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In this work, AlCr and AlCrFe coatings were deposited via magnetron sputtering on technical substrates of carbon steel C45 and titanium grade 2. The coatings feature an amorphous structure, a thickness of 3–4 μm, and are uniform in terms of thickness and chemical composition. No major defects were visible at the interface; however, there is no diffusion at the interface, which indicates the adhesive type of bonding and results in relatively low adhesion. The coatings are characterized by a hardness of about 8–10 GPa and a Young modulus above 150 GPa. Both values are slightly higher for steel substrate. The coatings assure good corrosion resistance for steel substrate while underperforming those of Ti grade 2.

The aim of the present study was to determine the evolution of resistance to pitting corrosion and changes in the mechanical properties of ultrafine-grained aluminium during annealing. In contrast to the numerous papers devoted to the topic of the corrosion resistance of severely deformed aluminium alloys, a unique approach has been taken in this study. The size and distribution of the primary intermetallic particles, which are crucial in terms of corrosion resistance, remain constant during annealing. Therefore, the influence of other microstructural features could be investigated and compare with the results of mechanical properties. It was shown that the ultrafine-grained structure of commercially pure aluminium was stable up to 200 °C. Higher annealing temperatures caused significant grain growth and a reduction in dislocation density, which resulted in a drop in mechanical strength. Also, the corrosion resistance slightly decreased, since with an increase in annealing temperature a decrease in the corrosion potential, pit size, and the area damaged by corrosion attack were noted. The best combination of mechanical strength and resistance to pitting corrosion has been achieved for as-deformed state.

This study describes the role of bimodal grain size distribution on the corrosion resistance of Mg–4Li–3Al–1Zn (LAZ431). The coarse-grained microstructure formed in the alloy after extrusion was compared with the bimodal grain size distribution observed in the alloy after additional annealing. The microstructure observations show that the extruded alloy, as well as the one after subsequent annealing, were composed of α(Mg), MgZn2, coarse AlMn-rich precipitations, and nanosized AlLi, Mg17Al12 and Li2MgAl. The annealing caused microstructure transformation and triggered anomalous and inhomogeneous grain growth of the alloy, which increased the ratio of cathodic grain interiors to anodic high-angle grain boundaries. This decreased the corrosion resistance of the annealed alloy in chloride-containing solution.The results of this work also show that the precipitations play only minor role in corrosion behavior of both alloys, and the major corrosion mechanism occurred between high-angle grain boundaries and grain interiors.

In this paper, the corrosion resistance and mechanical properties of the 7075 aluminum alloy are studied. The alloy was deformed by hydrostatic extrusion and then aged both naturally and artificially. Results are compared with those of coarse-grained material subjected to T6 heat treatment. The aim of the research is to find the optimal correlation between the mechanical properties and the corrosion resistance of the alloy. To this end, static tensile tests with subsequent fractography, open circuit potential, and potentiodynamic polarization tests in 0.05 M NaCl were conducted. Obtained results show that a combination of precipitate hardening and a deformed microstructure leads to increased mechanical strength with high anisotropy due to the presence of fibrous grains. Plastic deformation increases susceptibility to corrosion due to the increased number of grain boundaries, which act as paths along that corrosion propagates. However, further artificial aging incurs a positive effect on corrosion resistance due to changes in the chemical composition of the matrix as a result of the precipitation process.

In this study, the microstructure and corrosion resistance of the as-extruded and as-extruded with subsequent heat treatment Mg-3Al-1Zn-15Li (LAZ1531) alloys have been investigated. The alloys’ microstructures consisted of α(Mg), β(Li), Θ-MgLi2Al and Mg17Al12. As a result of annealing, the β(Li) to α(Mg) transformation occurred, and the recrystallization supported the reformation of the Mg17Al12. The electrochemical tests showed that the increased amount of α(Mg) and higher amount of Mg17Al12 in the heat-treated alloy favored reactions and determined it as having better corrosion resistance in 3.5 wt.% NaCl.

Aluminium (Al) and titanium (Ti) coatings were applied on AZ91E magnesium alloy using a low-pressure warm spray (WS) method. The deposition was completed using three different nitrogen flow rates (NFR) for both coatings. NFR effects on coating microstructure and other physical properties were systematically studied. Microstructural characterization was performed using scanning electron microscopy (SEM), and the porosity was estimated using two methods—image analysis and X-ray microtomography. The coating adhesion strength, wear resistance, and hardness were examined. The protective properties of the coatings were verified via a salt spray test. Decreasing NFR during coating deposition produced more dense and compact coatings. However, these conditions increased the oxidation of the powder. Al coatings showed lower hardness and wear resistance than Ti coatings, although they are more suitable for corrosion protection due to their low porosity and high compactness.

The effect of aging on the resistance to pitting corrosion of ultrafine-grained 7475 aluminium (Al) alloy processed by hydrostatic extrusion (HE) is studied. Differences in the microstructure were investigated using secondary electron (SEM) and transmission electron microscopy (TEM). Corrosion tests were performed in 0.1 M NaCl, and characterization of corroded surface was performed. The results of this work show that the pitting susceptibility of ultra-fine grained 7475Al is related to the distribution of MgZn2 precipitates. After HE, the formation of An ultrafine-grained microstructure at the grain boundaries of ultrafine grains is observed, while subsequent aging results in the formation of MgZn2 precipitates in the grain interior. Grain refinement increases susceptibility to localized attack, while the subsequent aging improves the overall corrosion resistance and limits the propagation of corrosion attack.

The effect of nitriding on the surface structure, mechanical properties and corrosion resistance of hydrostatically extruded 316 LVM stainless steel was evaluated and compared with coarse grained counterpart. Hydrostatic extrusion was performed at either room or elevated temperature and resulted in microstructure refinement. Nitrided layers of a similar thickness were formed on the samples irrespective of their microstructure. The nitriding process was performed at 430 °C for 5 h. The processing conditions did not affect the bulk mechanical properties of the micro and HE processed samples and their mechanical strength remained unchanged after nitriding. The electrochemical measurements revealed that the nitrided hydrostatically extruded 316 LVM steels had better corrosion resistance than their microcrystalline counterpart.

Thermally sprayed coatings are one of the potential ways to increase corrosion performance of Mg alloys dedicated for aircraft applications. In our research, a novel thermal spray process called Warm Spraying (WS) was used to deposit Ti coatings onto AZ91E magnesium alloy. WS gives us the possibility to control the temperature of the sprayed particles by changing the nitrogen flow rate (NFR) what as a result determine the porosity of WS coatings. The microstructure, porosity and oxygen content of coatings deposited under three different NFR was determined. A relation between porosity, oxygen content and NFR was revealed. The corrosion testing in 3.5% NaCl solution of as-sprayed coatings revealed their poor corrosion resistance that led to fast degradation of the substrate. The following post-treatment with epoxy-based polymer resulted in a significant improvement of the corrosion performance of Ti warm sprayed coatings.

Present study investigates the effect of microstructure on electrochemical response of commercially pure aluminium. Electrochemical testing included OCP measurements and potentiodynamic polarization. Results reveal insignificant differences for samples with different grain size, shape and fraction of HAGBs. These parameters are assumed as only slightly affecting electrochemical response. Fe-containing intermetallics have the highest impact, as pits nucleate in their vicinity. In examined materials intermetallic particles retained a consistent size and distribution for all samples. Therefore, no difference in electrochemical parameters or number of pits is observed. The only difference is in the shape of the pits, because dissolution occurred along HAGBs.

This study presents the corrosion and microbiologically influenced corrosion processes of steels in the highly mineralized geothermal water of Polish Lowland. The geothermal sediments were studied using various techniques to confirm the presence of sulphate-reducing bacteria, to determine the chemical composition of deposits and to describe their morphology. On-site and laboratory electrochemical tests were carried out to determine the corrosion rate of selected steels and the influence of sulphate-reducing bacteria to the electrochemical processes.

The present study investigates the correlation between mechanical properties and resistance to corrosion of hydrostatically extruded aluminum alloy 7075. Supersaturated solid solutionized samples undergo a plastic deformation process, followed by both natural and artificial aging. Furthermore, two types of hydrostatic extrusion are applied to the samples: single-stepped and double-stepped. This process is shown to influence grain refinement and the precipitation process, resulting in changes in the electrochemical properties of the samples. Hydrostatic extrusion combined with aging is shown to cause an increase in mechanical strength ranging from 50 MPa to 135 MPa in comparison to coarse-grained sample subjected to T6 heat treatment. The highest value of tensile strength is obtained for a sample subjected to single-step hydrostatic extrusion followed by natural aging. This strength increase is caused by refinement of the microstructure, in addition to the small size and number of precipitates at the grain boundaries, which are coarsened by artificial aging. Hydrostatic extrusion is also shown to increase resistance to corrosion, with the T6-treated coarse-grained sample being most susceptible to corrosion attack.

The effect of temperature and humidity on the heat effect of disposable warmers based on exothermic powder was investigated. A chemical analysis and microscopic observations were performed on exothermic powder consisting of iron powder, sodium chloride, vermiculite, diatomite and active carbon. The heat effect of warmers was investigated at temperatures of 15, 20, 25, 30 °C and humidities of 60, 70 and 80%. The microscopic observations revealed the morphology of the exothermic powder and the oxidation mechanism of the iron particles. The results indicate that temperature significantly affects the heat effect of the warmers investigated, whereas humidity has only a minor impact.

The effect of hydrostatic extrusion (HE) on the microstructure, uniform corrosion, and susceptibility to a localized attack of 316L stainless steel was studied. Both qualitative and quantitative analyses of inclusions before and after HE were carried out. The multiplication of non-metallic inclusions after HE lowered the stability of the passive film over a broad range of pH, while refinement of the matrix had a minor effect on it. The refined materials were prone to metastable pitting, but their pitting corrosion resistance was improved.

The material studied is a commercially available 316LVM stainless steel with an initial grain size of 30 μm. To refine the microstructure down to the nanoscale, hot (at 1000 °C) and room temperature hydrostatic extrusion were applied with a total true strain of 1.4. An annealed sample with coarse grains of 35 μm in diameter was used as a reference sample. The results indicate that after hot hydrostatic extrusion, the microstructure consisted mainly of cells with tangled dislocation walls, while after room temperature hydrostatic extrusion, twins of various width and shear bands could be distinguished. Hydrostatic extrusion is also an efficient way to tailor the corrosion resistance and mechanical properties of 316LVM stainless steel. Performed at room temperature, hydrostatic extrusion resulted in an ultra-high-strength material with limited but sufficient ductility. Performed at high temperature, hydrostatic extrusion resulted in a material with a very good combination of strength (approximately 900 MPa) and ductility (elongation to failure higher than 20%). Both hydrostatically extruded steels maintained good passivation behavior in 0.1 M H2SO4. In the presence of chloride ions, susceptibility to localized attack increased for the steel extruded at room temperature, but did not change for the hot-extruded steel. Keywords: Austenitic stainless steel, Hydrostatic extrusion, Severe plastic deformation, Dynamic recrystallization, Corrosion resistance

Corrosion tests were carried out to study the corrosive behaviour of medium carbon steels with a ferrite–pearlite microstructure during exposure to a synthetic flowback facturing fluid saturated with carbon dioxide. Metallographic investigations, screening tests, surface morphology investigations and identification of surface products were used for this purpose. The results obtained indicate that the corrosion of N80-1 carbon steel was significantly lower than that of K55 carbon steel. The layer of corrosion products consisted of an outer layer of carbonates and an inner layer with cementite lamellas. Higher grain refinement of N80-1 steel compared to that of K55 steel caused the formation of a denser, more homogenous layer of corrosion products, which significantly reduced the corrosion of the base material.

The formation, chemical composition and especially electrochemical reactivity of the passive oxide formed on the Al64.2Cr27.2Fe8.1 (at. %) and Al66.9Cu11.6Fe11.6Cr10.6 (at. %) complex metallic alloys (CMAs) were investigated in borate buffer electrolyte of pH8.4 and 0.1 M Na2SO4 electrolyte of pH 12. Open Circuit Potential evolution, potentiodynamic and potentiostatic anodic polarisation as well as electrochemical impedance measurements revealed high stability of the investigated materials in the alkaline domain relevant to cathodic areas. The high stability of these phases is attributed to the presence of a passive oxyhydroxide layer consisting of thin chromium oxyhydroxide as outermost layer and an inner aluminium oxyhydroxide layer close to the metal/oxide interface as found by XPS. The semiconducting properties characterised by means of photoelectrochemistry reveal further that the bandgap of the passive oxide on the CMAs corresponds to a less hydrated situation (closer to alumina) compared to the one grown on pure Al, thus supporting the higher stability of the CMAs phases.

The corrosion mechanisms of Al Cr Fe and Al Cu Fe Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al Cr Fe surface is exhibited from 1 M H2SO4 to 1 M NaOH solutions which was confirmed by ICP OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy hydroxide film. Although Al Cu Fe Cr showed passivation during potentiodynamic polarization heavy active corrosion at OCP was revealed by ICP OES. For the Al Cu Fe Cr alloy the 10 content of Cr is insufficient to maintain a protective "chemically stable" Cr oxide/hydroxide. (c) 2011 Elsevier Ltd. All rights reserved.

Al-based complex metallic alloys (CMAs) are crystalline intermetallic phases characterised by very complex crystal lattices, showing intriguing surface properties such as low wetting, low friction and hardness which include, for the Al–Cr–Fe system, high corrosion resistance. However, their passivation mechanisms (nm-thick oxide layer formation) still need to be understood in relation with localised corrosion susceptibility. New single phases were therefore characterised by electrochemical Microcell technique. The chromium cations in the oxide proved to play a significant role in stabilising the passive layer at low pH. Corrosion resistance of single- and polycrystalline samples was first compared by means of inductively coupled plasma mass spectrometer (ICPMS) analysis during immersion. Higher dissolution rates have been measured for the low Cr containing (12.5 at%) polycrystals compared to the single crystals. The resistance to localised corrosion attack of the single crystals in an aggressive 0.01 M HCl + 1 M NaCl solution at pH 2 was high, with an anisotropic behaviour of the anodic breakdown potential related to the grain orientation. The orthorhombic (0 0 1) termination with higher Cr/Al atoms ratio formed a passive layer with increased resistance against pitting. Ageing of the samples and the formation of surface Al oxy-hydroxide appeared to decrease the pitting corrosion resistance.

Joints made from ultrafine grained aluminium alloy 1050 are investigated in order to examine the corrosion behavior and microstructural changes between base materials and stir zones. Samples in the initial state, after four and eight passes of Incremental ECAP (I-ECAP) process were joined with similar plates using Friction Stir Welding. Initially refined microstructure after I-ECAP transformed to homogenous few micron sized grains structure in stir zones. AlFeSi particles present in the microstructure became fragmented during plastic deformation and welding process. The observed minor differences in corrosion resistance include slightly higher values of corrosion potentials but more complex pits' morphology for I-ECAP processed samples comparing to the stir zones.