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In the process of directed energy deposition (DED), the grain structure of the deposited samples is determined by two aspects. The first is the initial solidification grain structure; the second is the effect of the upper thermal cycle on the solidified grain structure of the lower layer. Dynamic recrystallization and grain growth can be activated under suitable strain and the temperature resulting from thermal cycles. The evolution of grain size and the geometric dislocation density (GND) of austenitic stainless steel 316 L under different strains and temperatures caused by thermal cycles was investigated. It is found that dynamic recrystallization requires an appropriate level of accumulated strain, temperature, and initial grain size. Under <2% accumulated strain and 400–1200 °C conditions caused by 30 layers of thermal cycles, fully dynamic recrystallization occurs with coarse initial grains (CIG), leading to the complete coarsening of grains. However, relatively fine initial grains (FIG) under the same conditions only display partial dynamic recrystallization. The next 2–4% strain and 400–700 °C by 60 layers of thermal cycles make up the driving force of fully dynamic recrystallization, and the grains coarsen completely. Larger accumulated strain (4–6%) and lower temperature (400–600 °C) by 90 layers of thermal cycles and FIG provide more nucleation sites for dynamic recrystallization, which leads to little coarsening of grains even after fully dynamic recrystallization. Temperature, accumulated strain, and the amount of δ-ferrite promote the formation of sub-grains during dynamic recrystallization caused by thermal cycles, which leads to the increase in GND. [ABSTRACT FROM AUTHOR]

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316 L steel-based human implants play an important role in the biomedical field. In order to address the problem of immune rejection of 316 L steel-based human implants and further improve the machining efficiency, the surface roughness (SR) and hydrophilicity of 316 L workpieces are improved by electrical discharge machining milling (EDM-milling) instead of die-sinking electrical discharge machining (EDM) and by the incorporation of nano hydroxyapatite (NHAP) powder into the dielectric. The effects of powder concentration of NHAP, reference voltage, peak current, pulse width, and pulse interval on the material removal rate (MRR), electrode wear rate (EWR), SR, and contact angle (CA) of 316 L workpiece processed by powder mixed EDM-milling with NHAP (NHAP-PMEDM-milling) are investigated by single-factor experiment, and comparisons are done with the powder mixed die-sinking electrical discharge machining with NHAP (NHAP-PMEDM). According to the results, the MRR, EWR, SR, and CA of 316 L by NHAP-PMEDM-milling are varied regularly with the variation of experiment parameters. The addition of NHAP powder into deionized water (DW) can reduce the CA of the surface of 316 L steel workpiece to a great extent, with a maximum reduction of 27.9%, while affecting MRR, EWR, and SR very little. In addition, NHAP-PMEDM-milling can increase MRR by 115.5% and reduce EWR, SR, and CA by 43.2%, 13.2%, and 15.9%, respectively, compared with NHAP-PMEDM. [ABSTRACT FROM AUTHOR]

Application of the 316 L stainless steel (SS) is limited by its relatively low wear resistance, insufficient strength, and poor corrosion resistance in special environments. To this end, effects of Mo particles addition on the microstructure, mechanical properties, and corrosion resistance of the laser powder bed fusion (LPBF) 316 L SS are investigated in this study. The results show that the addition of Mo particles from 0 wt.% to 10 wt.% can modify the crystal orientation and improve the strength, wear resistance, and corrosion resistance of LPBF 316 L SSs. Particularly, the LPBF 316 L SS forms a biphasic structure with a similar ratio of α-Fe to γ-Fe with 5 wt.% Mo addition. As a result, the corresponding samples possess both the excellent toughness of austenitic SSs and the high strength and corrosion resistance of ferrite SSs, which reaches a high tensile strength of about 830 MPa, together with a low friction coefficient of 0.421 μ. Since the Mo particles addition is beneficial to increase the content of Cr2O3 on the samples surface from 13.48% to 22.68%, the corrosion current density of 316 L SS decreases by two orders of magnitude from 569 nA to 6 nA, while the mechanical properties remain favorable. This study is expected to serve as a reference for the preparation of LPBF SSs with excellent integrated performance. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (LPBF) has unique metal processing characteristics that allow rapid heating and melting of metal powder to form the 3D objects in a layer-by-layer manner. The parts fabricated through LPBF inherited anisotropy behaviors in microstructure and mechanical performance. To effectively ensure the as-built part functionality in terms of microstructure and mechanical performance, scanning direction (SD), building direction (BD), and transverse direction (TD) were selected to be analyzed to build a quantitative process-quality model to control the tensile strength in this study. The influence of hatch distance on microstructure evolution is also investigated. X-ray diffraction (XRD) analysis indicated that (200) peak intensity of γ austenite (fcc) drop-down with hatch distance increased from 0.06 mm to 0.10 mm. Broadening of remelting zone of two adjacent tracks improved the epitaxial growth of column grain. The different ratios of tensile strength and elongation between scanning direction and building direction are 9.23, 19.26% with hatch distance of 0.06 mm, dropped to 3.27, 10.31% with hatch distance of 0.10 mm, respectively. When the hatch distance is over 0.1 mm, the tensile strength and elongation of TD samples drop sharply due to the lack of overlap between molten pools. The different ratio of mechanical anisotropy decreases with hatch distance increases, which also demonstrates that hatch distance can alter the anisotropic of LPBF-ed parts. [ABSTRACT FROM AUTHOR]

Purpose: The effect of processing parameters on the microstructure of steel produced by laser-based powder bed fusion (LPBF) is a recognized opportunity for property design through microstructure control. Because the LPBF generates a textured microstructure associated with high anisotropy, it is of interest to determine the fabrication plane that would generate the desired property distribution within a component. Design/methodology/approach: The microstructure of 316 L produced by LPBF was characterized experimentally (optical, scanning electron microscopy, glow discharge emission spectrometry and X-ray diffraction), and a finite element method was used to study the microstructure features of grain diameter, grain orientation and thermal parameters of cooling rate, thermal gradient and molten pool dimensions. Findings: The computational tool of Ansys Additive was found efficient in reproducing the experimental effect of varying laser power, scanning speed and hatch spacing on the microstructure. In particular, the conditions for obtaining maximum densification and minimum fusion defects were consistent with the experiment, and the features of higher microhardness near the component's surface and distribution of surface roughness were also reproduced. Originality/value: To the best of the author's knowledge, this paper is believed to be the first systematic attempt to use Ansys Additive to investigate the anisotropy of the 316 L SS produced by LPBF. [ABSTRACT FROM AUTHOR]

It is widely accepted that the corrosion resistance of stainless steel originates from a compact Cr2O3 layer in the native passive film that serves as a barrier to aggressive ions. However, this suggestion has been questioned by some researchers. They believe that protectiveness might be related to the film recovery. Herein, the pitting development of bare 316 L stainless steel was compared with a corrosion-resistance enhanced steel obtained by tuning the native passive film of the alloy. Statistical software was employed for tracing the size and number of pits on the alloy surface. The statistical results for 12 weeks in 1 M sodium chloride solution (80 °C) revealed that there was a crossover in the growing rates of stable pits (diameter > 9 µm) between the bare alloy and the film-enhanced one. Stable pits on bare 316 L occurred early but showed a comparatively slow increase in the following weeks, demonstrating that self-repairability of metastable pits rather than impermeability of the native passive film plays the key role in the early stage of pitting corrosion. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the feasibility of fabrication of a Fe53.4Cr20Mo16Cu0.6C10 amorphous and amorphous-crystalline crack-free layer with desirable corrosion resistance and hardness using the laser surface melting technique The phase analysis of clad layers has been characterised by X-ray diffraction (XRD). Also, the microstructure and phase analysis of the cross-section of clad layers has been studied by scanning electron microscopy, field emission scanning electron microscopy, and energy dispersive spectrometry. The effect of laser scanning speed on microstructure, corrosion behaviour, and hardness was investigated at 4, 6, and 8 mm s-1. The results showed that a high fraction of amorphous phase (90%) has been obtained at an 8 mm s−1 scan rate. The coating thickness is more than 150 μm, fully dense having low porosity. The corrosion resistance of Fe-based coatings was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopic tests, and pitting corrosion evaluated in HCl solutions. The laser-treated material coatings had a lower current density than the substrate due to the formation of an amorphous phase, and the corrosion resistance values were 56, 162, and 141 Ω.cm2 for 4, 6, and 8 mm s−1 scanning rate samples respectively. It was found that high corrosion resistance is related to coating with a 6 m s−1 scan rate due to the mixture of galvanic effects and amorphous structure. The average measured micro-hardness of the coatings demonstrated that the sample formed from the highest scan rate possessed the highest micro-hardness, which was 824 HV. [ABSTRACT FROM AUTHOR]

Microtextural characterization using electron backscatter diffraction analysis was performed on laser powder bed fusion manufactured SS316L (SS316L). The crystallographic textures of as-printed (AP) and hot isostatic pressed (HIP) samples have been determined using orientation distribution function maps. The AP sample consists of mostly <110>||BD and <100>||BD fiber textures without any clear presence of twins. Conversely, the HIP sample featured <110>||BD and <111>||BD grains. The formation of <111>||BD texture was due to the deformation associated with the HIP process. Moreover, HIP generated a significant fraction of coincident site lattice Σ3 boundaries due to the low stacking fault energy of SS316L. These twin boundaries allow considerable plasticity during subsequent deformation. The spacing of deformation twins is wider (1–5 μm) compared to the subgrain boundaries (0.2–0.7 μm). Kernel Average Misorientation maps depict the occurrence of dynamic recrystallization, which is assisted by deformation twinning. The results explain the increased ductility of LPBF-produced, HIP processed SS316L without sacrifice to its tensile strength. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Science & Engineering (1673-2812) is the property of Journal of Materials Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Today, a variety of implants with different applications are used to replace or support a damaged biological structure, the most common of which are dental and orthopedic implants. Due to the widespread use of stainless steel 316L in the manufacturing of implants and the occurrence of cracks and residual stresses during the process of electrical discharge machining for the production of these products, the use of effective and economical polishing methods such as burnishing is effective in increasing the surface properties and compatibility of these products with living tissue. In this study, after performing the electrical discharge machining process on the surface of the sample and making the ball burnishing, the burnishing operations were performed by changing the input parameters and in accordance with the experiments designed using the mini tab software. Thus, the effect of variable burnishing force, feed speed and number of tool passes on surface roughness properties, micro-hardness and corrosion resistance of the final surface of the work piece were investigated. During the optimization of the response surface methodology, the optimal value for surface roughness, micro-hardness and surface corrosion rate of the samples were obtained, respectively, 0.108 μm, 435.34 Vickers and 2.18x105 respectively. Compared to the control sample, the surface roughness of the samples decreased by about 97% and the micro-hardness and corrosion resistance of the samples increased by about 2 and 11 times, respectively. [ABSTRACT FROM AUTHOR]

Cyclonic atmospheric pressure plasma is developed to synthesize the organosilicon nano‐coating on 316 L stainless steel surface with hexamethyldisilazane (HMDSN) and HMDSN/N2 monomers. The modified 316 L stainless steel surface characteristics of cyclonic plasma deposited organosilicon nano‐coating were evaluated by the static contact angle measurement, FTIR, SEM, AFM, and XPS detections. The chemical analysis with FTIR and XPS depicts that cyclonic plasma deposited nano‐coating obtains the relatively inorganic characteristics. The surface morphological determination with SEM and AFM refers cyclonic plasma deposited 316 L stainless steel surface roughness alteration with switching monomer inputs. This study shows the potential of chamber‐less deposition to create the plasma deposited organosilicon nano‐coating for 316 L stainless. [ABSTRACT FROM AUTHOR]

This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data. [ABSTRACT FROM AUTHOR]

Metallic biomaterials used in making hip prosthesis are required to meet expectations in terms of fatigue strength, corrosion resistance, wear resistance, cost and biocompatibility. It is also desirable that the modulus of elasticity they possess is close to the level of the possible bone. Metallic biomaterials face the problem of ion release even though they meet the criteria mentioned above. As a result, the choice of metallic material to be preferred in the manufacture of hip prosthesis can be made by evaluating all these criteria among themselves and by the performances of biomaterials to be compared according to these criteria. In this study, firstly the criteria expected from the metals to be used as biomaterials have been determined. Expert opinions about the subject and criteria determined in accordance with the studies in the literature by using analytical hierarchy process have been graded according to each other. Afterwards, selection of the most appropriate material was ensured by making the order of importance according to the criteria of the candidate materials. [ABSTRACT FROM AUTHOR]

Abstract: Metallic biomaterials used in making hip prosthesis are required to meet expectations in terms of fatigue strength, corrosion resistance, wear resistance, cost and biocompatibility. It is also desirable that the modulus of elasticity they possess is close to the level of the possible bone. Metallic biomaterials face the problem of ion release even though they meet the criteria mentioned above. As a result, the choice of metallic material to be preferred in the manufacture of hip prosthesis can be made by evaluating all these criteria among themselves and by the performances of biomaterials to be compared according to these criteria. In this study, firstly the criteria expected from the metals to be used as biomaterials have been determined. Expert opinions about the subject and criteria determined in accordance with the studies in the literature by using analytical hierarchy process have been graded according to each other. Afterwards, selection of the most appropriate material was ensured by making the order of importance according to the criteria of the candidate materials. [ABSTRACT FROM AUTHOR]

In the present investigation, joining speed, laser power and stand-off distance were took up as joining process parameters in determining the laser transmission joining between PET films and 316 L stainless steel plates. The laser transmission joining process parameters were optimized using response methodology for obtaining maximum joint width. The Box-Behnken Design has been used to plan the experiments and response surface methodology (RSM) is selected to develop mathematical relationships between joining parameters and desired response (joint width). From the ANOVA (analysis of variance) it was concluded that stand-off distance is contributing more and it is followed by joining speed and laser power. In the range of process parameters, the result shows that joining speed increases, joint width decreases, while with the increase of laser power and stand-off distance, joint width increases. Optimum values of joining speed, laser power and stand-off distance was found to be 100 mm/min, 18 watt and 3 mm to get the maximum joint width (Predicted 2.232 mm). Corresponding average tensile strength of joint was found to be 84.38 MPa. There was approximately 6.61 % error in the experimental and modeled results of joint seam width. [ABSTRACT FROM AUTHOR]

This paper reports the outcome of morphological and microcompozitional (SEM, EDS, X-Ray Maps, Compo and Morpho images) and tribological investigations of biocompatible 316 L stainless steel. The most important conclusion that can draw based on optical microscopy observations is that sparked-in morphology differs depending on its place on the surface of the same sample. This is given by point-to-plate geometry that favors central discharges and a specific sample erosion/etching. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum - Gas University of Ploiesti Bulletin, Technical Series is the property of Petroleum - Gas University of Ploiesti and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A study on the progressive inelastic deformation behavior of the 316 L stainless steel cylindrical structure with plate-to-shell junction under moving temperature front was carried out by structural test and analysis. The structural test intends to simulate the thermal ratcheting behavior occurring at the reactor baffle of the liquid metal reactor as free surface of hot sodium pool moves up and down under plant transients. The thermal ratchet load that heats the specimen up to 550°C was applied repeatedly and residual deformation was measured. The thermal ratcheting test was carried out with two types of cylindrical structures, one with plate-to-shell junction and the other without the junction to investigate the effects of the geometric discontinuities on the global ratcheting deformation. The temperature distributions of the test specimens were measured and were used for the ratcheting analysis. The ratchet deformations were analyzed with the constitutive equation of the non-linear combined hardening model. The analysis results were in good agreement with those of the structural tests. [ABSTRACT FROM AUTHOR]

In-stent restenosis is a complication which impairs the success of coronary stenting. Recently, it was supposed that a delayed hypersensitivity reaction to nickel and molybdenum might be one of the triggering factors in in-stent restenosis. We have analyzed the data collected in our centre with respect to this hypothesis. Altogether, 34 patients were investigated (24 male, 10 female). Patch tests were performed with the standard series of the German Contact Dermatitis Research Group and a metal series containing the metal components of 316 L stainless steel. A positive patch test reaction to nickel was observed in 4 (11.8%) patients. None of the patients showed sensitization to the other metals. Retrospective analysis was performed in 20 patients: 2 of these patients had a positive patch test reaction to nickel, one of whom had an in-stent restenosis, and the other not. Restenoses were predominantly observed in patients with negative patch test reactions to nickel (6/18 patients). Out of the patients who were investigated prospectively only one showed sensitization to nickel. Restenosis was observed in 2 patients: neither patient had nickel allergy. Although it still cannot be excluded that metal allergy may play a role in the restenosis process in coronary stenting, there is at present little evidence for it. [ABSTRACT FROM AUTHOR]

This paper investigates the deformation mechanism and energy absorption behaviour of 316 L triply periodic minimal surface (TPMS) structures with uniform and graded wall thicknesses fabricated by the selective laser melting technique. The uniform P-surface TPMS structure presents a single-level stress plateau for energy absorption and a localized diagonal shear cell failure. A graded strategy was employed to break such localized geometrical deformation to improve the overall energy absorption and to provide a double-level function. Two segments with different wall thicknesses separated by a barrier layer were designed along the compression direction while keeping the same relative density as the uniform structure. The results show that the crushing of the cells of the graded P-surface TPMS structure occurs first within the thin segment and then propagates to the thick segment. The stress–strain response shows apparent double stress plateaus. The stress level and length of each plateau can be adjusted by changing the wall thickness and position of the barrier layer between the two segments. The total energy absorption of the gradient TPMS structure was also found slightly higher than that of the uniform TPMS counterparts. The gradient design of TPMS structures may find applications where the energy absorption requires a double-level feature or a warning function. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) has attracted great interest in the aerospace and medical sectors because it can produce complex and lightweight parts with high accuracy. Austenitic stainless steel alloy 316 L is widely used in many applications due to its good mechanical properties and high corrosion resistance over a wide temperature range. In this study, L-PBF-processed 316 L was investigated for its suitability in aerospace applications at cryogenic service temperatures and the behavior at cryogenic temperature was compared with room temperature to understand the properties and microstructural changes within this temperature range. Tensile tests were performed at room temperature and at −196 °C to study the mechanical performance and phase changes. The microstructure and fracture surfaces were characterized using scanning electron microscopy, and the phases were analyzed by X-ray diffraction. The results showed a significant increase in the strength of 316 L at −196 °C, while its ductility remained at an acceptable level. The results indicated the formation of ε and α martensite during cryogenic testing, which explained the increase in strength. Nanoindentation revealed different hardness values, indicating the different mechanical properties of austenite (γ), strained austenite, body-centered cubic martensite (α), and hexagonal close-packed martensite (ε) formed during the tensile tests due to mechanical deformation. [ABSTRACT FROM AUTHOR]