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Copper is commonly used in many applications such as electric wires, industrial machinery, boat propellers and heat exchangers. Although Cu is resistant to corrosion in ambient conditions, it is highly susceptible when exposed to harsh environments such as high-temperature air or marine atmospheres. The application of magnesium or aluminum coatings on Cu can efficiently smooth this disadvantage without affecting its primer properties. In the herein investigation, the deposition of these coatings was accomplished by pack cementation, a simple electrochemical technique which can be easily incorporated in the industrial scale. The final coatings were tested under high temperature environments by non-isothermal (dynamic) and isothermal thermogravimetric measurements, and in artificial sea water (3.5 wt.%-NaCl) by electrochemical corrosion. The structure of both coatings was compact with elevated thickness. The oxidation and corrosion measurements revealed that the coated samples had much better performance compared to the uncoated copper coupons. Furthermore, Al coatings were found to have the best performance when exposed in high temperature environment.

Nickel aluminides are ideal materials for protective coatings because they possess high-temperature oxidation resistance and low corrosion rates in marine atmospheres. In this work, a double layered coating was formed by the electrochemical deposition of an initial Ni layer followed by an Al top layer deposited by pack cementation. The coatings were found to contain several Ni-Al on the upper areas and Ni-Fe phases on the substrate/coating interface, as a result of Ni diffusion during the aluminization step. Thermogravimetric high temperature oxidation tests and electrochemical corrosion measurements revealed significant increase of the samples’ resistance, compared to the uncoated steel.

Corrosion properties of nanostructured coatings deposited by Suspension High Velocity Oxy-Fuel (S-HVOF) via an aqueous suspension of milled WC-Co powder were compared with conventional HVOF sprayed coatings. Microstructural evaluations of these coatings included X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The corrosion performance of AISI440C stainless steel substrate and the coatings was evaluated in a 3.5 % wt. NaCl aqueous solution at ~25oC. The electrochemical properties of the samples were assessed experimentally, employing potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The potentiodynamic polarization results indicated that coatings produced by S-HVOF technique show lower corrosion resistance compared to the coatings produced by HVOF-JK (HVOF Jet-Kote) and HVOF-JP (HVOF JP5000) techniques. Results are discussed in terms of corrosion mechanism, Bode and Nyqvist plots, as well as equivalent circuit models of the coating-substrate system.

The corrosion behaviour of cenospheres metal matric syntactic foams of different compositions in 3.5 wt-% NaCl aqueous solution at ∼25°C was investigated. The electrochemical properties of the composites were assessed experimentally, employing potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. Appropriate equivalent electrical circuits were proposed. Results showed that the corrosion rate is higher for the metal matrix syntactic foams compared to pure sintered aluminium. As the volume fraction of cenospheres increases cenospheres fragments and the presence of reaction zones seems to have a greater effect on the corrosion behaviour of the composites compared to the presence of unintended porosity.

Metal matrix syntactic foams of ceramic (mullite) cenospheres (10–40% v/v) embedded in pure aluminium matrix, were fabricated by powder metallurgy technique at different sintering temperatures (610–710 °C). Density, vis-a-vis porosity and microstructural characteristics were examined by using scanning electron microcopy and energy dispersive X-ray spectroscopy. A first systematic description of the sintering mechanism of the composites is presented. The in situ reaction between silica (phase of mullite) and aluminium particles, apart from any degradation of the mullite cell wall and the precipitation of silicon in the matrix, changes the sintering mechanism of syntactic foams due to the formation of eutectic aluminium–silica liquid quantities. Transient liquid phase sintering, with surface material diffusion, and liquid phase sintering, with bulk diffusion, selected to be the main sintering mechanisms, are described in detail for sintering temperatures below and above the melting point of aluminium matrix, respectively.

Corrosion behaviour of 304 austenitic stainless steel in simulated oilfield produced water at ∼25°C was investigated. The electrochemical properties of 304 stainless steel were assessed experimentally employing potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. The corrosion mechanism of 304 stainless steel in simulated oilfield produced water along with appropriate modelling equivalent electrical circuits were deducted. Results showed that the corrosion rate is reduced with time. This behaviour does not indicate protection of 304 stainless steel. Instead, pits were formed on the surface of the specimens, and their evolution continued with time.

Aluminum–cenospheres syntactic foams of different compositions and varying relative densities were fabricated by powder metallurgy using a low compaction load (ranging from 200 MPa to 300 MPa). The produced composites were examined in terms of density, porosity, macro- and micro-structural characteristics. Mechanical properties of the sintered samples, like compressive strength and deformation mechanisms, quasi-elastic modulus and absorbed energy were also investigated. A novel theoretical model reflecting the compressive strength of aluminum–cenospheres syntactic foams was developed with respect to the production conditions (compact pressure) of the “green body”. Finally, the influence of the powder metallurgy route on the deformation mechanisms and fracture strength of the metal matrix syntactic foams was elicited, providing refined insight to optimum production parameters. The yielded results stipulate that characteristic properties like porosity inhomogeneity or insufficient bonding between matrix particles have a direct impact on the final properties of metal syntactic foams. As the compact pressure and the volume fraction of the cenospheres increases, composites exhibit a mechanical response typical of metal matrix syntactic foams. Keywords: Metal matrix syntactic foams, Mechanical properties, Powder metallurgy, Fracture

In the present study, pressure infiltration is employed to synthesize aluminum alloy 7075-fly ash composites. The microstructure and chemical composition of the fly ash and the produced composite material was examined using optical and scanning electron microscopy, as well as x-ray diffraction. Several properties of the produced composite material were examined and evaluated including macro-hardness, wear, thermal expansion, and corrosion behavior. The wear characteristics of the composite, in the as-cast conditions, were studied by dry sliding wear tests. The corrosion behavior of composite material was evaluated by means of potentiodynamic corrosion experiments in a 3.5 wt.% NaCl solution. The composite specimens exhibit a homogeneous distribution of fly ash particles and present enhanced hardness values, compared to the matrix material. The high volume fraction of the fly ash reinforcement (>40%) in the composite material led to increased wear rates, attributed to the fragmentation of the fly ash particles. However, the presence of fly ash particles in the Al alloy matrix considerably decreased the coefficiency of thermal expansion, while resulting in an altered corrosion mechanism of the composite material with respect to the matrix alloy.

Conventional anodizing and carbon deposition coating treatment is applied to open-cell Al foams aiming to enhance the corrosion performance of the material. The Al foams used were fabricated utilizing a dissolution-sintering technique based on powder metallurgy route. X-ray computed tomography and SEM were utilized to assess the structural characteristics of the produced foams. The corrosion properties of all samples produced were assessed experimentally, employing both polarization curves and EIS measurements utilizing a 0.6 M NaCl aqueous solution. Corrosion mechanisms along with appropriate modeling circuits were deduced. Both anodizing and carbon coatings resulted in an augment of the corrosion properties of the Al foams.

In this paper, a methodology to optimize the production technique and properties of fly ash porous preforms, for liquid metal infiltration, is introduced. The preforms were produced by mixing fly ash with acid phosphate binder and acetone as liquid carrier, at varying compositions. The homogeneity of the green product was determined by micro computed tomography (μCT) and scanning electron microscopy. The effect of binder quantity, porosity, and compaction pressure of the preforms on the resulting bending strength was investigated and considered as one of the criterions for the production of crack-free metal matrix composites (MMCs). Finally the quality of the MMCs, resulting by liquid metal infiltration of the optimized preforms, was examined by μCT to locate micro cracks and uniaxial compression to determine variations in their compressive strength.

The effect of an external magnetic field on the corrosion behaviour of a galvanic couple, zinc (Zn)–stainless steel (SS 316L), has been investigated in a 0·055 mol L−1 potassium chloride (KCl) solution. The impact of the orientation as well as the magnetic flux density B (Wb m−2) on the corrosion progression of the galvanic couple, is evaluated heuristically by monitoring the corrosion potential Ecorr (mV) and the current density Icorr (μA cm−2) of the system. A strong influence of the magnitude and orientation of the magnetic field on the Zn–SS316L galvanic couple corrosion was observed, whereas the field was proven to act either protective or accelerating in terms of corrosion.

The aim of this paper is to obtain an experimental characterization of glucose-carburized substrates of α-Fe. The carburization process was achieved under vacuum condition using glucose as a carburizing medium. The process was carried out at several temperatures keeping the duration constant at 2h. The samples were treated at 400°C, 650°C and 900°C. The microstructure of the as produced coatings was observed by Scanning Electron Microscopy (SEM) and the formed phases were analyzed by X-Ray Diffraction (XRD). To investigate the corrosion properties of the carburized iron specimens, electrochemical tests were conducted. The samples were exposed to a solution of 3.5% wt. NaCl electrolyte, under quiescent conditions at room temperature and open to the air. The corroded samples were observed with use of Optical Microscopy in order to evaluate the corrosion effect on their surfaces. Carburization of iron samples at temperatures up to 650°C resulted in a shift of the polarization curves to lower current densities. Smaller corrosion rates were measured indicating higher corrosion resistance for these specimens.

The corrosion performance of two porous NiTi in physiological and Hank's solutions was investigated by potentiodynamic polarization, cyclic polarization and impedance spectroscopy. Electric models simulating the corrosion mechanism at early stages of immersion were proposed, accounting for both microstructural observations and electrochemical results. Results indicate that both porous samples were susceptible to localized corrosion. The porosity increase (from 7% to 18%) resulted in larger and wider pore openings, thus favoring the corrosion resistance of 18% porous NiTi. Strengthening of corrosion resistance was observed in Hank's solution. The pore morphology and micro-galvanic corrosion phenomena were determining factors affecting the corrosion resistance.