Search Results (385)

Today, the engineering of load-bearing bone tissue after severe trauma still relies on metal-based (Ti, CoCrMo alloys or stainless steel) permanent implants. Such artificial scaffolds are typically applied in the body and come into direct contact with the recipient’s cells, whose adhesion affects the patient’s implant acceptance or rejection. The present study aims to create a nano-rough texture by means of ultra-short femtosecond laser (fs)-induced periodicity in the form of laser induced periodic surface structures (LIPSS) on the surface of a stainless steel implant model, which is additionally functionalized via magnetron-sputtering with a thin Cu layer, thus providing the as-created implants with a stable antimicrobial interface. Calcium phosphate (CaP) crystal growth was additionally applied due to the strong bioactive interface bond that CaPs provide to the bone connective tissue, as well as for the strong interface bond they create between the artificial implant and the surrounding bone tissue, thereby stabilizing the implanted structure within the body. The bioactive properties in the as-created antimicrobial hybrid topographical design, achieved through femtosecond laser-induced nanoscale surface structuring and micro-sized CaP crystal growth, have the potential for subsequent practical applications in bone tissue engineering. Full article

Dissimilar material welding enables the integration of the superior properties of different materials, thereby achieving optimal structural performance and economic efficiency while meeting specific service requirements. The presence of solid-solution strengthening elements such as Ti, Co, and Al, and trace elements such as P and S, in GH3030 nickel-based superalloy leads to their segregation and the formation of intermetallic compounds in the welded joint, resulting in deterioration of joint performance. High-entropy alloys (HEAs), with their high-entropy effect and delayed diffusion effect working synergistically, can effectively suppress compositional segregation caused by uneven elemental diffusion and the formation of intermetallic compounds at interfaces, thereby improving the quality of welded joints and demonstrating great potential for dissimilar material joining. Therefore, in this study, fiber laser welding was used to effectively join AlCoCrFeNi2.1 eutectic high-entropy alloy and GH3030 nickel-based superalloy, with the expectation to improve welded joint element segregation, suppressing the formation of intermetallic compounds, and enhance the welded joint quality and its performance. The AlCoCrFeNi2.1/GH3030 joint exhibits an average yield strength of 1.31 GPa, which is significantly higher than that of the GH3030/GH3030 joint (1.07 GPa). In addition, the AlCoCrFeNi2.1/GH3030 joint shows a higher average work-hardening exponent of 0.337 compared with 0.30 for the GH3030/GH3030 joint, indicating improved plasticity. The results showed that under appropriate welding process parameters, the hardness of the weld zone, transitioning from the nickel-based superalloy to the eutectic high-entropy alloy, exhibited a stable increasing trend, and the joint exhibits good plasticity, with brittle fracture being unlikely. Full article

As well as having corrosion resistance and mechanical properties, medical metallic biomaterials used in metal implants must allow imaging by MRI for prognostic diagnosis. Alloys based on Ti, Fe, Co, etc., have the disadvantage that those constituent elements have higher magnetic susceptibility than the tissue surrounding the metallic implant, and this condition results in defects and distortions (“artifacts”) in MR images during MRI imaging. In consideration of this issue, MRI-compatible low-magnetic-susceptibility materials are currently being researched and developed. In this study, microstructural control of Zr-based alloys by alloy design and heat treatment was investigated. The problem with pure Zr is its low corrosion resistance due to the α-phase of its hexagonal-close-packed (HCP) structure. However, alloys that were alloyed and solution heat-treated to a β-phase (body-centered cubic (BCC) structure) showed high corrosion resistance. In particular, when Zr-15Nb-5Ti-3Cr, which has relatively high corrosion resistance, was subjected to aging heat treatment at 673 K for 1.8 ks, precipitation of fine ω-phase in the β-phase was confirmed. The metallographic structure in which the ω-phase precipitated in the β-phase provided high corrosion resistance [≧1000 mV (vs. SHE)] derived from the β-phase, as well as low magnetic susceptibility (approximately 1.2 × 10⁻⁶ cm³/g), due to the effect of the ω-phase. This study provides guidelines for microstructural control to achieve both low magnetic susceptibility and high corrosion resistance in Zr-based metallic biomaterials for medical use. Full article

Fe₄₂Mn₂₈Cr₁₅Co₁₀Si₅ is a highly strain-hardenable high-entropy alloy (HEA) that is challenging to machine with traditional metal cutting tools. The electrochemical behavior of this HEA was examined in nitrate- and chloride-based electrolytes to understand the electrochemical machining (ECM) process. Potentiodynamic and potentiostatic tests were conducted on this alloy in 1 M and 2.35 M NaNO₃ solutions, with and without additions of 0.01 M nitric acid and 0.01 M citric acid. A 20% NaCl solution was also tested as an electrolyte. Nitrate solutions caused passivation of the HEA, while no passivation was observed in chloride solutions. Surface analysis with X-ray photoelectron spectrometry (XPS) indicated that adding citric acid helped reduce surface passivation. The Faradaic efficiency of ECM increased with higher applied voltage. The chloride solution showed higher Faradaic efficiency than nitrate-based solutions. Specifically, the Faradaic efficiency of 20% NaCl at 10 V is 57.4%, compared to 21.9% for 20% NaNO₃ + 0.01 M citric acid at 10 V. Electrochemical parameters, including anodic and cathodic exchange current densities, Tafel slopes, and corrosion current densities, were calculated from the experimental data. The corrosion current densities in the 20% nitrate solutions ranged from 2.35 to 3.2 × 10⁻⁵ A/cm², while the 20% chloride solution had a lower corrosion rate at 1.45 × 10⁻⁵ A/cm². These electrochemical parameters can help predict the dissolution behavior of the HEA in nitrate and chloride solutions and aid in optimizing the ECM process. Full article

Eutectic high-entropy alloys (EHEAs) combine the casting advantages of eutectic alloys with the comprehensive properties of high-entropy alloys, making them a research hotspot in the field of metallic materials. Among them, the AlCoCrFeNi_2.1 EHEA has attracted significant attention due to its excellent strength–toughness balance characteristics. In this study, alloy samples of AlCoCrFeNi_2.1Si_x (x = 0, 0.1, 0.2, 0.3) were prepared to investigate the regulatory effects of trace Si on its phase composition, microstructure, and mechanical properties. The results show that the base alloy AlCoCrFeNi_2.1 is composed of an FCC and BCC phase composition. With the increase in the Si content to x = 0.3, the CrSi₂ phase gradually precipitates in the alloy, and its microscopic morphology transforms from the regular lamellar to the dendrite and network structure. The introduction of Si significantly enhances the room-temperature microhardness, wear resistance, and yield strength of the alloy through the mechanisms of solid solution strengthening and second phase strengthening. However, an excessive addition leads to a decrease in ductility and toughness. This study reveals the role of Si in phase control and the strengthening and toughening mechanism of eutectic high-entropy alloys, providing experimental evidence and a theoretical reference for the design of high-performance silicon-modified high-entropy alloys. Full article

To address the synergistic degradation mechanisms in engineering service environments, we propose a boron microalloying strategy to enhance the multifunctional surface performance of AlCoCrFeNiMo-based high-entropy alloys. AlCoCrFeNiMoTiBx coatings (x = 0, 0.5, 1, and 1.5) were fabricated on Q235 steel substrates using laser cladding. The microstructure of the coatings was characterized using scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), while their wear and corrosion resistance were evaluated through tribological and electrochemical tests. The key findings indicate that boron addition preserves the original body-centered cubic (BCC) and σ phases in the coating while promoting the in situ formation of TiB₂, leading to lattice distortion. With increasing B content, the BCC phase becomes refined, and both the fraction and size of TiB₂ particles increase. Boron incorporation improves the coating’s microhardness and wear resistance, with the highest wear resistance achieved at x = 1, where abrasive and oxidative wear predominate. At lower content (x = 0.5), B enhances the stability of the passive film and thereby improves corrosion resistance. In contrast, excessive formation of large TiB₂ particles introduces defects into the passive film, accelerating its degradation. Full article

This study investigates the mechanical properties of titanium (Titanflex®) and cobalt-chromium (Co-Cr) alloys for potential use in removable denture bases. Titanium alloys have gained attention due to their biocompatibility and regulatory concerns surrounding Co-Cr, which has been classified as a carcinogenic, mutagenic, and toxic to reproduction (CMR) substance under EU MDR (2017/745). Using selective laser melting (SLM), test specimens of Titanflex® and Co-Cr alloys were 3D-printed at different angles (0°, 45°, 90°) and compared to conventionally cast Co-Cr samples. Tensile testing was conducted to assess modulus of elasticity (E), proof stress (Rp_0.2), ultimate tensile strength (Rm), elongation parameters (Ag, Agt, At), and maximum load (Fm). Results showed that Titanflex® printed at 45° (Ti45) exhibited the highest Rp_0.2, Rm, and Fm, indicating superior strength and plastic resistance. Ti0 displayed the greatest elongation properties, highlighting titanium’s ductility. Co-Cr alloys demonstrated higher stiffness but lower ductility. Printing orientation significantly influenced mechanical properties, particularly in 3D-printed samples. Overall, Ti45 presented a balanced profile of strength and flexibility, making it a promising candidate for denture bases, while Co-Cr remains a rigid alternative with established clinical use. Future research should explore long-term performance under functional and biological conditions to guide clinical application. Full article

This study employs first-principles calculations combined with the Special Quasirandom Structure (SQS) technique to investigate the impact of three interstitial elements C, N, and O, on the mechanical properties and stacking fault energy (SFE) of NiCoCr medium-entropy alloys. The results indicate that non-metallic O, C, and N tend to occupy octahedral interstitial sites, which can effectively release stress concentration and enhance the strength and deformability of the material. Differential charge density analysis shows that the dissolution of C, N, and O significantly alters the surrounding electronic environment, strengthening the interaction between solute atoms and metal atoms, thereby hindering dislocation glide and increasing the strength and hardness of the material. Elastic property analysis indicates that NiCoCr alloys doped with C, N, and O exhibit good ductility and anisotropic characteristics. Furthermore, the study of stacking fault energy reveals that the doping with C, N, and O can significantly increase the stacking fault energy of NiCoCr alloys, thereby optimizing their mechanical properties. These findings provide theoretical evidence for the design of advanced high-entropy alloys that combine high strength with good ductility. Full article

Aircraft engine turbine discs operate under extreme conditions that limit their service life. Laser cladding of AlCoCrFeNi HEA coatings presents a viable solution to enhance their durability. This study optimizes the laser cladding process parameters—specifically, laser power, scanning speed, and powder feed rate—using the Taguchi method in conjunction with grey relational analysis. The optimal parameter set (1450 W, 480 mm/min, 4 r/min) resulted in a coating with a width of 2.93 mm, a height of 1.20 mm, a dilution rate of 22.6%, and a hardness of 532 HV. The optimized process significantly improved hardness by approximately 15% while reducing dilution and elemental segregation in comparison to the initial parameters. This research illustrates the effectiveness of multi-objective optimization in enhancing coating performance, providing a practical approach for the surface strengthening of critical components, such as turbine discs in aircraft engines, under extreme conditions. Full article

The aim of this laboratory study was to evaluate the fitting accuracy of complete-arch implant-supported fixed dental prostheses (ISFDPs) and the occurrence of possible constraint forces after ISFDP fixation using the All-on-four treatment concept. A titanium model was fabricated with support posts for implants in positions 15, 12, 22, and 25. The forces acting on these posts were assessed using strain gauge half bridges. Implants (BEGO Semados^® SCX Implantat 4.1 mm × 10 mm, BEGO Implant Systems, Bremen, Germany) were fixated on top of the support posts. Based on conventional impressions and intraoral scans, two 12-unit monolithic ISFDPs made from cobalt–chromium alloy (CoCr) and zirconia (ZrO₂) were fabricated, jointed with titanium adhesive abutments (PS TiB NH, BEGO), and successively attached to the model. Constraint forces caused by ISFDP fixation were measured for each implant without external force. After testing four ISFDPs with different materials and impression techniques, four new implants were fixated (n = 10 model situations). A standard linear mixed model was used to assess horizontal and vertical constraint forces. The horizontal constraint forces acting on the implants were oriented in the oral direction, indicating that the ISFDPs were too small. The highest constraint forces were measured on implant 22 in the horizontal and vertical directions. Within the limitations of the present laboratory study, the fitting accuracy of complete-arch CoCr and ZrO₂ ISFDPs based on the All-on-four concept was sufficient for clinical use. Restorations made using conventional impressions had better fitting accuracy and reliability than those made using intraoral scans. Full article

Aluminothermic reduction is gaining renewed interest as an alternative processing route for the circular economy. Aluminium is produced electrochemically in the Hall–Héroult process with minimal CO₂ emissions if electricity is sourced from non-fossil fuel energy sources. The Al₂O₃ product from the aluminothermic reduction process can be recycled via hydrometallurgy, with leaching as the first step. NaAlO₂ is a water-leachable compound that forms a pathway for recycling Al₂O₃ with hydrometallurgy. In this work, a suitable slag formulation is applied in the aluminothermic reduction of manganese ore to form a Na₂O-based slag of high Al₂O₃ solubility to effect good alloy–slag separation. The synergistic effect of added chromium metal as a collector metal is illustrated with an increased alloy yield at 68%, from 43% without added Cr. The addition of small amounts of carbon reductant to MnO₂-containing ore ensures rapid pre-reduction to MnO. This approach negates the need for a pre-roasting step. The alloy and slag chemical analyses are compared to the thermochemistry-predicted phase chemistry. The alloy consists of 57% Mn, 18% Cr, 18% Fe, 3.4% Si, 1.5% Al, and 2.2% C. The formulated slag exhibits high Al₂O₃ solubility, enabling effective alloy–slag separation, even at an Al₂O₃ content of 55%. Full article

Certain metal powders used in the synthesis and processing of high-entropy alloys (HEAs) pose significant health hazards, as many of these metals are toxic substances with no biological role in the human body. These metals can mimic essential elements or interfere with metabolic processes (the chemical reactions in living organisms that sustain life), leading to detrimental health effects. While some metals, such as aluminum, can be eliminated from the body through natural biological processes, others tend to accumulate, causing chronic illnesses over time. This review examines the toxicity mechanisms and health impacts of metals used in HEA synthesis, focusing on laboratory-scale processing. It also identifies potential health risks associated with occupational exposure in laboratory environments, including the inhalation of toxic metal powders and nanoparticles. A simple risk scoring model is introduced to systematically assess and quantify these risks based on factors such as toxicity levels, exposure limits, and carcinogenic potential (the ability of a substance to cause cancer) as given by the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) standards. The proposed model can be applied to evaluate the relative hazards of commonly used HEA constituent powders (e.g., Ni, Co, Cr, and Al), offering practical guidance for safer laboratory handling and material selection. By integrating this risk assessment framework, this review aims to enhance workplace safety, guide the development of better material handling practices, and assist researchers in mitigating health risks associated with HEA processing. Full article

In order to enhance the performance of 20# steel, this study successfully fabricated AlCoCrFeNi high-entropy alloy coatings with different WC contents (x = 0, 10, 20, 30 wt%) on its surface using plasma cladding technology. The effects of WC content on the microstructure, mechanical properties, and corrosion resistance of the coatings were systematically investigated. The results indicate that without WC addition, the coating consists of a dual-phase structure comprising BCC and FCC phases. With the incorporation of WC, the FCC phase disappears, and the coating evolves into a composite structure based on the BCC matrix, embedded with multiple carbide phases such as W₂C, M₇C₃, M_xC_γ, and Co₆W₆C. These carbides are predominantly distributed along grain boundaries. As the WC content increases, significant grain refinement occurs and the volume fraction of carbides rises. The coating exhibits a mixed microstructure of equiaxed and columnar crystals, with excellent metallurgical bonding to the substrate. The microhardness of the coating increases markedly with higher WC content; however, the rate of enhancement slows when WC exceeds 20 wt%. The hardness of 1066.36 HV is achieved at 30 wt% WC. Wear test results show that both the friction coefficient and wear rate first decrease and then increase with increasing WC content. The optimal wear resistance is observed at 20 wt% WC, with a friction coefficient of 0.549 and a wear mass loss of only 0.25 mg, representing an approximately 40% reduction compared to the WC-free coating. Electrochemical tests demonstrate that the coating with 20 wt% WC facilitates the formation of a dense and stable passive film in NaCl solution, effectively inhibiting Cl⁻ ion penetration. This coating exhibits the best corrosion resistance, characterized by the lowest corrosion current density of 1.349 × 10⁻⁶ A·cm⁻² and the highest passive film resistance of 2764 Ω·cm². Full article

A cost-effective Fe-Cr-Mo-B-Si-C metamorphic alloy (HXA5) was newly designed and fabricated as coating material using the high-velocity oxygen fuel (HVOF) thermal spray process, and its microstructure and dry wear resistance were investigated in comparison with a conventional HVOF WC-12Co coating. The HXA5 coating material consisted of a splat area and un-melted powder area. The splat area contained metallic glass, (Cr,Fe)₂B, Cr₂B, and minor Fe-based BCC phases, and the un-melted powder area was composed of Fe-based BCC, (Cr,Fe)₂B, and Cr₂B phases. Room-temperature wear tests revealed that HVOF HXA5 coating material exhibited wear resistance comparable to HVOF WC-12Co coating over ~8.4 km sliding and even superior performance at high-stress wear conditions. This superior wear behavior of HXA5 coating material was attributed to the minimal hardness difference between the metallic glass and boride, the plasticity of the metallic glass, and the formation of a lubricating tribofilm. The wear mechanisms and the influence of alloying elements on glass-forming ability were also discussed. Full article

CoCrFeNiMn high entropy alloy (HEA) fabricated via laser-based powder bed fusion (PBF-LB/M) exhibits exceptional mechanical properties, including high strength, better ductility than titanium alloy, and superior corrosion resistance. This study simulates the intergranular fracture behavior of PBF-LB/M CoCrFeNiMn HEA under tensile loading by embedding cohesive elements with damage mechanisms into polycrystalline representative volume elements based on the crystal plasticity finite element method. The simulation results show good agreement with reported experimental stress–strain curves, demonstrating that the crystal plastic constitutive model combined with the cohesive constitutive model can accurately describe both the macroscopic response behavior and fracture failure behavior of the CoCrFeNiMn HEA. Furthermore, this work investigates the mechanical properties of the HEA in different tensile directions, the improvement of anisotropy through columnar-to-equiaxed grain transition, and the effect of texture strength on crack initiation and propagation. The results show that the polycrystalline CoCrFeNiMn HEA exhibits anisotropic mechanical properties: simulated yield strengths (YSs) are 436.9 MPa (in the scanning direction) and 484.7 MPa (in the building direction), tensile strengths (TSs) reach 639 MPa and 702.5 MPa, and elongations (ELs) are 10.6% and 21.8%, respectively. After equiaxed grain formation, the EL in the scanning direction increased from 10.6% to 17.2%, while the EL in the building direction decreased from 21.8% to 20.3%. Concurrently, the anisotropy coefficients of YS, TS, and EL decreased by 1.8%, 2.2%, and 36.1%, respectively. The cracks initiate at stress concentrations and subsequently propagate along grain boundaries until final fracture. Variations in texture strength significantly influence the crack initiation location and propagation path in the CoCrFeNiMn HEA. Full article