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This study thoroughly examines the influence of conventional and selective laser melting (SLM) routes and surface mechanical attrition treatment (SMAT) on the microstructural and electrochemical properties of 316L steel. Compared to wrought specimens, the SLM specimens exhibit significantly smaller grains (∼41 vs. ∼83 µm) and higher dislocation density (∼7.2 × 1013 vs. ∼3.7 × 1012 m−2). Both specimens show nearly doubled surface hardness after SMAT, with the SLM surface displaying a ∼30 nm grain size and minimal α' phase. The microstructure significantly influences passivation and corrosion behaviour. The SLM specimens exhibit superior electrochemical characteristics to wrought counterparts in SMATed (0.00299 mmpy) and non-SMATed (0.00771 mmpy) conditions. SMAT effectively eliminates surface porosity, enhancing the passivation and corrosion resistance of SLM steel. [ABSTRACT FROM AUTHOR]

During the fabrication of Inconel 718–AISI 316L bimetallic components via laser powder-directed energy deposition, understanding the relationships between processes, microstructures, and material properties is crucial to obtaining high-quality parts. Physical–chemical properties, cooling rates, and thermal expansion coefficients of each material may affect the microstructure of parts, generating segregations and cracks. This paper analyzes how the process parameters affect the dimensions, chemical composition, and microhardness of bimetallic tracks. We created a dataset that included laser power, powder feed rate, material, skeletal density, dimensional features, chemical composition, and microhardness. Then, a deep learning methodology using a multilayer perceptron was used to estimate the relationship between these factors. The architecture comprised four inputs in the input layer and five hidden layers with 20, 40, 30, 30, and 30 neurons, respectively. This architecture was used to estimate the dimensional features, chemical composition, and microhardness. The model precision was evaluated using the determination coefficient (R2) and the mean absolute error (MAE) function. Lastly, we used a random forest classifier to select the bead quality from the optimal process parameters. The results showed a significant decrease in training loss and validation loss between 50 and 100 epochs. This decreasing trend continued until 350 epochs. This paper contributes to understanding the relationships between process–structure properties in the bimetallic tracks of Inconel 718 and AISI 316L. [ABSTRACT FROM AUTHOR]

This study investigates how welding travel speed and spindle speed influence the quality of welds in 270 mm diameter AISI 316L stainless steel pipes joined through friction stir welding (FSW). The FSW process was performed with spindle speeds of 250 rpm and 300 rpm, and travel speeds of 50 mm/min and 100 mm/min, utilizing a PCBN-coated W–Re tool in position control mode. Axial force, spindle torque and penetration depth were evaluated. The microstructure was analyzed using an optical microscope to understand the effects of spindle and travel speeds. High-resolution microscopy was employed to identify variable grain sizes across different weld zones. Vickers micro-hardness tests showed higher hardness in the stir zone and adjacent thermo-mechanically affected regions. The joint welded at 300 rpm and 100 mm/min displayed the highest hardness in the stir zone at 254 HV, indicating grain refinement confirmed by microstructural evaluation. [ABSTRACT FROM AUTHOR]

At present, in the directed energy deposition (DED) of metals, the heat transfer of the melt pool and microstructural evolution are not fully understood. This study investigates the thermal effect on the microstructure and the mechanical properties of DED AISI 316L, using in situ optical monitoring. Five thin-wall samples were tested to determine the effect on microstructural evolution and mechanical properties with variable laser powers and scanning speeds. A comprehensive optical monitoring system with a CMOS (coaxial complementary metal oxide semiconductor) visual module and an infrared camera was adopted in analyzing the temperature gradient and the solidification rate. The emissivity of the melt pool was calibrated, using the melt pool length, extracted from the coaxial visual image. The results showed that microstructures mainly consist of the coarse columnar grain and the equiaxed grain at the top layer of AISI 316L samples. The direction of epitaxial growth of columnar grains is affected by the compromise between directional heat flux and crystallographic direction. High numerical temperature gradient and high solidification rate are beneficial to obtaining fine grain size and high yield stress. A modified microstructure map for DED AISI316L was established, which correlates the solidification parameters with a solidification microstructure. This research study, combining temperature distribution, solidification parameter, microstructure, and tensile property, provides an experimental identification of solidification parameters and the model on the solidification theory for precision control of DED process. [ABSTRACT FROM AUTHOR]

Recently, the production of metal products has become more adaptable and rapid because of the use of 3-D technologies based on layer-by-layer manufacturing. The quality of products produced using selective laser melting (SLP technology) depends on many factors, which can be divided into main groups: equipment, materials, processes, details, and finishing. To ensure high-quality products, a systematic approach is necessary. Subject of research. Patterns of influence of changes in combinations of the main parameters of the manufacturing process (scanning strategy, distance between tracks, specific power of the process, scanning speed, power) of various elements (main body, border, post-border) of products manufactured using SLP technology on their quality (integrity and surface roughness). Purpose. Development of recommendations for border and post-border printing modes for 316L stainless steel with a layer thickness of 30 μm at different distances between tracks and with varying laser beam scanning speeds. Methods. For research purposes, samples of 10×10×5 mm were prepared using SLP technology from AISI 316L austenitic steel powder. The main body of the test samples was produced with constant parameters: layer thickness 30 μm, power 100 W, scanning speed, 1700 mm/s; distance between tracks, 0.05 mm; calculated specific energy density is 39.21 J/mm3, continuity ~ 99, 9%. The test samples of groups A, B, and C differed according to the scanning strategy (Out2In or In2Out) and the distance between the boundary tracks. Test samples of groups D, E, and F were made with constant power parameters of 100 W and the distance between the border tracks of 0.05 mm and with variable scanning speed parameters for group D 2.6...1.75 m/s; for group E 2.6...1.55 m/s; for group F 3.0...1.55 m/s. Samples were printed on an Alfa-150 3D printer by ALT Ukraine LLC. Etching of the structure was carried out in Kalling’s solution, and analysis of the microstructure was carried out using an AxioVert 200MMat optical microscope. Roughness control was performed using BioBase 220R with a constant control zone of 1.25 mm. Results. It was established that the borders of samples of groups A and C printed in the range of specific energy density ≈27-33 J/mm3 have thin borders that do not protrude and have no visible deviations. Roughness control showed that test samples A3, A4, C4, D5, E1, E2, and F6 had roughness values in the range of 9.7...11.2 microns. When comparing the obtained data with the manufacturing parameters and microstructure analysis, it was established that to achieve high continuity with minimal roughness in the finished products on the surface, it is necessary to apply the parameters in such a way that the post-contour manufacturing parameters energetically fluctuate in the range of ± 4 J/mm3 from the specific energy density main body.

This study focused on standard Compact Tension (CT) specimens and two loading modes during the numerical analyses carried out, namely: pure mode I and mixed-mode loading (Modes I+II). Numerical stress intensity factors, KI, were calculated using Abaqus® 2022 and compared with those given analytically under pure mode I loading, showing very good agreement. Additionally, KI, KII, and KIII results obtained from Abaqus® were presented for mixed-mode loading, analyzing crack growth and variation through the thickness of the CT specimen. Moreover, fatigue crack growth simulations under mode I loading were conducted on standard CT specimens using the Extended Finite Element Method (XFEM) and the Paris Law parameters of an AISI 316L stainless steel. It was shown that XFEM effectively determines crack propagation direction and growth, provided that an appropriate mesh is implemented. [ABSTRACT FROM AUTHOR]

The directed energy deposition arc (DED-Arc) has been extensively used to develop metallic parts with varying complexities. A major challenge for austenitic stainless steels is managing heat accumulation due to their low thermal conductivity. This study aimed to characterize the microstructure and mechanical properties of AISI 316L preforms manufactured by additive manufacturing (AM) under different deposition paths and cooling conditions. Samples underwent macro- and microstructural analyses, and tensile and hardness tests to evaluate their mechanical behavior. Additionally, the effect of active cooling using near immersion active cooling (NIAC) in water on the microstructure was assessed by examining the secondary interdendritic spacing and ferritic phase fraction. The NIAC technique has shown potential for enhancing productivity by producing preforms with more uniform thickness and consistent solidification/cooling conditions throughout the multiple layers. This approach eliminated deposition idle time, leading to a productivity increase of up to 108%. Microstructures obtained with active cooling were more refined than those resulting from natural cooling, evidenced by a reduction in secondary interdendritic spacing and an increased fraction of delta ferrite. These microstructural changes resulted in higher hardness and mechanical strength in the material processed with the NIAC technique. However, difficulties in precisely controlling the water level resulted in increased apparent porosity when using the NIAC technique. [ABSTRACT FROM AUTHOR]

The main objective of this study is to evaluate residual stresses in AISI 316L and 18Ni Maraging 300 functionally graded materials with continuous variation of composition within a single layer using the contour method. The manufacture of this kind of layer-level continuous functionally graded materials by employing a Powder Bed Fusion-Laser Beam system utilizing a blade/roller-based powder spreading technique has only been recently devised and a proper residual stress analysis is still required. In fact, as the mechanical properties of additively manufactured samples are significantly influenced by the direction of construction, the same holds true for the direction along which the compositional variation is made. Furthermore, in this study, the impact of solution annealing and aging heat treatment, which are necessary for enhancing the mechanical properties of martensitic steel, on residual stresses was explored. Additionally, the effect of adopting material-differentiated process parameters was investigated. The results indicated that each specimen displayed areas of tensile stress concentration on the upper and lower surfaces, balanced by compression in the center. The application of heat treatment led to a decrease in the maximum tensile stress of 8% and provided a uniform and significant stress reduction within the maraging steel. Finally, the implementation of material-specific process parameters for the three composition zones in conjunction with the heat treatment resulted in a reduction in the maximum residual stress of 35% and also a significantly lower residual stress field throughout the specimen. [ABSTRACT FROM AUTHOR]

In the present paper, a unique laser cladding-assisted high-frequency vibration device was applied to prepare the AISI 316L cladding layer by laser cladding on the surface of the AISI 316L stainless steel substrate. The macroscopic morphology, microstructure, microhardness, and wear resistance of the cladding layer were analyzed by optical microscope, scanning electron microscope, Vickers microhardness tester, friction and wear tester, and three-dimensional optical profiler. The laser cladding-assisted high-frequency vibration device uses a high-frequency oscillator with a fixed frequency (20 KHz) to transfer vibration energy through the probe in contact with the substrate and close to the molten pool. This paper explores the effect of different laser powers on the dilution rate of the cladding layer, compares and observes the cross-sectional morphology and microstructure of the cladding layer with and without high-frequency vibration, and analyzes the reasons for the different results. [ABSTRACT FROM AUTHOR]

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This study presented a numerical methodology to elucidate the local mechanical response of the surface layer during and after an EDM electrical discharge, aiming to refine the numerical prediction of the residual stress and strain hardening induced by this process. Advances in models, loads, and boundary conditions were proposed and simulated using the ABAQUS/Explicit computational software. A coherent thermomechanical model was formulated, incorporating Grüneisen's hydrodynamic behavior coupled with the Johnson-Cook plasticity model. Numerical findings highlighted the efficiency of the uniform heat flux distribution model in predicting residual stresses accurately. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) process parameters significantly influence the microstructure and mechanical properties of the final product. Using the Taguchi optimization method, this investigation refined 316L austenitic stainless steel SLM process parameters. Process factors included laser power, scanning speed, and layer thickness, while performance criteria included relative density and hardness. A laser power of 180 W, a scanning speed of 1200 mm/s, and a layer thickness of 0.03 mm produced optimal results, resulting in 125 J/mm3 energy density and a hardness of 220 HV. ANOVA analysis also showed that power influenced density by 27.49 %, scanning speed by 45.51 %, and layer thickness by 23.60 %. A parameter combination led to materials with impressive tensile strengths (649 ± 4 MPa), yield strengths (409 ± 3 MPa), and elongation (42 ± 1 %) for increasing scanning speed and lowering energy density, resulting in a decrease in ultimate strength. A SEM analysis of fracture characteristics was also conducted. As a result of a cellular microstructure, ductile dimple sizes were limited to the nanoscale, and crack propagation was impeded through a pinning effect, thus increasing defect tolerance in the SLM SS316L. According to the findings, internal defects play a significant role in crack propagation and subsequent reduction of mechanical properties.

The surface characteristics and corrosion behavior of electropolished AISI 316L stainless steel specimens were analyzed. The influence of the electropolishing process parameters, such as voltage, temperature, time, cathode material, cathode geometry, and cathode–anode distance, was also evaluated using an electrolyte composed of sulfuric acid, phosphoric acid, and water. The surface characteristics of the specimens were determined by means of scanning electron microscopy, X-ray diffraction, microindentation tests, and contact profilometry. Corrosion tests were carried out using 3.5% w/v NaCl aqueous solution as a corrosive medium. The results indicate that the electropolishing process on AISI 316L greatly reduces the roughness of the samples when proper parameters are used. However, the waviness exhibits a more irregular behavior. It is also demonstrated that the use of stainless steel cathodes instead of copper cathodes allows obtaining surfaces with less roughness. Electropolishing produces the elimination of the deformed surface layer and, if present, of the martensite phase. This results in a decrease in surface hardness. The corrosion resistance of AISI 316L increases after the electropolishing process. In the case of cylindrical specimens, greater homogeneity in roughness parameters is obtained by using a cylindrical cathode concentric with the specimen instead of flat cathodes. [ABSTRACT FROM AUTHOR]

We investigated the parametric optimization on incremental sheet forming of stainless steel using Grey Relational Analysis (GRA) coupled with Principal Component Analysis (PCA). AISI 316L stainless steel sheets were used to develop double wall angle pyramid with aid of tungsten carbide tool. GRA coupled with PCA was used to plan the experiment conditions. Control factors such as Tool Diameter (TD), Step Depth (SD), Bottom Wall Angle (BWA), Feed Rate (FR) and Spindle Speed (SS) on Top Wall Angle (TWA) and Top Wall Angle Surface Roughness (TWASR) have been studied. Wall angle increases with increasing tool diameter due to large contact area between tool and workpiece. As the step depth, feed rate and spindle speed increase, TWASR decreases with increasing tool diameter. As the step depth increasing, the hydrostatic stress is raised causing severe cracks in the deformed surface. Hence it was concluded that the proposed hybrid method was suitable for optimizing the factors and response. [ABSTRACT FROM AUTHOR]

In this study, the impact wear behaviour of Al-5Mg, used as a corrosion protective coating was investigated in seawater and air environments. Tests were conducted for up to 105 cycles on the plane surface of Al-5Mg coated AISI 316L samples. Wear at the frequency of 2.5 Hz kept the coating thickness at a reliable level. However, the wear that occurred under the frequency of 5Hz reached the substrate surface. In the experiments conducted in seawater, smoother wear scars were formed compared to those in the air environment tests. The coating particles separated by the wear effect were compressed by the impactor on the wear surface with repetitive impacts, causing delamination. Friction oxidation was formed on wear scars. The hydrodynamic effect of seawater reduced the delamination by removing the separated coating particles from the surface. Thus, in seawater, 70% more wear occurred compared to in the air environment. [ABSTRACT FROM AUTHOR]

AISI 316L is a metallic biomaterial used in Unified Health System (SUS) due to low cost. However, corrosion in AISI 316L is a major cause of premature failure and toxic reactions to implants. Nanotubular or nanoporous anodized layers have proven to be good and affordable alternatives to create greater interaction and less damage to human tissue. Thus, the main of this study was to obtain a nanoporous layer by anodizing on AISI 316L, aiming to improve its corrosion resistance for use as a biomaterial. AISI 316L were anodized in 10M NaOH, 0.6mA/cm2 for 5 and 10min. Transients of current density and potential and oxide color were evaluated. Anodized layers were characterized by scanning electron microscopy, X-ray diffraction analysis and electrochemical assays. Nanoporous anodized layers with nanoplate arrangement were obtained. The 5min anodized sample showed better corrosion resistance than the original steel, being considered promising for use as a biomaterial.

In recent years, the actual production of metal products directly from electronic data according to a three-dimensional model based on layer-by-layer manufacturing has evolved from rapid prototyping to additive manufacturing. As the quality of additively manufactured metal products continues to increase and their manufacturing processes improve and develop, the demand for additive manufacturing is increasing. Additive manufacturing technology, also known as 3D printing, has become increasingly popular recently. Using additive manufacturing, almost any complex geometry can be manufactured with high degree of precision. After the production of parts using the SLM technology from metal powder, post-processing is applied, in particular electrochemical polishing, the main purpose of which is to reduce surface roughness, increase the gloss of surface elements, and remove metal powder that has partially melted onto the outer surface of the product at the point of contact between the molten metal and the border of the part and the powder, which is located next to the melt. This is especially important for inclined surfaces, internal channels and cellular structures with developed outer surface. For research, samples were made using SLM technology from AISI 316L austenitic steel powder. The samples have a cube shape with a base of 10 mm, a height of 10 mm, and a thickness of 10 mm, with cell widths of 4 mm and 2 mm. The main body of both samples was printed using the same modes at a laser power of 220 W, a scanning speed of 1000 mm/s and a distance between laser passes of 0.14 mm. Samples were printed on Alfa-280 3D printer manufactured by ALT Ukraine LLC. Electropolishing was carried out in a solution of orthophosphoric acid (H3PO4) with glycerol (C3H8O3) by immersing the test samples in the electrolytic solution at a voltage of 17 V and a current density of 3 A/cm2. The control of weight and geometric parameters was carried out with the help of ADV-2000 analytical balances and MKC-25 micrometer. The electropolishing of the experimental samples took place in four stages: 1) visual - optical inspection with fixation, weight control before the start of the process; 2) electropolishing for 3 minutes, visual - optical inspection with photo fixation; weight control after 3 min. polishing process; 3) electropolishing of the same samples for another 3 minutes, visual – optical inspection with photo fixation, weight control after 6 minutes. polishing; 4) electropolishing of the same samples for another 3 minutes, visual - optical inspection with photo fixation; weight control after 9 min. electropolishing process. At each stage, a real current-voltage curve was recorded using an oscilloscope. As a result of weight control before and after the test, it was established that the samples lost approximately the same weight in the range of 6.9...7.1 % relative to the initial one. Based on the analysis of the obtained results, it was established that at a current density of 3 A/cm2 and at a voltage of 17 V, effective active uniform polishing of the surface of samples with a cellular structure of scaffold type with a variable cell size from 4 to 2 mm is realized.

Erosion of solids by liquid droplets is a phenomenon which is a compromise between mechanical properties of the material and droplet hydrodynamic parameters. While a number of studies deal with the deformation of drops, the deformation evolution inside the material has not yet been revealed, mainly from the point of view of the time action of the impinging drops The mechanical response of AISI 316L was investigated under gradually increasing numbers of impingements of liquid droplets, with a droplet volume of Vd ≅ 0.9 mm3, generated by an ultrasonic pulsating water jet with the frequency f = 40 kHz from 1 to 20 s. The surface roughness and the wear rates were determined using a laser profilometer. The cross-section of the selected samples was subjected to microhardness measurement with a load of 0.150 N in a 2D grid, which included the entire perimeter of the deformed area. The minimal microhardness measurement grid under the groove had dimensions of 15 × 15 indents, equal to an area of approximately 450 × 600 µm. A maximum hardness increase was observed at the lowest measured depth of 30 µm. An increase in hardness was observed at 300 µm below the surface. The hardening in the deeper subsurface area was most likely caused by shear stress. This shows the high degree of similitude between the solid and liquid droplet impingements. The results indicate that the currently accepted theory on the development of erosion over time has shortcomings, as demonstrated in this work by the ratio between the utilised droplet diameter and the grain size of the material.

Diffusion bonding has many advantages, but it also has its specifics. When creating heterogeneous joints, problems arise with the creation of intermetallic phases. For this reason, an interlayer is needed to prevent the creation of these unfavorable phases. It is important to ensure that the interlayer is of sufficient thickness to prevent the elements from diffusing through the entire interlayer and the intermetallic phases from being formed again. Conversely, too thick an interlayer causes an increase in the heterogeneity of the bond properties. The creation of the initial diffusion bonds in a heterogeneous diffusion joint of AISI 304 and AISI 316L steel with a 0.2 mm thick nickel interlayer was made in a Gleeble 3500. The experiments to determine the diffusion kinetics were carried out in a vacuum furnace, with subsequent evaluation by EDX (Energy Dispersive X-ray Spectroscopy) analysis. Subsequently, the diffusion coefficients of nickel into both steels were determined, and generalized equations were formulated to calculate the diffusion coefficients for temperatures in the range of 950 to 1150 °C and holding times in the range of 3600 to 18,000 s. Equations are also given to determine the width of the diffused zone between each steel and the Ni interlayer. [ABSTRACT FROM AUTHOR]

There are several methods of analysis used in the metalworking industry for dry machining processes and with Minimum Quantity Lubrication (MQL). Evolutionary methods [1] have been used in the decision-making process in the machining process to select the optimal data and to analyze the behavior of variables such as cutting speed (V), feed rate (f) and cutting depth (ap). This work addresses the use of evolutionary algorithms of low dominance class II and III (NSGA-II and NSGA-III) to analyze from the multicriteria approach the initial wear of the cutting tool (VB), the energy consumption (E) and the machining time (t) in the turning process of the AISI 316L steel workpiece for biomedical purposes. As input variables to the algorithm with 54 records, there are: cutting speed (V: 200, 300, 400 m/min) and feed rate (f: 0.1, 0.15, 0.2 mm/rev). The experiment was developed for a dry (1) turning operation and with the use of MQL (-1). For the MQL lubrication regime, a TRI-COOL MD-1 lubricant was employed, a vegetable type used in ferrous and non-ferrous metal cutting operations. A BIDEMICS JX1 ceramic cutting tool was used.

Additive manufacturing (AM) represents the present and the future of manufacturing production, thanks to a new design paradigm that allows the customization of components based on the needs of the final application, all framed in a perspective of sustainable and on-demand production. It has become an increasingly popular method for manufacturing complex and custom parts, especially those made from metallic materials, such as AISI 316L. AISI 316L is a type of austenitic steel widely used in industries such as aerospace, medical, automotive, and marine due to its excellent corrosion resistance and high strength. Thanks to its physico-chemical properties, AISI 316L stainless steel is one of the most used metals for AM. In this paper, a critical review of printing technologies, microstructural defects, mechanical properties, as well as industrial applications of AISI 316L are presented based on the state of the art. Furthermore, the main challenges with AM AISI 316L techniques are discussed, such as the influence of printing parameters, surface quality, and other common problems identified in the literature. Overall, this paper provides a comprehensive overview of AISI 316L AM techniques, challenges, and future research directions. [ABSTRACT FROM AUTHOR]

Intermetallic formation during dissimilar welding of Inconel and stainless steel significantly hinders producing sound-quality weld. In the present work, a high-power CO2 laser welding system is employed to join Inconel 718 and AISI 316L stainless steel without using any filler materials. The finite element based thermal model provides the temperature distribution in the weld zone and consequently the solidification parameters (G/R and G.R). The micro-segregation and intermetallic formation in laser welding are correlated with these solidification parameters. The segregation of principal alloying elements triggers the formation of intermetallic phases during solidification. The presence of various phases like Laves, NbC, and TiC in the fusion zone reduces with increase in heat input. The amount of these intermetallic phases present in the weld zone is estimated by XRD analysis. With an increase in heat input, the mode of solidification changes from columnar to equiaxed dendrites that is characterized at reduced value of solidification parameter (G/R). The intermetallic Laves particle diminishes significantly (more than 90%) with a reduction of G/R parameter. In equiaxed dendrites, the segregation and formation of these secondary particles reduces to more than 40% compared to the columnar dendritic structure. Overall, the reduction in the intermetallic particles improves the joint efficiency up to 100% with an elongation of 14.2% for the equiaxed structure of the laser welding system. Graphical abstract [ABSTRACT FROM AUTHOR]

There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, a gel electrolyte containing 3.5% NaCl and a measuring cell based on the three-electrode arrangement were developed to prevent the corrosion medium from infiltrating the typical microstructure of thermally sprayed coatings (pores and microcracks). The newly developed method was evaluated on AISI 316L coatings deposited by high velocity air fuel (HVAF) and atmospheric plasma spraying (APS). The polarization curves showed significant differences as a result of spraying process-related changes in the coating microstructure. Even slight differences in oxide content within the AISI 316L coating produced by APS can be detected by the new method. In order to verify the new findings, the coatings were analyzed regarding their microstructure by optical microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. The measuring cell and gel electrolyte developed offer a promising opportunity to evaluate the quality of thermally sprayed coatings in a largely non-destructive manner using polarization curves. [ABSTRACT FROM AUTHOR]

Ultra-short pulsed laser ablation may be used for high-precision machining with very low thermal influence on the processed materials. Due to this reason, lasers are increasingly used for processing of advanced materials, such as titanium alloys, nickel-based alloys or steel, every year. In this study, four advanced technical materials were analysed and compared under femtosecond laser irradiation with three different wavelengths. The main laser-material interaction parameters were identified, namely the ablation threshold and removal efficiency parameters. Higher removal rates were found for Ti6Al4V alloy with all three harmonic wavelengths. To increase process productivity, a method of increasing the repetition rate and scanning speed was presented. With the maximum repetition rate, the productivity increased five-fold with a similar removed depth and surface quality. Finally, the suitability of the identified parameters with regard to quality and productivity was demonstrated for fabrication of two complex structures – honeycomb and dot – which has the potential to improve friction properties of advanced materials.

Tungsten inert gas (TIG) welding is type of arc welding with area of applications in food industry, pharmaceutical industry, chemical plants, marine, aerospace, medical devices, and implants, etc. TIG welding process involve several parameters. Many parameters are controllable by the operator, and these parameters have a direct or indirect impact on the microstructure and mechanical properties of the joints. In the present study, three TIG welding parameters, arc current, voltage, and shielding gas flow rate, were changed up to three levels and their effects on surface roughness, hardness and tensile strength were investigated. Experiments were carried out on a 3 mm thick plate of austenitic stainless steel AISI 316L utilizing a TIG welding equipment and were designed according to Taguchi L9 orthogonal array (OA). ER308L was used as filler material. Results were analyzed using signal to noise S/N ratio and analysis of variance. It was observed that, for optimization of each response, arc current is the most influential factor. Minimum surface roughness was achieved at parametric combination of current 125 A, voltage 18 V and gas flow rate 12 L/min. Maximum hardness was achieved at parametric combination of current 125 A, voltage 20 V and gas flow rate 9 L/min. Maximum tensile strength was achieved at parametric combination of current 100 A, voltage 18 V and gas flow rate 6 L/min.

The damage mechanisms of metallic components produced by process laser powder bed fusion differ significantly from those typically observed in conventionally manufactured variants of the same alloy. This is due to the unique microstructures of additively manufactured materials. Herein, the focus is on the study of the evolution of creep damage in stainless steel 316L specimens produced by laser powder bed fusion. X-ray computed tomography is used to unravel the influence of the process-specific microstructure from the influence of the initial void distribution on creep damage mechanisms. The void distribution of two specimens tested at 600 °C and 650 °C is analyzed before a creep test, after an interruption, and after fracture. The results indicate that the formation of damage is not connected to the initial void distribution. Instead, damage accumulation at grain boundaries resulting from intergranular cracking is observed. [ABSTRACT FROM AUTHOR]

Calcium phosphate/Bioglass composite coatings on AISI 316L were investigated with regard to their potential role as a beneficial coating for orthopedic implants. These coatings were realized by the galvanic co-deposition of calcium phosphate compounds and Bioglass particles. A different amount of Bioglass 45S5 was used to study its effect on the performance of the composite coatings. The morphology and chemical composition of the coatings were investigated before and after their aging in simulated body fluid. The coatings uniformly covered the AISI 316L substrate and consisted of a brushite and hydroxyapatite mixture. Both phases were detected using X-ray diffraction and Raman spectroscopy. Additionally, both analyses revealed that brushite is the primary phase. The presence of Bioglass was verified through energy-dispersive X-ray spectroscopy, which showed the presence of a silicon peak. During aging in simulated body fluid, the coating was subject to a dynamic equilibrium of dissolution/reprecipitation with total conversion in only the hydroxyapatite phase. Corrosion tests performed in simulated body fluid at different aging times revealed that the coatings made with 1 g/L of Bioglass performed best. These samples have a corrosion potential of −0.068V vs. Ag/AgCl and a corrosion current density of 8.87 × 10−7 A/cm2. These values are better than those measured for bare AISI 316L (−0.187 V vs. Ag/AgCl and 2.52 × 10−6 A/cm2, respectively) and remained superior to pure steel for all 21 days of aging. This behavior indicated the good protection of the coating against corrosion phenomena, which was further confirmed by the very low concentration of Ni ions (0.076 ppm) released in the aging solution after 21 days of immersion. Furthermore, the absence of cytotoxicity, verified through cell viability assays with MC3T3-E1 osteoblastic cells, proves the biocompatibility of the coatings. [ABSTRACT FROM AUTHOR]

The focus of this paper is to compare the results of topological optimization (TO) of the rocker arm for following 3D printing out of AISI 316L stainless steel by the Selective Laser Melting (SLM) method. We used the Altair Inspire software to optimize the shape of the rocker arm. Two variants of optimization were created, first, a variant of optimization without the Shape Control function was carried out, which resulted in a complex mechanical component with an organic shape. This bionic design means more support for the SLM method of Additive Manufacturing (AM) and worse surface quality after their removal. Therefore, a second variant of optimization was produced with the application of the Shape Control function, which positively affects manufacturability and postprocessing. The use of shape control reduced the amount of supports to a minimum, helping to improve the surface finish. [ABSTRACT FROM AUTHOR]

Conventional processes are performed to improve the low hardness and low wear resistance properties of 316L steel, but these processes generally decrease the corrosion resistance. Electroless nickel alloy coatings provide a hard, wear‐resistant, and corrosion‐resistant surface. Thus, the present study aims to investigate the wear, corrosion, and tribocorrosion behaviors of monolayer and duplex coatings with nickel–boron (Ni–B) and nickel–phospore (Ni–P) on 316L steel in comparison with 316L steel in dry sliding and 0.9 wt% NaCl solution environments. It is determined that the coatings have a mixture of crystal and amorphous structures, the interfaces on the 316L are uniform, and the compatibility between the layers is good. The Ni–B, Ni–P/Ni–B, and Ni–B/Ni–P coatings are 2.3, 2.06, and 1.6 times as hard as the 316L, respectively. The wear rates of Ni–B, Ni–P/Ni–B, and Ni–B/Ni–P coatings show decrease by 99.3%, 92.5%, and 99.1% in the dry‐sliding condition and by 98.5%, 30.1%, and 19.1% in the tribocorrosion condition compared with that of 316L, respectively. It is observed that the monolayer Ni–B coating exhibits superior hardness, a higher contact angle, low electrical conductivity, and better tribological performance in both dry sliding and tribocorrosion conditions compared to the 316L and duplex coatings. [ABSTRACT FROM AUTHOR]

Bioimplants should meet important surface integrity criteria, with the main goal of the manufacturing process to improve wear and corrosion resistance properties. This requires a special approach at the cutting stage. During this research, the impact of the cutting parameters on improving the surface integrity of AISI 316L steel was evaluated. In this context of bioimplant applications, the mean roughness Sa value was obtained in the range of 0.73–4.19 μm. On the basis of the results obtained, a significant effect was observed of both the cutting speed and the feed rate on changes in the microstructure of the near-surface layer. At a cutting speed of 150 m/min, the average grain size was approximately 31 μm. By increasing the cutting speed to 200 m/min, the average grain size increased to approximately 52 μm. The basic austenitic microstructure of AISI 316L steel with typical precipitation of carbides on the grain boundaries was refined at the near-surface layer after the machining process. Changing the cutting speed determined the hardness of the treated and near-surface layers. The maximum value of hardness is reached at a depth of 20 μm and decreases with the depth of measurement. It was also noted that at a depth of up to 240 μm, the maximum hardness of 270–305 HV1 was reached, hence the height of the machining impact zone can be determined, which is approximately 240 μm for almost all machining conditions. [ABSTRACT FROM AUTHOR]

The present study aimed to critique the corrosion resistance of plasma-nitrided films of AISI 316L stainless steel with regards to their biomedical applications. The plasma nitriding process improves austenitic stainless steel's micro-hardness and corrosion resistance. Austenitic stainless steel was treated at a temperature of 470 °C for 12, 24, and 36 h, to observe the outcomes of plasma nitriding. The corresponding microstructure, microhardness, depth of the nitrided layer, and electrochemical parameters were systematically characterized. The corrosion resistance of the plasma-nitrided specimens was gauged using the weight loss method in simulated body fluids (Phosphate-buffered saline (PBS), saline water, and ringer solution) by static immersion for 9, 18, and 27 days. Optimization was catalogued using the Taguchi method L27 orthogonal array to determine the optimum combination of plasma nitriding time and immersion time in simulated body fluid. The material characterization showed that the corrosion resistance of the plasma-nitrided specimens improved with longer nitriding times by Tafel polarization curves. Microhardness was observed at 12, 24, and 36 h as 1060, 1150, and 1220 HV0.1. SEM, with an energy-dispersive X-ray analysis (EDS) used to characterize the surface before and after plasma nitriding testing. It was concluded that CrN, which precipitates during processing and contributes to the loss of chromium from the surrounding matrix and the onset of a corrosive environment, is the primary cause of this behaviour. [ABSTRACT FROM AUTHOR]

The present study aims to evaluate the microstructure, grain size, and mechanical properties of the dissimilar AISI 316L/Inconel 718 (IN 718) rotary friction welded joints under both the as-welded and post-weld heat treatment (PWHT) conditions. Because of reduced flow strength at elevated temperatures, the AISI 316L and IN 718 dissimilar weldments exhibited more flash formation on the AISI 316L side. At higher rotating speeds during friction welding, an intermixing zone was created at the weld joint interface due to the material softening and squeezing. The dissimilar welds exhibited distinctive regions, including the fully deformed zone (FDZ), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and the base metal (BM), located on either side of the weld interface. The dissimilar friction welds, AISI 316L/IN 718 ST and AISI 316L/IN 718 STA, exhibited yield strength (YS) of 634 ± 9 MPa and 602 ± 3 MPa, ultimate tensile strength (UTS) of 728 ± 7 MPa and 697± 2 MPa, and % elongation (% El) of 14 ± 1.5 and 17 ± 0.9, respectively. Among the welded samples, PWHT samples exhibited high strength (YS = 730 ± 2 MPa, UTS = 828 ± 5 MPa, % El = 9 ± 1.2), and this may be attributed to the formation of precipitates. Dissimilar PWHT friction weld samples resulted in the highest hardness among all the conditions in the FDZ due to the formation of precipitates. On the AISI 316L side, prolonged exposure to high temperatures during PWHT resulted in grain growth and decreased hardness. During the tensile test at ambient temperature, both the as-welded and PWHT friction weld joints failed in the HAZ regions of the AISI 316L side. [ABSTRACT FROM AUTHOR]

The present work discusses the macrostructure, microstructure, and microhardness of dissimilar metal weld joints between AISI 316L SS-DSS 2205 developed by gas tungsten arc welding (GTAW) welding. Post-weld heat treatments (PWHT) were carried out at temperatures of 750°C for 24 h and 850°C for 0.5 h. The macrostructure and microstructure of the welding joints at different welding conditions were observed by scanning electron microscope. The macrostructure study results indicated that all the welded joints were fully penetrated and free from defects. However, the microstructure investigation revealed a solid-state transformation of ferrite into grain boundary austenite, widmanstatten austenite, intergranular austenite, and partially transformed austenite. The post-weld heat treatment processes enhanced the precipitation of the sigma phase in the ferrite matrix. Secondly, the microhardness across and along the weld bead has been evaluated, and the results are compared. It was observed that the microhardness of the heat-affected zone of DSS 2205 is found to be higher as compared to a heat-affected zone of AISI 316L, the weld metal zone, and base metals at all welding currents (i.e. 90 A, 109 A, and 132 A). The microhardness values decrease when transverse from the face of the weld toward the root pass. Microhardness values at the fill (top) pass of the weld zone at 90 A, 109 A, and 132 A were 268.3 HV, 257 HV, and 255 HV respectively. It was found that the microhardness has improved significantly after post-weld heat treatments and was highest for 750°C/24 h. It may be due to higher holding time which led to the involvement of carbides. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) thin films are widely used in transparent optoelectronic devices due to their excellent properties, as well as in photocatalysis, cosmetics, and many other biomedical applications. In this work, TiO2 thin films were deposited onto AISI 304 and AISI 316L stainless steel substrates by atomic layer deposition, followed by comparative evaluation of the mixture of anatase and rutile phase by X-ray diffraction, Raman maps, morphology by SEM-FEG-AFM, and adhesion of the films on the two substrates, aiming to evaluate the scratch resistance. Raman spectroscopy mapping and X-ray diffraction with Rietveld refinement showed that the films were composed of anatase and rutile phases, in different percentages. Scratch testing using a diamond tip on the TiO2 film was employed to evaluate the film adherence and to determine the friction coefficient, with the results showing satisfactory adherence of the films on both substrates. [ABSTRACT FROM AUTHOR]

A hot press process was used as a technique to pound a polyamide type of polymer of a thickness (2mm) to stainless steel AISI 316L of the thickness (1mm). A hybrid joint of dissimilar material was accomplished by a hot press bonding process. During the joining process, three different parameters of process were used: processing temperature of 175, 170 and 165°C, processing pressure of 3, 6 and 9 bar and time of 1.5, 3 and 4.5 min. The surface of stainless steel was prepared and treated by a mechanical treatment (surface grinding) to improve the wettability to increase the shear strength. A shear tensile, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) tests were used to investigate and examine the joint (bounding) specimens. The Minitab program was used to analyze the effect of the parameters of the joining process on the joint properties. The maximum and minimum values of shear force are exhibited at a processing temperature of 165°C, applied pressure of 6 bars and processing time of 1.5 minutes; the minimum shear force was found to be 675 N, while the maximum shear force was 2182 N at a processing temperature of 175°C, applied pressure of 6 bars and processing time of 3 minutes. The tested joints failed by an interfacial shear and necking in the polymer side with a ductile fracture. The joining process occurred through a mechanical interlocking between the molten polymer and the treated surface of the steel specimen. The average thickness of the joining line for the tested specimens was 8m. [ABSTRACT FROM AUTHOR]

The laser powder-bed fusion (LPBF) process is one of the additive manufacturing processes used to produce intricate geometry without limits. LPBF processes materials layer-by-layer and can fabricate a wide spectrum of materials. However, its applicability as a coating method is rarely considered. The present study aims to fabricate Ti6Al4V coating on a 316L substrate. 316L plates were fabricated using the spark plasma sintering (SPS) process and are used as the substrate for the Ti6Al4V coating. The Ti6Al4V coating was performed on the substrate with/without laser pre-scanning using laser powder-bed fusion. Cracks were observed if the coating was performed without pre-scanning of the substrate and with pre-scanning the cracks disappear. A strong interfacing bonding was observed with the formation of FeTi and Fe2Ti intermetallic phases, which enhances the hardness of the coating. The compressive results show that both SPS 316L and Ti6Al4V coating on 316L show similar curves except that the sample with coating exhibits higher deformability. The present results portray the effectiveness of the LBPF process for coating purposes. [ABSTRACT FROM AUTHOR]

Nitrogen (N) in steels can improve their mechanical strength by solid solution strengthening. Processing N‐alloyed steels with additive manufacturing, here laser powder bed fusion (PBF‐LB), is challenging as the N‐solubility in the melt can be exceeded. This degassing of N counteracts its intended positive effects. Herein, the PBF‐LB processed 316L stainless steel with increased N‐content is investigated and compared to PBF‐LB 316L with conventional N‐content. The N is introduced into the steel by nitriding the powder and mixing it with the starting powder to achieve an N‐content of approximately 0.16 mass%. Thermodynamic calculations for maximum solubility to avoid N outgassing and pore formation under PBF‐LB conditions are performed beforehand. Based on the results, a higher defect tolerance under fatigue characterized by Murakami model can be achieved without negatively influencing the PBF‐LB processability of the 316L steel. The increased N‐content leads to higher hardness (+14%), yield strength (+16%), tensile strength (+9%), and higher failure stress in short time fatigue test (+16%). [ABSTRACT FROM AUTHOR]

• AISI 316L developed by LPBF process was subjected to heat and cryogenic treatments. • The crystal lattice structure is more orderly after cryogenic treatments. • Increased deformation of twins is observed after heat and cryogenic treatment. • Cryogenic treatment relieves internal residual stresses developed during printing. • Grain refinement occurs after the heat and cryogenic treatments. AISI 316L manufactured using laser powder bed fusion process was subjected to heat and cryogenic treatments. The effect of microstructural and mechanical properties, such as hardness, thermal residual stress, and Charpy impact, were investigated. The results indicate that after the heat and cryogenic treatment, the amount of austenite (FCC) phase increased, and the residual stress was removed after the heat and cryogenic treatment. The increase in deformation twins (Σ3) was observed after heat and cryogenic treatment. The cryogenic treatment altered the crystal lattice and orientation of crystal grains, resulting in grain refinement. [ABSTRACT FROM AUTHOR]

Surface coating through Laser Directed Energy Deposition (L-DED) of AISI 316L on low-carbon steel was carried out by varying laser fluence. The resulting melt pool characteristics, obtained through IR pyrometer, played a significant role in evolution of the microstructure. A higher heat input resulted in an equiaxed grain structure with finer grain sizes and improved deposition quality. The quantitative phase analysis revealed the presence of a dominant austenite phase and a secondary ferrite phase, along with traces of molybdenum carbide. Corrosion analysis reveals improved resistance at a higher laser fluence, attributed to increased content of corrosion-resistant alloying elements (Mo, Cr) and predominance of the austenite phase. Electrochemical Impedance Spectroscopy (EIS) confirms a higher corrosion resistance at a higher laser fluence, supported by a significantly higher polarization resistance and presence of a duplex-structured passive film. Results indicate that moderate laser fluence levels, ranging from 5 to 7.5 kJ/cm2, accompanied by medium to high thermal signatures and moderate cooling rates, yield coatings with refined microstructures, enhanced mechanical strength, and corrosion resistance. For superior corrosion resistance, a laser fluence of 10 kJ/cm2 is recommended, although careful consideration of its potential impact on mechanical properties is advised. • AISI 316L coatings on low carbon steel via L-DED to enhance material resistance against high temperature, corrosion, and wear. • Investigated melt pool characteristics, track geometry, phases, microstructure, and mechanical and electrochemical behaviour. • Moderate laser fluence (5 to 7.5 kJ/cm²) yields coatings with refined microstructures, and enhanced mechanical strength. [ABSTRACT FROM AUTHOR]