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Depassivation and repassivation of stainless steels by stepwise pH change
Emir Mujanović, Bojan Zajec, Andraž Legat, Tadeja Kosec, Janez Kovač, Gregor Mori, Stefan Hönig, Gerald Zehethofer, 2020, izvirni znanstveni članek

Povzetek: Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.
Ključne besede: stress corrosion cracking, surface finish impact, tapered tensile specimen, autoclave, accelerated testing, light water nuclear reactor, critical threshold stress
Objavljeno v DiRROS: 30.08.2023; Ogledov: 73; Prenosov: 25
.pdf Celotno besedilo (4,01 MB)
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Effect of laser texturing pattern on Ti6Al4Vtribocorrosion in a physiological solution
Marjetka Conradi, Tadeja Kosec, Bojan Podgornik, Aleksandra Kocijan, Janez Kovač, Damjan Klobčar, 2022, izvirni znanstveni članek

Povzetek: Laser texturing is a process that alters a material’s surface properties by modifying its morphology, which can improve properties like adherence, wettability, thermal and electrical conductivity and friction. Here, the effect of laser texturing was studied on an alpha-beta titanium alloy (Ti6Al4V) biomedical material. Two types of patterned surfaces, cross-hatch with varying scan-line separations, Dx = 100, 180 and 280 μm and dimples of 200 μm size, were prepared on the surface of alpha-beta titanium alloy by laser technology. Prepared samples were characterised for their surface properties, such as corrosion, wear-induced corrosion, friction and wettability. Electrochemical and tribocorrosion properties in a physiological solution were studied on the samples with different texture densities of cross-hatch pattern and dimples and compared to the as-received alpha-beta titanium alloy surface. Corrosion rate decreased for laser-textured samples, especially for cross-hatch texture (down to 1 μm/year for Dx = 180 μm) when compared to the as-received alpha-beta titanium alloy surface due to the changed laser-induced surface film and wetting properties. Friction coefficient slightly decreased for all laser-textured surfaces, most noticeably for cross-hatch patterns, from 0.38 (as-received) down to 0.34 (Dx = 180 and 280 μm). The main contribution to total wear in physiological solution increased due to the mechanical wear, which is governed by the removal of the surface oxide layer induced by laser texturing.
Ključne besede: TiAIV, laser texturing, tribocorrosion, open access
Objavljeno v DiRROS: 17.05.2023; Ogledov: 82; Prenosov: 30
.pdf Celotno besedilo (2,19 MB)
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