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This work investigates the evolution from superhydrophilic to superhydrophobic surface state on corrosion behaviour of SS316L produced by Nd:YAG nanosecond direct laser texturing (DLT). Results confirm perfect correlation among wettability and corrosion, hence superhydrophobic surface with a contact angle of 168 ± 3.0° reflects in enhanced passivity, lower anodic dissolution and corrosion current reduction. Characterization of the corrosion attack by 3D microscopy reveals high sensitivity of superhydrophilic surfaces on corrosion propagation direction in regard to the laser beam passage (90°/0°). However, this trend completely diminishes with superhydrophobic development. Further, DLT also completely prohibits intergranular corrosion detected with the non-processed sample.

This work reports for the first time the effect of femtosecond laser shock peening (fLSP) without a sacrificial overlay under atmospheric conditions (no confinement) on the corrosion behaviour of AA2024-T3. After fLSP and additional exposure to air a superhydrophobic state (θ=160 ± 4°) is achieved. Moreover, fLSPed corrosion-resistant surface contributes to increased polarization resistance, reduced corrosion current and lower anodic dissolution, with long-term stability in aggressive chloride solution. Furthermore, SEM/EDS characterisation reveals reduction in pitting and complete eradication of intergranular corrosion (IGC) attack due to reduced metal/electrolyte contact area and homogeneous, refined microstructure which prevents chain-link IGC propagation.

The susceptibility to intergranular corrosion of welded joints of austenitic stainless steel X5CrNi18-10 was examined. The testing was performed by the electrochemical potentiokinetic reactivation method with single loop (EPR) and double loop (DL EPR). Also, the susceptibility to intergranular corrosion of stainless steels after senzibilization heat treatment (675 °C/1h) was examined. At given welding parameters (current intensity, the thickness of welded samples of stainless steel, etc.) the base metal is completely resistant to intergranular corrosion, while the heat affected zone shows a relatively low susceptibility to intergranular corrosion. After senzibilization heat treatment the stainless steel showed something higher susceptibility to intergranular corrosion. The advantages of applied electrochemical methods in relation to the classical chemical methods for intergranular corrosion testing were analyzed. DL EPR and EPR methods provide quantitative data on the sensitization degree to intergranular corrosion (in welded joints) and also to intergranular stress corrosion cracking. Ispitana je sklonost zavarenog spoja austenitnog nerđajućeg čelika X5CrNi18-10 prema interkristalnoj koroziji. Ispitivanje je izvršeno metodom elektrohemijske potenciokinetičke reaktivacije sa jednostrukom petljom (EPR) i sa dvostrukom petljom (DL EPR). Takođe, određena je sklonost prema interkristalnoj koroziji navedenog nerđajućeg čelika posle senzibilizacione termičke obrade (675 OC/1h). Pri datim uslovima zavarivanja (primenjena jačina struje zavarivanja, debljina zavarenih uzoraka od nerđajućeg čelika, itd.) osnovni metal je potpuno otporan prema interkristalnoj koroziji, dok je zona uticaja toplote u maloj meri sklona prema interkristalnoj koroziji. Posle senzibilizacione termičke obrade nerđajući čelik pokazao je značajniju sklonost prema interkristalnoj koroziji. Analizirane su mogućnosti navedenih elektrohemijskih metoda u odnosu na mogućnosti klasičnih hemijskih metoda ispitivanja interkristalne korozije u ključalim rastvorima kiselina. EPR i DL EPR metode daju kvantitativne podatke o stepenu senzibilizacije (zavarenog spoja) nerđajućeg čelika prema interkristalnoj koroziji, a takođe i prema interkristalnoj naponskoj koroziji.

Namen našega dela je bil določiti značilnosti elektrokemijskega šuma, povzročenega z napetostno-korozijskim pokanjem. Želeli smo predvsem ugotoviti poveznanost značilnih elektrokemijskih fluktuacij z mehanskimi spremembami zaradi procesov pokanja ter tako posredno tudi oceniti primernost te metode za detekcijo in študij različnih oblik pokanja. Elektrokemijski šum smo merili med počasnim enakomernim nateznim obremenjevanjem delovne elektrode (modificiran Slow Strain Rate Test), izdelane iz nerjavnega avstenitnega jekla tipa AISI 304 v žarjenem ter toplotno neobdelanem stanju. Izrazite nenadne fluktuacije napetostnega in tokovnega šuma smo opazili po preseženi napetosti tečenja. Vse se časovno popolnoma ujemajo z nenadnimi spremembami raztezka natezno obremenjene elektrode, kar dokazuje zanesljivo možnost detekcije pokanja. Iz izmerjenih sprememb raztezka smo določili hitrost rasti razpok ter jih primerjali z amplitudami fluktuacij elektrokemijskega šuma. Dokazali smo, da obstaja med vrednostmi teh dveh količin linearna odvisnost. Poudariti je treba, da samo poznanje elektrokemijskih razmer ter spremljanje mehanskih sprememb, povzročenih s pokanjem, še ni dovolj za ovrednotenje mehanizmov napetostno-korozijskega pokanja, pač pa bo za to v prihodnosti treba vključiti še fraktografsko analizo prelomnih površin. The main aim of the research work was to asses basic characteristics of electrochemical noise generated by stress-corrosion cracking, and especially to find a correlation between the electrochemical and mehanical quantities. Electrochemical noise was measured during slow constant increasing of stress (modified Slow Strain Rate Test) on tensile tube made from austenitic stainless steel of the type AISI 304, in sensitized and nonsensitized condition. One of the objectives of this research was to investigate the possibility of electrochemical noise method for studying stress-corrosion processes. After the reaching yielding point, voltage and current spikes, as well as elongation transients, all appearing at the same time, were detected. Afterwards, the cracking velocities were determined from the time series of elongation, and compared to characteristic parameters of the measured electrochemical noise. The results of the comparision indicated that the amplitudes of the electrochemical noise spikes are lineary dependent upon cracking velocity. It has to be pointed out, that the knowledge of elecrochemical conditions and mechanical changes generated by cracking processes by themselves, cannot form revalant information concering the cracking mechanisms. In order to get better overview to this problem additional fractographic inspections of cracking surfaces has to be performed.

U radu je analizirana pojava i metode ispitivanja interkristalne korozije (IKK) zavarenih spojeva austenitnih, feritnih i dupleks nerđajućih čelika, kao i zavarenih spojeva aluminijumskih legura i legura nikla. Posebna pažnja posvećena je austenitnim nerđajućim čelicima, s obzirom na njihovu široku primenu u praksi. Klasične metode ispitivanja u ključalim rastvorima kiselina još uvek imaju veliku primenu u praksi. Njihov najvažniji nedostatak je dugo vreme trajanja ispitivanja (do 240 h). Tabelarno su prikazane osnovne karakteristike tih metoda, navedeni metali i legure na koje se metode mogu primeniti, faze u zavarenom spoju na koje deluje rastvor, temperatura i vreme trajanja ispitivanja. Posebna pažnja posvećena je elektrohemijskim metodama za ispitivanje IKK. Ove metode se u novije vreme sve više primenjuju, s obzirom na kvantitativni karakter dobijenih rezultata kao i kratko vreme ispitivanja (od nekoliko minuta do jednog sata).