In this study, tantalum (Ta) thin film was deposited on Si (100) and 316L stainless steel (SS) substrates by DC magnetron sputtering. The structural properties of Ta film were investigated by X-ray diffraction analysis. In addition, the scanning and transmission electron microscopies as well as atomic force microscopy were used to study the cross-section and the morphology of the coating. The corrosion behavior of the bare and Ta-coated 316L SS was evaluated by potentiodynamic polarization test. The electrochemical impedance spectroscopy was employed to study the corrosion mechanisms. The results revealed that the structure of Ta coating on either Si and SS substrates is a mixture of α +β phases, while pre-deposition of a thin tantalum nitride seed layer causes to the deposition of pure α-Ta and decreases the sheet resistance from 90 μ Ω . cm to 15 μ Ω . cm. Microscopic evaluations show that the Ta coating is compact, homogeneous and defect-free, exhibiting a columnar structure with a surface roughness of less than 6 nm. Furthermore, the corrosion studies show that the Ta coating act as a physical barrier between corrosive electrolyte and substrate and, in this way, provide a protective efficiency of more than 70%. In this regard, the diffusion of corrosive electrolyte toward the substrates through open porosities was found to be the corrosion mechanism of the Ta coating and the porosity index of the coating was calculated to be about 6%.

Galvanic corrosion is an ever-present problem in all different environments, particularly in tanks. The goal of this project is to develop a finite element model that can be used with experimental data to characterize the corrosion of a galvanic weldments couple in an electrolyte. In this study sample are welded by gas tungsten arc welding and friction stir welding. According to ASTM G8, Evaluation of corrosion properties examined with cyclic polarization test in 0. 5 molar H2SO4 andthe information required to validate the model was prepared. The finite element model is developed using COMSOL and Math Module through derivation of equations describing corrosion thermodynamics and electrochemical kinetics. The results showed that reducing in heat input to improve galvanic corrosion behavior in the weld sample. In addition to result of simulation reveal sample that welded by gas tungsten arc method had higher current density galvanic corrosion in comparison with friction stir sample.

The effect of ultrasonic impact treatment (UIT) was studied on the microstructure and corrosion behavior of Haynes 25 superalloy. The UIT was performed at a frequency of 20 kHz, tool feeding rates of 0.08, 0.12, and 0.16 mm/rev, vibration amplitudes of 10, 28, and 50% of the machine power, static pressures of 0.1 and 0.9 bar at the different number of passes (one, two, three, five, and seven). According to the results, the UIT severely deformed the surface layers up to a depth of about 100 μm and promoted the emergence of deformation bands/strain-induced martensite (-phase) up to a depth of about 400 μm. The UIT also produced ultrafine grain structure in the surface region and due to the deformation inhomogeneity developed surface compressive residual stresses. The Tafel polarization tests indicated that applying one pass UIT at the static pressures of 0.1 and 0.9 bar reduced the corrosion current (from 4.16 A/cm2 to 1.3 A/cm2 and 2.18 A/cm2, respectively), and the corrosion potential (from -0.6 V to -0.7 V and -0.8 V, respectively). This behavior was found to be due to promotion of surface oxidation and formation of protective layer on the surface. Despite increasing the surface smoothness, further increasing the UIT pass number to seven, probably due to encouraging the formation of surface pits/microcracks increased the corrosion current and corrosion rate by about 45%. According to the electrochemical impedance tests, at the static pressure of 0.9 bar, the as-received and seven-pass UITed samples showed the lowest corrosion resistance whilst one-pass and two-pass UITed samples revealed the highest corrosion resistance. The effect of tool feeding rate on the corrosion resistance was found to be minor.

The corrosion protection of aluminum flake pigments has been extended by means of an encapsulating inorganic/organic silica/polystyrene hybrid nanolayer. A silica nanolayer encapsulated the surface of aluminum flakes (Al) by hydrolysis and polycondensation of tetraethylorthosilicate via sol–gel process to yield Al/Si flakes. Then, 3-methacryloxypropyltrimethoxysilane (MPS) was used as surface modifier which has polymerizable groups to participate in polymerization reaction (Al/Si/MPS). A polystyrene (PS) coating layer was applied on Al/Si/MPS flakes by free radical polymerization of styrene initiating with Azobisisobutyronitrile at 60 °C and subsequent washing of free chains with solvent yielded Al/Si/PS flakes. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy showed that silica and PS nanolayers were formed on the aluminum flakes. The attached PS chains on the surface were detached by hydrofluoric acid aqueous solution and analyzed by gel permeation chromatography (GPC). Also, a transmission electron microscopy image showed clearly that the encapsulating layers are in the scale of nano. Good results were obtained in terms of corrosion protection in acidic and alkaline solutions, indicating that the silica/polymer hybrid nanolayer coating acts as an efficient protective film. After encapsulating the flakes, the evolved hydrogen volume was dropped and hybrid nanolayer resulted in no evolved hydrogen volume.

Ni-SiC nano-composite coatings with various contents of SiC were prepared by pulse electrodeposition from a modified Watts bath containing SiC nano-particles. The effect of SiC concentration, current density, duty cycle and pulse frequency on the corrosion behavior of the coatings was investigated by means of potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) methods. It has been found that the Ni-SiC composite coatings show better corrosion resistance in a 3.5% NaCl solution than pure nickel. The corrosion resistance of the coatings increases by increasing the amount of embedded SIC particles. This improvement can be attributed to the morphology and the crystallographic texture of the coatings.

In this paper a functional graded material (FGM) thermal barrier coating (TBC) is prepared using Atmospheric Plasma Spraying (APS) method. The FGM layers were deposited by varying the feeding ratio of CYSZ/NiCrAlY and conventional CYSZ on a NiCrALY-coated Inconel 738 substrates. Hot corrosion behavior, bonding strength and the related failure mechanisms of a conventional TBC and a FGM TBC are investigated. Hot corrosion studies were conducted in presence of 45% Na2SO4+ 55% V2O5 molten salt at 1000 oC temperature. The as-sprayed coatings and heat-treated coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Exposing to hot corrosion test, the FGM TBC showed better chemical stability and higher life service in comparison to the conventional TBC. As a result, functional graded material thermal barrier coating exhibited very promising potential as a novel TBC material.

In this study, nickel was electrodeposited onto the surface of AZ91 Mg alloy and its corrosion resistance was compared with those of AZ91 Mg alloy and pure nickel using polarization and electrochemical impedance spectroscopy (EIS) experiments in a 3.5 wt.% NaCl solution. The structure of coating was investigated by means of X-ray diffraction, and the specimen’s morphology and the coating’s chemical composition were analyzed using scanning electron microscope (SEM). The results showed that the coating has a nano-crystalline structure with the average grain size of 95 nm. The results of corrosion tests showed a decrease in the corrosion current density from 2.5×10-4 A.cm-2 for the uncoated sample to 1.5×10-5 A.cm-2 for the coated specimen, as well as an increase in the corrosion potential.