Surface performances of Ti-6Al-4V substrates coated PVD multilayered films in biological environments

Multilayered and nanostructured coatings of Ti based alloys (oxides and nitrides) are elaborated and tested for increasing protective properties such as corrosion and wear resistances. A pin-on-disc tribometer was used to evaluate the wear resistance in Hank's solution against bovine bone. Corrosion behavior in Hank's solution was determined by potentiodynamic and electrochemical impedance spectroscopy techniques. Besides, the specimen surfaces were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) microanalyses. The results showed that optimal tribological properties were obtained in the case of coatings having TiN as top layer. The main wear mechanism was abrasive third body wear. In vitro corrosion tests at 37 °C showed that the better corrosion resistance was obtained when TiN was the top layer. However all of them exhibited good tribological properties, good corrosion resistance and then may be promising options for biomedical applications

Nano- and micro-scale morghological defects in oxidized a-SiC: H thin films

Amorphous carbon rich a-SiC:H films were deposited on silicon substrates by RF-magnetron sputtering of SiC target in argon/methane gas mixture. The principal focus of this study was investigation of the effect of thermal oxidation on structure and morphology reconstruction in a-SiC:H amorphous network. The density of the films was varied over the range 1.6-2.2 g/cm2 by varying the magnetron discharge power. The local nano- and micro-scale surface morphology and chemical composition distribution were examined by atomic force microscopy, scanning electron microscopy equipped with Auger electron scanning system and optical profilometry. It was found that partial oxidation leads to local structure reconstruction accompanied by transformation of mechanical stresses from compressive to tensile. Formation of carbon-enriched nano- and micro-scale regions was observed after oxidation in low density samples. We attrribute these morphological defects to migration and precipitation of carbon species released in the process of oxidation of the SiC amorphous network. The mechanism of tensile stresses generation is also discussed.Science and Technology Center of Ukraine, project No. 5513, National Academy of Science project No. 2-2-15-28 and Arts et Métiers ParisTech (invited professor

Effects of low and high temperature plasma nitriding on electrochemical corrosion of steel

This study concerns plasma nitriding of tool steel at different temperatures and its effects on corrosion resistance. Inside the nitriding reactor steel samples were placed on the sample holder after metallographic polishing and then the vacuum chamber was evacuated to a pressure of 0.5 Pa. At a lower temperature of 450 C and the higher temperature of 550 C nitriding was performed for a fixed duration of 10 h. All the nitrided and the bare steel samples studied under X-ray diffraction (XRD) and scanning electron microscopic analysis/energy dispersive X-ray spectroscopy (EDS). Iron nitride (FexN, x = 2–3, 4) peaks were revealed in the nitrided steels after XRD analyses. EDS revealed the increased amount of nitrogen in the nitrided sample treated at 550 C. For the assessment of corrosion resistance of these steel samples potentiodynamic polarization tests were performed in 3.5% NaCl. On comparison, it was found that the steel nitrided at higher temperature is more effective in enhancing the corrosion resistance

Plasma Nitriding of 90CrMoV8 Tool Steel for the Enhancement of Corrosion Resistance

In the present studies, efforts were made to improve corrosion resistance of 90CrMoV8 tool steel by following plasma nitriding. Plasma nitriding of this steel at 500 oC for6and 8 h significantly improved the corrosion resistance when compared to the as-received steel. X-ray diffraction reveals γ′ (Fe, Cr)4 N) and ε ((Fe, Cr) 2–3 N) phases formed after nitriding. Potentiodynamic polarization tests in 3.5% NaCl reveal that plasma nitriding significantly improved the corrosion resistance as compared to untreated steel. The improvement in corrosion resistance may be attributed to the N solid solution and the presence of Fe-nitrides formed in the compound laye

Electrochemical study on the corrosion resistance of surface modified Cr-Mo-V steel by elevated temperature plasma nitriding

This study presents the effect of plasma nitriding on corrosion resistance of low alloy 90CrMoV8 steel. At a selected temperature of 500 °C, nitriding was performed by varying the exposure time. X-ray diffraction of nitrided steel revealed the presence of Fe, γ′ (Fe, Cr)4Nand ε-(Fe, Cr)2–3N) phases. The cross section of the nitrided steel was analyzed by scanning electron microscope. To understand the effect on corrosion resistance, potentiodynamic polarization along with the electrochemical impedance spectroscopy (EIS) was performed in 3.5% NaCl. The corrosion resistance of the nitrided steel was found to be much higher than the as-received steel. It was also found that the steel nitrided for shorter duration of 6 h has better corrosion resistance than that for 8 h. This enhancement of corrosion resistance may be attributed to the presence of nitrogen in solid solution, γ′-(Fe, Cr)4Nand ε-(Fe, Cr)2–3Nphases

Recrystallization mechanisms and associated microstructure evolution during billet conversion of a gamma-gamma' nickel based superalloy

A partially recrystallized sample of the Ni-based superalloy AD730 was taken from an intermediate stage of the ingot to billet conversion process and isothermally forged in a single stroke compression test at a sub-solvus temperature (1080 °C). The as-received material had a heterogeneous microstructure, containing a mixture of coarse and much finer recrystallized grains as well as unrecrystallized ones, and also heterogeneous γ′ precipitation. The recrystallization mechanisms occurring dynamically in the different grain populations were investigated via electron backscatter diffraction (EBSD). It was found that local microstructure could affect the operative recrystallization mechanism, with different mechanisms seen in the deformed and recrystallized regions, owing to their different precipitate distributions. Within a single deformed grain, three apparently distinct dynamic recrystallization (DRX) mechanisms were identified. The interaction of recrystallization with precipitates plays a central role in DRX. In certain cases precipitates may stimulate discontinuous DRX by providing recrystallization nuclei, alternatively they may impede and limit the growth of recrystallized grains, or in other cases still they promote continuous recrystallization

Nano- and micro-scale morghological defects in oxidized a-SiC: H thin films

Amorphous carbon rich a-SiC:H films were deposited on silicon substrates by RF-magnetron sputtering of SiC target in argon/methane gas mixture. The principal focus of this study was investigation of the effect of thermal oxidation on structure and morphology reconstruction in a-SiC:H amorphous network. The density of the films was varied over the range 1.6-2.2 g/cm2 by varying the magnetron discharge power. The local nano- and micro-scale surface morphology and chemical composition distribution were examined by atomic force microscopy, scanning electron microscopy equipped with Auger electron scanning system and optical profilometry. It was found that partial oxidation leads to local structure reconstruction accompanied by transformation of mechanical stresses from compressive to tensile. Formation of carbon-enriched nano- and micro-scale regions was observed after oxidation in low density samples. We attrribute these morphological defects to migration and precipitation of carbon species released in the process of oxidation of the SiC amorphous network. The mechanism of tensile stresses generation is also discussed.Science and Technology Center of Ukraine, project No. 5513, National Academy of Science project No. 2-2-15-28 and Arts et Métiers ParisTech (invited professor