Volume 61 (2017): Edizione 5 (December 2017)

Nowadays a large number of mechanical surface treatments of constructions materials is used in industry, mainly focusing on steel surface treatment. The aim of this study was to evaluate the effects of mechanical surface pre-treatment (grinding and shot peening) on corrosion resistance of high strength low alloy Domex 700 steel. Suitable mechanical surface treatment can by used for surface homogenization (eg. grinding) or for improvement of mechanical, strength and fatigue properties (shot peening). 0,1M NaCl solution of ambient temperature was used as an environment for electrochemical tests. Evaluation of the mechanical surface treatment effect on corrosion resistance of Domex 700 steel surface was realized by electrochemical tests: potentiodynamic polarization tests (using Tafel analysis) and electrochemical impedance spectroscopy (using equivalent circuit). From the obtained results it is possible to conclude, that the process of mechanical surface treatment by shot peening at choosen conditions has negative effect on corrosion resistance of Domex 700 steel.

Increasing of nuclear safety, higher demands for longer nuclear fuel campaign and higher levels of burnout are based on improving the properties of zirconium alloys. Protective coatings appears to be a promising way to reduce their chemical reactivity and increase resistance to hydriding. In this work, a thin chromium coating applied to a standard Zr1Nb zirconium alloy was studied using in-situ impedance spectroscopy. Exposure was carried out at a temperature of 280 ° C and a pressure of 8 MPa in a simulated WWER primary coolant environment. The results show that the chromium-coated Zr1Nb alloy is under these conditions oxidized significantly slower than the non-coated alloy.

This paper deals with the behavior of the ferritic-martensitic steel T91 samples covered with an AlTiN black coating, which is mainly used for high temperature applications (> 800 ° C) because of its resistance to oxidation. The coating was applied by use of a combination of High Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (DCMS). Samples were subjected to a tensile test in a static tank CALLISTO. The environment was liquid PbBi eutectic at a temperature of 550° C. Two types of samples, with a notch in the middle and without a notch, were tested. After exposure, the samples were subjected to morphological and chemical analyzes on SEM and EDX. Although the coating cracked over the entire length of the sample, high adhesion of the layer was demonstrated, the coating was delaminated locally only in the notch.

Vliv střídavého indukovaného proudu na korozní rychlost oceli St3 a 17GS byl pozorován v simulovaných půdních elektrolytech typických pro Ukrajinu. Ocel St3 je citlivější na přirozené korozní napadení v půdě i na napadení vyvolané střídavým proudem. Byla stanovena nejhorší prostředí z hlediska koroze v elektrolytech obsahujících chloridy či směs chloridů se sírany.

This paper describes behaviour of the ferritic-martensitic steel T91 after long-term exposure in liquid eutectic PbBi. Small specimens of the steel were pre-loaded according to the ISO Standard No. 7539-2 and subsequently exposed to PbBi. The experiment was carried out in a flowing and static liquid metal medium at 350°C. The experimental time was selected for the flowing environment at 1000 hours and for static environment at 2000 hours. After exposure, the specimens were analysed by use SEM and EDX. Surface changes of the specimens from different experimental conditions were compared and discussed. The initiation of the cracks wasn´t observed in the monitored expositions.