Comparison of corrosion behavior of zirconium bombarded with self-ion and molybdenum ion

In order to study the effects of zirconium and molybdenum ion bombardment on the aqueous corrosion behavior of zirconium, one group of specimens was implanted with zirconium ions with ions surface densities ranging from 1 × 10¹⁵ to 2 × 10¹⁷ ions/cm² at about 170 °C, using a metal vapor vacuum arc (MEVVA) source operated at an extraction voltage of 50 kV. The other group of specimens was bombarded with molybdenum ion with ions surface densities ranging from 1 × 10¹⁶ to 5 × 10¹⁷ ions/cm² at about 160 °C, using a MEVVA source operated at an extraction voltage of 40 kV. The valence states and depth distribution of elements in the surface of the samples were analyzed by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), respectively. Polarization curves measurement was employed to evaluate the aqueous corrosion resistance of the zirconium samples in a 1N H₂SO₄ solution. It was found that the aqueous corrosion resistance of zirconium implanted with 5 × 10¹⁶ Zr ions/cm² is the best in first group samples. For molybdenum ion implantation, the aqueous corrosion resistance of samples declined with raising ions surface densities. The natural corrosion potentials of zirconium samples bombarded with self-ions are more negative than that of the as-received zirconium. While, as for molybdenum ion implantation, the results are opposite. Finally, the mechanisms of the corrosion behavior of the zirconium samples implanted with zirconium and molybdenum ions are discussed.     

Influence of temperature and hydrodynamic conditions on the corrosion behavior of AISI 316L stainless steel in pure and polluted H3PO4: Application of the response surface methodology

Phosphoric acid is mainly produced by the wet acid process, where corrosion problems could be intensified due to the presence of impurities in the phosphate ores. Operating temperatures and flowing conditions aggravate the aforementioned problems. This work studies the influence of temperature (25–60 °C) and hydrodynamic conditions (Reynolds numbers from 1456 to 5066) on the corrosion of AISI 316L stainless steel in pure and polluted phosphoric acid solutions, by means of cyclic potentiodynamic polarization curves in a hydrodynamic circuit. The effect of temperature is the same as that caused by impurities, that is, higher corrosion rates and hindered passivation and repassivation resistance of the alloy. Statistical analysis by means of surface response methodology proved that the effect of temperature on the corrosion parameters of AISI 316L is more influential than the Reynolds number effect. The Reynolds number seems to have no significant influence on the corrosion behavior of stainless steel. Furthermore, the influence of temperature on the corrosion rate is much higher than on the rest of the corrosion parameters analyzed, especially in polluted phosphoric acid solutions. AISI 316L stainless steel has a clear interest for the phosphoric acid industry as a component material of some equipment due to its good corrosion properties at the different temperatures and Reynolds numbers studied even in polluted media.     

Effect of post-oxidizing temperature on tribological and corrosion behavior of plasma nitrided austenitic stainless steel

In this study, the effect of temperature of post-oxidation process on tribological and corrosion behavior of AISI 316 plasma nitrided stainless steel has been studied. Plasma nitriding was carried out at 450 °C for 5 h with gas mixture of N₂/H₂ = 1/3. The plasma nitrided samples were post-oxidized for 1 h with gas mixture of O₂/H₂ = 1/5 at different temperature of 400, 450 and 500 °C. The structural, tribological and corrosion properties were analyzed using XRD, SEM, microhardness testing, pin-on-disk tribotesting and electrochemical polarization. The results indicated that the nitride layer was composed of S-phase. The amount of S-phase decreased as the treatment temperature rose from 400 °C to 500 °C. In addition, it was found that oxidation treatment reduces wear resistance of plasma nitrided sample. It was demonstrated that the corrosion characteristics of the nitrided sample were further improved by post-oxidation treatment. The difference in corrosion resistance is mainly attributed to the thickness of the oxide top layer, which is governed by the post-oxidizing temperature.     

Corrosion behavior of ion nitrided AISI 316L stainless steel

In the present work the corrosion susceptibility of ion nitrided AISI 316L stainless steel was investigated for two different nitriding times and compared with the corrosion susceptibility of the untreated material. Plasma nitriding for short times (30 min) produced the “S” phase or expanded austenite (γ_N), with a thickness of ∼ 5 μm and a micro-hardness of 1300-1400 HV_0.025 (6.5 times higher than the untreated material). Plasma nitriding for long times (6 h) resulted in the precipitation of iron and chromium nitrides.To evaluate the corrosion resistance of both untreated and nitrided samples, anodic potentiodynamic polarization curves and immersion tests were performed in 1 M NaCl at room temperature. It was found that the corrosion resistance depends on the nitriding time. Samples nitrided for half an hour developed a much better corrosion resistance - close to that observed in the untreated samples - than those nitrided for 6 h. Samples nitrided for half an hour showed high roughness probably due to the presence of sliding bands developed in the expanded austenite phase. These sliding bands provide appropriate sites for the developing of the corrosion process. This would explain the results obtained in the corrosion tests. Samples ion nitrided for 6 h showed a severe and massive surface damage due to corrosion.Ion nitriding of AISI 316L stainless steel for short periods of time (30 min in the present case) may be an interesting surface treatment process that efficiently improves the surface hardness of the steel with some reduction in its corrosion resistance.     

Surface hardness improvement of plasma-sprayed AISI 316L stainless steel coating by low-temperature plasma carburizing

Low-temperature carburizing below 773 K of austenite stainless steel can produce expanded austenite, known as S-phase, where surface hardness is improved while corrosion resistance is retained. Plasma-sprayed austenitic AISI 316L stainless steel coatings were carburized at low temperatures to enhance wear resistance. Because the sprayed AISI 316L coatings include oxide layers synthesized in the air during the plasma spraying process, the oxide layers may restrict carbon diffusion. We found that the carbon content of the sprayed AISI 316L coatings by low-temperature carburizing was less than that of the AISI 316L steel plates; however, there was little difference in the thickness of the carburized layers. The Vickers hardness of the carburized AISI 316L spray coating was above 1000 HV and the amount of specific wear by dry sliding wear was improved by two orders of magnitude. We conclude that low-temperature plasma carburizing enabling the sprayed coatings to enhance the wear resistance to the level of carburized AISI 316L stainless steel plates. As for corrosion resistance in a 3.5 mass% NaCl solution, the carburized AISI 316L spray coating was slightly inferior to the as-sprayed AISI 316L coating.     

The wear and corrosion resistance of shot peened–nitrided 316L austenitic stainless steel

316L austenitic stainless steel was gas nitrided at 570 °C with pre-shot peening. Shot peening and nitriding are surface treatments that enhance the mechanical properties of surface layers by inducing compressive residual stresses and formation of hard phases, respectively. The structural phases, micro-hardness, wear behavior and corrosion resistance of specimens were investigated by X-ray diffraction, Vickers micro-hardness, wear testing, scanning electron microscopy and cyclic polarization tests. The effects of shot peening on the nitride layer formation and corrosion resistance of specimens were studied. The results showed that shot peening enhanced the nitride layer formation. The shot peened–nitrided specimens had higher wear resistance and hardness than other specimens. On the other hand, although nitriding deteriorated the corrosion resistance of the specimens, cyclic polarization tests showed that shot peening before the nitriding treatment could alleviate this adverse effect.     

Preparation and characterization of sol-gel derived yttria doped zirconia coatings on AISI 316L

A stable 4 mol% yttria-stabilized zirconia (YSZ) sol has been synthesized for coating stainless steel AISI 316L for biomedical applications. The sol was prepared by controlled hydrolysis of zirconium n-butoxide using acetylacetone and nitric acid as chelating agent and catalyst, respectively. X-ray diffractograms of calcined YSZ xerogel indicated a tetragonal structure at temperature as low as 400 °C. Stainless steel was dip-coated in transparent yellow YSZ sol followed by heat treatment between 400 and 600 °C for 2 h in air. A homogeneous and crack-free YSZ film was, thus, obtained on the stainless steel surface. Adhesion strength, measured by scratch test in progressive loading sequence on coated AISI 316L, showed 27 ± 3 N critical load. Corrosion performance of the surface coating was evaluated through open-circuit potential (OCP) measurement, impedance, polarization and chronoamperometry in Ringer's solution at 37 °C. The coating enhanced the pitting potential of the substrate. The metal ions released from AISI 316L was effectively controlled by the coating.     

Investigation of dry sliding wear properties of boron doped powder metallurgy 316L stainless steel

This paper describes wear behavior of powder metallurgy (PM) 316L stainless steel with additions of elemental boron with the aim of producing superior mechanical properties. The wear test of the samples is conducted using a pin specimen of PM 316L stainless steel doped with elemental boron and a steel disc specimen with hardness of 180 HV10. Densification achieved with boron addition due to the liquid phase formation up to 95% of theoretical density with 0.6 wt.% boron addition. Most mechanical properties such as hardness, tensile strength and yield strength were improved with boron addition. The wear rate of PM 316L stainless steel decreased from 4.3 × 10⁻⁶ to 0.8 × 10⁻⁶ mm³/Nm with the addition of 0.6 wt.% elemental boron. The abrasive-induced delamination wear dominated at the samples. Scanning electron microscopy observations of the worn surfaces revealed that plastic deformation occurred with delamination of surface layers in the sintered conditions.     

Improvement of wear and hardness of steel by nitrogen implantation

This paper reports a study of the influence of atomic nitrogen implantation on the improvement of hardness and wear of AISI 8642 steel. The hardness and wear tests were carried out over the dose range 10¹⁷ -7×10¹⁷ ions/cm² and energy 200 keV. Characterization of the surface and depth profiling of the implanted samples was performed using RBS and XRD techniques. Tribological tests for measuring friction and wear were made on a pin-on-disk stand with different loads for implanted and non-implanted samples. Hardness was measured with a Vickers diamond square-faced pyramid indenter. Nitrogen implantation of steel increased the hardness by about 150% in comparison to the non-implanted samples. The influence of a ‘long-range effect’ established beyond the implanted zone during the ion implantation process on the increase of hardness was discussed. No improvement of the friction coefficient was observed in the steel samples due to nitrogen implantation. On the other hand, the wear at a dose 7×10¹⁷ ions/cm² decreased by a factor of about 20 times compared with the non-implanted steel.     

In vitro corrosion resistance of Lotus-type porous Ni-free stainless steels

The corrosion behavior of three kinds of austenitic high nitrogen Lotus-type porous Ni-free stainless steels was examined in acellular simulated body fluid solutions and compared with type AISI 316L stainless steel. The corrosion resistance was evaluated by electrochemical techniques, the analysis of released metal ions was performed by inductively coupled plasma mass spectrometry (ICP-MS) and the cytotoxicity was investigated in a culture of murine osteoblasts cells. Total immunity to localized corrosion in simulated body fluid (SBF) solutions was exhibited by Lotus-type porous Ni-free stainless steels, while Lotus-type porous AISI 316L showed very low pitting corrosion resistance evidenced by pitting corrosion at a very low breakdown potential. Additionally, Lotus-type porous Ni-free stainless steels showed a quite low metal ion release in SBF solutions. Furthermore, cell culture studies showed that the fabricated materials were non-cytotoxic to mouse osteoblasts cell line. On the basis of these results, it can be concluded that the investigated alloys are biocompatible and corrosion resistant and a promising material for biomedical applications.     

Corrosion behavior of nitride layer obtained on AISI 316L stainless steel via simple direct nitridation route at low temperature

Newly developed low-temperature nitride synthesis route was used to introduce interstitial nitrogen into the passive layer of as-received and as-polished 316L stainless steel. The new thermochemical route is based on treating the stainless steel samples in potassium nitrate melt in an ultra pure nitrogen atmosphere at 450 °C. Electrochemical impedance spectroscopy (EIS) and dc polarization measurements have been used to evaluate the nitride layer performance in 3.5% NaCl solution. Results showed a marked increase in the corrosion resistance of nitrided stainless steel even after maintaining two weeks in NaCl solution. The effect of the treatment temperature was also studied. Data showed that the as-polished samples nitrided at 450 °C have the highest corrosion resistance. The polarization resistance (R_p) for the as-polished and as-received blank stainless steel samples was estimated by EIS were approximately 4.0 × 10⁴ Ω cm² and 2.0 × 10⁴ Ω cm², respectively. The R_p increased by a factor of 2.5–5 for the nitrided samples. Increasing the nitriding temperature from 450 to 600 °C affects negatively the corrosion resistance of stainless steel in NaCl solution. The R_p of the samples nitrided at 600 °C decreased sharply being almost 1/30 of the R_p of the samples nitrided at 450 °C. Linear polarization measurements showed that the lowest corrosion rates and highest polarization resistances obtained from the as-polished nitrided samples at 450 °C. It has been found from the potentiodynamic measurements that the E_corr of the as-polished nitrided samples at 450 °C is nobler than that measured from the other groups. The surface morphology was analysed by optical microscope and SEM-EDS under different nitriding conditions.     

Microstructure and Corrosion Resistance of Dissimilar Weld-Joints between Duplex Stainless Steel 2205 and Austenitic Stainless Steel 316L

The microstructure and corrosion resistance of dissimilar weld-joints between stainless steel SAF 2205 and stainless steel AISI 316 L were investigated. Welding was accomplished by different types of welding wires AWS ER 347, AWS ER 316 L and AWS ER 309 L. To verify soundness of welded samples, nondestructive tests were performed. Metallographic samples were prepared from cross-section areas of weldjoints to investigate microstructure of different regions of weld-joints by optical microscopy and scanning electron microscopy. Corrosion resistance of weld-joints was evaluated in NaCl solution by potentiodynamic polarization and electrochemical impedance techniques. In the weld metal AWS ER 347, the brittle sigma phase was created, resulting in the decrease of weld-joint corrosion resistance. According to the results of metallurgical investigations and corrosion tests, welding wire AWS ER 309 L was suitable for welding duplex stainless steel(SAF 2205) to austenitic stainless steel(AISI 316L) by gas tungsten arc welding(GTAW)process.     

Microstructure and wear behavior of a porous nanocrystalline nickel-free austenitic stainless steel developed by powder metallurgy

This paper investigates the microstructure and dry sliding wear characteristics of a porous Cr–Mn–N austenitic stainless steel prepared by powder metallurgy. The densification of the mechanically alloyed 18Cr–8Mn–0.9N stainless steel powder is performed by sintering at 1100 °C for 20 h and subsequently water-quenching. This procedure gives rise to the development of a nanostructured austenitic stainless steel with a relative density of 85%. The porous biocompatible stainless steel exhibits an outstanding wear resistance compared with AISI 316L stainless steel samples. This is attributed to its considerable intrinsic hardness and its specific configuration of pores.     

Corrosion protection of CrN/TiN multi-coating for bipolar plate of polymer electrolyte membrane fuel cell

The electrochemical corrosion cells will be generated from the possible pinholes of the promising CrN and TiN coatings in a PEMFC environment. To prevent the elution of possible pinholes, CrN/TiN multi-coatings on SS have been considered. This study examined the electrochemical behavior of three CrN/TiN coatings on 316L stainless steel deposited at different CrN/TiN thickness ratios by rf-magnetron sputtering as potential bipolar plate materials. Potentiodynamic tests of CrN/TiN-coated 316L stainless steel carried out in a 1 M H₂SO₄ + 2 ppm HF solution at 70 °C revealed a significantly lower corrosion current density than that of uncoated 316L SS, as well as a decrease in the corrosion current density with decreasing inner-layer CrN thickness. Electrochemical impedance spectroscopy also showed that the CrN/TiN-coated 316L SS sample had higher charge transfer resistance than the uncoated 316L SS sample, which increased with decreasing inner-layer CrN thickness. This was attributed to the crystalline-refined CrN/TiN(200).     

Ultrafine 316 L stainless steel particles with frozen-in magnetic structures characterized by means of electron backscattered diffraction

Electron Backscatter Diffraction (EBSD) studies clearly revealed a different crystallographic structure of the smallest particle size fraction of gas-atomized AISI 316 L stainless steel powder (< 4 μm) compared with larger sized fractions of the same powder (< 45 μm). Despite similar chemical compositions, the predominating structure of the smallest particle size fraction was ferritic (i.e., has ferromagnetic properties) whereas the larger sized particle fractions and massive 316 L revealed an expected austenitic and non-magnetic structure. From these findings, it follows that direct magnetic separation can be applied to separate very fine sized particles. These structural differences explain previously observed dissimilarities from corrosion and metal release perspectives.     

Effect of silicon-ion implantation upon the corrosion properties of austenitic stainless steels

The structure of the surface layers and the corrosion resistance of austenitic stainless steels after silicon-ion implantation, were examined. The implanted silicon doses were 1.5×1017, 3×1017 and 4.5×1017 Si+ cm-2. Implantation with all these doses gave an amorphous surface layer. When samples implanted with 1.5×1017 Si+ cm-2 were annealed at temperatures of 300 and 500 °C, their surface structure remained unchanged. After annealing at 650 °C, the amorphous layer vanished. It was determined how, in terms of corrosion resistance, the amount of implanted silicon, subsequent heat treatment and long time exposure, affect highly corrosion-resistant austenitic stainless steel (18/17/8) in comparison to the 316L austenitic stainless steel subjected to the same treatment. Corrosion examinations were carried out in 0.9% NaCl at a temperature of 37 °C. After silicon-ion implantation the corrosion resistance of the 316L steel increased while that of highly resistant (18/17/8) did not. The corrosion resistance of the investigated steels, both implanted and non-implanted, increased with the exposure time of the samples in the test environment. © 1998 Kluwer Academic Publishers     

Fatigue behaviour of friction welded medium carbon steel and austenitic stainless steel dissimilar joints

This paper reports the fatigue behaviour of friction welded medium carbon steel–austenitic stainless steel (MCS–ASS) dissimilar joints. Commercial grade medium carbon steel rods of 12 mm diameter and AISI 304 grade austenitic stainless steel rods of 12 mm diameter were used to fabricate the joints. A constant speed, continuous drive friction welding machine was used to fabricate the joints. Fatigue life of the joints was evaluated conducting the experiments using rotary bending fatigue testing machine (R = −1). Applied stress vs. number of cycles to failure (S–N) curve was plotted for unnotched and notched specimens. Basquin constants, fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated for the dissimilar joints. Fatigue strength of the joints is correlated with microstructure, microhardness and tensile properties of the joints.     

Influence of the microstructure on the corrosion resistance of plasma‐nitrided austenitic stainless steel 304L and 316L

Austenitic stainless steels are widely used in medical and food industries because of their excellent corrosion resistance. However, they suffer from weak wear resistance due to their low hardness. To improve this, plasma nitriding processes have been successfully applied to austenitic stainless steels, thereby forming a thin and very hard diffusion layer, the so‐called S‐phase. In the present study, the austenitic stainless steels AISI 304L and AISI 316L with different microstructures and surface modifications were used to examine the influence of the steel microstructure on the plasma nitriding behavior and corrosion properties. In a first step, solution annealed steel plates were cold‐rolled with 38% deformation degree. Then, the samples were prepared with three kinds of mechanical surface treatments. The specimens were plasma nitrided for 360 min in a H₂–N₂ atmosphere at 420 °C. X‐ray diffraction measurements confirmed the presence of the S‐phase at the sample surface, austenite and body centered cubic (bcc)‐iron. The specimens were comprehensively characterized by means of optical microscopy, scanning electron microscopy, glow discharge optical emission spectroscopy, X‐ray diffraction, surface roughness and nano‐indentation measurements to provide the formulation of dependencies between microstructure and nitriding behavior. The corrosion behavior was examined by potentio‐dynamic polarization measurements in 0.05 M and 0.5 M sulfuric acid and by salt spray testing.     

AES investigation of the stainless steel surface oxidized in plasma

Auger electron spectroscopy (AES) depth profiling was used to study the oxidation phenomena of AISI316L stainless steel during treatment with oxygen plasma. Samples were exposed to low-pressure RF plasma with a high dissociation degree, so that the flux of oxygen atoms onto the sample surface exceeded 10²⁴ m⁻² s⁻¹. A set of samples was oxidized 4 min at different temperatures up to 1300 K during plasma treatment. AES measurements showed that the oxide film thickness increased with the increasing temperature. The thickness of the oxide film on the samples oxidized in plasma at 300 K was nearly the same as for the untreated sample. The thickness of the oxide film of the samples which were oxidized at 1000 K was about 170 nm and it consisted of iron oxide. The thickest oxide film of about 350 nm was found on the samples heated in oxygen plasma to 1300 K. Depth profiling showed the uppermost layer of manganese oxide, followed by a mixture of chromium oxide and iron oxide. The scanning electron microscope analyses showed a dramatic increase of the surface roughness.     

Effects of chloride ions on electrochemical reaction of 316 stainless steel in mixtures of molten nitrate salts

Effects of chloride ion on decomposition of ternary nitrate and corrosion behaviors of 316 stainless steel (316 SS) were studied by electrochemical corrosion tests in molten salt. Chemical composition and morphology of the corrosion products were analyzed using x-ray diffraction and scanning electron microscopy equipped with energy disperse spectroscopy. Composition analysis for molten salt combined with morphology analyses of corrosion layer showed that presence of chlorine ions slowed down decomposition of ternary nitrate and increased corrosion rate of stainless steel markedly. The polarization curve obtained indicated that the corrosion current density increased from 3.02 mA ⋅ cm⁻² to 8.76 mA ⋅ cm⁻² with the addition of 10 % NaCl. Electrochemical impedance spectroscopy indicated a decrease in charge-transfer resistance of the double layer between 316 SS and ternary Nitrate containing 10 % NaCl, resulting in a decreased corrosion resistance of 316 SS.