摘要: Titanium and its alloys are widely used in aerospace and aviation industries because of their high strength-to-weight ratio, high fracture resistance and corrosion resistance at elevated temperatures. However, chemical reactivity and low thermal conductivity of these alloys lead to adhesion and diffusion wears on carbide tools, respectively. In addition, fluctuations in cutting forces occur during the cutting process due to chip shear band formation; and chipping wear is observed at the tool cutting edge as a result. Therefore, machining of these alloys is a challenge for researchers. A common method to increase the lifetime of carbide tools is to coat them with a thin hard coating. In this study, a nanolayer AlTiN/TiN coating was deposited on carbide cutting tools using an industrial magnetron sputtering system in order to enhance their wear resistance and lifetime in milling of Ti6Al4V. The cutting tests with the coated tools were performed at a cutting speed of 50 m/min, feed rate of 0.1 mm/tooth and depth of cut of 1 mm under dry conditions. Tool wear and surface roughness on the workpiece were measured and recorded as a function of cutting distance. Wear mechanisms and types were revealed using optical and scanning electron microscopy and energy dispersive spectroscopy. It was found that the nanolayer AlTiN/TiN coated tools provide higher wear resistance and 4 times longer lifetime when compared to uncoated ones. The main observed wear types are notch wear and build-up edge formation on the cutting edge. A slight improvement in surface roughness of the workpiece was observed with the nanolayered coating.
摘要: The Inconel 718 superalloy is one of the most-used nickel based superalloys in the aerospace industry due to its superior mechanical properties, for instance, high thermal and chemical resistance, and high strength at elevated temperatures. However, the work hardening tendency, low thermal conductivity and high hardness of this superalloy cause early tool wear, leading to the material to be called as a hard-to-cut material. Therefore, deposition of a wear resistant hard coating on carbide cutting tools has a critical importance for longer tool life in milling operations of the Inconel 718 superalloy. In this study, carbide cutting tools were coated with multilayer nanocomposite TiAlSiN/TiSiN/TiAlN coating using the magnetron sputtering technique, and wear behavior of the coated tool was investigated during face milling of the Inconel 718 superalloy under dry conditions. Abrasive and adhesive wear mechanisms were founded as main failure mechanisms. The nanocomposite TiAlSiN/TiSiN/TiAlN coated carbide cutting tool gave better wear resistance, and thus it provided 1.7 times longer tool life and a smoother surface (Ra<0.18 μm) on the Inconel 718 material than the uncoated one.
摘要: Silver nanoparticles have been used in the medical area due to their remarkable antimicrobial properties. In this sense titanium dioxide nanoparticles obtained by the sol-gel method were used as coating of catheters for subsequent impregnation of silver nanoparticles with gamma irradiation and electron beam at 25 and 50 kGy. This work aimed to study the use of the silver nanoparticles and titanium dioxide as coating of polyurethane Central Venous Catheter (CVC) for antimicrobial activity. Furthermore the amounts of titanium and silver present in the coated catheters had been evaluated by Inductively Coupled Plasma – Optical Emission Spectrometry (ICP OES). Therefore the Raman spectrometry was used to identify the polymorph of titanium oxide, rutile.
摘要: AISI 1020 steel is considered to be one of the most applicable structural steels, in particular in the cold drawn form. Heating of this grade of steel prior to AC1 must have been applied to spheroidize the lamellar cementite, and consequently enhances the cold formability character of the steel. Si3N4 nanoinoculation of this grade of steel has been used in this study, where it is added to the molten steel, in order to avoid the high cost long term heat treatment process prior to cold deformation process. Optical microscopy and SEM have been used to evaluate the morphology of cementite after nanoinoculation process with Si3N4. Tensile properties of nanoinoculated steels have been investigated. Finally, wear adhesive resistance of investigated samples has been evaluated. The obtained results showed a great enhancement in the mechanical properties, strength, ductility and adhesive wear resistance, as a result of the nucleation of cementite into a new spheroidal phase and grain refinement by Si3N4 inoculation and allow usage of AISI 1020 steels inoculated by nanoinoculant Si3N4 in further technological applications.
摘要: This study aims to describe the influence of adding graphene oxide to TiO2-noble metal (Me=Ag, Au or Pd) composite nanoparticles on their bioactivity (formation of RGO/TiO2-Me nanocomposite system). The obtained nanocomposite flakes and reference TiO2-Me nanoparticles were characterized using SEM, HRTEM and XPS spectroscopy, N2 sorption analysis and helium pycnometer. The analysis of the antibacterial properties of synthesized nanocomposites revealed a growth inhibiting effect of TiO2-Ag particles on gram positive bacteria such as: Staphylococcus aureus, Sarcina lutea and Bacillus subtilis. In the case of nanocomposite flakes containing RGO the visible changes in bacteriostatic properties were observed, including unexpected reversal of the antimicrobial activity of silver-containing nanoparticles into the stimulation of growth of applied bacterial strains. The stimulation of growth was not observed for TiO2-Au and Pd nanoparticles deposited on the surface of RGO.
摘要: Hydrothermal processes have the potential for the direct preparation of crystalline ceramic powders and offer a low-temperature alternative to conventional powder synthesis techniques in the production of oxide powders. These processes can produce fine, high-purity, stoichiometric particles of single and multi-component metal oxides. Furthermore, if process conditions such as solute concentration, reaction temperature, reaction time and the type of solvent are carefully controlled, the desired shape and size of particles can be produced. Uniform distribution of the particles is key for optimal control of grain size and microstructure in order to maintain high reliability. It has been demonstrated that such powders are composed of much softer agglomerates and sinter much better than those prepared by calcination decomposition of the same oxides. These powders could be sintered at low temperature without calcination and milling steps. The objective of this study was to synthesis TiO2-CeO2 nanosized crystalline particles by a hydrothermal process.TiO2-CeO2 nanosized powders were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. The TiO2-CeO2 nanosized powder was obtained at 185°C and 6 h. The average size and size distribution of the synthesized particles were below 10±5 nm and narrow, respectively. The XRD diffraction pattern shows that the synthesized particles were crystalline. This study has shown that the synthesis of TiO2-CeO2 nanosized crystalline particles is possible under hydrothermal conditions in aqueous solution.
摘要: YCrxAl1-xO3 nanoparticles were synthesized by a reverse micelle processing for inorganic pigment. Y(NO3)2·6H2O, Cr (NO3)2·6H2O and Al (NO3)3·9H2O are used for precursors in order to synthesis YCrxAl1-xO3 nanoparticles. The aqueous solution consists of mixing the molar ratio of Y/Cr/Al at 1:x:1-x and heat treated at 900~1300°C for 2h. The average size and distribution of synthesized YCrxAl1-xO3 powders was in the range of 10-20nm and narrow, respectively. The average size of the synthesized YCrxAl1-xO3 powders increased with increasing water to surfactant molar ratio and heating temperature. The crystallinity of synthesized YCrxAl1-xO3 powder increased with increasing heating temperature. The synthesized YCrxAl1-xO3 powders were characterized by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and color spectrophotometer. The properties of the synthesized powders were affected by such variables as molar ratio, heating temperature etc.
摘要: This study is a kinematic model of a mechanical mill that works with a single ball in motion, and which is operated by a crank and connecting rod system for producing nanocrystalline powders by the process of ball milling. The geometric and dynamic parameters play an important role on the variation of forces created upon impact of the ball with the inside wall of the vial, which caused energy transfer required for the mechanical alloying process. The determination of these forces enables us to know their specific magnitudes on the intensity and milling efficiency, with the advantage of low operating power consumption of the mill and absence of the contamination problem. In addition, we have defined a model for calculating the temperature of the powder trapped between the ball and the wall of the vial of the mechanical mill whose start-up is provided by an electric motor.
摘要: Commercial copper and iron powders were used as starting materials. These powders were mechanically alloyed to obtain Cu(100-x) Fex supersaturated mixture. The milling duration was chosen in such a way as to obtain a nanostructured mixture and to form a supersaturated solid solution of CuFe; the powder mixture was used to deposit CuFe on a glass substrate.
The elaboration of our films has been carried out using thermal evaporation process (physical vapor deposition) under 1 × 10-6 mbar vacuum from an electrically heated tungsten boat, using the supersaturated solid solution Cu(100-x) Fex powder obtained by mechanical alloying. The films deposition has been done on glass substrates. In this study, we present the composition effect on the structural and magnetic proprieties of Cu(100-x) Fex powder and thin films. The chemical composition, structural and magnetic proprieties of milled powders and thin films were examined by SEM, TEM, XRD, XRF and VSM.