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Povzetek: The impact of the microstructural properties of a Ti6Al4V alloy on its electrochemical properties, as well as the effect of the α- and β-phases present within it, is still unclear. With the introduction of new, emerging technologies, such as selective laser melting and post heat treatments, the effect of the microstructure on an alloy's corrosion properties has become increasingly interesting from a scientific perspective. When these alloys are produced through different methods, despite an identical chemical composition they have diverse microstructures, and consequently display varying resistance to corrosion. In the present research study, Ti–6Al–4V alloy specimens produced by three different processes, leading to the formation of three different microstructures were investigated: heat treated specimen fabricated by selective laser melting, wrought and cast specimens. The impact of the microstructure of these alloys when immersed in artificial saliva was studied through the use of various electrochemical techniques, by microscopical examinations, and time-of-flight secondary ion mass spectrometry. Corrosion properties were investigated by the measurement of open circuit potential, linear polarization, and potentiodynamic curve measurements followed by microscopical examinations, and time-of-flight secondary ion mass spectrometry examination was conducted to reveal spatial distribution of alloying species on oxide film. It was found that the difference between specimens containing an α+β microstructure was small and not dependent on the aspect ratio of the β-phase, alloy grain size, and vanadium partitioning coefficient, but rather on the size, shape, and content of this phase.
Ključne besede: Ti6Al4V, dental alloy, microstructure, corrosion resistance, heat treatment, ToF-SIMS
Objavljeno v DiRROS: 26.10.2023; Ogledov: 457; Prenosov: 228
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Povzetek: Bronze reacts with oxygen, humidity, and pollutants in the atmosphere so that a patina forms. Natural exposure to an outdoor atmosphere can be simulated and accelerated in order to achieve a patina that mimics outdoor ancient patina. In order to avoid the uncontrolled dissolving of either the natural or artificially formed patina, protection of the patina is needed. In this study, a multi-component fluoropolymer based coating for the protection of bronze patina was developed. In order to provide various functionalities of the coating (such as the hydrophobicity of the coating surface, obtaining interactions within the coating itself as well as a bronze substrate and inhibiting the corrosion processes), a fluoroacrylate coating with appropriate adhesion promoter was suggested, with and without a silane modified benzotriazole inhibitor. The protective efficiency and durability of the applied coatings were investigated electrochemically using potentiodynamic tests and electrochemical impedance spectroscopy in a simulated acid rain solution. All of the developed coatings showed a significant decrease in the corrosion current density. The self-assembled single layer coating (FA-MS) also showed 100% inhibition efficiency. After ageing the coating remained transparent and did not change by UV exposure and/or thermal cycling. The patina and coating investigations using FIB-SEM and EDX showed that the latter coating (FA-MS) successfully covered the surface of the patinated bronze. The mechanism of the bonding was proposed and supported with the spectroscopic observation of a thin and even coating.
Ključne besede: bronze, patina, fluoropolymer coating, atmospheric corrosion
Objavljeno v DiRROS: 25.10.2023; Ogledov: 345; Prenosov: 186
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Povzetek: Blended cements might change the chemistry of the pore solution and subsequently affect the corrosion of steel in concrete. Pore solutions were extracted, analyzed and compared from mortars made of CEM I, CEM II, CEM III and CEM IV cements. Three combinations of carbonation and chloride states were studied, i.e., non-carbonated without chlorides, non-carbonated with chlorides and carbonated with chlorides. Different electrochemical and spectroscopic techniques were used to study the electrochemical properties, the type and the extent of the corrosion products, as well as the type and the extent of the corrosion damage. It was confirmed that the most corrosive environments were pore solutions extracted from the carbonated mortars with chlorides. In this environment the highest corrosion rate was observed for the CEM III pore solution, and the lowest for the CEM I. The extent and the type of corrosion products and the corrosion damage varied according to the environment.
Ključne besede: corrosion, blended cements, pore solution, mortar
Objavljeno v DiRROS: 14.09.2023; Ogledov: 292; Prenosov: 111
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Povzetek: The applicability of an accelerated test technique using tapered tensile specimens for investigating the stress corrosion crack (SCC) initiation behaviour of structural materials in high-temperature water was assessed in the framework of a European collaborative research project (MICRIN – MItigation of CRack INitiation). The main advantage of using a tapered geometry is, that in a single test a stress gradient is obtained through the gauge length, and therefore a stress threshold for SCC initiation can be determined in a reasonable timeframe. This method was used to investigate two different materials that were known to be susceptible to SCC in light water reactor environment: a high-Si stainless steel and a Ni-base weld metal (Alloy 182). The results of the international test programme confirmed that the tapered specimen test methodology could be used to identify a SCC initiation stress threshold, albeit that significant scatter was present in the data.
Ključne besede: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Objavljeno v DiRROS: 28.08.2023; Ogledov: 275; Prenosov: 147
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Povzetek: Reinforced concrete structures require continuous monitoring and maintenance to prevent corrosion of the carbon steel reinforcement. In this work, concrete columns with carbon and stainless steel reinforcements were exposed to a real marine environment. In order to monitor the corrosion processes, two types of corrosion probes were embedded in these columns at different height levels. The results from the monitoring of the probes were compared to the actual corrosion damage in the different exposure zones. Electrical resistance (ER) probes and coupled multi-electrodes (CMEs) were shown to be promising methods for long-term corrosion monitoring in concrete. Correlations between the different exposure zones and the corrosion processes of the steel in the concrete were found. Macrocell corrosion properties and the distribution of the separated anodic/cathodic places on the steel in chloride-contaminated concrete were addressed as two of the key issues for understanding the corrosion mechanisms in such environments. The specific advantages and limitations of the tested measuring techniques for long-term corrosion monitoring were also indicated. The results of the measurements and the corrosion damage evaluation clearly confirmed that the tested stainless steels (AISI 304 and AISI 304L) in a chloride-contaminated environment behave significantly better than ordinary carbon steel, with corrosion rates from 110% to 9500% lower in the most severe (tidal) exposure conditions.
Ključne besede: corrosion in concrete, steel reinforcement, long-term exposure, field exposure, electrical resistance (ER) probes, coupled multi-electrodes
Objavljeno v DiRROS: 21.08.2023; Ogledov: 246; Prenosov: 154
Celotno besedilo (4,42 MB)
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