Investigating the effect of post-annealing treatment of CrN/CrTiSiN nanolayered coating on the tribological and corrosion behavior and studying its mechanism

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Investigating the effect of post-annealing treatment of CrN/CrTiSiN nanolayered coating on the tribological and corrosion behavior and studying its mechanism

ارائه دهنده: Provider: MohammadAli Sohrabizadeh

اساتید راهنما: Supervisors: Dr. Hassan Elmkhah

اساتید مشاور: Advisory Professors: Dr. Meisam Nouri and Dr. Massoud Attapour

اساتید ممتحن یا داور: Examining professors or referees: Dr. Hamid Esfahani, Dr. Shahrokh Ahangarani and Dr. Ali Shanaghi

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: In recent years, the use of Arc-PVD coatings based on transition metal nitrides has increased day by day in various industries. Therefore, it is considered important to study the changes and transformations of these coatings at different working temperatures. Therefore, in this research, the effect of heat treatment on phase and microstructural transformations of CrN/CrTiSiN multilayer nanocomposite coating on Ti6Al4V substrate was investigated. The applied coating was heat treated for 1 hour at temperatures of 500, 600, 700, 800, 900, and 1000 °C in the ambient air. In order to investigate the properties obtained from the coatings, X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), nano serration, adhesion by the Rockwell C method, and finally pin wear tests on the plate and polarization corrosion tests were performed. Structural studies of the cross-sectional surface of the coating showed that the layered coating has a thickness of 4 microns and alternating layers of CrN and CrTiSiN with a share of 62.5 and 37.5%, respectively. On the other hand, the phase studies showed that after the layering operation, Si3N4 amorphous phase was placed next to TiN and CrN crystalline phases with crystal sizes of 3 to 6 nm, and by applying the annealing operation, new phases such as SiO2, Cr2N, Cr2O3, and TiO2 were added to the structure. The cover will be formed. In layering conditions, the structure of the coating consists of the dominant phase of CrN, and the volume fraction of this phase will decrease from 56 to 29% by increasing the annealing temperature from 500 to 800 °C and will be decomposed into the Cr2N phase. By increasing the annealing temperature to 800 °C, a completely uniform structure of the Cr2N phase was obtained. It was observed that by increasing the temperature of annealing to more than 900 °C, phase transformation of Cr2N to Cr2O3 occurred, so that by increasing the annealing temperature to 1000 °C, the volume fraction of the Cr2O3 phase will increase to 38%. The phase transformation of Cr2N to Cr2O3 is associated with an increase in the network volume (about 4 times). This increase in network volume will lead to the formation and growth of microcracks in the CrN layer and will eventually lead to the destruction of the coating. The results obtained from the hardness test showed that, after layering, the maximum hardness was obtained with a value of 49 GPa. Applying the annealing operation up to 600 °C reduces the hardness to 39 GPa, and then by increasing the annealing temperature to 800 °C, the hardness increases again to 47 GPa. In fact, increasing the size of the crystals, increasing the tensile residual stress, and increasing the increasing the network strain caused a decrease in hardness, and increasing the volume fraction of the Cr2N phase caused an increase in hardness, which was introduced as the dominant mechanism of hardness changes. The results of the adhesion test showed that the best adhesion of the coating to the substrate is obtained at an annealing temperature of 600 °C. It seems that the formation of a structure consisting of CrN and Cr2N phases with a volume fraction ratio of 55% to 45% plus a protective layer of Cr2O3 at an annealing temperature of 600 °C improves the properties of the coating compared to other annealing conditions. The results of the wear tests showed that the dominant wear mechanism up to the annealing temperature of 500 °C is plastic deformation, and when the temperature increases to more than 700 °C, the wear mechanism changes to oxidative wear. The results of the corrosion test showed that the presence of macro-particles scale can always have destructive effects on the corrosion properties of the coating, and the application of annealing operations will improve the corrosion properties in a favorable way due to the formation of a surface oxide layer. The results obtained from the wear and corrosion tests clearly showed the superiority of the properties at the annealing temperature of 600 °C.

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