Search Results (307)

Objectives: To evaluate the corrosion behavior and surface characteristics of four nickel-containing orthodontic archwires (stainless steel (SS), superelastic nickel–titanium (NiTi), copper–nickel–titanium (CuNiTi), and multiforce NiTi) under unused, in vitro artificial saliva-immersed, and clinically used (in vivo) conditions. Methods: Rectangular SS, NiTi, CuNiTi, and multiforce NiTi archwires were analyzed in the following three conditions: as received, after one week of immersion in artificial saliva (pH 6.4), and after clinical use for 6–8 weeks. Corrosion behavior was assessed using cyclic voltammetry (CV), open-circuit voltammetry (OCV), and electrochemical impedance spectroscopy (EIS). Surface morphology was examined by scanning electron microscopy (SEM). Results: Corrosion behavior was dependent on archwire type and exposure condition. SS archwires exhibited reduced impedance response after clinical use, indicating passive-film degradation. In the clinically used NiTi specimen, pronounced electrochemical instability was observed, characterized by a deep OCV transient, slow repassivation, and SEM evidence compatible with localized pitting corrosion. In the CuNiTi specimens, minimal differences were observed between the unused and clinically used conditions, which may be consistent with stable passive-film integrity in these specimens. In the multiforce specimen, clinical use was associated with a higher impedance response than the unused and saliva-immersed conditions of that same specimen. In the saliva-immersed specimens, possible passive-film formation and a higher impedance response were observed relative to the other conditions of the same specimens, but these did not reproduce the electrochemical and morphological changes observed after clinical use. Conclusions: In vitro artificial saliva immersion does not reliably replicate in vivo aging of nickel-containing orthodontic archwires. Corrosion behavior evolves during clinical service in an archwire-specific manner, with NiTi archwires showing susceptibility to clinically induced surface degradation. Full article

Additive manufacturing (AM) technologies, such as laser powder bed fusion (LPBF), allow for rapid fabrication of geometrically complex components that would be difficult to create using traditional casting or subtractive fabrication processes; however, research into AM metals has shown that fabrication defects resulting from LPBF processes (i.e., voids, un-melted particles, etc.) can have deleterious effects on mechanical behavior. Material testing using traditional macro (coupon-scale) volumes may not accurately capture scalable material behavior in LPBF metals, as the distribution of fabrication defects is volume-dependent. To understand fundamental material behavior at scales independent of geometrical fabrication defects (including print-induced material arrangements), in situ micro-mechanical testing of AM LPBF 17-4 PH stainless steel materials is conducted, opening possibilities for future bottom-up material simulation scaling. In this study, the tensile and compressive behavior of LPBF-fabricated 17-4PH stainless steel is characterized at the micron scale to aid future efforts in the predictive upscaling of structural components, while eliminating void effects and micro-scale print-induced material arrangements in any characterizations. Not surprisingly, behavior comparisons between multiple length scales (micro and macro scales) indicate strength reductions in larger bulk volumes. Micro-tensile measurements resulted in ultimate tensile strength (1359 MPa ± 99.9 MPa standard deviation) and strain before failure (0.31 ± 0.063 μm/μm) values that exceeded those of the macro-tensile specimens (1025 MPa tensile strength and 0.190 μm/μm strain at fracture, respectively). Full article

This work presents an experimental characterization of 17-4PH stainless steel fabricated by Atomic Diffusion Additive Manufacturing (ADAM). The microstructure, porosity, local chemical composition, and residual stresses were investigated using optical microscopy, SEM-EDS, digital image analysis, and sin²ψ X-ray diffraction. Pronounced porosity anisotropy was observed, with a lower porosity area fraction in the transverse section (1.45%) than in the longitudinal section (3.48%), where elongated channel-like inter-layer defects were identified. Isothermal sintering at 1315 °C produced a predominantly martensitic microstructure with equiaxed morphology. Local chemical variations were detected in selected macro-voids and interfacial regions, including elevated concentrations of C, Cr, and Nb, reaching 1.61 wt.%, 42.58 wt.%, and 16.31 wt.%, respectively. These anomalies may be related to localized binder-derived residues or secondary phase formation, although their origin cannot be conclusively determined by EDS alone. Residual stress measurements at 12 surface locations revealed spatial variations, with maximum axial tensile stress of 185.6 ± 21.9 MPa and local compressive stress of −46.7 ± 10.9 MPa. All measured stresses remained below the reported yield strength. The findings highlight the importance of optimizing inter-layer bonding and thermal debinding conditions in ADAM. Full article

The electrical response of conductive textile structures to liquid exposure was investigated as a basis for electrical resistance-based haemorrhage detection. The sensing principle relies on changes in the electrical resistance of the conductive network following liquid exposure, with the resulting resistance variation used as the sensing parameter. Nine conductive textile variants were developed and evaluated, comprising three knitted structures (K1–K3) and six woven structures produced in raw and finished states (W1–W3). The structures incorporated silver-coated polyamide and stainless-steel conductive yarns and were exposed to water, acidic perspiration (pH 5.5), alkaline perspiration (pH 8.0), and saline solution. Saline solution was used as a controlled conductive aqueous medium for comparison and does not reproduce the physical, chemical, rheological, cellular, or biochemical properties of whole blood. Electrical resistance measurements, together with physical and mechanical characterization, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR), were performed to assess structural stability and electrical response. Saline solution produced the largest resistance variations among the tested liquids, whereas water and perspiration resulted in lower responses. Localized mechanical deformation further induced pronounced resistance changes in several woven structures. Among the evaluated variants, W2 exhibited the most favorable combination of structural stability and electrical responsiveness. These results support further investigation of W2 (conductive yarn: Filix DA5393 yarn) as an electrical resistance-based sensing structure for potential haemorrhage-related liquid detection applications. Full article

Background: ExPEC9V was a 9-valent vaccine candidate intended for the prevention of invasive extraintestinal pathogenic Escherichia coli (ExPEC) disease (IED). Here, we describe more than a decade-long formulation development trajectory of this vaccine candidate aimed at establishing a stable, robust and scalable drug product that maintains long-term stability while addressing potential manufacturing challenges and increasing the probability of successful global deployment. Methods: Selected formulation development studies of the ExPEC multivalent vaccine candidate are summarized, spanning formulation screening, confirmation, and design of experiments (DoE)-based robustness, stability and compatibility studies. A formulation initially developed for an early low-valency vaccine candidate was subsequently tested and confirmed for candidates with additional serotypes incorporated based on antigen heterogeneity evidence. Contact materials employed included primary packaging—polycarbonate (PC) and polyethylene terephthalate glycol (PETG) bottles, borosilicate glass vials, stoppers, and prefilled syringes; vessel types—bags and stainless steel vessels used in drug substance (DS) and drug product (DP) manufacturing; and varying concentrations of tungsten and hydrogen peroxide. An evolving analytical panel was applied to assess attributes such as purity, protein concentration and degree of O-acetylation. Results: A phosphate-based formulation containing sorbitol, methionine, and polysorbate 80 showed superior stability in screening and was confirmed as fit for purpose across increasing vaccine valency. The ExPEC 9V drug product displayed remarkable thermal and formulation robustness, long-term (3 years) stability at 2–8 °C in glass vials and prefilled syringes, and compatibility with assessed primary containers and manufacturing materials. DoE-based robustness studies defined acceptable excipient and pH ranges, supporting a wide formulation design space. Conclusions: The development trajectory of the ExPEC9V vaccine candidate demonstrates that early prioritization of a robust, scalable formulation that remains fit for purpose across valency evolution supports a stable late-stage manufacturable drug product. Full article

This study investigates the laser powder bed fusion (LPBF) fabrication of 17-4 PH stainless steel triply periodic minimal surface (TPMS) structures and the wettability response of corresponding flat plates subjected to selected post-processing treatments. Five TPMS geometries were fabricated and visually examined to document their overall condition and manufacturing irregularities. Thermal aging, steel shot blasting, commercial hydrophobic coating, and selected treatment combinations were evaluated on flat plates manufactured using the same material and LPBF process. Wettability was assessed using time-dependent static contact angle (CA) measurements and a preliminary comparison of three steel shot grades. The fabricated TPMS structures retained their overall geometries but exhibited localized burnt edges, distortion of thin boundary features, and differences in surface appearance. The untreated LPBF-fabricated surface was hydrophilic and exhibited time-dependent wetting, with the CA decreasing from approximately 81° to as low as 48° within 4 min and complete wetting occurring within approximately 8–10 min. Among the evaluated blasting media, S-330 produced the highest CA values; however, blasted surfaces remained hydrophilic, and the response depended on whether the plate was untreated or aged. The coating produced CA of approximately 153–170° across all coated regions, both with and without prior blasting. These findings identify manufacturing considerations for LPBF-fabricated TPMS structures and demonstrate the effects of the investigated treatments on the wettability of corresponding flat surfaces, thereby providing insights for future studies of TPMS-based condensation surfaces in atmospheric water generation applications. Full article

6061 aluminum alloy is lightweight and has good thermal conductivity, while 304 stainless steel possesses excellent mechanical properties and corrosion resistance; both have broad application prospects in cooling circuits. Propylene glycol coolant shows great potential in liquid cooling systems due to its low toxicity and good antifreeze properties. However, during operation, galvanic corrosion may occur when the two metals come into direct contact within the coolant, thereby threatening system safety and service life. This study focuses on 6061 aluminum alloy, 304 stainless steel, and their galvanic couples. Electrochemical testing, SEM, 3D confocal microscopy, and XPS were used to systematically investigate their self-corrosion and galvanic corrosion behavior in propylene glycol coolant at pH values of 4.8, 6.8, and 8.8. The results indicate that 6061 aluminum alloy is more sensitive to pH changes; its corrosion resistance first increases and then decreases as pH rises, with the least corrosion occurring at pH = 6.8 and the most severe at pH = 4.8. 304 stainless steel exhibited lower corrosion rates at pH 6.8 and 8.8, but corrosion significantly worsened at pH 4.8. For the 6061 aluminum alloy/304 stainless steel couple, the galvanic current first decreased and then increased with rising pH, while the galvanic potential first increased and then decreased. The 6061 aluminum alloy consistently acted as the anode, and the 304 stainless steel consistently acted as the cathode, with the highest sensitivity to galvanic corrosion observed at pH 4.8. XPS analysis shows that under different pH conditions, the corrosion products of 6061 aluminum alloy are Al(OH)₃ and Al₂O₃, while the main components of the passivation film on 304 stainless steel remain unchanged. Full article

The corrosion behavior of ferritic–martensitic 17Cr stainless steel in CO₂-saturated brine was investigated using static autoclave immersion tests in 4.12 wt% NaCl solution at 230 °C under CO₂ partial pressures of 6.36, 18.28, and 24.57 MPa. The calculated in situ pH values obtained using the OLI System were 3.79, 3.55, and 3.49, respectively. Corrosion morphology, microstructural evolution, and corrosion products were characterized by SEM, EDS, EBSD, and Raman spectroscopy. The average mass-loss corrosion rate increased from 0.138 ± 0.0221 mm/year at 6.36 MPa pCO₂ to 0.326 ± 0.0142 mm/year at 24.57 MPa pCO₂. Although the specimens did not show severe macroscopic pitting, localized attack preferentially occurred in fine-grained martensitic banded regions. EBSD analysis revealed that these regions exhibited higher local misorientation and defect density, which may reduce the stability of Cr-rich surface films. Raman spectra identified Cr(OH)₃ in the corrosion products, and the Cr(OH)₃ signal became more evident with increasing CO₂ partial pressure. The results indicate that, under fixed temperature and salinity, the corrosion behavior of 17Cr stainless steel is governed by CO₂ partial pressure and microstructural heterogeneity. Full article

The corrosion resistance of metallic materials is closely related to their service environment. In ammonia-based desulfurization post-treatment systems, 316L stainless steel, 2507 duplex stainless steel, and TA2 commercially pure titanium are widely used as candidate materials for key components such as desulfurization heat exchangers. In this study, the pitting corrosion behavior of 316L, 2507, and TA2 was investigated in simulated ammonia desulfurization post-treatment solutions with different pH. The results show that increasing solution acidity leads to a decrease in the capacitive arc radius and polarization resistance, while the donor concentration and pitting susceptibility of the three materials increase. Under the same pH condition, TA2 exhibits the highest stability and corrosion resistance, followed by 2507, whereas 316L shows the poorest corrosion resistance. The composition of the TA2 passivation film (TiO₂) does not change as the pH of the simulated solution is modified. With increasing solution acidity, the relative XPS peak-area fraction of TiO₂ in TA2 increases, indicating that TiO₂ remains the dominant component of the passive film. In contrast, the relative contents of Cr- and Mo-containing oxides/hydroxides in 316L and 2507 decrease, and MoO₃ is replaced by MoO₂ under acidic conditions. These changes suggest weakened passive-film stability and reduced protection of the substrate. Full article

Graphene-reinforced CrCoNiFeMo high-entropy alloy composite coatings were fabricated on 17-4PH stainless steel by laser cladding for the surface protection of industrial robotic end-effector grippers. The effects of graphene content on microstructure, hardness, wear behavior and corrosion resistance were investigated. Graphene-derived carbon suppressed Laves and σ phases and promoted the in situ formation of M23C6, M7C3 and Co2C carbides, transforming the coating into a carbide-reinforced FCC/BCC composite structure. The average hardness increased from 462 HV0.2 to 676 HV0.2 with increasing graphene content. The 0.4 wt.% graphene coating showed the best wear resistance, with the lowest friction coefficient of 0.42 and minimum wear scar width and depth of 546 μm and 5.72 μm, which was attributed to carbide strengthening and the possible formation of a carbonaceous lubricating tribo-layer. The 0.2 wt.% graphene coating exhibited the best corrosion resistance, with the lowest corrosion current density of 5.81 μA/cm² and the highest impedance response. Excessive graphene caused carbon-rich agglomeration, excessive carbide precipitation and weakened passivation. This work provides a feasible surface strengthening strategy for 17-4PH stainless steel robotic gripper components. Full article

Stainless-steel bipolar plates (BPPs) are attractive for proton exchange membrane water electrolysis (PEMWE) due to their low cost and manufacturability, yet their use is limited by severe corrosion. Despite the advantages of plasma-enhanced atomic layer deposition (PEALD) in producing dense films, ion bombardment may induce surface damage and increase roughness. This paper describes a cross-flow PEALD strategy with a remote plasma source to deposit metallic tantalum (Ta) coatings on stainless steel. In a cross-flow reactor, plasma species reach the substrate primarily through diffusion across the boundary layer of the gas flow, providing a gentler plasma–surface interaction and enabling the formation of dense, smooth Ta coatings. The roughness of the Ta films is markedly reduced from 1.45 nm to 0.24 nm, which is favorable for interfacial electrical contact. The process exhibits self-limiting growth with a linear growth rate of ~0.49 Å cycle⁻¹. In a simulated PEMWE environment, Ta-coated stainless steel shows improved corrosion resistance, with the corrosion potential increasing from −0.27 to 0.07 V vs. Ag/AgCl (pH 0.3) and the corrosion current density decreasing to 2.05 × 10⁻⁷ A cm⁻². Overall, cross-flow PEALD enables high-quality metallic Ta coatings that enhance corrosion protection and interfacial electrical performance for BPPs. Full article

The demand for large-scale high-performance components with tailored properties in the aerospace and automotive industries has increased interest in multi-material additive manufacturing (AM). Among AM techniques, the Wire Arc Additive Manufacturing (WAAM) process is preferred for bimetallic fabrication due to high deposition rates, low equipment costs, and efficient material utilization. However, differences in metallurgical and thermal properties between dissimilar alloys can cause heat accumulation, leading to thermal stresses, cracking, and weak interfacial bonds. To the best of the authors’ knowledge, no study has reported the fabrication and characterization of a 17-4PH SS/Inconel 625 joint using the large-scale CMT-WAAM Process. To fill this gap, this study characterizes the microstructure and elemental distribution of the joint using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray Microscopy (XRM) and energy dispersive spectroscopy (EDS). Microstructural analysis revealed a martensitic matrix with retained δ-ferrite in the 17-4PH region, a fully austenitic γ-phase in the Inconel 625 region, and a mixed BCC–FCC transition zone at the interface. EDS results demonstrated a Fe–Ni compositional gradient across the interface. Radiographic inspection confirmed a defect-free build, and XRM results showed a porosity of less than 0.003% only in the 17-4PH region. Tensile testing confirmed joint integrity, with fracture occurring in the Inconel 625 region, and average yield and ultimate tensile strengths of 391 ± 7 MPa and 676 ± 9 MPa, respectively. The simplified Johnson-Cook constitutive model successfully predicted the ultimate tensile strength (UTS), with a prediction error of 9.3% compared to the experimental result. Furthermore, a novel 3D-structured light scanner technique was developed and validated with an extensometer to provide insight into localized strain behavior. Full article

This study presents a novel in situ reinforcement strategy for 17-4PH stainless steel by using Nb and Cr₃C₂ powders as precursors, addressing the challenge of poor particle dispersion and interfacial bonding in conventional ex situ ceramic additions. The coatings were systematically compared with 17-4PH coatings without the addition of a reinforcing phase. The results show that the coating without Nb addition is dominated by α-Fe martensite, exhibiting a coarse columnar/dendritic microstructure. After adding Nb and Cr₃C₂, the coating successfully forms in situ face-centered cubic NbC, with a significantly refined and uniformly distributed microstructure. The 10 wt.% Nb+Cr₃C₂ coating exhibits a refined microstructure with an average grain size reduced from 1.12 μm to 0.85 μm and a microhardness of 495.5 HV, representing an 86% increase over the substrate and a 34% improvement compared to the unreinforced coating. Friction–wear tests demonstrate that the composite coating reduces wear track width and depth by approximately 50% and 45%, respectively, compared to the substrate, with the wear mechanism transitioning from severe adhesive and fatigue wear to mild abrasive wear and localized micro-delamination. In situ synthesized NbC effectively optimizes the coating microstructure, enhances interfacial bonding, and markedly improves the hardness and wear resistance of 17-4PH coatings, providing theoretical and technical support for their engineering application under severe service conditions. Full article

Understanding the finishing behavior of hybrid structures produced by additive manufacturing based on FDM is critically important in systems where phases with different thermal and mechanical properties coexist. In this study, the drilling performance of hybrid structures with a PLA/17-4 PH/PLA layer arrangement was comprehensively investigated in terms of thrust force, moment, surface roughness, temperature variation, vibration behavior, and surface integrity. For this purpose, a total of 16 drilling tests were performed on 56 × 56 × 15 mm hybrid specimens with 100% infill density, in a full factorial configuration, at cutting speeds (V) of 80–170 m/min and feed rates (f) of 0.04–0.16 mm/rev. The middle layer was used in the as-printed green state as a 17-4 PH metal-filled filament containing metal particles and binder, without any debinding or sintering step. The results showed that increasing feed rate increased thrust force, moment, and surface roughness in all layers, whereas increasing cutting speed decreased these values and promoted a more stable drilling regime. The middle 17-4 PH layer exhibited lower surface roughness than the outer PLA layers, while thermal measurements indicated limited variation at the hole entrance and higher temperature accumulation at the hole exit. The most favorable drilling condition within the studied hybrid configuration was obtained at 170 m/min and 0.04 mm/rev, whereas the least favorable condition was obtained at 80 m/min and 0.16 mm/rev. Overall, the combination of high cutting speed and low feed rate provided the most suitable drilling window for the studied hybrid structure. The findings also indicated that surface quality was more strongly associated with cutting load and high-frequency vibration components than with vibration level alone. Full article

Rod ends are critical structural components primarily designed to sustain axial loads in mechanical and aeronautical assemblies. However, operational conditions may involve transverse loading, which induces significant bending stresses concentrated in the threaded shank region. This research presents an experimental investigation aimed at characterizing the elastoplastic bending behavior of the threaded portion of rod ends subjected to such off-axis loads. Specimens manufactured from precipitation-hardened stainless steel 17-4 PH were tested under both displacement and force control strategies. Each specimen was subjected to incremental loading until failure to determine the elastic limit, yield point, ultimate bending strength and fracture mode. The experimental results enabled a preliminary assessment of the static resistance of the threaded region; furthermore, a comparison with analytical formulations and empirical estimation methods available in the literature revealed promising agreement. These findings highlight the importance of accounting for non-axial loading in the design of threaded joints for critical applications. This study establishes a baseline for broader experimental campaigns aimed at validating these results and exploring fatigue behavior under cyclic transverse loads. Full article