Volume 60 (2016): Edizione 5 (December 2016)

Magnesium and its alloys are perspective bio-degradable materials used mainly due to their mechanical properties similar to those of mammal bones. Potential problems in utilization of magnesium alloys as bio-materials may relate to their rapid degradation which is associated with resorption problems and intensive hydrogen evolution. These problems can be eliminated by magnesium alloys surface treatment. Therefore, this work aims with analysis of the influence of fluoride conversion coating on corrosion characteristics of magnesium alloy. Unconventional technique by insertion of wrought magnesium alloy AZ61 into molten Na[BF₄] salt at temperature of 450 °C at different treatment times was used for fluoride conversion coating preparation. The consequent effect of the coating on magnesium alloy corrosion was analyzed by means of linear polarization in simulated body fluid solution at 37 ± 2 °C. The obtained results prove that this method radically improve corrosion resistance of wrought AZ61magnesium alloy even in the case of short time of coating preparation.

This study is focused on an influence of heat transfer on corrosion behaviour of structural materials for radioactive waste canister in synthetic bentonite pore water and bentonite suspension. Experiments were carried out in special cell on cylindrical sample of carbon steel, copper, titanium-palladium alloy and two types of stainless steel. Samples were subjected in synthetic bentonite pore water to sixty-fold higher heat transfer compared to real repository, and approximately thirty-fold higher in bentonite suspension. Corrosion behaviour was observed in two-electrode setup with platinum wire as counter electrode by means of electrochemical impedance spectroscopy. Results showed negligible effect of heat transfer compared to surface temperature.

In this work, the main aim is focused on the decomposition products of film-forming amines which are used as corrosion protection of devices against surface corrosion at frequent short outages. Filming amines are a mixture of volatile alkaline and contact organic amines, which protect both the water and the steam environment. It was confirmed, the organic matter is not stable at high temperature and decomposes to organic acids with short chain (acetic, formic) which decrease pH value and increase conductivity value.

The article is aimed at evaluation of chosen properties of thermally sprayed coatings based on tungsten carbide. It was evaluated two types of coatings – WC-FeCrAl and WC-WB-Co. The coatings were deposited on basic material steel AISI 316L. The aim of experimental works was to determine the quality and resistance of coatings in corrosion environment depending on number of thermal cycles. The quality of coatings was evaluated by determination of their adhesion depending on thermal cycles, determination of microhardness and indentation fracture toughness. Coatings were exposed in tribo-corrosion conditions with the presence of 1% NaCl. The results of experimental showed a higher quality of coating WC-WB-Co.

Clinching is a joining method in which sheet metal parts are deformed locally by creating a mechanical interlock without the use of any additional elements such as screws or rivets. Steel sheets are plastically deformed and the shape of the tools remains theoretically unchanged during the clinching process. The clinching tool with a rigid die of ø5 mm with a specially formed gap and a punch of ø3.6 mm were used for mechanical joining of hot-dip galvanized dual-phase steel sheets HCT600X of 0.8 mm thickness. The punch and die were deposited by PVD coating of CrN and TiCN type with LARC technology. The state of the coating was evaluated and documented by scanning electron microscopy – SEM. The wear of the coating was evaluated after each 50 manufactured joints starting with the initial state of tool.