Nuevos recubrimientos basados en nitruros con adiciones de silicio para el mecanizado de la aleación inconel 718 con herramientas de metal duro

Resumen

The microstructures and mechanical properties of mixed nitride based coatings AITiN and AICrN and two vairants alloyed with silicon (AITiSiN and AICrSiN) have been studied as-deposited, after annealing and after diffusion couples tests. The crystallite size and the microstrain have been obtained from the diffraction peaks broadening. These results confirmed that the nitrides showed B1 NaCI crystal structure. All the coatings showed columnar growth, moreover AITiSiN showed multilayer structure with a period of 15 nm. The nanoindentation, AFM and X ray diffraction tests, shows that Si incorporation in the AITiN and AICrN incrase of hardness, elastic modulus, roughness and residual stresses. The annealing carried out at 900ºC shows that in the AITiN and AITiSiN a slight residual stress relaxation and an increase in the crystallite size takes place; these changes are more accentuated in the chromium based coatings. At 1100ºC, the AITiN and AITiSiN oxidizes; meanwhile catastrophic oxidation and delamination of the AICrN and AICrSiN takes place. In the diffusion couples carried out at 900ºC, the AITiN and AITiSiN coatings show less reactivity than the AICrN and AICrSiN in contact with the Inconel 718; whereas at 1100ºC it is observed that the damage produced on the AITiN and AITiSiN is bigger than the annealing tests. The AICrN and AICrSiN coating turn out to be conpletely oxidised. In the dirlling test the deterioration of the cutting edges takes place for the chip adhesion of the Inconel 718 in the top and in three principal flank faces of the drills. The BUE formation is lower in the drills coated with AITiN or AITiSiN compared to AICrSiN or the uncoated ones. In the corrosion tests, the combination of and corrosion inhibitors allowed the elimination of the coating controlling the damage produced on the substrate. The mechanism of inhibition is physisorption.