Formation Of Protective Passive Film Research Articles

A comparative study on passive films of Fe–11Cr stainless steel and Fe–20Mn–11.5Al–1.4C–5Cr lightweight steel

Fe–20Mn–11.5Al–1.4C–5Cr (wt%) lightweight stainless steel (LWSS) was found to have equivalent or better resistance to pitting corrosion than Fe–11Cr (wt%) stainless steel (SS). The desirable resistance to pitting corrosion of the LWSS alloy was attributed to the formation of protective passive film. On LWSS, an (Al,Fe,Cr)-oxide was formed, and on SS, a (Fe,Cr)-oxide was formed. The passive film of LWSS had a higher Cr + Al content than that of SS. In addition, compared to the passive film of SS, the passive film of LWSS was found to be thick and the concentration of point defects was also low.

The Effect of Ni Content on the Corrosion Resistance of Some Fe–Cr–Ni Alloys in Simulated Body Fluids in the Presence of H2O2 and Albumin

The stainless steel alloys are greatly utilized for human orthopaedic and implants. The electrochemical behaviour of the stainless steel of Fe–17Cr–xNi alloys (x = 8, 10, 14) has been studied in simulated body fluid containing H2O2 and albumin at 37 °C. The electrochemical behaviour of the Fe–17Cr–8Ni, Fe–17Cr–10Ni and Fe–17Cr–14Ni has been investigated using the potentiodynamic polarization and electrochemical impedance spectroscopy, EIS. The surface morphology of the three alloys was examined before and after immersion in the simulated body fluid containing H2O2 and albumin using scanning electron microscope. The elemental composition of the oxide layer formed on the surface of the alloys after immersion in the electrolyte was obtained using energy dispersive X-ray analysis, EDX, technique. The metals released into the electrolyte has been determined using atomic absorption spectrophotometry. The EIS and potentiodynamic polarization results demonstrate that the Fe–Cr–14Ni alloy attains highest polarization resistance and the smallest rate of corrosion than Fe–17Cr–8Ni and Fe–17Cr–10Ni alloys. Fe–17Cr–14Ni is slightly influenced by immersion in simulated body fluid containing H2O2 and albumin which is confirmed by SEM images and metal release via formation of protective passive film. The surface analysis has shown the participation of the different alloying elements in the passive film.

Corrosion resistance mechanism of the passive films formed on as-cast FeCoCrNiMn high-entropy alloy

The present work investigates the corrosion resistance of as-cast FeCoCrNiMn high-entropy alloy in borate buffer solution. Compared with 304 and 316L stainless steels steel, as-cast FeCoCrNiMn high-entropy alloy exhibited excellent passivation ability. This should be attributed to homogenization of alloying elements. Highly corrosion-resistant elements in as-cast FeCoCrNiMn alloys, for example, Cr, Co and Ni, could promote the formation of protective passive film in borate buffer solution. Moreover, combined effect of high mixing entropy and sluggish diffusion also could improve the corrosion resistance. The formation mechanism of the passive films on the surface of as-cast FeCoCrNiMn alloys satisfied the point defect model.

Composition-controlled active-passive transition and corrosion behavior of Fe-Cr(Mo)-Zr-B bulk amorphous steels

Various corrosive environments in daily life and industry have put forward high requirement on corrosion resistance of metals, especially steels. Unlike the strict demand in Cr content of crystalline stainless steels, amorphous steels (ASs) with lower Cr content can be endowed with outstanding corrosion resistance, while the intrinsic mechanism is not fully understood. Herein, we present a novel Fe92−x−y−zCrxMoyZr8Bz (6 ≤ x ≤ 40, 0 ≤ y ≤ 22, and 12 ≤ z ≤ 18) bulk amorphous steel (BAS) forming system and reveal the synergistic effect of Cr and Mo in determining the chemical stability of oxide films. It has been found the Fe92−x−zCrxZr8Bz BASs with 1 mm in diameter display a Cr-controlling active-passive transition at the Cr threshold of ∼25% in 1 M hydrochloric acid. When adding minor Mo into the BASs, the Cr threshold can be remarkably reduced by forming favorable hexavalent Mo oxides. The generation of Mo6+ is facilitated by atomic selective dissolution at the interface and can promote the passivation. In contrast, when the Cr content of the Mo-doped glasses exceeds 25%, few Mo6+ oxides would produce as the prior formation of protective passive films inhibits the further oxidation of Mo. Therefore, manipulating the active-passive transition properly is crucial to designing ASs with high stainlessness.

The effect of tempering temperature on the microstructure and electrochemical properties of a 13 wt.% Cr-type martensitic stainless steel

The effect of tempering temperature on the microstructure and electrochemical behavior of 13wt.% Cr-type martensitic stainless steel (MMS) in 3.5wt.% NaCl aqueous solution has been studied. Based on XRD, SEM and TEM-EDS analysis, it has been found that the precipitates in the steels that were tempered at 300°C, 500°C and 650°C, are nano-sized ϵ-M3C carbides, nano-sized Cr-rich M23C6 carbides and micron or submicron-sized Cr-rich M23C6 carbides, respectively. Potentiodynamic polarization curves and electrochemical impedance spectroscopy studies indicate that the pitting potential of the as-quenched steel is higher than those of the tempered steels, and decrease with the increase in tempering temperature. Especially when tempered at 500°C, the corrosion resistance of the steel decreases abruptly. It shows that the precipitation of the massive-amount of nano-sized Cr-rich M23C6 carbides would provide lots of interface of carbides/matrix as the pitting initation and then hinder the formation of protective passive film on the steel surface due to the short interspace between the tempered carbides.

Kinetic regularities and mechanism of formation of nanosize passive films on titanium alloys for medical application and their electrochemical behavior in simulated physiological media

Chronopotentiometry and potentiodynamic voltammetry simulated were used to study the electrochemical behavior of the new pseudoelastic medical Ti-Nb-Ta alloy in simulated physiological media (neutral and acidified Hank’s solution, artificial saliva) at temperatures of 37 and 50°C as compared to titanium and nitinol. The mechanism of formation of protective passive films on the alloy surface is proposed on the basis of analysis of kinetic regularities used to establish steady-state potentials during exposure to the corresponding solutions. X-ray photoelectron spectroscopy technique was used to study the composition of passivating layers on the surface of the Ti-Nb-Ta alloy after corrosion tests. It is found that the new alloy is as good as titanium as regards its corrosion-electrochemical characteristics and is not subjected to pitting corrosion, as opposed to nitinol.

Corrosion Resistance of Welded Joints of Austenitic Steel Microalloyed with Rare-Earth Metals

We study the influence of rare-earth metals (REM) on the electrochemical and corrosion behavior of deposited austenitic metals in solutions of sulfuric acid. The corrosion resistances of 12Kh18N10T, 07Kh19N11M3, and 10Kh20N9G6T steels are measured by the electrochemical and gravimetric methods. It is shown that the corrosion resistance of the deposited metal in aggressive media can be made 2–4 times higher by introducing metallic yttrium, yttrium oxide, yttrium fluoride, or an yttrium–silicon hardener in the material of the electrode. It is demonstrated that the rate of corrosion processes noticeably decreases as a result of complex microalloying with yttrium and cerium up to their residual concentrations of 0.0019 and 0.0035 wt.%, respectively. The protective action of REM becomes more pronounced as temperature increases. It is also shown that REM modify the structure of the weld metal and promote the formation of protective passive films on the metal surface characterized by the elevated concentrations of yttrium, cerium, and chromium and suppressing the anodic and cathodic reactions. The proposed electrodes containing REM can be recommended for welding corrosion-resistant austenitic steels. The welds microalloyed with REM exhibit high corrosion resistance in aggressive media.

Effects of Chromium on the Glass Formation and Corrosion Behavior of Bulk Glassy Fe-Cr-Mo-C-B Alloys

Bulk glassy Fe60−xCrxMo15C15B10 (x=0, 7.5, 15, 22.5 and 30 at%) alloys with high thermal stability were synthesized and the effects of chromium on the glass formation and corrosion behavior were clarified. The maximum diameter for glass formation is 2–2.5 mm for the 7.5 and 15 at%Cr alloys and 1 mm for the other alloys. In the present glassy alloy system, the temperature interval of the supercooled liquid region (ΔTx) changed with chromium and was enlarged from around 70 K at x=0, 22.5 and 30 at% to over 80 K at x=7.5 and 15 at%. Both corrosion rate and anodic current density by potentiodynamic polarization in HCl solutions decreased with an increase of chromium content in the alloys. For the Cr-free alloy, molybdenum was significantly concentrated in the surface film after immersion in 1 N HCl solution. The bulk glassy alloys containing chromium was immune to corrosion by the formation of protective passive film enriched with chromium during immersion in the solution.