E. Vera

Optimisation of TiN-IBAD coatings for wear reduction and corrosion protection

Abstract Hard TiN layer coatings are commonly used as a single layer or sometimes as multilayers in order to improve wear resistance due to their outstanding mechanical characteristics. Usually the corrosion protection by these films is only moderate. Pores and defects can easily be formed in the processing stage. The mechanical properties as well as the porosity can be influenced by ion bombardment during deposition. This contribution has the objective of studying the correlation between corrosion and mechanical properties of the TiN layers and TiO2/TiN multilayers on steel (Ck45) produced by ion beam assisted deposition (IBAD) as a function of deposition parameters. The examination of the electrochemical phenomena occurring on the surface of the layer was based on the current density/potential measurements and on the scanning electrochemical microelectrode (SEME). Furthermore friction and wear resistance of the layer was determined by pin-on-disk measurements, and structure and morphology studied by X-ray diffraction (XRD) and AFM. The most important result was the finding that the degree of crystallinity of the coatings affected directly the hardness and wear resistance. The corrosion protection power on the other hand, increased with low crystallinity and high content of amorphous TiO2 or TiN.

Corrosion properties of alumina coatings on steel and aluminum deposited by ion beam assisted deposition

Abstract Hard and corrosion-resistant ceramic coatings like Al 2 O 3 have shown promising protective properties in previous investigations. The aim of this work is to deposit optimized Al → Al 2 O 3 layers on tool steel (Ck45) and a common aluminum alloy (AlMgSi 0.5 ). The major consideration is to examine the influence of a graded metal-ceramic interface on internal stress, adhesion and corrosion properties. For this purpose the width of the Al → Al 2 O 3 interface was varied by controlling the process parameters during deposition. The electrochemical and corrosion behaviour was determined by potentiodynamically controlled current-potential measurements under conditions of uniform corrosion attack and pitting corrosion. Further examinations of the local surface conditions were made by scanning-micro-electrode (SME) microscopy. The adhesion was determined by scratch and pull-off tests and the internal stress was recorded in situ during the deposition process. The results show that optimized Al → Al 2 O 3 graded interfaces increase the hardness and improve the corrosion resistance in comparison with pure Al 2 O 3 coatings. The adhesion is very good in all cases.

Use of the electrochemical impedance spectroscopy to evaluate the performance of a primer applied under different surface preparation methods

Electrochemical impedance spectroscopy (EIS) was used in this work in order to evaluate primer behaviour, applied on metals with different conditions of superficial preparation. The substrate surface preparation plays an important role in the final quality of coatings. The cleaning and surface finishing can be carried out using different methods. The most common are sand- and wet-blasting. In this paper the EIS technique was used to evaluate the influence of three different methods of surface preparation (sand-blasting, wet-blasting without inhibitor and wet-blasting with inhibitor). A red epoxy primer was applied on a steel panel, using each of these three clean methods. These primer systems were exposed in a salt atmosphere, which was simulated using a salt-fog chamber during an 870 h exposure time. During this time the electrochemical properties of the primer were periodically evaluated using the EIS technique. Moreover, visual inspection was carried out at the same time as the EIS. The final results of these evaluations confirm the power of the EIS technique to evaluate and determine the best protection performance of a primer applied on steel panels with different superficial preparation.

Tribo-electrochemical characterization of hafnium multilayer systems deposited on nitride/vanadium nitride AISI 4140 steel

In this work is presented the synergistic behaviour among corrosion/wear (tribocorrosion) of the multilayer coatings hafnium nitride/vanadium nitride [HfN/VN]n. The multilayers were deposited on AISI 4140 steel using the technique of physical vapor deposition PVD magnetron sputtering, the tests were performed using a pin-on-disk tribometer, which has an adapted potentiostat galvanostat with three-electrode electrochemical cell. Tribocorrosive parameters such as: Friction coefficient between the coating and the counter body (100 Cr6 steel ball); Polarization resistance by means of electrochemical impedance spectroscopy technique and corrosion rate by polarization curves were determined. It was observed an increase in the polarization resistance, a decrease in the corrosion rate and a low coefficient of friction in comparison with the substrate, due to an increase on the number of bilayers.

Effect of glow discharge sintering in the properties of a composite material fabricated by powder metallurgy

Composite samples of 316 stainless steel and SiC were produced by powder metallurgy. Starting materials were mixed in different proportions and compacted to 700MPa. Sintering stage was performed by abnormal glow discharge plasma with direct current in an inert atmosphere of argon. The process was conducted at a temperature of 1200°C±5°C with a heating rate of 100°C/min. This work shows, the effectiveness of plasma sintering process to generate the first contacts between particles and to reduce vacancies. This fact is confirmed by comparing green and sintered density of the material. The results of porosity show a decrease after plasma sintering. Wear tests showed the wear mechanisms, noting that at higher SiC contents, the wear resistance decreases due to poor matrix-reinforcement interaction and by the porosity presence which causes matrix-reinforcement sliding.

The most stable mono-layers of (111)-Pt (fcc) on Graphene: A first-principles GGA study

We investigate monolayers of planes (111) of Pt in the FCC structure located on graphene. The energy of formation showed that the most stable structure is √3×√3 — Pt on 2 × 2 — graphene. This system has a mismatch in the lattice constant of 0.45. The layers are completely flat, and its band structure shows that the new structure is metallic and the Diracs cones are displaced 0.6eV above of the Fermi level. In this work we present the dependence of the enthalpy of formation of these structures and we calculated all structural parameters of their relaxation.

Influence of thermal spraying parameters on the corrosion resistance of aluminium oxide coatings deposited on steel 1020

Parameters required for the preparation of coatings of aluminium oxide deposited on AISI 1020 steels were determined according to their thickness and type of flame to differentiate their behaviour against corrosion. Commercial powders were used by the method of thermal spraying deposition. The coatings were analysed by OM (optical microscopy), the thickness was measured by means of a coating thickness gauge and electrochemical techniques variables measured was the Linear Polarization Resistance (LPR) and approximation Tafel potentiodynamic curves. The corrosion current for steel 1020 with Na2SO4 electrolyte of 3.5% is of the order of hundreds of A/cm2 and coated steel given in the order of A/cm2, which leads to think that the projection produces coatings uniform low closed porosity, although techniques DC indicate a significant porosity as is observable current response to the potentiodynamic curve. The observed thicknesses fall into the hundreds of microns and little uniformity was noted in this coatings. The coatings deposited by oxidizing flame was better performance in corrosion than the coating deposited by neutral flame.

Design and Optimization of an Electrochemical Equipment for the Synthesis and Evaluation of Conducting Polymers

Abstract A potentiostat system, focused towards the synthesis and evaluation of conducting polymers, was developed. This equipment consists of two main modules: the acquisition and control module, activated by means of a microcontroller which is connected through serial port to a computer, and the potentiostatic module, specially designed for handling the signals from the synthesis and characterization processes of the polymers. The user environment was programmed with Visual Basic 6. The resolution of the system AD/DA is of 12 bits; this allows sensibilities of 1 nA in current measurements. The achieved potential sweep is between −2 and +2 V. By means of this equipment, ClO4 −doped polypyrrole (PPy) and biphthalate doped PPy films were synthesized. The conducting polymers were synthesized by potential square waves. The thicknesses of the polymeric films were determined throughout the polymerization charge. The error percentage in the polymerization charge recorded by the developed potentiostat, relative to a commercial potentiostat, was about 6%. The ability to store the charge of the biphthalate PPy (biphthalate) films in potassium biphthalate aqueous solution was determined by cyclic voltammetry at various scan rates.