Effet des traitements de surfaces sur le comportement microstructural, mécanique et résistance à l’oxydation des aciers

Mr. ATHMANI, Moussa (2022) Effet des traitements de surfaces sur le comportement microstructural, mécanique et résistance à l’oxydation des aciers. Doctoral thesis, Faculté des Sciences et de la technologie.

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Abstract

In this work, the influence of vanadium addition to TiSiN/CrVxN multilayer coatings, deposited by D.C. reactive magnetron sputtering, on the microstructure, mechanical properties, thermal stability and oxidation resistance, was investigated. The results showed that all coatings exhibited a face-centered cubic (fcc) structure; the incorporation of vanadium has no effect on the adhesion and residual stresses values. However, the hardness and Young’s modulus of the coatings increased with increasing vanadium content in the films, reaching the maximum value of 30 and 347 GPa, respectively, for the highest vanadium concentration, due to solid solution hardening. Annealing has a beneficial effect on the hardness and elastic modulus of the coatings due to the changes on the structure. Inversely, vanadium degrades the oxidation resistance of the films and lowered the onset point of oxidation. Three oxide-layers were formed in the case of the reference TiSiN/CrN film, i.e. TiO2 layer on the top followed by a continuous layer Cr2O3 and, underneath, a continuous Si-O layer. The diffusion kinetics of V rules the oxidation behavior of V containing films, i.e. the higher the V concentration is, the easier the disruption of the formation of the protective continuous oxide layers. However, the friction coefficient is constant independently on the chemical composition of the coatings, and the wear of the coating is driven by polishing wear in case of V-containing coatings.

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