Behavior Of Different Coatings Research Articles

Effect of Ni Concentration on the Surface Morphology and Corrosion Behavior of Zn-Ni Alloy Coatings

This research work aims to develop electrodeposited Zn-Ni alloy coatings with controlled dissolution tendencies on a mild steel substrate. The varying Ni concentration in the electroplating bath, i.e., 10, 15, 20 and 25 g·L−1, affected the surface morphology and electrochemical properties of the deposited Zn-Ni alloy coatings. SEM and EDS analysis revealed the resulting variation in surface morphology and composition. The electrochemical behavior of different coatings was evaluated by measuring the open circuit potential and cyclic polarization trends in 3.5 wt.% NaCl solution. The degradation behavior of the electrodeposited Zn-Ni coatings was estimated by conducting a salt spray test for 96 h. The addition of Ni in the coating influenced the coating thickness and surface morphology of the coatings. The coating thickness decreased from 38.2 ± 0.5 μm to 20.7 ± 0.5 μm with the increase in Ni concentration. Relatively negative corrosion potential (<−1074 ± 10 mV) of the Zn-Ni alloy coatings compared to the steel substrate (−969 mV) indicated the sacrificial dissolution behavior of the Zn-rich coatings. On the other hand, compared to the pure Zn (26.12 mpy), ~4 times lower corrosion rate of the Zn-Ni coating (7.85 mpy) was observed by the addition of 25 g·L−1 Ni+2 in the bath solution. These results highlighted that the dissolution rate of the sacrificial Zn-Ni alloy coatings can effectively be tuned by the addition of Ni in the alloy coating during the electrodeposition process.

Corrosion Behavior of Different Coatings Prepared on the Surface of AZ80 Magnesium Alloy in Simulated Body Fluid

A laser shock peening (LSP) layer, a micro-arc oxidation (MAO) bio-coating, and an LSP/MAO bio-composite coating were fabricated on the surface of AZ80 magnesium (Mg) alloy. The LSP-, MAO-, and LSP/MAO-treated samples were subjected to a dynamic immersion test for 24 h in simulated body fluid (SBF) with a flow rate of 1 mL/s. The corrosion evolution behavior of the three samples in SBF solution was investigated by electrochemical tests at 0.5, 2, 4, 12, 16, and 24 h during the dynamic immersion. The results indicated that the three surface-treated samples exhibited different corrosion behaviors at different degradation stages. The LSP/MAO sample showed the best corrosion resistance. The anti-corrosion effect of the LSP nanocrystalline layer on the substrate material during dynamic degradation is discussed.

Mechanical Properties and Corrosion Behavior of Different Coatings Fabricated by Diglycidyl Ether of Bisphenol-A Epoxy Resin and Aradur®-3282 Curing Agent

Mechanical Properties and Corrosion Behavior of Different Coatings Fabricated by Diglycidyl Ether of Bisphenol-A Epoxy Resin and Aradur®-3282 Curing Agent

Solid-Phase Microextraction in Combination with GC--FID for Quantification of the Volatile Free Fatty Acids in Wastewater from Constructed Wetlands

A headspace solid-phase microextraction (HS-SPME) followed by gas chromatography coupled to flame ionization detector (GC-FID) is developed for the direct determination of volatile fatty acids (VFAs) in wastewater from constructed wetlands. Through the investigation on extraction behavior of different coatings for VFAs and the chromatographic behavior of VFAs in a Stabilwax-DA capillary column (30 mx0.32 mm i.d., 0.25 microm film thickness) using nitrogen as carrier gas, the polyacrylate fiber is selected as the satisfactory coating for VFAs analysis, and optimum chromatographic conditions are obtained. The oven temperature is programmed at 70 degrees C for 2 min, then a 4 degrees C/min rate until 180 degrees C, holding 2 min, and then a 20 degrees C/min rate until 200 degrees C, holding the final temperature for 3 min. The various parameters including extraction time, extraction temperature, pH value, ion strength, sample volume, and desorption conditions are investigated for the optimization of HS-SPME performance for VFAs in the wastewater. The experimental results show that the linear dynamic ranges are 10-45000 microg/L, and over two to four orders of magnitude depending on different acids. The detection limit (3sigma) for VFAs are low to microg/L levels and the relative standard deviations are less than 10%, and the recoveries are between 85% and 117%. By using 2-ethylbutyric acid as internal standard, the proposed method is successfully applied to the determination of VFAs in wastewater from the constructed wetlands.

Thermally induced deformations measured by shearography

In the present work, the thermo-mechanical behavior, temperature versus thermal deformation with respect to time, of different coating films were studied by a non-destructive technique (NDT) known as shearography. Organic coatings, i.e., Epoxy on metallic alloys, i.e., carbon steels, were investigated at a temperature range simulating the severe weather temperatures in Kuwait especially between the day-time and the night-time temperatures. The investigation focused on determining the in-plane displacement of the coatings, which amounts to the thermal deformation and stress with respect to temperature and time. Along with the experimental data, a mathematical relationship was derived describing the thermal deformation and stress of a coating film as a function of temperature. Furthermore, results of shearography indicate that the technique is a very useful NDT method not only for determining the thermo-mechanical behavior of different coatings but also can be used as a 2D microscope for monitoring the deformation of the coatings in real-time at a microscopic scale.

Tribological behavior of coatings for continuous casting of steel

There are a large number of steel making processes in which great demands are made on the surface behavior of several components that come into direct contact with steel under various conditions. Continuous casting is mainly a heat-extraction process. The mold must rapidly transfer heat from the steel to the cooling water. In continuous casting, steel solidification starts when it comes in contact with the mold liner's interior surface. The key job of every mold consists in cooling the molten steel in a controlled way. The mold is a major element in the overall economics of a continuous casting plant which explains the number of innovative approaches to increase the working life (length of time during which the mold shows acceptable dimensional stability to meet the quality standards) or to satisfy the new demands to be met by the mold liners. Coating the mold inner is a firmly established practice, in particular with electrolytic surface modification treatments, to cope with the various operating needs including low wettability, high hardness, good wear resistance and low cost. Several pin-on-disk tests were carried out to determine the friction and wear behavior of different coatings. The friction partner for all coatings was a K30 (WC–Co 9%) chip, the sliding speed was 10 cm/s at a temperature of 250°C and a load of 5 N. The sliding time was 200 h (720 000 revolutions for a radius of friction 16 mm). Additional tests for shorter times allowed verification of the morphological evolution of the wear track. All coatings were also evaluated using a scratch test. This test introduces stresses at the interface between the coating and the substrate as the sample is displaced at constant speed. The critical load ( L c) recorded from the scratch test translates the complex intrinsic properties of a specific coating into a very reproducible figure of great practical significance. This paper presents a tribological characterization of conventional electrolytic coatings, bare copper alloys and some new surface solutions for continuous steel casting molds.

High‐temperature behavior of different coatings in high‐performance gas turbines and in laboratory tests

Turbine blades of advanced engines are often subject to a surface attack caused by oxidation or hot corrosion. Typical features of the different modes of high‐temperature surface attack are presented using results of failure analysis of turbine parts and of laboratory experiments. At very high temperatures, interactions take place between the coatings, which are indispensable in this temperature range, and the base metal. Some examples are described that have been gained from cyclic oxidation tests with a nickel‐base single‐crystal alloy and different types of coatings. The development of a broad diffusion zone and the depletion of β phase of the coatings indicate that interdiffusion plays an important role in determining the coating life. In a particular temperature range platelike phases precipitate in the matrix close to the coating. Kirkendall porosity, which frequently occurs at the coating substrate interface at very high temperatures, can markedly reduce the adhesive strength. The behavior of coated parts under mechanical loading is influenced by the coating–substrate combination. Some examples are shown describing creep and thermal fatigue properties of coated components.

Chemical vapor deposition and physical vapor deposition coatings: Properties, tribological behavior, and applications

The main differences between chemical vapor deposition (CVD) and physical vapor deposition (PVD) processes are discussed in relation to a number of properties which are important for the functional behavior of coatings: chemical composition, phase composition, microstructure, thickness, hardness, texture, internal stresses, morphology, and roughness; each of which is discussed. Results of friction and wear tests which were performed under different conditions are reported, which reveal important aspects of the tribological behavior of different coatings. Examples of the application of CVD and PVD coatings are presented which show the possibilities for decreasing friction and wear of tools and machine elements.

Low-Electroosmotic-Mobility Coatings for ASTP Free-Fluid Electrophoretic Separation

The Apollo 16 Electrophoresis Experiment demonstrated the need for a low-electroosmotic-mobility coating in a free-fluid electro-phoretic separation.1 The photographs of the experiment showed parabolic particle profiles that are characteristic of electroosmosis in the cell and which render a practical separation impossible. These paraboiic particle profiles were in good agreement with theoretical profiles calculated assuming an electroosmotic mobility of the cell walls equal to −lOμm cm/volt sec.2 Therefore, a major effort was initiated to develop a coating that would reduce the zeta potential at the cell-wall/liquid interface to zero or near-zero, to eliminate the driving force responsible for electroosmotic flow in the presence of an applied electrical potential. The initial work was directed towards the electrokinetic behavior of different coatings on a variety of surfaces in the presence of different buffer systems because neither the buffer nor the electrophoresis cell material were decided upon unti...