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AISI 316 L stainless steel is widely used as material to produce components by means of additive manufacturing. To increase the circular economy, the powders are collected and re-used after the printing process, thus the effect of powder recycling on microstructure and properties of printed components is of the utmost importance. This work focused the attention on non-metallic inclusions by examining virgin and recycled powders, and products printed by using both types of powders in a laser powder bed fusion (L-PBF) process.Recycled powders exhibit an irregular shape due to fragmentation, spatters and satellites and, compared to the virgin ones, have a higher gas (O, H and C) content. Both powders contain non-metallic inclusions with a larger quantity in the recycled ones.The printed samples have a similar microstructure, however those produced by using recycled powders exhibit voids of larger size and a little greater amount of inclusions. XRD and EDS examinations of inclusions extracted from the metallic matrix showed that they consist of a mix of amorphous and crystalline silica. Large part of these particles are already present in virgin powders and only a minor part forms during repeated printing operations. Accordingly, the quality of virgin powders is the factor that mainly affects the inclusion content of printed products indicating that the powder production process is the most critical stage of the whole manufacturing process.

In this work, an attempt was made to identify the optimised parameter combination in cold metal transfer (CMT) cladding process of AISI 316 L austenitic stainless steel. cladding process was carried out using stellite 6 filler wire. Experiments were carried out based on L31 central composite design (CCD). Cladding was done with current, Voltage, torch angle and travel speed as input parameters. Quality of the clad was analysed by measuring depth of penetration, weld area, hardness of the clad surface, corrosion rate and clad interface thickness. Grey relation analysis was used to identify the optimised parameter combination. Trial number 18 was identified as the optimised parameter combination. The optimised input parameters are Welding Current 200 Amps, Voltage 19 V, Torch Angle 70° and Welding Speed 150 m/min. ANOVA was used to identify the most influencing parameters on the overall multi-objective function and it was understood that the combined effect of torch angle, travel speed had a significant influence on the clad quality. Further investigation was carried out through an optimised set of parameters. The cladding experiment was conducted and their surface was investigated through clad profile, hardness of the cladded area, interface thickness of cladding region and corrosion rate. [ABSTRACT FROM AUTHOR]

In this study; The abrasion performances of uncoated Ti-6Al-4V and uncoated AISI 316 L stainless steel material were investigated in a ball-disc test apparatus. The experiments were carried out with 100Cr6 balls 10 mm in diameter in dry and sodium hyaluronate media to give a 500 m path under the influence of 7,5 N and 10 N forces at shear rates of 1-1,5-2 m/s. The wear quantities of the test specimens were examined for the ball and disc. As a result, it is observed that Ti-6Al-4V material is more resistant to abrasion than stainless steel material. The erosions in the medium added with sodium hyaluronate are very small compared to the dry medium and the erosion is reduced by 30-35% compared to the dry medium. [ABSTRACT FROM AUTHOR]

Titanium and Ti-based alloys possess good biocompatibility and excellent corrosion resistance. This paper is devoted to an effort to create Ti-based surface alloy on specimens made of the AISI 316 L austenite steel. The Ti-based surface alloy is created by the Ti film deposition using the magnetron sputtering method followed by the low-energy high-current electron beam irradiation of the Ti film–316 L steel substrate system surface. Transmission electron microscopy shows that the surface alloy consists of several sublayers having different structures and phase compositions. In particular, these are α-Ti; TiSi 2 ; FeTi and Fe 2 Ti; Fe 2 SiTi; Fe 2 Ti 3 O 9 phases and more complex Cr 13 Fe 35 Ni 3 Ti 7 , Cr 12 Fe 32 Mo 7 Ni 7 , Cr 12 Fe 36 Mo 10 , Mo 5 Cr 6 Fe 18 phases nearby the substrate. Phase compositions of the surface alloy layers are determined by the change in the chemical composition of the titanium–steel system and the heat depth distribution. It is shown that the formation of the Ti-based surface alloy on the AISI 316 L austenite steel surface, provides the increase in the polar component of the free surface energy from 3.2% to 34.5%. • Ti-based surface alloy was created on AISI 316 L austenite steel. • The structure and composition of a surface alloy was studied by TEM. • Surface alloy consists of several layers with different structure and composition. • Surface alloy increases the polar component of free surface energy from 3.2% to 34.5%. [ABSTRACT FROM AUTHOR]

In this study the effect of feed rate, depth of cut and cooling system on surface roughness and cutting force during machine turning of AISI 316L stainless steel is investigated. The Taguchi method was used for optimization of machine turning. Furthermore, variance analysis was performed to determine the effect of each parameter on the results. As a result of this analysis, the effect of feed rate, depth of cut and cooling system on surface roughness and cutting force during machine turning of AISI 316L stainless steel was determined. Consequently, the ANOVA method was used to determine optimal parameter levels. [ABSTRACT FROM AUTHOR]

In this study, the effects of cutting insert rake face forms and cutting parameters on the surface integrity in machining of AISI 316 L steel were investigated experimentally. The cutting forces occur during chip removal, surface roughness values on the machined surfaces with residual stresses on machined workpiece were measured, and metallurgical structure (microhardness and microstructural variations) of the surface layers formed as a result of machining were evaluated. The surface integrity was evaluated in terms of surface roughness, residual stress, microhardness, and microstructure analysis. In experiments, the best surface integrity results were obtained by cutting tools having QM form, and the worst surface integrity results were obtained by cutting tools having MR form. Under all these cutting conditions, it was observed that the surface integrity worsened when depth of cut and cutting feed were increased; however, the surface integrity improved when cutting speed was increased. In terms of cutting parameters, the best surface integrity was obtained with cutting speed 200 m/min, cutting feed 0.1 mm/rev, and depth of cut 1.25 mm; on the other hand, the worst surface integrity was obtained with cutting speed 125 m/min, cutting feed 0.3 mm/rev, and depth of cut 2.5 mm. [ABSTRACT FROM AUTHOR]

This research investigation articulates the joining of AISI 316 L austenitic stainless steel plates of thickness 5 mm by activated tungsten inert gas (A-TIG) welding. Prior to the welding, the optimization of process parameters and the selection of suitable flux have been carried out to join the plates in a single pass welding. The experimental results show that the complete weld penetration can be achieved by using activating flux. The microscopic study divulges the presence of delta ferrite, sigma phase and various forms of austenite in the weld zone. Fischer Feritscope result indicates that the delta ferrite content in the weld is higher (7.8 FN) than the base metal (1.3 FN) which results in superior mechanical properties of the weld. Field Emission-Scanning Electron Microscope (FE-SEM) fractography reveals that the failure of weldments occurs in ductile mode. 180° bend test study reveals the good ductility of the joint. [ABSTRACT FROM AUTHOR]

In this investigation, the EDM process was applied to modify the surfaces of Ti-6Al-4 V alloy and AISI 316 L steel by the formation of hydroxyapatite coatings with the objective of providing a favorable environment for osseointegration of implants. The EDM process has the advantage of simultaneously machining and increasing surface roughness increasing surface contact area with bone tissue and implant anchorage. The hydroxyapatite coatings were formed during EDM currents of 30 A and 40 A with calcium phosphate additions. The coatings were analyzed in terms of hardness, roughness, surface profile, wear and tribological characteristics (pin on disk) and were characterized SEM/EDS and XRD. It was possible to show that on all processed surfaces the development of apatite coatings was achieved. Coating thickness and hardness were approximately 120 µm, 700HV and 12 µm, 300HV for the Ti-alloy and stainless steel, respectively. On both substrates, a significant increase in surface roughness was observed after EDM. The pin on disk tests revealed that the coefficient of friction varied from 0.54 to 0.80, and superior wear resistance of the coating formed on the AISI 316 L steel. • Increased hardness in the remelted zone in EDM-welded alloys. • Improved bioactivity in EDM alloys with increased roughness. • Improvements in relative wear resistance for AISI 316 L steel by EDM. • Study of the mechanical properties of alloys welded by EDM for biomaterials. [ABSTRACT FROM AUTHOR]

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.

In this work, a new approach to experimental study of cutting forces and heating in milling is carried out. Work is done without cooling, over type AISI 316L austenitic stainless steel, and a comparison between up-milling and down-milling is performed. Maximum values of cutting force (Fc), resultant force (R) or maximum temperature (Tmax) are used to obtain qualitative and quantitative analyses. The results show that major influencing determinant is not the instant undeformed chip thickness. This is significant if orthogonal turning models want to be directly applied to milling modelling. [ABSTRACT FROM AUTHOR]

In this study, AISI 316 L austenitic stainless steel and AH36 low-alloy ship building steel pair were joined with flux-cored arc welding method by using E309LT1-1/4 filler metal under four different shielding gas compositions containing CO at different ratios. Microstructure, impact toughness of welded materials, and their microhardness distribution throughout joining were determined. In macro- and microstructure examinations, stereo optical microscope, scanning electron microscope (SEM), SEM/energy dispersive spectroscopy, and SEM/mapping analysis techniques were used. After notched impact toughness, fracture surfaces were examined using the scanning electron microscope. This study investigated effects of shielding gas composition on microstructure, impact toughness, and microhardness distribution of transition zone between AH36 steel and weld metal of joined material. It is observed that based on an increase in amount of CO in shielding gas, impact toughness values of the weldment decreased. Microhardness values change throughout weld metal depended on shielding gas composition. Moreover, an increase in amount of CO within shielding gas decreased δ-ferrite amount in weld metal. The increase in amount of CO within shielding gas leads to expanded transition zone in interface between AH36 and weld metal and also affects notched impact toughness values negatively due to the inclusion amounts occurring in weld metal and hence caused it to decrease. [ABSTRACT FROM AUTHOR]

Abstract: Total hip arthroplasty has been one of the most successful techniques in orthopedics providing good results for long term. The rate of fatigue failure of total hip arthroplasty stem today is very low due to improvements of the technique along many decades. However, any rare case of stem fracture should be treated carefully due to the problems that can result in the revision for the patient. This paper presents failure analysis of three cemented hip stem which experienced fatigue with less than 5years in use. The failure is associated to design concept which includes a weld procedure at the proximal third of the stem to attach a metallic wire mesh aiming to improve the bonding to the cement mantle. The failure also is associated with the misuse of AISI 316 L as implant material. [Copyright &y& Elsevier]

A slurry immersion technique of alumina coatings was carried out on several AISI 316 L stainless steels using two types of binding agents; commercial starch and Sarawakian starch (sago), which were also mixed with polyvinylchloride (PVA) for strengthening purposes. The sintering temperatures in this work were varied from 500 to 1000°C. Prior to sintering process, all stainless steels were metallographically ground and polished to approximately 0.6 µm of average roughness. Detailed characterisations on the sintered specimens were carried out with the aid of the secondary electron microscopy (SEM), microhardness and a profilometer. The results revealed that coated steels using sago binder showed improved adhesion and homogenous microstructures with greater hardness of 2642 HV than those found in coated steel with commercial starch after sintering process. [ABSTRACT FROM AUTHOR]

The advantages of the Laser Powder Bed Fusion process have led to growing interest from an industrial and academic point of view. However, the diffusion of this process has been slowed by technical challenges that have yet to be resolved, including non-optimal surface quality and low repeatability. To fix these issues and recover surface quality, several treatments are available. Our study focuses on one of them: the Directed Energy Deposition (DED) treatment, which in addition can be exploited for the repair of damaged components. In fact, the proposed study has been conducted by using AISI 316 L alloy both for producing parts throughout the L-PBF process and for coating them. Furthermore, a final Laser Scanning (LS) treatment has been carried out with the aim of maximizing the DED coating performances, in terms of surface roughness, microhardness and microstructural properties. To detect the anomalies that can emerge during the previous surface treatments, an optical monitoring system was implemented in the visible range by using a coaxial CCD camera, to monitor the geometry and morphology of the melt pool related to the DED and to the subsequent LS treatment. The results revealed many improvements in terms of surface roughness for the DED coating and even more for the LS treatment. Moreover, the latter was fundamental to improve the microhardness and the microstructural characteristics of the final coating. The data gathered and analyzed by the implemented monitoring system will allow making the treatment more stable and performing for future applications on complex geometries. • Coatings using DED + LS treatment on a L-PBF substrate were successfully achieved. • Laser scanning significantly improves DED coating performances. • Microstructure after the laser scanning treatment is an equiaxial fine grain. • The produced coating is uniform due to the stability of the melt pool. • Coatings quality was monitored in-process through optical and thermal systems. [ABSTRACT FROM AUTHOR]

Results are presented and compared with strain-controlled ‘isothermal fatigue’ (IF), strain-controlled ‘thermal–mechanical fatigue’ (TMF) and ‘complex thermal–mechanical fatigue’ (CTMF) tests. The IF and TMF tests were carried out with a common single-specimen testing system while the CTMF tests were performed with a two-specimen testing system which allows the interaction between a ‘hot’ and a ‘cold’ location of a component, e.g. the outer and the inner side of a cooled turbine blade, to be simulated. The test samples were made from the austenitic steel AISI 316 L. The complex interaction between both specimens in a CTMF test results in cyclic creep to negative total strains, which does not occur in strain-controlled IF and TMF tests. The cyclic deformation behaviour under CTMF conditions is not only determined by the hardening or softening of the material investigated, but even to a larger extent by the interaction of the specimens within the CTMF system. However, the microstructural changes under CTMF conditions can be correlated with the respective observations made under IF and TMF loadings. [Copyright &y& Elsevier]

This study on laser powder bed fusion (L-PBF) of AISI 316 L addresses the anisotropy in microstructure and micro-mechanical properties, from the observation of electron backscatter diffraction (EBSD) and nanoindentation maps in parts made with different volumetric energy densities (VED) and in grains at different crystallographic orientations. Similar experimentation was done with conventionally made AISI 316 L, with the aim of comparing anisotropy and micro-mechanical response. It was observed that the variations of VED, calculated from different process parameters combinations, have an influence on crystallographic oriented grain growth evolution affecting the nanoindentation performance. This progression was responsible of the variation in grain size and average misorientation angles and played important role in determining the micro-mechanical behavior. The highest nanoindentation response was obtained at a VED = 56.67 J/mm3, with an average indentation modulus of 196.77 GPa and hardness of 3.68 GPa. From Texture Pole Figures (PFs) and Inverse Pole Figures (IPFs) of EBSD maps, it was revealed that the highest texture strength of 〈101〉 oriented grains along with the evolution and domain of 〈111〉 oriented grains enhanced the micro-mechanical properties at that VED value. The other causes of this behavior are the relatively lower grain size (11.62 μm) and a higher average misorientation angle (11.74°), when comparing it with rest of the L-PBF AISI 316 L parts. The additional but undesirable strong 〈001〉 texture somehow contributed to the slight mitigation on the micro-mechanical properties in conventional AISI 316 L stainless steels and these parts were found to be comparatively less anisotropic than the parts obtained from L-PBF process. • Nanoindentation and EBSD techniques are used to map the micro-mechanical behavior in laser powder bed fusion of AISI 316 L. • The anisotropy of L-PBF and conventionally made parts was compared via Texture Pole Figures and Inverse Pole Figures. • Volumetric energy density (VED) affects micro-mechanical anisotropy, grain growth evolution and nanoindentation response. • At particular values of VED, the crystallographic orientation played an important role in micro-mechanical behavior. [ABSTRACT FROM AUTHOR]