316L Stainless Steel Samples Research Articles

One-Step Electrodeposition of Superhydrophobic Coating on 316L Stainless Steel

Superhydrophobic coatings were fabricated through a one-step electrochemical process onto the surface of 316L stainless steel samples. The presence of hierarchical structures at micro/nanoscale and manganese stearate into the coatings gave superhydrophobicity to the coating, with contact angle of ~160°, and self-cleaning ability. Corrosion resistance of 316L samples was also assessed also after the electrodeposition process through Electrochemical Impedance Spectra recorded in an aqueous solution mimicking seawater condition.

Towards the Optimization of Post-Laser Powder Bed Fusion Stress-Relieve Treatments of Stainless Steel 316L

The use of post-processing heat treatments is often considered a necessary approach to relax high-magnitude residual stresses (RS) formed during the layerwise additive manufacturing laser powder bed fusion (LPBF). In this work, three heat treatment strategies using temperatures of 450 °C, 800 °C, and 900 °C are applied to austenitic stainless steel 316L samples manufactured by LPBF. These temperatures encompass the suggested lower and upper bounds of heat treatment temperatures of conventionally processed 316L. The relaxation of the RS is characterized by neutron diffraction (ND), and the associated changes of the microstructure are analyzed using electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM). The lower bound heat treatment variant of 450 °C for 4 hours exhibited high tensile and compressive RS. When applying subsequent heat treatments, we show that stress gradients are still observed after applying 800 °C for 1 hour but almost completely vanish when applying 900 °C for 1 hour. The observed near complete relaxation of the RS appears to be closely related to the evolution of the characteristic subgrain solidification cellular microstructure.

Slurry erosion behavior of hydro-turbine steel treated cryogenically at different soaking periods

The influence of deep cryogenic treatment on the erosive wear performance of Stainless Steel-316L (SS-316L) used in hydropower plants is studied. For this purpose, several SS-316L samples were held at deep cryogenic temperatures (−196 °C) for different soaking periods (12, 24, 36 h). The erosive wear tests were conducted on a self-fabricated slurry erosion test rig and the same was evaluated by weighing the cumulative mass loss (CML) of samples for every 30 min post erosion. From experimental analysis, it was found that the erosive wear was found to be minimum and the hardness reaches to maximum value after 24 h of the soaking period which could be attributed to the significant microstructural changes such as the transformation of γ-austenite phase into (δ-ferrite+α′-martensite) along with precipitation of numerous carbides after deep cryogenic treatments.

An additively manufactured locking fixation system for potential application in patient-specific implants

This study introduces a novel technique to implement a locking hole system into AM patient-specific implants without the need of additional post-processing steps such as mechanical machining. This has the potential to decrease the time and cost of manufacturing these implants, providing surgeons with an additional option, that is better suited in cases where the underlying bone is already weakened or bone porosis is an inherent risk. A commercially available locking system was chosen and replicated using high-resolution X-ray CT. A biocompatible material, 316L stainless steel was used to print specimen on a L-PBF machine in different orientations. The specimen were heat treated to tune the mechanical properties to enable the locking system to work. The accuracy of the printed holes was confirmed using a nominal/actual comparison between the original and printed holes. The strength of the system was evaluated by measuring the force needed to push the screw out of the locking plate. The 316L stainless steel samples, when annealed to tailor hardness, performed similarly to the commercial system. This included different build orientations that suggest the locking system can be included in AM implants without the need for additional post-processing steps.

Effects of geometrical characteristics on defect distributions in alloy components produced by selective laser melting

Selective laser melting (SLM) has been applied to manufacture various alloy components with excellent properties, but its further application is restricted by the intrinsic defects. In this work, the internal defect distributions in samples of three alloys (316L stainless steel, AlSi10Mg and Inconel 718) were investigated respectively, considering the effects of geometrical characteristics of the samples. The defects in the 316L stainless steel sample tend to be formed densely in the central part with large wall thickness, indicating a strong sensitivity to heat accumulation. Contrarily, the Inconel 718 sample shows a higher relative density with homogeneous defect distribution, indicating better formability for the SLM process. For the AlSi10Mg sample, the defect density keeps increasing as the deposition goes on. Typically, the defect density located at sample edges shows an abnormally high level comparing with the inner part, especially in the top sections of AlSi10Mg and Inconel 718 samples. The results are helpful for the geometrical design, the adjustment of building orientation and the further optimization of process parameters in the SLM process.

Experimental characterization of stainless steel 316L alloy fabricated with combined powder bed fusion and directed energy deposition

Powder bed fusion (PBF) is an additive manufacturing (AM) technique commonly used to manufacture metallic components. External geometry of parts printed by PBF process can be extended by regular processes, namely, laser cladding and spraying powder metal. But these methods have disadvantages such as increased heat-affected zone (HAZ) and extended deficiencies like cracks and pores, whereas samples produced with directed energy deposition (DED) exhibited strong metallurgical bonding and has reduced HAZ due to least dilution. The present work investigates the properties of stainless steel 316L (SS316L) sandwich structure built by combining PBF and DED process. The external geometry of the SS316L samples built by PBF was extended by using DED technique. Metallurgical and mechanical characteristics of DED extended PBF samples were studied. Tensile properties such as percentage elongation and tensile strength were compared for PBF, DED, and SWS (DED extended PBF). It was found that the yield stress for the DED samples, PBF samples, and SWS samples is in the range of 486 MPa, 564 MPa, and 401 MPa. Moreover, the average hardness of the interface portion is found to be 220.5 HV and it is higher than the hardness observed in the PBF and DED regions.

Precipitation formation on ∑5 and ∑7 grain boundaries in 316L stainless steel and their roles on intergranular corrosion

In sensitized (700°C for 10 h) AISI 316L stainless steel samples attacked by an HF solution, coincidence site lattice (CSL) ∑7 grain boundaries (GBs) always show corrosion while ∑5 GBs never do. This distinct corrosion behaviour can be related to the distinct precipitation behaviour of the different GBs, which itself depends on the GB characters. It is found that ∑5 GBs, although being curved both macro- and microscopically, neither show facets nor precipitates. The amount of segregation is enhanced in sensitized ∑5 GBs compared to solution-annealed ones. In contrast, ∑7 GBs show clear faceting in both the solution-annealed and sensitized state, with one facet orientation showing strong segregation while the other not. GB energy anisotropy is applied to explain the faceting phenomenon. The formation of two kinds of precipitates, i.e., C14 Laves phase and M23C6 carbide, holding responsible for two distinct morphologies of corrosion, are believed to be both linked to intensive faceting and the anisotropic segregation of ∑7 GBs. For the carbide, a preferred {111} orientation out of all ∑7 facets measured by trace analyses is presumed to facilitate its nucleation.

Subgrain microstructures and tensile properties of 316L stainless steel manufactured by selective laser melting

316L stainless steel samples were manufactured by selective laser melting (SLM). The microstructure of SLM-made 316L stainless steel and the room temperature tensile properties both perpendicular and along the building direction were studied and characterized. The static temperature field during the molten pool formation was simulated by finite element simulation. It indicates that the nonlinear asymmetrical inclined temperature gradient in SLM process produces a large surface tension gradient. The melt forms a Marangoni flow with different convection modes under the action of surface tension as well as a micro-molten pool morphology with subgrain structures such as strip, hexagonal and elongated cellular structures. In addition, there are also epitaxially grown columnar grains. The growth of columnar crystals is not affected by the boundary of the molten pool. Subgrain structures and low-angle grain boundaries make the tensile strength and the elongation of SLM-made 316L sample higher as compared to those of the cast and wrought samples. The room temperature tensile strength of the sample perpendicular to the building direction is higher than that of the sample along the building direction, while the elongation is lower than that of the sample along the building direction.

Microwave Boriding to Improve the Corrosion Resistance of AISI 304L Austenitic Stainless Steel

In this study, the corrosion behaviors of AISI 304L austenitic stainless steel samples were subjected to pack-boriding at 850, 900 and 950 °C process temperatures for 2, 4 and 6 hours with microwave hybrid heating, and examined. Boride layers were characterized by optical microscope and XRD. As a result of XRD analyses, the presence of FeB, Fe‎‎‎‎‎2B, Cr2B and Ni2B compounds in the boride layers were determined formed on the sample surfaces. As an alternative to conventional heating, AISI 304L austenitic stainless steel samples subjected to pack-boriding with microwave hybrid heating, as a result of the corrosion tests carried out during the 3rd, 7th and 10th days in 2% V/V (for volume per volume) HNO3 acid solution, the corrosion resistance of the AISI 304L austenitic stainless steel samples as loss in mass increased with the increase in the temperature and duration of the boriding process and the corrosion resistance increased 95 times compared to the untreated AISI 304L stainless steel samples.

Comparative evaluation of supervised machine learning algorithms in the prediction of the relative density of 316L stainless steel fabricated by selective laser melting

To find a robust combination of selective laser melting (SLM) process parameters to achieve the highest relative density of 3D printed parts, predicting the relative density of 316L stainless steel 3D printed parts was studied using a set of machine learning algorithms. The SLM process brings about the possibility to process metal powders and built complex geometries. However, this technology’s applicability is limited due to the inherent anisotropy of the layered manufacturing process, which generates porosity between adjacent layers, accelerating wear of the built parts when in service. To reduce interlayer porosity, the selection of SLM process parameters has to be properly optimized. The relative density of these manufactured objects is affected by porosity and is a function of process parameters, rendering it a challenging optimization task to solve. In this work, seven supervised machine learning regressors (i.e., support vector machine, decision tree, random forest, gradient boosting, Gaussian process, K-nearest neighbors, multi-layer perceptron) were trained to predict the relative density of 316L stainless steel samples produced by the SLM process. For this purpose, a total of 112 data sets were assembled from a deep literature review, and 5-fold cross-validation was applied to assess the regressor error. The accuracy of the predictions was evaluated by defining an index of merit, i.e., the norm of a vector whose components are the statistical metrics: root mean square error (RMSE), mean absolute error (MAE), and the coefficient of determination (R2). From this index of merit, it is established that the use of gradient boosting regressor shows the highest accuracy, followed by multi-layer perceptron and random forest regressor.

Additive Manufactured 316L Stainless-Steel Samples: Microstructure, Residual Stress and Corrosion Characteristics after Post-Processing

Additive manufacturing (AM) is a relatively new manufacturing method that can produce complex geometries and optimized shapes with less process steps. In addition to distinct microstructural features, residual stresses and their formation are also inherent to AM components. AM components require several post-processing steps before they are ready for use. To change the traditional manufacturing method to AM, comprehensive characterization is needed to verify the suitability of AM components. On very demanding corrosion atmospheres, the question is does AM lower or eliminate the risk of stress corrosion cracking (SCC) compared to welded 316L components? This work concentrates on post-processing and its influence on the microstructure and surface and subsurface residual stresses. The shot peening (SP) post-processing levelled out the residual stress differences, producing compressive residual stresses of more than −400 MPa in the AM samples and the effect exceeded an over 100 µm layer below the surface. Post-processing caused grain refinement and low-angle boundary formation on the sample surface layer and silicon carbide (SiC) residue adhesion, which should be taken into account when using the components. Immersion tests with four-point-bending in the heated 80 °C magnesium chloride solution for SCC showed no difference between AM and reference samples even after a 674 h immersion.

Effect of process route on powder three-dimensional-printing of metal powders

Purpose The purpose of this study is to investigate the effect of two unique processing routes (solvent jetting (SJ) and binder jetting (BJ)), on the green density of printed stainless steel 316L (SS316L) and Nickel (Ni) powders. Design/methodology/approach In the SJ processing route, a solvent is jetted unto the powder/binder mixture to selectively activate the binder, layer by layer. In the BJ processing route, a solution of the binder mixture is jetted onto the powder bed to selectively bind powder particles. The effects of printing parameters such as layer height, roller speed, shaker speed and nozzle temperature on the green density of printed components are investigated and compared for both processing routes. Findings Results show that layer height and nozzle temperature affect the relative density of the printed compact for both processing routes. Slightly higher relative densities were achieved via the SJ route, with the overall highest relative density being 42.7% at 100 µm layer height and 70% nozzle temperature for the SS316L components and 43.7% at 150 µm layer height and 90% nozzle temperature for the Ni components, respectively. Results also show an increase in the final sintered relative density with an increase in green (printed) relative density of the solvent jetted SS316L components, with the highest relative density being 87.2%. Originality/value The paper studies the influence of printing parameters on the green density of printed SS316L and Ni samples in an unprecedented effort to provide a comparative understanding of the process-property relationships in BJ and SJ of SS316L and Ni components to the additive manufacturing research community.

Corrosion Behaviour of 316L Stainless Steel in CNTs-Water Nanofluid: Effect of Temperature.

The inhibition behavior of carbon nanotubes (CNTs) and Gum Arabic (GA) on the corrosion of 316L stainless steel in CNTs–water nanofluid under the effect of different temperatures was investigated by electrochemical methods and surface analysis techniques. Thereby, 316L stainless steel samples were exposed to CNTs–water nanofluid under temperatures of 22, 40, 60 and 80 °C. Two concentrations of the CNTs (0.1 and 1.0 wt.% CNTs) were homogenously dispersed in deionized water using the surfactant GA and tested using three corrosion tests conducted in series: open circuit test, polarization resistance test, and potentiodynamic scans. These tests were also conducted on the same steel but in solutions of GA-deionized water only. Tests revealed that corrosion increases with temperature and concentration of the CNTs–water nanofluids, having the highest corrosion rate of 32.66 milli-mpy (milli-mil per year) for the 1.0 wt.% CNT nanofluid at 80 °C. In addition, SEM observations showed pits formation around areas of accumulated CNTs that added extra roughness to the steel sample. The activation energy analysis and optical surface observations have revealed that CNTs can desorb at higher temperatures, which makes the surface more vulnerable to corrosion attack.

Interplay between the composition of the passive film and the corrosion resistance of citric acid‐passivated AISI 316L stainless steel

Citric acid passivation is an attractive alternative to increase the corrosion resistance of stainless steels. In this work, the correlation of passive film composition and the corrosion properties of citric acid‐passivated AISI 316L stainless steel samples was assessed. The concentration of citric acid in the passivating solution was varied from 10 to 30 wt.%. Passive film composition was examined by X‐ray photoelectron spectroscopy. The corrosion behavior was investigated by potentiodynamic polarization curves. The citric acid passivation treatment led to Cr2O3 enrichment of the passive film, especially for the 20‐wt.% concentration. By increasing the citric acid concentration to 30 wt.%, the corrosion resistance decreased. In addition to chromium compounds, the passivation treatment also affected the relative concentrations of Fe, Mo, and Ni compounds in the passive films. The formation of Mo oxides was triggered at citric acid concentrations of 10 and 20 wt.%, contributing to slower anodic dissolution rate. The corrosion resistance of the passivated samples was favored as the relative concentration of Fe oxides (FeO and Fe2O3) increased with respect to FeOOH.

Electrochemical studies and corrosion resistance of activated Tungsten inert gas AISI SS316L weldments

Welding is the most convenient fabrication process with tremendous development in past few decades. The noteworthy technique is Activated flux TIG welding method (also known as A-TIG welding) that was well-equipped a little while back, which enhances productivity and quality of weld joints by better depth of penetration. In this research work, the electrochemical studies are performed to investigate the corrosion resistance of excellent depth of penetration A-TIG welded 316L stainless steel (SS316L) sample at room temperature. At dilute aqueous ambience, Potentiodynamic studies reveal that the SS316L welding joints have an apathetic attitude with certain range. Electrochemical Impedance calculations illustrate the breakdown occurs due to corrosion in alkaline circumstances.

Cavitation erosion resistance of 316L stainless steel fabricated using selective laser melting

Cavitation erosion degrades the performance and reliability of hydraulic machinery. Selective laser melting (SLM) is a type of metal additive manufacturing technology that can fabricate metal parts directly and provide lightweight design in various industrial applications. However, the cavitation erosion behaviors of SLM-fabricated parts have rarely been studied. In this study, SLM 316L stainless steel samples were fabricated via SLM technology considering the scanning strategy, scanning speed, laser power, and build orientation. The effect of the process parameters on the cavitation erosion resistance of the SLM-fabricated 316L stainless steel samples was illustrated using an ultrasonic vibratory cavitation system. The mass loss and surface topography were employed to evaluate the surface cavitation damage of the SLM-fabricated 316L stainless steel samples after the cavitation test. The cavitation damage mechanism of the SLM-fabricated samples was discussed. The results show that the degree of cavitation damage of the sample fabricated via SLM with a few defects, anisotropic build direction, and columnar microstructure is significantly decreased. Defects such as pores, which are attributed to low laser power and high scanning speed, may severely aggravate the cavitation damage of the SLM-fabricated samples. The sample fabricated via SLM with a low laser power and exposure time exhibited the highest porosity and poor cavitation erosion resistance. The cellular structures are more prone to cavitation damage compared with the columnar structures. A sample with a high density of grain boundaries will severely suffer cavitation damage.

Wearing Behavior of the α-Al9FeMnSi Intermetallic Compound Formed by Reactive Sintering onto AISI 304L Stainless Steel

In this study, using mixtures of pure Al, Si, Mn, and Fe powders, the α-Al9FeMnSi intermetallic compound was formed onto AISI 304L stainless steel samples by reactive sintering. The processing parameters were temperature (800, 850, and 900 °C) and applied pressure (15 and 20 MPa), using a constant holding time of 7200 s. In this paper, the influence of pressure and temperature on the microstructure, microhardness, and wear resistance of the formed layers was studied. Using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing, and wearing measurements (pin on disc tests), the cross-section and top side of the coatings were observed and analyzed. We were able to determine the phase composition of cladded layers and interfaces as well as their morphology. The results indicated that several layers were formed during reactive sintering, i.e., an Al-diffusion layer on the top of the substrate, an interface, and the α-Al9FeMnSi coating itself. The microhardness values of the different layers formed were determined, ranging from 400 to 500 HV for the intermetallic coating, to 120 HV for the substrate. In this way, it was found that the formed intermetallic coating is suitable to increase the corrosion resistance of stainless steel. Additionally, all the coating showed high adherence to the substrate, exhibiting high microhardness and wear resistance. Pin on disc wearing tests showed the wearing mechanisms are predominantly delamination and ablation of the cladded layers and substrate.

Influence of substrate temperature on microstructural and mechanical properties of 316L stainless steel consolidated by laser powder bed fusion

This study investigates the microstructure and mechanical properties of 316L stainless steel (316LSS) samples fabricated by additive manufacturing (AM), in order to optimise the process for improving the properties of 316LSS parts built by laser powder bed fusion (LPBF). Accordingly, a substrate heating was performed on an SLM 280HL printer fitted with an experimental heating device. During the process, samples are built on a substrate heated up to 600 ∘C. The substrate temperature significantly influences the microstructural evolution and mechanical properties of manufactured parts. Concerning tensile properties, the ultimate tensile strength (UTS) and yield strength (YS) decrease as a function of the substrate temperature whereas the elongation (El) increases as a function of the substrate temperature. These results are similar to those obtained with a post-heat treatment performed on parts manufactured by forging or LPBF. The tensile and impact energies reach values higher than the minimum requirement for 316LSS manufactured by forging, according to the RCC-MRx code used for materials dedicated to French nuclear applications. When the substrate temperature is equal to 350 ∘C, the UTS, YS, El and impact energy reached 596 ± 5 MPa, 489 ± 3 MPa, 48 ± 3% and 123 ± 20 J, respectively. Finally, this study demonstrates that heating the substrate during the process is a promising solution to optimise the fabrication route by suppressing post-process heat treatment of 316LSS made by LPBF.

Additive manufacturing of multiple layered materials (Ti6Al4V/316L) and improving their tribological properties with glow discharge surface modification

Selective Laser Melting (SLM), which is a kind of laser powder bed fusion additive manufacturing technology, is commonly used in the manufacturing of AISI 316L stainless steel components. This study aims to enhance the mechanical and tribological properties of 316L manufactured by using SLM and plasma oxidation treatment in a glow discharge atmosphere. For that reason, Ti6Al4V layers were formed on 316L stainless steel samples by selective laser melting. Samples with a duplex structure (316L substrate and Ti6Al4V layer) were oxidized at 650 °C and 750 °C for 1 h and 4 h in the plasma atmosphere. The characterization of the formed Ti6Al4V and oxide layers is determined by the Vickers micro-hardness tester, scanning electric microscope, 3D profilometer, Energy dispersive X-ray spectrometer, and X-ray diffractometer. Wear tests were performed against Al2O3 balls under a load of 10 N, dry sliding ambient air conditions by a pin-on-disk tribometer. It was observed that the hardness and wear resistance of Ti6Al4V layered and plasma-oxidized samples were better than the uncoated 316L samples due to the formation of titanium oxide phases and diffusion zone depth. The best wear resistance is obtained in the sample with the highest hardness value.

Investigation of effective coating of the Ti–6Al–4V alloy and 316L stainless steel with graphene or carbon nanotubes with finite element methods

BackgroundThe Ti–6Al–4V alloy and 316L stainless steel are widely used biocompatible implant materials for repairing bone fractures and their mechanical properties are now being considered for various other applications. Due to the mentioned reasons, we initially investigated and determined the mechanical effects of these biocompatible implant materials. In the sequel, as a novelty of this study, we adopted a unique approach to investigating these materials and sought to determine if coating the Ti–6Al–4V alloy and 316L stainless steel with graphene or carbon nanotubes (CNTs) could provide superior mechanical properties compared to when their surface is uncoated. MethodsTo investigate the mechanical effects of the Ti–6Al–4V alloy and 316L stainless, finite element method was utilized. Finite element analyses (FEAs) of the Ti–6Al–4V alloy and 316L stainless steel samples were comparatively conducted with the numerical results in literature. Static structural analyses were generated for the externally fixated femur in the single-leg stance position. Comparative static load analyses were performed for six distinctive cases of the uncoated Ti–6Al–4V alloy and 316L stainless steel, and graphene-coated Ti–6Al–4V alloy, CNT-coated Ti–6Al–4V alloy, graphene-coated 316L stainless steel, and CNT-coated 316L stainless steel. ResultsThe results of the static load analyses of the six distinctive cases show that the uncoated Ti–6Al–4V, graphene-coated Ti–6Al–4V, and CNT-coated Ti–6Al–4V samples stress values are 48.29 MPa, 36.24 MPa, and 87.574 MPa for the femur, the first screw, and plate stresses, respectively. These stresses are the minimum stress values occurred on the femur, the first screw, and the plate, respectively. On the other hand, the graphene-coated 316L and CNT-coated 316L stainless steel samples had the minimum displacement values, which were obtained as 1.558 mm, 1.5576 mm at the femoral head, and 0.13029 mm, 0.13028 mm at the fracture line, respectively. ConclusionThe main result and conclusion of this study is that coating the Ti–6Al–4V alloy and 316L stainless steel samples with graphene or CNTs results in superior mechanical performance in comparison to when they are uncoated. Considering the FEAs of the six different materials, CNT- or graphene-coated Ti–6Al–4V and CNT- or graphene-coated 316L stainless steel are the most recommended finite element models (FEMs) in terms of stress and displacement values, respectively. By using CNT- or graphene-coated Ti–6Al–4V and CNT- or graphene-coated 316L stainless steel, more durable, stable externally fixated implants can be obtained for femoral shaft fractures in terms of stress and displacement reduction occurred on both femur and implants.