused first on behaviour evolution underirradiation of alpha-Al2O3 and then of GaN thin film, in order to establish a profile of damage evolution asfunction of the depth. Concerning lattice parameter, a similar behaviour was observed for both materials.An important increase of lattice parameter parallel to ion beam was highlighted while few variations wasnoted for the lattice parameter perpendicular to ion beam. Formation of amorphous layer for alpha-Al2O3and highly disordered layer for GaN were observed in surface. Layers thicknesses increase as functionof the fluence with an increase of residual stresses in material. Using different results and assumptions,two damage profiles as function of the depth have been proposed. In addition, nanoindentation hasshown hardness and modulus of elasticity parameter evolve highly under irradiation as function of thefluence.