Search Results (599)

Additive manufacturing (AM) has revolutionized industrial production. However, the repair of AM components remains a critical challenge due to their unique microstructural features. While repair approaches for conventionally manufactured alloys are well established, their direct transferability to AM parts remains largely unexplored due to the unique thermal history and anisotropic microstructure of additive components. This study investigates a novel repair and improvement strategy for Powder Bed Fusion–Laser Beam/Metal (PBF-LB/M)-fabricated AlSi10Mg components, combining Electrospark Deposition (ESD) for dimensional restoration with subsequent Ultrasonic Peening Treatment (UPT) for surface enhancement. Microstructure, porosity, surface roughness, hardness profiles, residual stresses, and corrosion behaviour were systematically characterized using SEM, optical microscopy, profilometry, Vickers microhardness testing, XRD, and electrochemical polarization tests. The results show that the ESD process is capable of producing coatings with excellent interfacial adhesion to the substrate, with an initial porosity of 3.6 ± 0.5%. The subsequent UPT induces a significant densification effect on the deposited material, reducing porosity by approximately 50% and increasing surface hardness by up to 48% in the upper region of the coating. Furthermore, XRD analysis reveals that UPT completely reverses the residual stress state from tensile (typical of the ESD process) to compressive in all measured directions, thereby improving the overall structural integrity. Ultimately, the combined ESD + UPT alters the electrochemical response of AlSi10Mg deposits, resulting in a nobler corrosion potential, albeit with a slightly higher corrosion current density. Full article

Electrolytic-plasma hardening of steel components requires reliable non-contact temperature monitoring, but traditional pyrometry is complicated by the variable emissivity of steel and the intense radiation of the plasma envelope. This work presents an approach that repurposes a compact multispectral AS7341 sensor into a virtual temperature sensor based on physically grounded spectral feature engineering and regularized machine learning. The use of logarithmic ratios of the near-infrared channel (940 nm) to the visible channels suppresses the plasma contribution and linearizes Wien’s radiation law. On a controlled dataset of 20 cycles, this increases the Pearson correlation with the peak temperature from r = 0.498 (raw NIR channel) to r = 0.781 for the log(NIR/Clear) feature. Current is identified as a confounding variable; normalizing the NIR/Clear ratio by the cycle-averaged current (r = 0.761) ensures correct signal interpretation under varying process conditions. Two narrow channels–NIR (940 nm) and F8 (680 nm)–provide accuracy equivalent to the broadband Clear channel (r = 0.778 vs. 0.781), thus simplifying hardware implementation. Ridge regression using three weakly correlated features (log(NIR/Clear), cycle duration, and initial temperature) achieves a mean absolute error of 91.4 °C under leave-one-out cross-validation (LOOCV) and 85.5 °C on an independent current-group test (R² = 0.536). Independent verification by scanning electron microscopy and Vickers microhardness on 30KhGSA steel confirms reliable separation of the three thermal regimes: underheating (<800 °C, 280–320 HV), optimal quenching (800–900 °C, 620–680 HV, fine-needle martensite), and overheating (>900 °C, 540–590 HV). The proposed set of spectral features provides a physically justified basis for a low-cost industrial temperature sensor for electrolytic-plasma processing. Full article

S136 mold steel is widely used in the injection molding industry due to its excellent properties. However, during actual production, the mold is inevitably exposed to harsh service conditions involving high temperature, high pressure, chemical corrosion, and mechanical wear, leading to risks of failure caused by pitting corrosion, intergranular corrosion, electrochemical corrosion, selective dissolution, and surface fatigue wear. To enhance the surface protection performance of the mold, a TiC-reinforced 440C stainless steel composite coating was fabricated on the S136 substrate using plasma spray welding technology. Composite powders with different TiC contents (wt.%) were prepared via mechanical mixing. The phase composition, microstructure, microhardness, corrosion resistance, and wear resistance of the coatings were characterized by XRD, SEM, Vickers microhardness tester, electrochemical workstation, and vertical universal friction and wear tester. Furthermore, the corresponding strengthening mechanisms were elucidated. The results show that the incorporation of TiC refines the microstructure and synergistically enhances both corrosion and wear resistance. Among the tested coatings, the one with 1.0 wt.% TiC exhibits the best overall performance, with a significantly increased microhardness of 858.85 HV (approximately 1.5 times that of the substrate), an Ecorr of –0.286 ± 0.002 V, an Icorr of 4.51 × 10⁻⁷ A·cm⁻², and a friction coefficient of 0.591. This study provides important theoretical and technological insights for the surface strengthening of S136 mold steel using plasma spray welding of TiC/440C composite coatings to improve corrosion and wear resistance and extend service life. Full article

Bulk metallic glasses (BMGs) exhibit high strength and hardness due to their amorphous atomic structure; however, their wider application is often limited by intrinsic brittleness and localized shear deformation. Metallic glass matrix composites (MGMCs) represent an effective approach to overcome these limitations by introducing crystalline phases into the amorphous matrix, thereby improving mechanical stability and deformation behavior. In this study, an Fe-based MGMC was produced by copper mold casting and its micro-structure and mechanical properties were investigated. Microstructural observations revealed a heterogeneous structure consisting of an amorphous matrix with dispersed crystalline phases, which was confirmed by X-ray diffraction showing a broad amorphous halo with superimposed crystalline peaks. The mechanical response was evaluated using Vickers microhardness measurements under different indentation loads, revealing a pronounced indentation size effect (ISE), where hardness decreases with increasing load and stabilizes at higher loads. The load–indentation relationship follows Meyer’s law with the empirical relation $P=0.663d^{1.9245}$ and an excellent correlation coefficient ($R^2=0.9996$). The Meyer index $n<2$ confirms normal ISE behavior. The indentation data were further analyzed using proportional specimen resistance (PSR) and modified PSR models, enabling estimation of the load-independent hardness and providing insight into the deformation behavior of the composite material. Full article

Copper-bearing low-carbon high-strength steels are widely employed in marine engineering. However, the microstructural homogeneity, strength–toughness matching, and low-temperature toughening mechanisms of such steels at high copper contents remain unclear. Existing studies have predominantly focused on the Cu content range of 1–2 wt.%, lacking systematic comparisons regarding microstructural evolution and property regulation throughout the entire rolling-heat treatment process at higher Cu levels. To clarify the influence of Cu content on the microstructural evolution and mechanical properties of CuxNi2.7Mn steels during processing and heat treatment, and to fully exploit the Cu precipitation strengthening effect while suppressing its embrittlement drawback, this study investigates CuxNi2.7Mn steels with Cu contents of 1.35 wt.%, 3.1 wt.%, and 6 wt.%. The specimens were fabricated via vacuum melting and two-stage rolling. Combining in situ observation using a high-temperature laser confocal microscope, optical microscopy, scanning electron microscopy, X-ray diffraction, and mechanical property tests, the effects of different Cu contents on the microstructure, conventional mechanical properties, and low-temperature toughness at −40 °C of the steels in both as-rolled and optimally heat-treated states (solid solution at 900 °C for 1 h + aging at 540 °C for 2 h) were systematically investigated. The results demonstrate that in the as-rolled condition, with increasing Cu content, the Vickers microhardness (HV1) of the steel increases from 183.9 HV1 to 271.9 HV1, the yield strength rises from 556.55 MPa to 852.87 MPa, and the tensile strength increases from 758.53 MPa to 1162.59 MPa. Nevertheless, excessive Cu content induces austenitic grain coarsening, aggregation of Cu-rich precipitates, and stress concentration, resulting in significant deterioration of ductility and toughness. Following optimal heat treatment, the banded structure is completely eliminated, the microstructural homogeneity is substantially improved, and the ductility and toughness are remarkably enhanced compared with the as-rolled state. Meanwhile, the strength continues to increase with rising Cu content, with the 6 wt.% Cu steel achieving a yield strength of 922.51 MPa and a tensile strength of 955.17 MPa. In terms of low-temperature toughness, the 3.1 wt.% Cu steel exhibits the poorest performance (90.8 J), whereas the 6 wt.% Cu steel presents a sharply increased low-temperature impact energy of 152.6 J. This is attributed to the precipitation of particulate phases such as TiC and MnS, which effectively disperse low-temperature stress and hinder crack propagation. Overall, the CuxNi2.7Mn steel with 6 wt.% Cu possesses the highest strength as well as excellent low-temperature toughness after optimal heat treatment, providing theoretical and experimental foundations for the composition design and heat treatment process optimization of high-copper steels for marine applications. Full article

This in vitro study evaluated the effect of irrigation on different polishing protocols and their influence on the surface roughness, microhardness, and mass of resin composites. Three resin composites (Admira^® Fusion, Filtek Supreme™ XTE, and Ceram.X Spectra™ STHV) were polished using four systems (Sof-Lex™, DIATECH^® ShapeGuard, Astropol^®, and Enhance™/PoGo™) under wet and dry conditions. Eight test groups were established for each resin composite (n = 10 per group). Vickers microhardness, surface roughness (R_a), and specimen mass were measured before and after polishing with one of the four systems, applied either with or without irrigation. For Admira^® Fusion polished with Sof-Lex^™, R_a values were lower without irrigation (p = 0.048), whereas Filtek Supreme^™ XTE and Ceram.X Spectra^™ STHV polished with the Enhance^™/PoGo^™ system showed lower R_a values when irrigation was used (p = 0.010 and p = 0.004, respectively). Sof-Lex^™ and DIATECH^® ShapeGuard produced the highest microhardness values for both Admira^® Fusion and Filtek Supreme^™ XTE. Moreover, specimens of Admira^® Fusion and Ceram.X Spectra^™ STHV polished with DIATECH^® ShapeGuard exhibited higher microhardness under irrigation (p = 0.048 and p = 0.027, respectively). Overall, polishing resulted in measurable material removal, reflected by a reduction in specimen mass, and in an increase in microhardness. Wet polishing generally increased microhardness, although the effect varied depending on the polishing system and resin composite. Clinicians should therefore consider both the resin composite and the polishing system when deciding whether to use irrigation, as appropriate irrigation control may help optimize the surface smoothness and microhardness of resin composite restorations. Conference Presentation: Preliminary data from this study were previously presented as an oral communication at the 32nd Portuguese Dental Association Annual Meeting. This manuscript represents a substantially expanded and revised version, developed as a full research article. Full article

This study evaluated how the addition of 5 wt% bioactive glass and 15 wt% short glass fibers to EQUIA Forte HT affects the microhardness, micromorphology, and elemental composition of demineralized dentin. Class I cavities in 28 human third molars were demineralized with 37% phosphoric acid and restored with: (1) Filtek Universal composite, (2) EQUIA Forte HT, (3) EQUIA Forte HT + 5wt% BAG, or (4) EQUIA Forte HT + 15wt% short glass fibers. After 4 weeks of storage in phosphate-buffered saline at 37 °C, the teeth were cut in half, obtaining two samples from each tooth (n = 14). Vickers microhardness (HV0.1) was measured on demineralized dentin 50–100 μm apical to the restoration interface. Representative specimens (n = 2) were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Data were analyzed with one-way ANOVA (α = 0.05). Unmodified EQUIA Forte HT showed the highest mean dentin microhardness recovery (25.06 ± 1.42 HV0.1), followed by composite (17.31 ± 0.66 HV0.1), BAG-modified (23.74 ± 1.37 HV0.1) and fiber-reinforced (22.15 ± 1.06 HV0.1) groups (p < 0.001, all pairwise comparisons p ≤ 0.039). Glass hybrids showed prominent Ca/P peaks; modified groups had elevated Si (BAG) and Al (fibers). SEM revealed smoother surfaces with fewer cracks in modified materials. Unmodified EQUIA Forte HT produced the highest short-term microhardness recovery, while BAG and fiber additions altered surface morphology and elemental composition but slightly reduced early hardness. Full article

Background: The aim of this in vitro study is to comparatively evaluate the effects of toothpaste formulations containing and not containing vitamin C on the surface roughness and microhardness of different composite resin materials. Methods: Four different toothpastes (Sensodyne, Colgate, Klorhex, Dentiste) and three composite resin materials (Arabesk—microhybrid, Charisma Smart—nanohybrid, Estelite Sigma Quick—supra-nano filled) were used in the study. Composite discs measuring 10 mm in diameter and 2 mm in thickness were prepared and subjected to brushing simulations equivalent to 1 month (150 s) and 3 months (450 s). Surface roughness was measured using a mechanical profilometer, and microhardness was evaluated with a Vickers hardness tester. Surface morphology was further examined in detail using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For statistical analyses, one-way ANOVA, repeated measures ANOVA, Kruskal–Wallis test, and Friedman test were employed, with the significance level set at p < 0.05. Results: Brushing procedures resulted in statistically significant changes in the surface roughness (ΔRa) and microhardness of the composites across all toothpaste groups (p < 0.05). The increase in surface roughness varied depending on the composite type, with the highest increase observed in the ESQ composite. In the ESQ composite, higher ΔRa values were obtained, particularly in the Dentiste (≈1.70 µm) and Colgate (≈1.52 µm) groups. Microhardness results, however, differed depending on the composite and toothpaste type. While a general trend toward increased microhardness was observed, a significant decrease in microhardness was detected in the Colgate and Dentiste groups of the ESQ composite (p < 0.05). Conclusions: This study demonstrates that the addition of vitamin C to toothpaste formulations increases the surface roughness of restorative materials and results in significant changes in their microhardness properties. These findings highlight the importance of considering the type of toothpaste used by patients in clinical practice, particularly in terms of restorative material selection and the long-term preservation of surface integrity. Full article

Titanium and its alloys are widely used in orthopedic and dental implantology for their corrosion resistance and biocompatibility supporting osseointegration; however, their usage is accompanied by release of wear debris that may induce inflammatory responses. The necessity of formation of multifunctional coatings that accelerate osseointegration and provide long-term mechanical stability of titanium implants remains highly relevant. We propose a new simple and scalable coating method based on the laser shock processing technique, with TiO₂ and SrCO₃ powder mix used as an absorption layer. Our results show that this treatment created an approximately 158.3 ± 35.8 μm thick coating consisting of a mixed SrTiO₃-TiO₂ phase. The hardness of this coating evaluated by Vickers microhardness measurements showed a hardness increase of 3.3 times compared to the initial titanium substrate. Piezoelectric force microscopy (PFM) analysis revealed the presence of a reverse piezoelectric effect in the obtained structure confirming the highly likely successful synthesis of coating impregnated with SrTiO₃. This piezoelectric coating can be readily deposited onto titanium substrates using the proposed method, enabling exploration of potential biomedical applications in future research. Full article

This research investigates the effects of electrochemical oxidation on surface properties and corrosion performance of the Ti-6Al-4V ELI alloy intended for biomedical applications. Electrochemical anodization is performed in 1 M H₂SO₄ and 1 M H₃PO₄ electrolytes at applied potentials of 200, 250, and 275 V for 1 min. Morphological characteristics and chemical constitution of the oxide films are investigated by SEM-EDS analysis, while surface roughness, wettability, and microhardness are evaluated using profilometry, contact angle measurements, and Vickers microhardness testing. Electrochemical behavior is assessed by monitoring free potential (OCP) and electrochemical impedance spectroscopy in Ringer solution and Ringer solution containing 40 g/L hydrogen peroxide. Among the investigated conditions, anodization at 200 V for 1 min provides the most favorable surface morphology, producing well-defined and uniformly distributed nanopores while maintaining the structural stability of the oxide layer. Oxidation in 1 M H₂SO₄ leads to a more homogeneous nanoporous structure, higher surface roughness, improved hydrophilicity, and increased microhardness compared to 1 M H₃PO₄ treatment. Electrochemical impedance spectroscopy analysis reveals superior corrosion resistance for all oxidized samples in comparison with the untreated alloy. The oxide layers obtained in sulfuric acid exhibit the highest polarization resistance and electrochemical stability in simulated physiological environments. Full article

This study systematically investigates the influence of CeO₂ content (0–0.6 wt.%) on the microstructure and mechanical properties of Stellite6/WC composite coatings fabricated by plasma spray welding. The phase composition and microstructure of the coatings were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while microhardness and tribological performance were evaluated using a semi-automatic Vickers microhardness tester and a ball-on-disk tribometer. The results indicate that the coating with 0.4 wt.% CeO₂ exhibits the optimal combination of mechanical and tribological properties, achieving a maximum microhardness of 1107.62 HV_0.3—a 50.5% improvement over the unmodified coating—and a minimum wear mass loss of 1.4 mg, corresponding to a 78.1% reduction compared to the CeO₂-free counterpart. These findings demonstrate that appropriate CeO₂ addition significantly enhances both the microhardness and wear resistance of Stellite6/WC coatings, offering an effective strategy to mitigate surface degradation and extend the service life of 45 steel substrates under demanding operating conditions. Full article

To enhance the utilization rate and mechanical performance of recycled sand (RS) in extrusion-based 3D printing, this study investigates the influence of varying incorporation ratios of RS across two particle size fractions: 0.075–1.18 mm (RS01) and 1.18–2.36 mm (RS12). The RS utilization rate was determined via the material balance method, while microstructural mechanisms were analyzed using scanning electron microscopy and Vickers microhardness testing. The results indicate that: a combination of 75% RS01 and 25% RS12 achieves the maximum RS utilization rate of 84.3%. At an RS12/RS01 ratio of 1:3, the printed specimens exhibit the smallest tilt angles in bidirectional buildability tests, measuring 7.6° and 7.2°, with corresponding tan θ values of 0.066 and 0.063. Compared to mortar with 100% RS01, this optimized mixture yields average increases of 36.5% in compressive strength, 40.7% in flexural strength, and 6.8% in interlayer splitting strength. Analysis of variance indicates that different particle size combinations have a significant effect on the mechanical properties. Microhardness analysis reveals that the combination of 75% RS01 and 25% RS12 achieves a minimum interfacial transition zone width of 46 µm. Utilizing larger-particle-size RS in 3D printing effectively enhances its utilization rate while maintaining satisfactory printability and mechanical properties. Full article

Erosion–corrosion at elevated temperature represents a critical degradation mechanism in components exposed to particle-laden gaseous flows, such as industrial boilers and combustion systems. This study evaluates the combined erosion–corrosion behaviour of atmospheric plasma-sprayed (APS) coatings based on Al₂O₃/TiO₂ (97/3, 87/13, and 50/50 wt.%), TiO_2, and a hybrid Al₂O₃/NiCrAlY (90/10 wt.%) system. Coatings were characterised by scanning electron microscopy, X-ray diffraction, Vickers microhardness and porosity analysis, and subsequently tested under solid particle erosion and cyclic oxidation at 200 and 400 °C with impact angles of 30° and 90°. All coatings exhibited significantly higher hardness (446–597 HV) than the AISI 310 substrate (181 HV), together with distinct differences in porosity and interlamellar cohesion. Erosion rates decreased with increasing temperature for both impact angles; however, the synergistic contribution to total degradation increased, particularly under normal impact (90°). This behaviour indicates that thermochemical activation enhances the nonlinear interaction between mechanical damage and oxidation. Coatings with lower defect connectivity showed reduced synergistic effects, demonstrating that microstructural architecture governs the magnitude of combined degradation. The Al₂O₃/NiCrAlY system exhibited improved thermomechanical stability associated with the formation of protective Al- and Cr-rich oxides. Full article

Friction stir welding (FSW) of dissimilar aluminium alloys often results in non-uniform microstructure and hardness distributions due to asymmetric temperature fields and material flow. The objective of this study is to establish a quantitative relationship between thermal history, microstructural evolution, and hardness distribution in dissimilar AA5052-H32/AA6061-T6 FSW joints by combining experimental characterisation with validated thermal modelling. AA5052-H32 and AA6061-T6 plates were welded under five different parameter sets. A thermal finite element model was developed in COMSOL Multiphysics to simulate temperature evolution during welding and was validated using embedded thermocouple measurements, with predicted peak temperatures ranging from 455 °C to 641 °C. Optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) were employed to characterise grain structure and dynamic recrystallisation (DRX) behaviour, while Vickers microhardness mapping was used to evaluate the local mechanical response. The results show that DRX occurred in the nugget zone (NZ), leading to significant grain refinement, with a minimum grain diameter of 6.07 µm, representing an approximately eightfold reduction compared with the base material AA5052-H32. In contrast, the thermo-mechanically affected zone (TMAZ) experienced limited recrystallisation due to insufficient plastic deformation and temperature. The lowest hardness was observed in the TMAZ on the AA5052-H32 side, with the hardness reduction of 22% primarily caused by work hardening loss. Hardness was also reduced by 34% on the AA6061-T6 side due to decreased precipitation strengthening caused by high temperatures. This combined experimental–numerical study provides a systematic thermal–microstructure–hardness framework for understanding and predicting local property variations in dissimilar FSW joints. Full article

Cr₂O₃-based ceramic coatings are widely used in wear-critical applications; however, their tribological performance under dry sliding conditions can be limited by brittleness and frictional instability. In heavy-duty vehicles, the king pin–bushing contact operates under severe dry sliding conditions, motivating the investigation of composite Cr₂O₃–nTiO₂ coatings as a potential surface engineering solution. In this study, Cr₂O₃–TiO₂ coatings containing 0, 10, 20, 30, and 40 wt% TiO₂ were deposited by atmospheric plasma spraying (APS) from mechanically mixed powders. Phase composition was analyzed by X-ray diffraction using an X’Pert PRO MRD diffractometer, while microstructure and elemental distribution were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) on a FEG Quattro C microscope. Mechanical properties were evaluated by Vickers microhardness, instrumented indentation and scratch testing, while dry sliding wear behavior was assessed by pin-on-disc tests performed on a CETR UMT-2 tribometer against a bronze counterbody, with continuous monitoring of the coefficient of friction (COF). The results show that plasma spraying produces lamellar composite coatings with intrinsic porosity and locally modified phase composition. Cr₂O₃-rich coatings exhibit higher hardness (1198 HV2 compared with 877 HV2 for Cr₂O₃–40TiO₂ corresponding to an increase of approximately 36%) and improved resistance to indentation, reflected by lower penetration depths and higher elastic modulus values (134 GPa for S0 compared with 77 GPa for S2). These coatings also exhibit a more stable friction response and reduced material transfer from the bronze counterbody, as confirmed by the lower mass loss of the pins (0.0295 g for S0 compared with 0.0473 g for S4, corresponding to a reduction of about 38%). Increasing TiO₂ content leads to changes in friction stability and wear behavior associated with microstructural heterogeneity. These findings indicate that the sliding wear performance of Cr₂O₃–nTiO₂ coatings is governed by elastic–plastic stability under localized contact loading and support their applicability for dry sliding king pin–bushing systems in heavy-duty vehicles. Full article