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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]

Copyright of Journal of Central South University is the property of Springer Nature 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.)

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]

The widespread use of stainless steels (SS) in various applications is hindered by their inadequate wear resistance, hardness and high density. Structural metallic components fabricated via powder metallurgy (PM) exhibit lower densities compared to those produced by conventional methods due to their inherent high porosity. However, this compromises their mechanical and corrosion performance. This study has investigated the application of pure Al2O3 and Al2O3 + 13 %TiO2 powders with varying particle sizes on PM AISI 316L substrates to enhance their mechanical and wear properties. The phase composition, microhardness, coating morphology, surface roughness, porosity and wear rate of coated and uncoated samples were comparatively analysed to elucidate the influence of both TiO2 addition and coating powder particle size on the mechanical properties and surface morphology of the samples. Microstructural and XRD studies confirmed good mechanical and metallurgical bonding of the coatings to the substrate. All of the coated samples exhibited 24 to 34 times higher surface roughness and 1.3 to 2.1 times lower porosity values compared to the substrate. The finer sized TiO2 added alumina-based coating powder reduced the surface roughness and porosity value to 1.8 and 1.4 times respectively while the use of the coarser sized one reduced these values to 1.3 and 1.2 times respectively compared to the pure Al2O3 coated surface. 8-times higher hardness and 70-times lower wear rate values compared to the substrate were the most significant improvements observed in the pure Al2O3 coated surface among all coated samples. Although TiO2 addition to the coating powder decreased hardness by 1.1 times and increased wear rate by 1.8 times, spraying finer TiO2 added coating powders resulted in a slight improvement in both hardness and wear resistance compared to the coarser one.

Metal powder injection molding (MIM) has been a popular technique in production of alloy materials. Through this technique, near-net-shape alloy products can be molded with one-step production. Stainless steel 316 L (SS 316 L) is an important material in aerospace and marine industry for its excellent material strength and resistance to corrosion. As the industry grows with upgraded techniques, the standard for next generation material strength has improved tremendously. Here we present a practical method strengthening SS 316 L via MIM technique, which might provide a pathway for exploration of high strength materials. TiC was introduced into SS 316 matrix with polyoxymethylene (POM) binder. The metallography indicates that the introduction of TiC facilitates the refinement of the 316 L grain. As the TiC content increases from 0 wt% to 3 wt%, the material properties improve significantly, including a rise in hardness from 151 HV to 301 HV, tensile strength from 689 MPa to 792 MPa, and yield strength from 221 MPa to 339 MPa. Additionally, there is a noticeable reduction in the coefficient of friction and the wear cross-section.

An original container was designed to measure the ferritic content of powder batches by the Eddy Current (EC) technique. As opposed to the standard X-Ray Diffraction (XRD) or Electronic BackScatter Diffraction (EBSD) methods, the EC measurements can be implemented on powder batches of significant sizes, say a hundred grams or so. Using a methodology based on the multiple recycling of an initially ferrite-free virgin powder, it was shown that the EC signals are sensitive to the ferritic content of the recovered powder. On the other hand, in the frequency range scanned by the sensor, the EC signals are virtually independent on the oxygen concentration within the tested powder.

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]

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]

• Stress concentration induces micro-cracks at the bottom of pitting after the passive film damage. • Mechano-electrochemical effects at the crack tip location promote AD and HE. • Proposed a novel stress corrosion cracking mechanism model for 316L stainless steel. This paper analyzes the failure mechanisms of stress corrosion cracking (SCC) in 316L stainless steel flow promoter strings in corrosive oilfield environments. Electrochemical tests and passive film analysis techniques were employed to elucidate the degradation behavior of the 316L stainless steel passive film. The fracture characteristics were analyzed using slow strain rate tensile tests, scanning electron microscopy, and electron backscatter diffraction techniques to clarify the SCC mechanisms. The results indicate that the SCC of 316L stainless steel is controlled by anodic dissolution due to passive film breakdown in the oilfield environment. The degradation of the passive film, induced by Cl- and CO 2 , promotes SCC in 316L stainless steel, with cracks propagating in a trans granular manner. [ABSTRACT FROM AUTHOR]

In this study, the rough surfaces of additive manufactured parts were polished using an innovative combined treatment of continuous wave (CW) laser and inclined femtosecond (fs) laser techniques. The high-temperature friction and wear performances of the initial surface and the polished surface were investigated. The results indicate that the surface roughness was reduced to 0.21 µm and a fine-grained layer of approximately 25 µm was generated through CW-fs laser polishing. The coefficient of friction and wear volume of the CW-fs laser polished surface showed the most significant reductions of 52.2 % and 88.3 %, respectively, compared to those of initial surface under high-temperature conditions. • A new treatment was proposed to improve the friction and wear performance of SLM processed 316L stainless steel. • The surface roughness reduces from 16.2 μm to 2.4 μm and a fine-grained layer was formed by CW laser polishing. • CW-fs laser polishing can reduces COF and wear volume of initial surface by 52.2% and 88.3%, respectively. • The CW-fs polishing reduces COF, surface defects, wear rate due to a protective oxide glaze. [ABSTRACT FROM AUTHOR]

Electron transport via sulfate-reducing bacteria (SRB) is a major cause of anaerobic corrosion. In this study, we elucidated the attachment process and metabolic mode of Desulfovibrio bizertensis SY-1 on 316L SS via surface analysis and transcriptomic. Surface morphology observation revealed D. bizertensis could survive on SS surfaces for long time through end-to-end connections. Reducing the carbon source in the medium decreased the time needed to form these end-to-end connections and increased their length, creating more obvious pitting on the coupons. Gene expression found that attached cells obtained energy mainly through oxidative phosphorylation and the oxidation of succinate, while sulfate reduction genes were downregulated. These findings further expand our understanding of SRB biofilm and metabolic mechanism. [Display omitted] • D. bizertensis can reduce the passivation interval of SS and promote pitting. • D. bizertensis can survive on SS for long time through end-to-end connections. • Reducing the carbon source can increase these end-to-end connections length. • Attached cells obtain energy mainly through oxidative phosphorylation and the oxidation of succinate. [ABSTRACT FROM AUTHOR]

316L porous skeletal scaffolds prepared by selective laser melting (SLM) technology are currently widely used in bone injuries. Its successful implantation is predicated on having properties that match those of natural bone. The process parameters significantly influence the performance of SLM-316L porous scaffold. In this study, the nine-group shaping process parameters were determined by orthogonal method. The 316L porous scaffolds were tested in compression, electrochemistry, XRD and microstructure. The influence of process parameters on the performance of body-centered cubic peripheral square structure bracket was investigated. The influence laws of process parameters on microstructure, mechanical properties and corrosion resistance were obtained. The results show that process parameters have a significant effect on the microstructure, properties and defect distribution. The reduction of defects and grain refinement in the stent is conducive to the improvement of compressive properties and hardness of the stent. The magnitude of the hardness is inversely related to the grain size. The corrosion current density of porous scaffolds are also affected by their microscopic defects and grain size. At an energy density of 78.70 J mm ^−3 presents the least defects and obtains smaller grains, resulting in the best mechanical properties and corrosion resistance.

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]

In this paper, the effects of chloride ions, oxygen, and carbon dioxide on the corrosion resistance of passive films formed on 316 L stainless steel were investigated in the aggressive oilfield environment using electrochemical testing and microscopic characterization techniques. The results showed that Cl− accelerated the anodic dissolution of the metal and compromised the structure and densification of the passive film, thus reducing its corrosion resistance. An increase in the partial pressure of carbon dioxide initially promotes pitting, but subsequently inhibited further corrosion development. The presence of oxygen enhanced the cathodic reaction and passive film formation, effectively preventing the invasion of aggressive chloride ions, thus inhibiting further corrosion. These findings provide a significant scientific basis for material selection and protection of oil extraction equipment in oilfield environments. [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.)

Study examines binder deposition methods (bulk vs. selective printing) and sintering atmospheres (vacuum vs. H 2) on binder jetted 316 L stainless steel components. The density of the H 2 -sintered specimens was found to be lower (up to 5%) compared to the vacuum-sintered parts with the final density of 99.7%. Grain size analysis indicated smaller grains in the H 2 -sintered parts (∼26 μm) compared to vacuum-sintered condition (∼33 μm) in the bound area which could be attributed to the presence of residual pores that impeded grain growth. The H 2 -sintered specimens exhibited an elongation of 25% and an ultimate tensile strength (UTS) of 460 MPa, whereas the vacuum-sintered parts displayed an elongation of 70% and a UTS of 550 MPa. Fractography analysis using microscopy and micro-computed tomography revealed ductile fracture in the vacuum-sintered samples, while the H 2 -sintered parts exhibited a combination of brittle and ductile fracture due to remnant pores in the microstructure. [Display omitted] • Studying selective shell printing strategy in binder jet additive manufacturing. • Analysis of defects in green state or consolidated parts using computed tomography. • Microstructure analysis using electron backscattered diffraction. • Assessing mechanical properties via microhardness, tensile strength and bend tests. • Perspectives and challenges of shell printing was discussed. [ABSTRACT FROM AUTHOR]

Fretting crevice corrosion at the fastening interfaces of stainless-steel products is an unavoidable issue in the medical, marine, and nuclear industries. In this study, the effects of the fretting regimes on the fretting corrosion in artificial crevices were investigated, and the results showed that fretting initiated severe corrosion inside the crevice under the stick regime. Under the stick–slip and slip regimes, the volume loss was dominated by fretting corrosion, without initiating crevice corrosion. • Whether fretting can cause crevice corrosion is related to the fretting state. • In the stick regime, fretting can initiate severe corrosion inside the crevice. • In the stick–slip and slip regimes, only fretting corrosion occurs inside the crevices. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) techniques have been widely used to fabricate structural components with complex geometries. Understanding AM materials under extreme environments is crucial for their implementation in various engineering sectors. In this study, the deformation behavior and irradiation damage of 316 L stainless steel (SS) fabricated by the direct energy deposition (DED) process are investigated. The fabrication-induced nanopores with an average diameter of 200 nm exhibit a core-shell structure with a local tensile strain. The precession electron diffraction (PED) reveals that austenite-to-martensite phase transformation preferentially occurs around the nanopores under tension test at room temperature. Proton irradiation experiments performed at 360 °C to a fluence of 1.09 × 1019 cm−2 and 5.42 × 1019 cm−2 show that the DED fabricated 316 L SS exhibits a stronger void-swelling resistance and lower dislocation loop density than its wrought counterpart. AM-induced features, such as nanopores and sub-grain boundaries, could serve as defect sinks to absorb irradiation-induced defects. The design of microstructure using AM processes opens up new avenues for the development of irradiation tolerant materials for nuclear applications.

Additive Manufacturing (AM) processes enable the reduction of manufacturing time, material waste, and allows for the creation of complex structures. However, anisotropic mechanical behaviour is frequently observed in additively manufactured parts, and it is directly linked to the component's grain structure characteristics, which itself is dependent on the process parameters. The formation of grain structure in 316 L stainless steel fusion lines is investigated in this paper, combining experimental results and numerical simulations. Experimentally, fusion lines are built on a 316 L substrate, using an instrumented LPBF process. The high-speed camera recordings combined with the characterization of the samples enables capturing of melt-pool sizes and grain characteristics. The numerical modelling is based on a three-dimensional “CAFE” model, coupling Cellular Automata and Finite Element models to predict grain formation. The thermal model is defined and calibrated using the experiments. The experimental and numerical grain characteristics are compared. Numerical results are discussed with regards to the growth models and the process parameters. The growth model defined here is compared to existing models and is well fitted to capture grain formation in single-track configurations. Finally, the average grain size and aspect ratio of the grains increase with an increase of the process' linear energy.

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]

Relationships between microstructures and hardening nature of laser powder bed fused (L-PBF) 316 L stainless steel have been studied. Using integrated experimental efforts and calculations, the evolution of microstructure entities such as dislocation density, organization, cellular structure and recrystallization behaviors were characterized as a function of heat treatments. Furthermore, the evolution of dislocation-type, namely the geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs), and their impacts on the hardness variation during annealing treatments for L-PBF alloy were experimentally investigated. The GND and SSD densities were statistically measured utilizing the Hough-based EBSD method and Taylor's hardening model. With the progress of recovery, the GNDs migrate from cellular walls to more energetically-favourable regions, resulting in the higher concentration of GNDs along subgrain boundaries. The SSD density decreases faster than the GND density during heat treatments, because the SSD density is more sensitive to the release of thermal distortions formed in printing. In all annealing conditions, the dislocations contribute to more than 50% of the hardness, and over 85.8% of the total dislocations are GNDs, while changes of other strengthening mechanism contributions are negligible, which draws a conclusion that the hardness of the present L-PBF alloy is governed predominantly by GNDs.

A 10 mm 316 L stainless steel plate was joined using multi-layer laser-MIG hybrid welding. Results showed that unmixed zone and “real” fusion zone (FZ) existed near the fusion line. Frequently met dendritic ferrite (δ) and newly encountered spherical nanoscale particles trapped in austenite (γ) were only observed in the latter region. Chemically, these particles turned out a SiO2 phase. From base metal to FZ, δ morphology was altered from originally linear to relatively diversely dendritic. Meantime, γ exhibited a converse manner where previously randomly oriented equiaxed was replaced by coarse, columnar and textured. Accordingly, a comparably high Schmidt factor in γ phase was obtained in FZ. Moreover, δ exhibited a relatively higher stress level than γ which presented a decrease in residual stress with grain coarsening in heat affected zone. In FZ, δ fraction displayed a dramatical increase with special BCC-FCC orientation relations established. Finally, tensile test and fracture appearance implied that FZ was exactly the weakest link of the whole welded joint in spite of a qualified strength achieved. In summary, lack in Σ3, largely increased δ fraction, high Schmidt factor in γ and especially being rich in SiO2 particles collectively led to the micro-void coalescence fracture in FZ.

Fretting-crevice-corrosion at the modular interface of artificial joints can cause failure of the joint replacement. In this study, long-term fretting crevice corrosion tests of 316 L stainless steel were carried out at the center of an artificial crevice in a saline solution with and without proteins. The results showed that fretting initiated significant crevice corrosion without proteins and corrosion of large areas was observed in the non-contact area inside the crevice. In the presence of proteins, proteins can migrate into the crevice and block the crevice mouth. The enriched proteins had a lubricating effect and inhibited the occurrence of crevice corrosion. • Fretting within artificial crevices can initiate obvious corrosion reaction • Proteins could migrate into the crevice and accumulate at the crevice mouth. • Lubrication of proteins in wear marks alters the fretting regimes. • Proteins enriched inside the crevice and inhibited corrosion reactions [ABSTRACT FROM AUTHOR]

The underwater direct metal deposition (UDMD) was employed to deposit 316 L stainless steel (SS316L) coatings on NV E690 steel. The chemical composition gradient from monolayer to trilayer SS316L induces an in-situ phase transformation, thereby enhancing the corrosion resistance. The steady-state passive film grew linearly with the applied potential and exhibited a bilayer structure: a high resistivity barrier layer and a low resistivity outer layer. The growth kinetics of the UDMD fabricated SS316L coatings align with the point defect model. Passive film is enriched in Cr while depleted in Fe and Ni, whereas the altered zone is enriched in Ni. [Display omitted] • Corrosion resistance was enhanced by coating SS316L through the UDMD technique. • Quantitatively studied the electrochemical and physical properties evolution of the passive film. • The passive film consists of a high-resistivity barrier layer and a low-resistivity outer layer. • The growth kinetics of the UDMD fabricated SS316L coating aligns with the point defect model. • Passive film is enriched in Cr while depleted in Fe and Ni, whereas the altered zone is enriched in Ni. [ABSTRACT FROM AUTHOR]

This work focuses on the influence of the feedstock powders on the microstructural properties and corrosion behavior of 316 L stainless steel (SS) produced by laser powder bed fusion (L-PBF) from two different suppliers. Microstructural investigations conducted after additive manufacturing reveal many particularities depending on the powders. These microstructural differences lead to a different corrosion behavior in boiling nitric acid containing oxidizing ions. The presence of the triple structuration (grains, large cells, small internal cells) shows a positive effect on intergranular and cellular corrosion resistance. In both cases, L-PBF 316 L SS provides better resistance to intergranular corrosion than wrought 316L SS. • Impact of raw material properties on the microstructure of 316L SS produced by laser powder bed fusion. • A new triple structuration (grains, large cells and small internal cells) has been evinced. • Printed samples exhibited better corrosion resistance compared to wrought 316L SS in strongly oxidizing acidic medium. • The new microstructure shows a slightly intergranular attack and improves cell corrosion resistance. [ABSTRACT FROM AUTHOR]

Additively manufactured (AM) 316 L stainless steel (SS) after hot isostatic pressing (HIP) was found to exhibit superior resistance to irradiation-assisted stress corrosion cracking (IASCC) in high-temperature water, as compared to wrought 316 L SS. The well-accepted IASCC factors of radiation-induced segregation (RIS) and radiation hardening are not accurate descriptions of IASCC susceptibility in this case. A decreased strain localization along grain boundaries, caused by dislocation channel broadening, was confirmed to suppress crack initiation. A unique distribution of irradiation-induced defects in HIP AM 316 L SS eased dislocation cross-slip compared to those in the wrought counterpart, thus increasing the channel width near the grain boundaries. For the first time, this study highlights the importance of dislocation channel broadening as a potential mechanism to further improve the IASCC resistance of 316 L SS and provides direct experimental evidence based on commercial-grade materials. Dislocation channel broadening decreased strain localization near grain boundaries and enhanced the IASCC resistance of additively manufactured 316 L stainless steel treated by hot isostatic pressing. Different sizes and densities of radiation induced loops and precipitation behavior are believed to be the underlying causes. [Display omitted] [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]

Abstract Selective Laser Melting (SLM) was applied to Additive Manufacturing (AM) of carbide ceramic particulate reinforced 316 L stainless steel matrix composites. The dense and ultrafine-grained Austenite matrix with uniformly distributed and nano-sized VC x particulate reinforcements were obtained according to the tailored SLM process parameters and 3 wt% submicron-sized V 8 C 7 ceramic particle addition into 97 wt% 316 L powder via ball-milling treatment. The influences of SLM process parameters on the SLM printed composites in terms of density, surface roughness, phase constitution, microstructure characteristics and mechanical tensile performance were investigated in detail, comparing with the SLM printed 316 L in absence of vanadium carbides. Based on the electron back-scattered diffraction analyses, the number of grains with grain size less than 2 µm accounted for more than 90% in the printed composites. The formation mechanisms of the printed composites with their unique microstructure characteristics were elaborated. The room-temperature ultimate tensile strength of the printed 316 L matrix composites achieved higher than 1400 MPa, which was more than twice as high as that of printed 316 L stainless steel. It contributed substantially to the strengthening effect on the printed composites of the ultrafast laser-induced and highly nonequilibrium melting-solidification nature of SLM process, the dispersed carbide ceramic particulate reinforcements, the nanoscaled nucleation sites of VC x for the equiaxed Austenite grains, and the inhibition against Austenite matrix growth by particulate dispersedly distributed along Austenite grain boundaries. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) or rapid prototyping has become a crucial tool for reducing both cost and time while increasing efficiency in qualifying structural materials for reactor use. In this study, directed energy deposition (DED) was used to develop an as-built 316 L stainless steel sample with three regions of increasing Hf-dopant to study the effects of Hf on the irradiation response of the material. Morphological and microstructural changes were analyzed before and after 2 MeV proton irradiation at 360 °C to a damage of 2.5 dpa at ∼ 10 µm below the surface. The addition of Hf effectively suppressed radiation-induced damage (dislocation loops, radiation-induced segregation) due to enhanced point defect recombination. The radiation damage seen in the as-built sample was further compared to a thermo-mechanically treated counterpart of the same fabrication and irradiation parameters which was found to behave superiorly. The increased radiation resistance of this material may be attributed to the as-built microstructure, which includes undissolved Hf particles, delta ferrite grains and cellular sub-grain boundaries that can hinder defect motion. [ABSTRACT FROM AUTHOR]

Fretting crevice corrosion of total hip joints have been associated with joint replacement failure. However, researchers have not considered the interaction between fretting corrosion and crevice corrosion. In this study, an artificial crevice system that could perform fretting in the center of the crevice was designed, and fretting-initiated crevice corrosion (FICC) under different crevice widths, along with the effect of crevice corrosion on fretting corrosion, were studied. The results showed that FICC was more obvious under a smaller crevice, and pitting corrosion initiated at the shear band, resulting in crevice corrosion. Furthermore, corrosion pre-treatment significantly increased the fretting corrosion current. • Fretting corrosion was carried out inside the crevices with different widths. • Pits expand in shear bands due to fretting, resulting in accelerated corrosion. • Crevice corrosion pretreatment increases fretting corrosion current inside crevice. • Interaction of fretting and crevice corrosion is more marked at smaller crevice width. [ABSTRACT FROM AUTHOR]

316 L stainless steel is prone to failure under high-strength conditions due to low strength and poor wear resistance, which limits its further application severely. In this study, 2 wt% FeCoNiAlTi high entropy alloy (HEA) powders and 316 L stainless steel powders were mixed to fabricate HEA reinforced 316 L stainless steel matrix composites (MMCs) via laser powder bed fusion (LPBF). The influence of scanning speed on microstructure evolution, the mechanical properties and the strengthening mechanisms have been investigated systematically. The LPBF-fabricated HEA/316 L MMCs consists of both γ-Fe and α-Fe phases. For HEA/316 L MMCs, the grains are refined with the increase of scanning speed and the minimum size is around 0.64 µm. The precipitation of nanoparticles is observed, and the nanoparticles form a strong interfacial bounding with matrix, which indicates the good metallurgical bonding between HEA and 316 L stainless steel. The tensile strength of the LPBF-fabricated composites increases from 1164 MPa to 1276 MPa with increased scanning speed, which is approximately twice as high as the strength of LPBF processed 316 L stainless steel matrix. The contribution of each strengthening mechanism is calculated, and the contribution of particle strengthening is the largest (from 241 MPa to 300 MPa, changing with scanning speed). This work demonstrates the feasibility of using HEA as potential reinforcement in metallic systems and can further enlarge the application field of metallic materials. • Fabrication of HEA reinforced 316 L composite. • Improved mechanical properties with the addition of reinforcement. • Hardening of the material by reinforcement particles. [ABSTRACT FROM AUTHOR]

• A 3D numerical model was established to reproduce the SLM process of 316 L powder. • Effects of powder bed structure on macro/microscopic characteristics were analysed. • The role of initial temperature on printing quality was identified. • The underlying mechanisms were investigated. Understanding the essential role of initial powder bed states (e.g., structure and temperature) in the printing process is crucial to obtain high-quality components in powder-bed-based additive manufacturing. In this article, a 3D high-fidelity model which considered the Marangoni effects and recoil pressure was established based on the computational fluid dynamics (CFD) approach to simulate the printing process of 316 L stainless steel through selective laser melting (SLM). The influences of powder bed structure and temperature on the macro- and microscopic characteristics of the molten layer during printing were comprehensively investigated. On this basis, corresponding mechanisms were analyzed. Results show that the developed numerical model can vividly reproduce the SLM process of 316 L stainless steel. With the increase of powder bed thickness from 32.02 μm (H spreading =2 D 90 and V spreading =0.2 m/s) to 40.65 μm (H spreading =2 D 90 and V spreading =0.01 m/s), the height of the molten layer will increase from 16.37 to 32.86 μm, the depth will decrease from 21.69 μm to 10.52 μm, and the width will decrease from 100.67 to 94.94 μm. Meanwhile, this will make the fluctuation of the depth (CV) increase from 0.31 to 0.85. When the initial temperature increases from 300 K to 773.15 K, the height, depth and width of the molten layer increase by 3.88 μm, 12.68 μm and 17.37 μm, respectively. In this case, the CV is reduced from 0.34 to 0.23, implying the improvement of the molten layer quality. Under the current laser parameters, the defects such as warping, pores, faults, and balling induced by the insufficient melting in the thick powder bed can to a certain extent be reduced or even eliminated using the high initial temperature. The melting pool collapse will occur in a thin powder bed, the resultant entrained bubble defect in the molten layer can also be properly avoided by the high initial temperature. However, a special groove structure will appear due to excessive energy input. During multi-track melting, the rough surface, irregular molten layer and the pores between the molten tracks are likely to occur due to the insufficient energy input, these problems can be properly solved by employing a high initial temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract 316 L stainless steel, high density dislocations (~1.14 × 1015 m−2) obtained by selective laser melting process that play an important role in high yield strength. Dislocation slip and twinning during entire plastic deformation process, which maintained strain hardening rate at an ideal level and obtained outstanding ductility and resulting high yield ratio. [ABSTRACT FROM AUTHOR]

316 L stainless steel has been widely used in orthopaedic and dental implants due to its good corrosion resistance, good biocompatibility and strong mechanical strength. However, limited cell attachment, osseointegration failure and bacterial infection of 316 L stainless steel are the main challenges for its clinical application, and these problems can lead to severe implant failure. Among all solutions, surface modification is one of the most promising techniques without damaging the structural integrity of the base metal. In this research, polyelectrolyte multilayers (PEM) coating was applied on plasma treated 316 L stainless steel. PEM coating was fabricated composing two biocompatible materials: collagen and γ-poly-glutamic acid. In addition, a chitosan barrier was applied at the 11th layer to seal and control the drug release rate. Bone morphogenetic protein 2 (BMP-2) and basic fibroblast growth factor 2 (FGF-2) were loaded at the 1st and 11th layers of PEM. Plasma treatment was found to enhance the hydrophilicity and adhesion of PEM coating on 316 L stainless steel. The degradation rate of PEM was ~80% on day 70. Releases of FGF-2 and BMP-2 from PEM were 58% and 50% after 768 h. PEM coating with dual growth factors was demonstrated with good biocompatibility and promoted cell proliferation of rat bone mesenchymal stem cells (rBMSCs). Furthermore, alkaline phosphatase activity and mineralization of rBMSCs were also enhanced with the addition of BMP-2 and FGF-2. In conclusion, the extreme mechanical properties of 316 L stainless steel was greatly reduced by PEM coating while the BMP-2 and FGF-2 loaded further endowed osteoconductivity and osteoinductivity of the metal substrate. [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]

The microstructure and corrosion resistance evolution of 316 L heat-affected zone were studied by simulated welding thermal technology. The different thermal simulation parameters affected the ferrite content and grain boundary characteristics. The ferrite content and grain boundary characteristics in thermal simulation samples were studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Combining the electrochemical test, it was observed that the Cr-depleted zone existed at the austenite/ferrite interface and the high angle grain boundary (HAGB) of the austenite interface usually became the nucleation point of pitting corrosion. • Retained ferrite can be found due to chromium aggregation during welding thermal cycle. • Cr-depleted zone and random high angle grain boundary are conducive to pitting nucleation. • Corrosion extends from ferrite/austenite phase boundary to austenite matrix. [ABSTRACT FROM AUTHOR]

The high-temperature deformation behavior of additively manufactured 316 L stainless steels prepared via the laser powder bed fusion (LPBF) technology was investigated using Gleeble compression testing in a wide temperature range of 473–1273 K under a constant strain rate of 0.001 s−1, perpendicular to the building direction (BD). The softening flow property upon continuous concurrent isothermal heating deformation displayed an excellent thermal stability performance up to the temperature of 873 K, preserving the material strength higher than 600 MPa compared to the room-temperature property of the as-built material. By the gradual increase of testing temperature, the compressive strength of the material was continuously decreased to even <50 MPa at a temperature of 1273 K. After hot compression; all tested specimens were characterized across different regions in terms of deformation substructure evolution and crystallographic texture using electron backscattering diffraction (EBSD) and constitutive analyses. Accordingly, the estimated activation energies based on established constitutive modeling proposed the operation of dynamic recovery (DRV) and discontinuous dynamic recrystallization (DDRX) mechanisms for the hot deformation of additively manufactured 316 L stainless steel below (∼ 9.77 kJ mol) and higher (∼ 553.23 kJ mol) than the critical temperature of 873 K, respectively. The competition between strain accumulation and thermal heating induced two different Brass deformation and Goss recrystallization textures below and above this critical temperature by altering the operative dominant dynamic restoration mechanism, with various texture severity depending on the testing temperature. • Hot deformation behavior of additively manufactured 316 L prepared by LPBF was assessed. • A good stability of this alloy' mechanical strength up to the temperature of ∼873 K measured. • Discontinues DRX was characterized as the leading dynamic restoration mechanism at elevated temperatures. • Constitutive analysis supposed an activation energy of ∼ 553.23 kJ mol for compression at temperatures >873 K. • A strong Goss recrystallization texture induced by the shear flow localization and dynamic restoration. [ABSTRACT FROM AUTHOR]

• The temperature gradient and thermal strain show different characteristics in continuous-wave (CW) mode and pulsed-wave (PW) mode during laser additive manufacturing. • In the direct laser deposition process, residual stress was reduced by about 61% using PW laser mode. • The reduction of temperature gradient and stress release contributing to the reduction and homogenization of the residual stress in PW laser mode. Components manufactured by direct laser deposition (DED) are prone to produce excessive residual stress due to its rapid heating by laser and cooling. Excessive residual tensile stress leads to cracking of deposited sample, even cause failure to serve. Understanding thermodynamic behavior during processing is critical for controlling residual stress. In this study, in-situ transient strain and temperature gradient evolution of each layer on deposited sample 316L stainless steel thin wall during DED using both continuous-wave (CW) and pulsed-wave (PW) laser modes were emerged by digital image correlation (DIC) method and thermal imager. The longitudinal residual stress of deposited sample was evaluated using two laser modes. The results demonstrated that the PW mode creates a smaller temperature gradient and hence a lesser thermal strain than the CW mode. Furthermore, the cyclic thermal stress characteristics of PW mode was observed. All these factors contribute to the reduction of residual stress. [ABSTRACT FROM AUTHOR]