Nitrided 316L Stainless Steel Research Articles

Evaluation of adhesive damage in a nitrided stainless steel under cyclic contact loading

In this study, adhesive damage in a nitrided AISI 316L stainless steel is evaluated by cyclic contact loading. The AISI 316L steel was hardened by the salt bath nitriding process at a constant temperature (580 °C) and three different exposure times (1 h, 3 h and 5 h). Mechanical properties such as Young's modulus (E) and hardness (H) were obtained by nanoindentation testing, where the H3/E2 ratio was used as an indicator of the fracture resistance of the nitride layers. Cyclic contact loads were applied to the nitrided steels using a spherical indenter of 3 mm in diameter. The layer/substrate systems were evaluated under 50,000 load cycles and a constant frequency of 5 Hz. Adhesive damage was observed at the interface between the compound-layer and the diffusion zone, where the samples with a thicker nitride layer showed more severe damage. In addition, the finite element method was used to obtain the stress field in the nitrided AISI 316L steel caused by cyclic contact loading, where both the maximum principal stress and the maximum shear stress were related to the adhesive damage observed in the experimental test.

Investigation of the Structural, Tribological, and Electrochemical Properties of Nitrided and Boronized AISI 316L Stainless Steel

Investigation of the Structural, Tribological, and Electrochemical Properties of Nitrided and Boronized AISI 316L Stainless Steel

Performance evaluation of plasma nitrided 316L stainless steel during long term high temperature sodium exposure

Enhancement of wear resistance of components used in fast reactors is necessary for long service life of the components. Plasma nitriding is a promising surface modification technology to impart high hardness and improved wear resistance of various steel components. This study discusses the characterization of chrome nitrided SS316L casing ring used in secondary sodium pump of fast breeder reactor and its stability under long term sodium exposure. Microstructural and hardness analysis showed that stress relieved component could be chrome nitrided successfully to a thickness of about 100 μm. Assessment of in-sodium performance of the chrome nitrided casing ring subjected to long term exposure up to 5000h at 550°C, showed retention of chrome nitrided layer with a case depth almost similar to that before sodium exposure. A slight decrease in the hardness was observed due to prolonged high temperature sodium exposure. Tribological studies indicate very low coefficient of friction indicating the retention of good wear resistance of the coating even after long term sodium exposure.

Comparison of Wear Performance of Low Temperature Nitrided and Carburized 316L Stainless Steel under Dry Sliding and Corrosive-Wear Conditions

Comparison of Wear Performance of Low Temperature Nitrided and Carburized 316L Stainless Steel under Dry Sliding and Corrosive-Wear Conditions

Hemocompatibility of plasma nitrided 316L stainless steel: Effect of processing temperature

The influence of plasma nitriding temperature on the hemocompatibility of 316LSS was evaluated through in vitro thrombogenicity tests. The nitriding processes were carried out using an industrial furnace at a temperature range that does not impair the corrosion resistance. The crystallographic phases, topography, chemical composition, wettability, and thrombogenicity of the modified surfaces were evaluated and compared to untreated 316LSS samples. The results revealed the formation and evolution of the γN phase with increasing the temperature. The γN phase development was assessed with the stacking fault probability, which rose with temperature leading to rougher surfaces. Nitrided samples at 380 ˚C exhibited polar groups at the surface, increasing the surface energy. There was a substantial reduction of these groups in samples nitrided at 400 ˚C and almost negligible at 420 ˚C. Lower amounts and less activation of platelets was observed on the nitrided surface at the lowest temperature, contrary to the results obtained at the highest nitriding temperature. It was correlated with the hydrophobicity and roughness of the plasma nitrided surfaces. Through this investigation it is possible to propose adequate conditions of plasma nitriding to improve the hemocompatibility of 316LSS samples, reinforcing the feasibility of this processing technique for biomaterials on an industrial-scale.

Characterization of Cavitation-Erosion Resistance of Plasma Ion Nitrided 316L Stainless Steel Under Shock Wave in Seawater

In this study, the characteristics of cavitation-erosion resistance of 316L stainless steel after plasma ion nitriding at various temperatures were investigated in natural seawater. Plasma ion nitriding was performed with N₂ and H₂ at a ratio of 1:4 from 400 to 500 °C for 10 hours. Micro-Vickers hardness measurement showed that the mechanical properties were improved by increasing hardness due to the formation of expanded austenite (S-phase) at 400 °C and 450 °C and γ'-Fe₄N and CrN phases at 500 °C. In the cavitation-erosion test, weight loss and damage rate decreased with increasing nitriding temperatures up to 450 °C, while the depth of damage was found to be increased at 500 °C. The lowest weight loss and damage depth were obtained at 450 °C, which measured the thickest layer of γN phase. At 500 °C, cavitation-erosion damage was significantly occurred due to the internal residual stress accumulated during the plasma ion nitriding.

Influence of the Pre-Treatments and Process Temperature on the Adhesion of TiN Films Deposited by PBII&D Over Nitrided Austenitic Stainless Steel

In this work the influence of pre-treatment cleaning processes in the adhesion of TiN films deposited by the plasma based ion implantation and deposition (PBII&D) process over plasma nitrided AISI 316L stainless steel was investigated, varying the gas composition, the duration of the sputtering process and the temperature in the same deposition chamber. The TiN film morphology was scrutinized with scanning electron microscopy on the surface complemented with focus ion beam for the cross section. The film microstructure was characterized with X ray diffraction. The adhesion of the coatings was studied using the Scratch Test with constant load at different values and the Rockwell C indentation method as well. It was found that only with the sputtering carried out in a H2 - Ar gas mixing at 300 oC temperature used as pre-treatment was successful to prepare the nitrided surface for the subsequent TiN deposition by the PBII&D process.

Microstructure and Nanosize Precipitate of Nitrided 316L Stainless Steel

The microstructure and nanosize precipitates of nitrided 316L stainless steel were investigated mainly by transmission electron microscopy (TEM) and X-ray diffraction analysis. Nitriding treatment performed in a molten salt bath followed by cooling down to ambient temperature and further diffusion treated. Produced layer consist of surface layer at the top, compound layer in the middle and final diffusion layer. Supersaturated phase is γ′N not γ-Fe4N. The lattice parameter of γ′N is expanded about 16% by nitrogen supersaturation. Precipitates size of few nm were observed in the compound layers. These nanosize precipitates were coarsening up to ~ 40 nm by further heat treatment at 450 °C for 1 h. It was identified as Si3N4 by energy dispersive X-ray spectrometer, selected area electron diffraction patterns at two different zone axes [110], [114] and high resolution TEM analysis.

Antimony microelectrode for measurement of the near-surface pH during corrosion of untreated and nitrided 316L stainless steel

Antimony microelectrode for measurement of the near-surface pH during corrosion of untreated and nitrided 316L stainless steel

Optimum temperature on corrosion resistance for plasma ion nitrided 316L stainless steel in sea water solution

The aim of this research is to investigate the optimum plasma ion nitriding temperature on corrosion resistance in natural sea water for plasma ion nitrided 316L stainless steel. Plasma ion nitriding was conducted at different temperatures of 350, 400, 450, and 500 °C with a mixture of 75% of nitrogen and 25% of hydrogen during 10 h. In conclusion of anodic polarization test, a wide passive potential region and a high corrosion potential were observed at a plasma ion nitriding temperature of 450 °C. Moreover, relatively less damage depth and clean surface micrographs were observed at 450 °C as results of observation of three-dimensional (3D) microscope and scanning electron microscope (SEM) after polarization experiments. In addition, higher corrosion potential and lower corrosion current density were indicated at plasma ion nitrided samples than the value of untreated substrate after Tafel analysis. Hence, plasma ion nitrided at 450 °C in sea water solution represented optimum corrosion resistance among the all the plasma ion nitriding temperature parameters.

Effects of Ti-C:H coating and plasma nitriding treatment on tribological, electrochemical, and biocompatibility properties of AISI 316L.

Ti-C:H coatings were deposited on original, nitrided, and polished-nitrided AISI 316L stainless steel substrates using a closed field unbalanced magnetron sputtering system. Sliding friction wear tests were performed in 0.89 wt.% NaCl solution under a load of 30 N against AISI 316L stainless steel, Si3N4, and Ti6Al4V balls, respectively. The electrochemical properties of the various specimens were investigated by means of corrosion tests performed in 0.89 wt.% NaCl solution at room temperature. Finally, the biocompatibility properties of the specimens were investigated by performing cell culturing experiments using purified mouse leukemic monocyte macrophage cells (Raw264.7). In general, the results showed that plasma nitriding followed by Ti-C:H coating deposition provides an effective means of improving the wear resistance, anti-corrosion properties, and biocompatibility performance of AISI 316L stainless steel.

Effect of grain refinement and electrochemical nitridation on corrosion resistance of the 316L stainless steel for bipolar plates in PEMFCs environment

The stain-induced nanocrystalline α'-martensite was obtained by cryogenic cold rolling at liquid-nitrogen temperature for 316L stainless steel. The electrochemical results showed nanocrystalline 316L stainless steel deteriorated its corrosion resistance in a typical proton exchange membrane fuel cell environment compared with coarse grained one. However, comparing with electrochemically nitrided coarse grained stainless steel, electrochemically nitrided nanocrystalline stainless steel improved significantly corrosion resistance in the same environment, which was supported further by Mott–Shottky analysis. X-ray photoelectron spectroscopy analysis revealed that the nanocrystalline promoted the enrichment of nitrogen and chromium and inhibited form of NH3 on the surface, which could significantly improve the corrosion resistance of the 316L stainless steel. The present study showed that the electrochemically nitrided 316L stainless steel was more suitable for the bipolar plates in proton exchange membrane fuel cell environment than the untreated one, especially for nanocrystalline stainless steel.

Using of artificial neural network for the prediction of tribological properties of plasma nitrided 316L stainless steel

In the present study, wear rate of the 316L stainless steel was predicted by using artificial neural network (ANN). The influence of plasma nitriding on mechanical and tribological properties of 316L stainless steels were investigated using X-ray diffraction, microhardness tester, scanning electron microscopy and pin-on-disk tribotester. Plasma nitriding treatments were performed for 1, 4 and 8h in 50% H2–50% N2 gas mixture, at the temperatures of 350, 375, 400, 425, 450 and 500°C. The results show that CrN and γ'-Fe4N phases were observed at the higher temperatures than 400°C while s-phase formed at the temperatures under 400°C, Also, modeling results showed that the wear rate of the 316L stainless steel was predicted with high accuracy by ANN.

Mechanical Behavior of Nitrided 316L Austenitic Stainless Steel Coated with a:C-H-Si

The austenitic stainless steel AISI 316L is used in chemical and other industries due to its good corrosion properties; however, it has a poor wear resistance. Plasma assisted treatments such as diffusion process and/or coatings can be used in order to improve the tribological properties. The a:C-H-Si coatings have low friction coefficient and wear resistance; in addition, they are chemically inert although they present adhesion problems when they are deposited on metallic substrates. In this work, the mechanical behavior and adhesion of the a:C-H-Si coatings deposited on nitrided AISI 316L stainless steel (duplex sample) and without nitriding (coated sample) were studied. The coatings were characterized by EDS and Raman. The hardness and Young Modulus were assessed with nanoindentation. The microstructure of the nitrided layer and the coatings was analysed by OM, SEM-FIB and XRD. Pin on disk and linear sliding tests were carried out. The adhesion was evaluated using Indentation Rockwell C and Scratch test. The coatings had high hydrogen content, over 40%, and the film thickness was about 20μm. The hardness was about 13GPa and Young's Modulus was 73GPa. The friction coefficient was less than 0.2 and the wear resistance was better than in stainless steel without any treatment. In the linear sliding tests, the track depth in the duplex and coated samples was six times lower than in the untreated sample. The nitriding had influence on the adhesion; the critical load was 16.2N in the duplex sample and of 9.6N in the coated sample. In the indentation Rockwell C test, the duplex sample also had better adhesion than the only coated sample.

Structure, hydrophilicity and corrosion resistance of sol–gel derived Ag-containing TiO2 film on plasma nitrided 316L stainless steel

Pure and Ag-containing TiO2 films (Ag/Ti = 3.3 at.%) are coated on plasma nitrided 316L stainless steel by sol–gel method for biomedical applications. The addition of Ag does not cause obvious change in TG–DSC curves of the dried gels. The rough surface generated by plasma nitriding and the addition of Ag improve structural integrity of the TiO2 films. X-ray diffraction reveals N loss and oxidation of the nitride layer during calcination treatment, and peaks of Ag or its oxides are not detected. X-ray photoelectron spectroscopy analysis indicates that Ag presents as metallic state in the film. Water contact angles of the coating samples decrease with UV irradiation treatment. The potentiodynamic polarization tests in a Ca-free Hank’s balanced salt solution show that the TiO2 coated samples have decreased corrosion resistance due to N loss and oxidation of the nitride layer. The methods for crystallization of TiO2 gel layers with minimized or avoided structural changes of the nitride layer will be tried in order to improve corrosion resistance of the duplex treated 316L stainless steel.

Investigating the correlation between some of the properties of plasma nitrided AISI 316L stainless steel

When AISI 316L stainless steels are submitted to the nitriding process at temperatures lower than 450 °C, a high nitrogen content expanded austenite phase is formed, which shows higher hardness and higher pitting corrosion resistance compared to the untreated material. As a result, this material becomes adequate for biomedical application. The conditions of the nitriding technique, such as gas mixture, pressure, time and temperature, play an important role in some properties of the modified layer, including: thickness, hardness and N concentration along the layer. This paper explores a set of six samples of AISI 316L, nitrided at different times and temperatures, whose properties show important differences. The aim of this research is to investigate the correlation between the nitrided layer thickness (in the range of 0.77 to 11 µm) with both X-ray patterns characteristics and hardness measurements, which used two distinct loads. The results of this study show that: whereas the 3.6 gf load was suitable to measure the real hardness for four of the nitrided layers showing thickness ≥ 2.9 µm, the 50 gf load measured a substrate contribution, probably even for the highest thickness, 11 µm. Moreover, analyzing different reflections of the X-ray patterns showed evidence of the clear consistency between the X-Ray depths and the nitrided layer thicknesses: if the layer thickness is lower than the penetration depth of X-rays, two phases (austenite and expanded substrate) are present. If the layer thickness is higher, only the austenite is observed. Finally, concerning the citotoxicity property, all the samples, nitrided or not, were approved in the test for biocompatibility, indicating their potential use for biomedical applications.

Monitoring the near-surface pH to probe the role of nitrogen in corrosion behaviour of low-temperature plasma nitrided 316L stainless steel

Low temperature plasma nitriding of stainless steels improves tribological properties and pitting resistance, but it can activate anodic dissolution in acidic solutions. This work aimed at determining how anodic behaviour can be affected by nitrogen present in the steel. The electrochemical behaviour of AISI 316L steel after nitriding at 415°C (with up to 17at.% N) was examined in solutions of 0.1M Na2SO4+0.4M NaCl acidified down to pH 2.4. An antimony microelectrode was used to measure pH close to the sample surface. It was found that the nitrided layer was resistant to pitting corrosion at all pH's, but at pH below about 3.5 anodic currents were higher than those on untreated steel. For nitrided steel the near-surface pH was increasing when anodic current was rising in the active region, evidently due to binding of protons into NH4+. Nitrided steel underwent reactivation during reverse cathodic sweeps which is characteristic of low content of chromium oxide in surface film. Injection of NH4OH into the solution improved the passivation. Thermodynamic data indicated that the accompanying pH rise enabled the formation of Fe3O4, Fe2O3, Cr2O3, FeCr2O4, NiFe2O4, MoO42− and NO2−. It is suggested that the pitting resistance of nitrided steel results from an easy repassivation of incipient pits due to the formation of the above species.

Improvement of Wear Resistances of AISI 316L Austenitic Stainless Steels by Anodic Nitriding

The nitriding of AISI 316L stainless steels has been carried out at anodic potential in a space enclosed by an active screen that consists of two cylinders with different diameter. These two cylinders made up a hollow cathode in a discharge system. Nitriding experiments were carried out on AISI 316L stainless steel at 450°C for times ranging from 1 to 24h in ammonia atmosphere. The intensity of electron bombardment on the surface of sample was low due to the anodic sheath, the disadvantages attached to conventional plasma nitriding were completely avoided. The phase composition, the thickness and the surface topography of the nitrided layer, as well as its hardness, were investigated by X-ray diffraction, scanning electron microscopy and a micro-hardness tester. The surface microhardness values and the thickness of the hardened layers increased as the nitriding time increased. Tribology properties of the untreated and nitrided 316L stainless steel have been investigated using a ball-on-disc tribometer with AISI52100 ball as the counterface. The results showed wear resistance of the AISI 316L stainless steels were greatly increased by anodic nitriding, owing to the strengthening effect of expanded austenite formed in the modified surface layer.

Development of eco-friendly surface modification process for 316L austenitic stainless steel weld cladding

Austenitic stainless steels are used for industrial applications due to their improved corrosion resistance properties. Their poor tribological behaviour is a barrier for their wider application under corrosion–wear conditions taking place between rolling and sliding contacts. The present work has been conducted to develop a low temperature liquid nitriding process for austenitic stainless steel claddings to impart better resistance to corrosion–wear. This work presents the results of the corrosion and wear tests performed on liquid nitrided AISI 316L stainless steel claddings. The wear tests were conducted with a Ducom pin on disc machine under rolling–sliding conditions. Surface and subsurface were studied by an optical microscope. The hardness and depth of the modified layer were measured in the sectioned samples using a microhardness tester. The optical metallographic microstructures of the liquid nitrided specimens were revealed using Marbles reagent. The electrochemical behaviour of the liquid nitrided specimens was investigated with a dc anodic potentiodynamic polarisation technique.

Sol-gel derived TiO2 coating on plasma nitrided 316L stainless steel

Titania film is coated on plasma nitrided 316L stainless steel by sol-gel method. Crystallization of titania as well as N loss and formation of Fe2O3 occurs during the annealing heat treatment. The titania film has short cracks within the grooves of plasma etched grain boundaries. With the increase of annealing temperature and duration, surface hardness of the samples is increased, but the toughness is decreased due to oxidization of the surface layer. The coating sample heat treated at 350 °C for 10 min and 450 °C for 10 min has better corrosion resistance than the nitrided stainless steel tested by the potentiodynamic polarization in 0.9% NaCl solution. Water contact angle of the titania film on the rough nitrided steel substrate decreases with UV irradiation treatment, reaching 17° after 3 h treatment.