Search Results (3,741)

Four compositions of rapidly quenched ribbon brazing alloys based on Ag–Cu–Ti (Ag–26.5Cu–1.5Ti, Ag–25Cu–5Ti) and Ag–Cu–Zr (Ag–26.5Cu–1.5Zr, Ag–25Cu–5Zr) systems were produced. Initial ingots were synthesized by arc melting. Rapidly solidified ribbons, 50–100 μm thick, were then fabricated from homogenized ingots using a “Crystall-702” facility. A comparative analysis of the microstructure and phase composition of both the ingots and ribbons was conducted using scanning electron microscopy and X-ray diffraction. The analysis revealed the presence of Cu₄Ti and CuTi intermetallic compounds in the Ag–Cu–Ti alloys, and AgCu₄Zr and Zr₂Cu in the Ag–Cu–Zr alloys. Rapid quenching was found to produce metastable structures and significantly refine the intermetallic phases. Microhardness measurements of the ingot and ribbon states demonstrated a substantial influence of the processing route on the mechanical properties. The tensile strength of the ingots was also evaluated. The wetting angles of the rapidly quenched alloy melts on 99% Al₂O₃ (alumina) ceramic substrates under vacuum were determined. All produced ribbons, except for the Ag–26.5Cu–1.5Zr composition, demonstrated adequate wettability. Thus, these materials are considered promising for further research into heat-resistant metal–ceramic joints. Full article

The formation of hard/brittle layers (HBLs) forming in proximity to the transition-layer interface during the welding process of stainless steel clad plates constitutes a pivotal element in determining the limitations on joint homogeneity and toughness. In order to elucidate their formation mechanisms and develop viable suppression routes, S31603/Q420qENH clad plates were utilised to fabricate five butt joints. This was achieved by varying the carbon content of the welding consumables and the heat input in the transition layer. A programme was conducted that combined microstructural and microhardness characterisation, mechanical testing, and numerical welding simulations. The findings indicate that base-layer consumables with comparatively elevated carbon content (w(C) ≥ 0.06%) expeditiously engender a constricted, localised hardened band in close proximity to the transition-layer interface. This is characterised by the predominance of martensite and Cr-rich compounds of the M_xCr_y type, which function as the principal genesis of bending cracks. Conversely, the utilisation of low-carbon welding consumables has been shown to markedly reduce interfacial carbon activity and C-Cr segregation, thereby suppressing the precipitation of M_xCr_y phases and effectively decreasing the overall thickness of the HBLs. Further numerical analysis shows that moderately increasing the transition-layer heat input lowers the T_8/5 cooling rate and shifts the cooling path away from the martensite region. This transforms the interfacial microstructure from a localised hardened band into a more uniform, graded structure. These findings provide an engineerable process-control strategy for enhancing both microstructural uniformity and toughness in stainless steel clad joints. Full article

Laser Powder Bed Fusion (L-PBF) can enable in situ microstructural tailoring of metallic components by precisely controlling the layer-wise processing parameters. Layer rescanning is one such strategy used to induce localized microstructural modification. In this study, we investigated the effect of a lattice-based selective rescanning approach applied to different base scan strategies for Ti-6Al-4V samples. The lattice regions were selectively rescanned at 50% reduced laser power relative to the initial scan along the same laser path. Relative density, porosity, martensitic α′ morphology, phase fraction, and Vickers microhardness were compared with those of non-rescanned reference counterparts. Different scan strategies, including unidirectional, stripes, and chess, exhibited distinct responses to selective rescanning, resulting in localized variations in martensitic phase formation and hardness values. The extent of localized microstructural modification and hardness enhancement was strongly governed by the underlying scan strategy. Selective rescanning using the stripes strategy yielded the largest contrast between non-rescanned and rescanned regions. The unidirectional strategy showed strong effects of rescanning, but the heat-affected zones extended to the non-rescanned regions. In contrast, the chess strategy exhibited comparatively moderate changes owing to its inherent thermal-management characteristics. These findings demonstrate that selective rescanning can provide an effective, localized approach for tailoring microstructure and hardness enhancement in L-PBF Ti-6Al-4V, with its effectiveness strongly dependent on the underlying scan strategy. Full article

This study analyses the effect of electrolytic plasma treatment on improving the wear resistance of 30CrMnSi steel used under conditions of high abrasive and impact-abrasive loads. The samples were processed using various technological regimes, namely electrolytic plasma quenching, nitriding, nitrocarburising, and carburising. A range of analytical methods were employed to comprehensively characterise the structure, phase composition, and mechanical properties, including SEM/EDS, XRD, and microhardness testing. The tribological properties of the materials were evaluated using a TRB³ tribometer, and abrasive and impact-abrasive wear tests were performed in accordance with GOST 23.208–79 and GOST 23.207–79 standards. The results show that electrolytic plasma treatment leads to the formation of diffusion layers with a thickness of 50–150 μm, accompanied by the formation of carbide, nitride, and carbonitride phases (Fe₄C, Fe₇C₃, Fe₄N, Fe₂N, Fe₃(CN)). This process results in a significant increase in surface hardness (up to 610–930 HV) and improved wear resistance. The study indicates that electrolytic plasma nitrocarburising provides a favourable combination of hardness and tribological behaviour, leading to a low friction coefficient (0.25–0.35) and enhanced resistance to abrasive and impact-abrasive wear. The obtained results demonstrate the potential of this technology for improving the performance of components made of 30CrMnSi steel operating under severe wear conditions. Full article

The study aims to strengthen cylindrical liners by plasma electrolytic oxidation (PEO) and to determine the optimal processing parameters for forming wear-resistant coatings. The results of laboratory experiments were transferred to practical application for liner strengthening, followed by testing coatings formed directly on real components. PEO was applied to cylindrical sleeves made of eutectic aluminum–silicon alloy EN AC-48000 to form mechanically strong and wear-resistant oxide coatings. The coating had a two-layer structure: a dense inner barrier layer and a porous outer layer. The effect of SiO₂ (~20 nm) and Al₂O₃ (~30 nm) nanoparticles in the electrolyte on the morphology, phase composition, microhardness and tribological characteristics of the coatings was evaluated. The optimal PEO parameters were determined as 325 V, duty cycle 25%, processing time 12 min, average current density 1.4 A·dm⁻², and concentration of Al₂O₃ + SiO₂ (5 + 5 g L⁻¹). Under these conditions, the coating achieved a maximum microhardness of 259 HV, a low coefficient of friction of ~0.50 and a wear rate of 0.81 × 10⁻⁴ mm³·N⁻¹·m⁻¹. X-ray diffraction analysis confirmed the formation of γ-Al₂O₃ without changing the silicon phase. The results provide quantitative data on the effects of nanoparticles and PEO parameters on coating properties, which is important for the development of long-life part surfaces. The increased microhardness and wear resistance are attributed to the formation of the ceramic γ-Al₂O₃ phase and the densification of the porous structure due to the incorporation of Al₂O₃ and SiO₂ nanoparticles, which reduce defect density and limit the adhesive–abrasive wear mechanism. Full article

This study investigates the effects of current density on the microstructure and properties of electrodeposited NiCo-CeO₂ composite coatings. Results demonstrate that current density significantly influences coating composition, with higher CeO₂ and lower Co content increasing surface roughness (minimum at 30 mA/cm², maximum at 100 mA/cm²). Microstructural homogeneity improves with optimized Co/CeO₂ content, where the A30 coating (30 mA/cm²) exhibits the weakest texture among all coatings due to peak Co incorporation. Texture intensifies at higher current densities (30–100 mA/cm²) as Co and CeO₂ contents diminish. Internal stress depends on electrodeposition kinetics and particle dispersion, ranging from −2.22 MPa (A20) to 651 MPa (A50). Hardness correlates with (111) plane dominance and Co/CeO₂ content, reaching 449.8 HV for A30 but dropping to 288.8 HV for A100. Optimal current density tuning refines grains, enhances (111) texture, and improves compositional uniformity, endowing the A30 coating with balanced hardness and corrosion performance (corrosion potential: −224 mV; current density: 0.225 μA/cm²). These findings provide guidelines for tailoring high-performance NiCo-CeO₂ coatings through current density regulation. Full article

Soft-tissue management is critical for guided bone regeneration (GBR), yet conventional titanium meshes lack the ability to regionally regulate fibroblast behavior where opposite biological responses are needed. Here, we fabricated two femtosecond-laser patterned stripe topographies on titanium using a unidirectional scanning strategy with parameter tuning, generating LSFL with a periodicity of 820 ± 30 nm and micro-grooves with a periodicity of 4.7 ± 0.1 μm. Surface morphology and physicochemical properties were characterized by SEM/AFM, XPS, microhardness testing, and wettability measurements. Human gingival fibroblasts (HGF-1) were used to assess adhesion, cytoskeletal organization, spreading area, and proliferation (CCK-8). The submicron LSFL promoted robust fibroblast adhesion, aligned cytoskeletal organization, larger spreading areas, and higher proliferation, whereas the micro-groove surface markedly restricted spreading and was associated with poorer cytoskeletal organization and lower proliferation. Alternating patterned regions further demonstrated geometry-driven spatial selectivity, with preferential cell occupation on LSFL stripes. These findings support a fabrication-ready surface-engineering strategy to synchronize rapid soft-tissue sealing while restricting unwanted fibroblast advancement at defined regions, offering a promising route toward more predictable GBR outcomes. Full article

This study evaluates the effects of sintering time and applied pressure on the microstructure and Vickers microhardness of the CoCrFeMnNiAl_1.5 alloy during consolidation. Samples were obtained by mechanical alloying and consolidated using two routes: conventional sintering (CS) and high-frequency induction sintering followed by high-temperature heating (HFIHS + HTH). For both methods, the pressure (0.3–1.5 GPa) and holding time (1–4 h) were varied. The results show that the HFIHS + HTS route produces a finer microstructure, with notably more homogeneous Cr segregation at high pressures, resulting in higher Vickers hardness values (up to 770 HV). In addition, the pressure applied during HFIHS promotes a mechanism of forced atomic mobility. This mechanism facilitates the migration of atoms toward energetically favorable sites, such as grain boundaries. At the same time, it restricts precipitate growth and Cr-rich segregation and activates densification mechanisms without requiring sustained pressure. The optimal parameters (0.9 GPa and 1 h) produce the best microstructural and mechanical response, highlighting the potential of this alloy for use in coatings and structural components in the automotive and aerospace industries. Full article

Previous research indicates that WC-12Co contents above 60 wt.% in feedstock powders for cermet coatings impair adhesion and wear resistance. This study characterizes NiCrFeSiAlBC coatings—unreinforced or reinforced with 65 wt.% or 85 wt.% WC-12Co—applied via high-velocity oxy-fuel (HVOF) spraying onto stainless steel substrates under controlled parameters. It quantifies the influence of high carbide volume fractions within the NiCrFeSiAlBC matrix on microstructure and tribomechanical performance. Microstructural analysis revealed uniformly distributed cermet layers featuring dissolved reinforcements and WC hard phase formation, with minimal W₂C crystallization. Elevated WC-12Co incorporation promoted densification and reduced porosity. Vickers microhardness tests (HV 0.3) demonstrated increased hardness upon WC-12Co addition, attributable to finer particle sizes, lower porosity, and the presence of WC phases alongside crystallographic refinements. Under dry reciprocating sliding conditions, friction coefficients and wear volumes decreased markedly. Consequently, the coating with 85 wt.% WC exhibited the best mechanical and tribological properties. Full article

The effect of process inputs in the friction welding of Ti6Al4V alloy rods was investigated through the analysis of residual stresses, microstructure, chemical phases and hardness testing of the weld joints. The rods were welded using different combinations of process inputs. The results revealed variations in residual stresses, hardness and microstructure of the weld joints when weld inputs were varied. Peak compressive residual stresses were obtained at the centre of the weld interface, where the grains were very fine. The joints with a greater volume fraction of martensitic grains had elevated residual stress values. The maximum compressive residual stress values were obtained at the weld interface, with high hardness results. A further investigation was conducted to study the relationship between the residual stresses, microstructure and mechanical properties of the weld joint. Full article

In this study, an annular laser beam shaping optics and a wire feeding system are used for additive manufacturing. A discrete concentric layering trajectory strategy (DCL-TS) and a continuous deposition trajectory strategy (CD-TS) for the laser-directed energy deposition (WL-DED) of aluminum alloy stud structures are developed. Initially, combinations of parameters, such as laser power, transverse speed, and wire feeding speed, which lead to a process that produces a single-layer structure with good morphology and no visible pores and cracks, are identified. Then, DCL-TS and CD-TS manufacturing strategies are used to produce aluminum alloy studs of similar dimensions. The EBSD results indicate that the CD-TS produces finer grains in the aluminum alloy studs compared to the DCL-TS; correspondingly, mechanical testing reveals superior microhardness and tensile strength in the circularly fabricated studs. The latter tensile value testing verifies that aluminum alloy studs using WL-DED on the substrate can meet the requirements for practical application in mobile phones, computers, etc. This research method enhances the mechanical properties of additively manufactured items. Consequently, manufacturing efficiency is significantly improved, providing a promising solution for rapid production. Full article

High-entropy alloys (HEAs) provide a broad compositional space for tuning phase stability and surface durability. CoCrFeNiMn_x (x = 0.5, 1.0, 1.5, and 2.0) alloys were fabricated by vacuum arc melting and characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), microhardness testing, electrochemical testing in 3.5 wt.% NaCl, and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations and first-principles molecular dynamics were further employed to analyze the Mn-dependent electronic structure and oxygen–metal bonding. The XRD results indicate a transition from a single FCC solid solution at x ≤ 1.0 to an FCC + BCC constitution at x ≥ 1.5. With increasing Mn, microstructures evolve from coarse dendrites toward higher fractions of equiaxed grains. Hardness decreases from 163.6 HV (x = 0.5) to 125.1 HV (x = 1.0) and then increases to 162.6 HV (x = 2.0), indicating competing solid-solution and phase/segregation effects. Electrochemical measurements show enhanced corrosion resistance with Mn addition; the x = 2.0 alloy exhibits the lowest fitted corrosion current density (icorr = 0.3482 × 10⁻⁶ μA·cm⁻²) and the most stable passivation response. XPS reveals passive films dominated by Fe₂O₃ together with Mn³⁺ oxides, whose synergistic formation promotes a denser barrier layer. DFT predicts a monotonic decrease in Fermi level and a narrowed conduction band range as Mn increases, consistent with reduced electron transfer activity during anodic dissolution. Interfacial simulations show that O preferentially bonds with Cr and Mn, while Ni–O bonds have the lowest estimated rupture barrier, rationalizing a tendency toward localized corrosion at Ni-associated sites. Full article

To meet the demand for high-performance heat-resistant aluminum alloy conductors in energy transmission, this study systematically explores the effects of synergistic aging and deformation treatment on the microstructure, mechanical properties, and heat resistance of Al-0.04Er-0.08Zr alloy. Through isochronous/isothermal aging, rolling with varying deformation amounts, and microstructural characterization coupled with performance testing, the following findings emerged: 425 °C represents the peak aging temperature, at which a dispersed L1₂ structure of Al₃(Er_1−xZr_x) composite precipitates with an average size of 4 nm is formed; Dispersed L1₂ structure Al₃(Er_1−xZr_x) composite precipitation phase achieved an alloy hardness of 49.45 HV and electrical conductivity of 58.68% IACS; the synergistic treatment of peak aging (425 °C) with 60% deformation amount yielded optimal comprehensive properties. After 150 h of isothermal annealing at 350 °C, hardness decreased by less than 5%, and the alloy demonstrated stable service life of approximately 40 years at 227 °C based on Arrhenius model extrapolation. This study reveals the synergistic regulation mechanism between deformation and aging, providing theoretical support and technical reference for developing low-cost, high thermal stability, and high-conductivity aluminum alloys. Full article

Background/Objectives: Chlorhexidine (CHX) and alcoholic (A+) mouthwashes are associated with adverse oral effects. Therefore, this study compared the efficacies of non-alcoholic mouthwashes, including fluoride (A−) and herbal (Hr) rinses, for preventing bacterial accumulation and enamel demineralization around metal brackets (MBs), ceramic brackets (CBs), and resin composite attachments (RCAs). Methods: Following the exposure to CHX, A+, A−, and Hr rinses for 1 min, the growth of Streptococcus mutans on MB, CB, and RCA was assessed using colony-forming units and scanning electron microscopy (SEM). Controls included attachments without intervention. In another setting, enamel with bonded attachments was exposed to mouthwashes for 1 min and subjected to cariogenic demineralization for 24 h. Enamel’s Vickers microhardness was measured before and after the demineralization challenge. Data were analyzed using paired t-tests and one-/two-way ANOVA with Tukey’s tests. Results: CHX mouthwash demonstrated superior antimicrobial efficacy against S. mutans biofilms across all orthodontic attachments (p < 0.05). On metallic brackets, CHX (0 ± 0 log₁₀) and A− (1.7 ± 0.4 log₁₀) significantly (p < 0.001) outperformed controls (6.9 ± 0.1 log₁₀), Hr (6.08 ± 0.2 log₁₀), and A+ (6.2 ± 0.6 log₁₀). Similar patterns emerged for ceramic brackets, with CHX (0 ± 0 log10) and A− (1.4 ± 0 log10) superior to controls (6.6 ± 0.4 log₁₀). On resin composite attachments, CHX (2.9 ± 0.05 log₁₀) and Hr (3.4 ± 0.08 log₁₀) exceeded controls (5.4 ± 0.09 log₁₀) in inhibiting the biofilm growth (p < 0.05). Enamel microhardness reduction was significantly influenced by attachment type (p < 0.0001) and mouthwash type (p = 0.0063), with significant interaction between variables (p = 0.0052). Conclusions: CHX and A− mouthwashes effectively inhibited S. mutans biofilms on orthodontic attachments, while attachment type and mouthwash significantly influenced enamel microhardness reduction. Full article

Softening in the heat-affected zone (HAZ) of high-strength pipeline welds compromises its service safety but the corresponding softening mechanism is not well-understood. Softening behavior in the HAZ of two X80 pipeline girth welds with different base metal microstructures, i.e., acicular ferrite (AF)-dominated (X80-AF) and granular bainite (GB)-dominated (X80-GB), were investigated through microhardness tests and detailed microstructure characterization. The results showed that softening in the HAZ of two girth welds primarily occurred in the fine-grained (FG) HAZ, while hardening was found in the coarse-grained (CG) HAZ. X80-AF showed higher softening resistance than X80-GB, with softening ratios of 3.44% vs. 12.46%, and softened zone widths of 2.1 mm vs. 3.9 mm, respectively. Due to its high dislocation density and refined interlocking structure, AF could effectively inhibit phase transformation and grain coarsening during reheating, which resulted in smaller grains and a lower fraction of polygonal ferrite (PF) in the FGHAZ (28%). In contrast, coarse GB was more prone to grain coarsening and hence engendered higher PF proportion (68%). Therefore, for the microstructural design of high-strength pipeline steels, increasing the proportion of refined AF is beneficial to the softening resistance and thereby elevates the service safety of pipelines. Full article