The contribution is aimed at corrosion propertied and wettability of basic graded of stainless steel commonly used in medicine as a standard for construction of instruments and other applications. Samples of AISI 304 (1.4301) steel were chemical passivated by nitric acid and tested for corrosion resistance in environment of sodium hypochlorite (NaClO), which is commonly used for basic disinfection of surfaces or devices in hospital facilities. It was found that chemical passivation of stainless steel surface increases its corrosion resistance and lower corrosion rate. Passivation layer also shows more polarization resistance. The wettability of passivated surface was measured by sessile drop method. Wettability itself determinates effectivity of disinfection process as the surfaces with lower contact angle may be cleaned and disinfected with more efficiency. It was proofed that chemical passivation increases wettability by lowering contact angle of treated surface.
In this paper corrosion properties and microstructure features of amorphous self-organised TiO2 nanotubes electrochemically deposited on titanium are discussed. There was titanium of second grade used as a substrate for these experiments. There was a specific solution of ammonium fluoride, ethylenglycol and deionized water used to create an oxide layer with advantageous properties. Relation between changes of roughness indexes before and after anodization was found out. The wettability (contact angle) of artificial plasma on surface was measured using sessile drop method. It was found out that titanium dioxide nanotubes formed on the surface significantly decreases contact angle and time of anodization reduces it even more. Corrosion potentials, corrosion rate or polarization resistance were determined by linear polarization methods performed by ASTM standards. Corrosion potential of anodized samples is substantially more positive (≈ -50mV) compared with non-treated sample (≈ -280mV). On the other hand polarization resistance was significantly higher for non-treated sample. Also potentials of passive layer breakdowns were found. Structure of nanotubes and influence of anodization on surface profile was studied by SEM.
Three types of corrosion attack frequently suffered by type Cr18Ni10 stainless steel in the
heat-affected zone of welds were studied – knife-line, fusion-line, and fissure corrosion. Possible
mechanisms and selected preventative measures were discussed in the light of microstructural
findings.
The wide application of Nd-Fe-B permanent magnets in addition to the rare-earth metal resource constrains determine the necessity of their recycling. One of approaches to magnet-to-magnet recycling consists in using the grain boundary modification of sintered magnet material, which includes the grain-boundary diffusion (GBD) and grain-boundary structuring (GBS). The preparation of magnets with the modified structure determines a need for research their corrosion resistance. The corrosion resistance of magnets prepared by powder blending techniques, namely, magnets, which were recycled from hard-disk drivers, in using Dy/NdH2 additions in the powder mixture and magnets, which were prepared from strip-casting alloy, in using TbH2 hydride in the powder mixture, is studied. The corrosion potential and polarization resistance were measured, and the average corrosion rate was estimated based on polarization measurements of the magnet samples in the aqueous solution 0.1 M NaCl. Furthermore, a pitting resistance corrosion test was conducted and the values of pitting and repassivation potential were determined. The corrosive properties of the magnet samples are discussed from the viewpoint of the phase compositions of the material.
Certain failures of stainless steels interpreted purely in terms of fracture mechanisms may in fact be closely associated with previous damage caused by localized corrosion. The closeness of the link between fatigue and corrosion is documented by the case history of compressor blades made of grade 14Cr17Ni2 (X14CrNi17-2) stainless steel. Fatigue fracturing observed in areas near the blade root tended to follow intergranular pathways, indicating that some additional mechanism other than fatigue might be involved. This suspicion was confirmed by electrochemical potentiokinetic reactivation (EPR) measurements in situ, which revealed sensitization to intergranular corrosion. It has been found that at the transition between the blade root and the blade proper the surfaces had been ground and polished too vigorously, heating the subcutaneous layers to within the danger zone of 400-600°C. Preferential integranular attack in these locations was the initiation mechanism that provoked a subsequent failure of the blades by fatigue fracture. Abstrakt Určité poruchy korozivzdorných ocelí zdůvodňované čistě ve smyslu lomové mechaniky mohou být ve skutečnosti úzce spojeny s dřívějším poškozením způsobeným místní korozí. Souvislost mezi únavou a korozí představuje případ lopatek kompresoru vyrobených z korozivzdorné oceli typu 14Cr17Ni2. Únavové poškození (praskání) pozorované v oblastech blízko paty lopatky má tendenci sledovat mezikrystalovou cestu. To naznačuje, že přichází v úvahu i jiný mechanismus vzniku trhlin, než je únava materiálu. Toto podezření bylo potvrzeno elektrochemickým potenciokinetickým reaktivačním (EPR) měřením "in situ-, které odhalilo zcitlivění k mezikrystalové korozi. Bylo zjištěno, že v přechodu mezi patou lopatky a ostatními povrchy byla broušena a leštěna příliš razantně a došlo k ohřátí povrchových vrstev v rozsahu teplot 400-600°C. Přednostní mezikrystalové napadení v těchto místech bylo iniciačním mechanizmem pro vyvolání následujícího poškození lopatek únavovým lomem.
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