A nanosecond laser was used to define different morphologies of a Ti6Al4V surface: lines, crosshatching and dimples. We analysed the influence of the surface morphology, texture density and ...orientation (parallel, perpendicular and at 45°) on the friction/wear under dry and lubricated (Hank’s solution) sliding conditions to evaluate the specific laser texturing of Ti alloys for biomedical applications. Under dry conditions, the lowest steady-state coefficient of friction was measured for dimples, whereas in Hank’s solution the lines and crosshatching showed better frictional characteristics after running-in and the removal of the bulges around the laser textures. In terms of wear resistance, the low-density lines pattern and particularly the dimples were the most promising in contact situations likely to occur during starved/dry-lubrication conditions.
•Laser-texturing of Ti6Al4V surface: lines, crosshatch and dimple texture.•Friction/wear study under dry/lubricated conditions:effect of texturing direction.•Reduced friction in Hank's solution for lines and crosshatch texture.•Combination of abrasive and adhesive wear under both sliding conditions.•Biomedical applications:transition form lubricated to starved/dry conditions.
In metal-forming processes friction leads to the generation of heat, adhesion and the pick-up of work material, tool wear, inhomogeneous deformations, defects and a poor surface quality. Therefore, ...the use of suitable lubricants is required, especially in the case of aluminium and aluminium alloys. With the increased complexity of the parts being formed, higher strength requirements and the introduction of new alloys, the forming lubricants are also being subjected to ever-increasing demands in terms of temperature stability, reduced friction, galling prevention and surface protection. Graphite is a well-known, solid lubricant that is successfully used in the cold and hot forming of aluminium. However, it leaves dark stains on the surface of the formed part, which means that additional grinding or polishing is required. One of the possible substitutes for graphite is hexagonal boron nitride (h-BN), also known as white graphite.
In this work the possibility of replacing graphite with h-BN in Al-forming lubricants was investigated, including the influence of h-BN powder size and concentration on its tribological performance and the aluminium’s surface quality. The results of the investigation show that h-BN, as a solid lubricant, is capable of successfully replacing graphite in Al-forming processes, while at the same time maintaining a clean surface without staining. The study has shown that the tribological performance, including the friction and wear, the lubrication-film stability and the surface quality, very much depend on the powder size and the concentration. Under the investigated contact conditions, the best performance was obtained for 30-µm h-BN powder when added to the grease in a concentration between 10 and 20%.
•h-BN is a solid lubricant found as a suitable graphite replacement for Al forming operations.•Tribological properties greatly depend on h-BN particle size and concentration.•For mild contact conditions concentration shouldn’t exceed 10%.•In highly loaded contacts concentration over 20% and size larger than 5µm are required.
•Homogeneous 130nm silica/epoxy coating on austenitic steel.•Nanosilica increases coating's hardness, roughness and induces hydrophobicity.•Silica/epoxy coating a successful barrier in a ...chloride-ion-rich environment.•Nanosilica reduces corrosion and zigzags diffusion path available to ionic species.
Homogeneous, 50-μm-thick, epoxy coatings and composite epoxy coatings containing 2wt% of 130-nm silica particles were successfully synthetized on austenitic stainless steel of the type AISI 316L. The surface morphology and mechanical properties of these coatings were compared and characterized using a profilometer, defining the average surface roughness and the Vickers hardness, respectively. The effects of incorporating the silica particles on the surface characteristics and the corrosion resistance of the epoxy-coated steel were additionally investigated with contact-angle measurements as well as by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5wt% NaCl solution. The silica particles were found to significantly improve the microstructure of the coating matrix, which was reflected in an increased hardness, increased surface roughness and induced hydrophobicity. Finally, the silica/epoxy coating was proven to serve as a successful barrier in a chloride-ion-rich environment with an enhanced anticorrosive performance, which was confirmed by the reduced corrosion rate and the increased coating resistance due to zigzagging of the diffusion path available to the ionic species.
18Ni-300 maraging steel manufactured by selective laser melting was plasma nitrided to improve its wear and corrosion resistance. The effects of a prior solution treatment, aging and the combination ...of both on the microstructure and the properties after nitriding were investigated. The results were compared with conventionally produced 18Ni-300 counterparts subjected to the same heat- and thermo-chemical treatments. The plasma nitriding was performed under the same conditions (temperature of 520 °C and time of 6 h) as the aging in order to investigate whether the nitriding and the aging could be carried out simultaneously in a single step. The aim of this work was to provide a better understanding of the morphology and chemical composition of the nitrided layer in the additive-manufactured maraging steel as a function of the prior heat treatments and to compare the wear and corrosion resistance with those of conventional maraging steel. The results show that nitriding without any prior aging leads to cracks in the compound layer, while nitriding of the prior-heat-treated additive-manufactured maraging steel leads to benefits from the thermochemical treatment in terms of wear and corrosion resistance. Some explanations for the origins of the cracks and pores in the nitride layers are provided.
•Homogeneous 130nm silica/epoxy coating on duplex stainless steel.•Nanosilica increases coating's hardness, toughness and induces hydrophobicity.•Nanosilica improves damage resistance as well as ...adhesion on to steel substrate.•Silica/epoxy coating is a successful barrier in a chloride-ion-rich environment.
Silica nanoparticles surface-capped with diglycidyl ether of bisphenol A were dispersed in a solution of epoxy resin, hardener and acetone. The resultant suspension was then coated onto the surface of duplex stainless steel of type DSS 2205 and cured with temperature, generating a 50μm thick silica/epoxy coating. Epoxy coating without nanosilica was also prepared as a reference in the same manner. Mechanical properties of these coatings were compared and characterized using the Vickers hardness test. Three-point bending test was performed in combination with acoustic emission to analyze the damage initiation and development in the coating. The effects of incorporating the silica particles on the surface characteristics and the corrosion resistance of the epoxy-coated steel were investigated with contact-angle and surface energy as well as by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5wt.% NaCl solution. Results indicate, that silica particles significantly improved the microstructure of the coating matrix, which was reflected in an increased damage resistance, reduced degree of delamination, increased surface roughness and induced hydrophobicity. The silica/epoxy coating was proven to serve as a successful barrier in a chloride-ion-rich environment with an enhanced anticorrosive performance, which was confirmed by the reduced corrosion rate.
•Dendrites built from elongated cells lead to a dislocation cell structure•After a solution heat treatment the dislocation density is significantly decreased•Nitrided AM structures can be built to ...match the properties of conventional 316 L•A solution treatment prevents CrN precipitation by eliminating stress•A solution treatment plus nitriding are beneficial for corrosion and wear properties
Due to the limited wear and corrosion properties of the austenitic stainless steel AISI 316 L, some applications require the benefits of nitriding. The aim of this work was to investigate whether the same positive effect of nitriding could be obtained for 316 L that was additive manufactured using the laser powder-bed fusion process and further solution treated at 1060 °C for 30 min, low-temperature plasma nitrided at 430 °C or both. This study was designed to better understand the additive-manufactured and solution-treated microstructures as well as developing a nitride and a diffusion layer. The comparison of the wear and corrosion resistance, the microhardness and the microstructure changes of the additive-manufactured steel in different post-treated conditions with a commercial steel was carried out. It was found that the post-treated low-temperature plasma nitriding improves the wear and corrosion resistance of the additive-manufactured samples. The obtained values are similar to the values of conventionally fabricated and nitrided 316 L. The solution treating itself (without further nitriding) did not have any significant impact on these properties. It was possible to explain the microstructure at the nano level as well as correlating the wear and corrosion properties.
Summary
We analyzed volumetric bone mineral density (vBMD) and bone microstructure using HR-pQCT in subjects with normouricemia (NU) and subjects with hyperuricemia (HU) with and without psoriasis ...(PSO). HU was associated with higher cortical vBMD and thickness. Differences in average and trabecular vBMD were found between patients with PSO + HU and NU.
Introduction
Hyperuricemia (HU) and gout are co-conditions of psoriasis and psoriatic arthritis. Current data suggest a positive association between HU and areal bone mineral density (BMD) and a negative influence of psoriasis on local bone, even in the absence of arthritis. However, the influence of the combination of HU and psoriasis on bone is still unclear. The aim of this study was to assess the impact of HU with and without psoriasis on bone microstructure and volumetric BMD (vBMD).
Methods
Healthy individuals with uric acid levels within the normal range (NU), with hyperuricemia (HU), patients with hyperuricemia and psoriasis (PSO + HU), and patients with uric acid within the normal range and psoriasis (PSO + NU) were included in our study. Psoriasis patients had no current or past symptoms of arthritis. Average, trabecular, and cortical vBMD (mgHA/cm
3
); trabecular number (Tb.N, 1/mm) and thickness (Tb.Th, mm); inhomogeneity of the network (1/N.SD, mm); and cortical thickness (Ct.Th., mm) were carried out at the ultradistal radius using high-resolution peripheral quantitative computed tomography. In addition, bone turnover markers such as DKK-1, sclerostin, and P1NP were analyzed.
Results
In total, 130 individuals were included (44 NU participants (34% female), 50 HU (24%), 16 PSO + HU (6%), 20 PSO + NU (60%)). Subjects were aged: NU 54.5 (42.8, 62.1), HU 57.5 (18.6, 65.1), PSO + HU 52.0 (42.3, 57.8), and PSO + NU 42.5 (34.8, 56.8), respectively. After adjusting for age, sex, BMI, and diabetes, patients in the HU group revealed significantly higher values of cortical vBMD (
p
< 0.001) as well as cortical thickness (
p
= 0.04) compared to the NU group. PSO + NU showed no differences to NU, but PSO + HU demonstrated both lower average (
p
= 0.03) and trabecular vBMD (
p
= 0.02). P1NP was associated with average, cortical, and trabecular vBMD as well as cortical thickness while sclerostin levels were related to trabecular vBMD.
Conclusion
Hyperuricemia in otherwise healthy subjects was associated with a better cortical vBMD and higher cortical thickness. However, patients with both psoriasis and hyperuricemia revealed a lower vBMD.
Polyethylene glycol (PEG)- and polydimethylsiloxane (PDMS)-based corrosion protection coatings of the AISI 316L stainless steel surface were investigated. X-ray photoelectron spectroscopy (XPS) was ...used to confirm successful deposition of the coatings on the substrate as well as to estimate the thickness for both coating types. Contact angle measurements were used to evaluate wetting properties of noncoated, PEG-coated, and PDMS-coated substrates. Hydrophobicity was achieved by applying PDMS coating on the substrate. Potentiodynamic measurements established enhanced corrosion stability of PEG- and PDMS-coated stainless steels. Electrochemical impedance spectroscopy was also performed. It showed superior corrosion protection vs immersion time dependence for PDMS coating in NaCl solution compared to PEG coating.
The aim of the present work was to provide a better understanding of the biocompatibility of Co-based alloys in the physiological environment. Co-based alloys are widely used in orthopaedics for the ...manufacture of prosthetic devices. Two alloys, Co-Cr-Mo and Co-Ni-Cr-Mo, and their individual metal components were studied in simulated physiological solution at 37 deg C, with and without the addition of two complexing agents, EDTA and citrate, in the concentration range from 0.1 to 50 mm. The processes were studied using electrochemical techniques: cyclic voltammetry, anodic potentiodynamic measurements, linear polarization and electrochemical impedance spectroscopy. The results are discussed in the context of the dependence of the passivation behaviour of the two alloys on their composition. Both alloys are shown to passivate very well in simulated physiological solution. The effect of complexing agents is more evident on Co-Ni-Cr-Mo than on Co-Cr-Mo alloy. This appears to be related to the presence of Ni.
In this work, we focus on wetting and morphology properties of fluoroalkylsilane modified TiO2 (FAS-TiO2) and as-received TiO2 nanoparticle coatings. TiO2 nanoparticles of two sizes (30nm and 300nm) ...were spin coated onto steel substrate covered with 300nm layer of epoxy via layer-by-layer (LbL) deposition until the desired wetting characteristics were achieved. Static water contact angles, advancing and receding contact angles and contact angle hysteresis were measured to evaluate the wetting properties of FAS-TiO2 and as-received TiO2 nanoparticle coatings. The morphology of coatings was analyzed with average surface roughness (Sa) measurements and SEM imaging. We have presented a simple step-like procedure to fabricate TiO2 nanoparticle coatings with target wetting properties, either (super)hydrophobic or (super)hydrophilic. Order of the LbL deposition of dual-size nanoparticles for the fabrication of superhydrophobic/superhydrophilic coatings was found to be an important factor influencing on surface roughness and hence wettability. SEM images revealed a typical morphology and Sa difference between FAS-TiO2 and as-received TiO2 nanoparticle coatings reflected in the discrepancy of the average size of the agglomerates that are coating the substrate. Based on these results we can fine-tune the surface roughness and wettability by controlling the LbL deposition of dual-size FAS-TiO2 and as-received TiO2 nanoparticles.
•Fabrication of (super)hydrophobic/(super)hydrophilic TiO2 coatings•Order in layer-by-layer TiO2 nanoparticle deposition controls wettability•(Super)hydrophobic/(super)hydrophilic coatings undergo different wetting mechanism.•(Super)hydrophobic and (super)hydrophilic coatings reveal different morphology.
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