Volume 61 (2017): Edizione 4 (October 2017)

The main advantage of magnesium and its alloys is high specific strength and biocompatibility. A modern approach to magnesium-based materials preparation is powder metallurgy. This technique allows preparation of new materials with a unique structure, chemical composition, and controlled porosity. In this study, cold compaction of magnesium powder was studied. Magnesium powder of average particle size of 30 μm was compacted applying pressures of 100 MPa, 200 MPa, 300 MPa, 400 MPa and 500 MPa at laboratory temperature. Influence of compacting pressure was studied with microstructural and electrochemical corrosion characteristics analysis. The resulting microstructure was studied in terms of light and electron microscopy. Obtained electrochemical characteristics were compared with those of wrought magnesium. Compacting pressure had a significant influence on microstructure and electrochemical characteristics of prepared bulk magnesium. With the increase in compaction pressure, the porosity decreased. Compacting pressures of 300 MPa, 400 MPa and 500 MPa led to the similar microstructure of the prepared material. Polarization resistance of compacted magnesium was much lower and samples degraded faster when compared to wrought magnesium. Also, the corrosion degradation mechanism changed due to the microstructural differences between the material states.

The paper evaluates extent of corrosion damage to composite glass-fibre fabric reinforcement in environment simulating concrete pore solutions (pH 12.6, 13.0, 13.5) and carbonated concrete contaminated with chlorides (pH 8.1 + Cl^-) using the FT-IR and SEM/EDS techniques. Also, the effect of corrosion damage on tensile strength of segmented glass fibre as well as the presence of specific protective organic coating on glass fibre were studied. The results demonstrate local corrosion damage of samples at pH 13.5 and on the other hand high stability in environment simulating carbonated concrete and carbonated concrete contaminated with chlorides. The study also suggests unevenness of organic coating with occurrence of localized porosity which is related to aforementioned corrosion damage. Corrosion damage in FT-IR spectra manifests by changes in peaks signalling hydrolysis of protective organic coating and occurrence of peaks suggesting presence of Ca²⁺ rich corrosion products.

Carbon Capture and Storage (CCS) technologies are a perspective solution to reduce the amount of CO2 emissions. One of promising methods is Ca-looping, which is based on carbonation and calcination reactions. During both of these processes, especially calcination, high temperatures (650-950°C) are required. This means high demands on the corrosion resistance of equipment materials. Therefore, we carried out a study to suggest materials with suitable properties for calciner construction, which have to be particularly heat resistant: stainless steels (AISI 304, AISI 316L and AISI 316Ti) and nickel alloys (Inconel 713, Inconel 738, Incoloy 800H). A special device simulating calciner environment was built for this purpose. Chosen materials were tested in temperature 900°C, atmospheric pressure and gaseous environment with composition that can be possible in a calciner. The surfaces of materials were evaluated to determine composition and properties of formed oxide layers. High temperature oxidation was observed on all tested materials and oxide exfoliation occurred on some of tested materials (304, 316L).

In the present study, we investigated the influence of hammer peening (HP) with tungsten carbide surface coating (WCSC) on high cycle bending fatigue performance of the carbon steel (CS) manufactured as specified in Bureau of Indian Standards BIS 2062 steel. Totally there are twenty-four numbers of specimens cast and tested to investigate fatigue performance. Constantly high cycle bending fatigue load (HBFL) were applied for all specimen, different range of bending stress applied to the specimen and the stress ratio maintained as R = 1. Investigation results show there is up to 40 percent of the fatigue life improvement possible by the surface treatments to the CS material. From the research to date the corrosion and pitting corrosion can be treated by modifying the surface layer of the metal by treating different peening methods and coating.

An overview of protection mechanisms of organic coatings for metallic constructions and products is given. The barrier effect of coatings and protection in local defects are discussed. Basic degradation mechanisms of organic coatings such as anodic and cathodic delamination in vicinity of defects, osmotic and cathodic blistering, mechanical stress assisted blistering, loss of adhesion and chalking are described. Appropriate laboratory tests are proposed for each degradation mode.