Vickers Hardness Research Articles

Technological dental sealants: in vitro evaluation of material properties and antibiofilm potential

BackgroundDue to the launch of new self-etching and self-adhesive sealing materials combined with the release of bioactive ions in the dental market, this in vitro study aimed to compare physical values of surface roughness (RS), vickers microhardness (VM), compositional energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), microbiological tests (inhibition halo-HI and surface microbial adhesion-MAS) and mechanical microshear bond strength (MBS).MethodsThe following groups were analyzed: Beautisealant® self-etching sealant (Shofu)(G1), FluroShield® conventional sealant (Dentsply)(G2- Control Group), Flow Constic® self-adhesive/self-etching resin (DMG)(G3) and Beautifil Flow Plus F03® conventional resin (Shofu)(G4). For the physical and compositional tests, specimens were molded and submitted to finishing/polishing in a metallographic polisher. RS and VM were measured through 5 readings. For the HI test, specimens were exposed to S. mutans for 24 h in brain–heart infusion (BHI) agar under microaerophilic conditions, with the diameter of the HI (mm) measured by digital caliper. For the MAS test, a bacterial biofilm of S. mutans was induced for five days in BHI broth + 5% sucrose and measurement of CFU/ml (log10 from serial dilutions). For the MBS test, specimens were made in bovine enamel with the addition of the experimental group FluroShield® (Dentsply) + Single Bond Universal® adhesive (3 M)(G5) and measured in a universal testing machine. Data were submitted to ANOVA and Tukey's post hoc tests (p < 0.05) using the SPSS software.ResultsDifferent compositions proven in the EDS test were not determinants of the promotion of different RS: G1 = 0,19 (± 0,07), G2 = 0,15 (± 0,053), G3 = 0,13 (± 0,046), G4 = 0,14 (± 0,056); HI: G1 = 17,7 (± 1,36), G2 = 18,7 (± 3,47), G3 = 18,9 (± 4,87), G4 = 17,9 (± 3,61) and MAS: G1 = 5,22 (± 0,12), G2 = 5,15 (± 0,15), G3 = 5,12 (± 0,20), G4 = 5,06 (± 0,24). However, statistically influenced the values of VM: G1 = 16,71 (± 1,93), G2 = 16,28 (± 4,91), G3 = 26,11 (± 3,46), G4 = 37.9 (± 4.87), promoted lesser bacterial adhesion (G4 = 5.06 ± 0.24), and demonstrated fluoride ion only in the G4. Higher MBS was found in the conventional materials G5 = 8.38 (± 2.05) and G2 = 6.28 (± 1.35).ConclusionsBioactive materials and self-adhesive/self-etching for sealing pits and fissures did not demonstrate superior mechanical and antimicrobial properties performance compared to conventional techniques.

Tantalum-lanthanum mixing effect on structural and mechanical properties of aluminate glasses

Aluminate glasses are known for their superior mechanical and optical properties. Here, we investigated the tantalum (Ta)-lanthanum (La) mixing effect on structural and mechanical properties of these glasses. Using the aerodynamic levitation and laser melting technique, we prepared a series of aluminate glasses with the molar composition 54Al2O3·(46-x)La2O3·xTa2O5, where x = 0.0, 9.2, 18.4, 23.0, 32.2, 36.8, and 46.0. The structural, thermal, and mechanical analyses revealed that substituting Ta for La strongly impacted the local Al environment in the glasses, thereby affecting their glass transition temperature and mechanical properties. The Vickers microhardness (HV) varied non-monotonically with the molar ratio R (defined as Ta/(Ta+La) = x/46), reaching a maximum HV value of 8.59 GPa at R = 0.8. This trend was explained in terms of both the average bond energy and the bond number density. Moreover, the crack initiation resistance of the studied glasses increased as R rose. This work aids in the design of oxide glasses with high crack resistance and hardness.

Dual-layered carbonated hydroxyapatite/polypyrrole: A novel strategy for bone fracture repair implants

This study presents the fabrication of a carbonate-doped hydroxyapatite/polypyrrole thin film on 304 stainless steel (CHA/PPY/304 SS) using a cyclic voltammetry electrochemical method to enhance bone fracture repair. The in-situ substitution mechanism was evaluated through estimated reaction energy, and the impact of surface modification on structural properties was examined using the Rietveld refinement method. Following the electrodeposition of CHA on PPY-coated 304 SS, a distinctive flower-like structure emerged, with average cluster and pore sizes of 3 ± 1 μm and 130 ± 10 nm, respectively. Rietveld refinement analysis revealed A-type carbonate substitution, indicated by an increase in the a parameter and a reduction in the c parameter compared to the standard. Subsequent deposition of the bilayer coating on 304 SS significantly improved adhesion strength to 10.7 ± 0.2 MPa, along with increased hydrophilicity and Vickers hardness. Notably, enhanced bioactivity was observed, evidenced by thickened nanoflake-like structures and the formation of island-like apatite deposits after immersion in simulated body fluid (SBF) for 7 days. This bilayer coating shows promise for surface modification of metallic implants and tissue engineering scaffolds.

Investigation of the antibacterial activity, cytotoxicity, and effects on enamel and composite resin of mouthwash formulations prepared with three different Boron compounds.

This study investigated the use of oral rinse solutions formulated with boron-containing compounds, known for their antibacterial activity, as an alternative to chlorhexidine (CHX). Boron nitride (BN), boric acid (BA) and sodium borate (SB) were used in the study. BN was used in nanosuspension (BN-NS) due to its low solubility in water. BA and SB were also prepared and used in solution form (BA-S, SB-S). Antibacterial activity against cariogenic bacteria was evaluated using agar well diffusion and microdilution techniques, and antibiofilm activity was evaluated using the crystal violet method. Cytotoxicity in human gingival cell lines (HGF-1) was evaluated using MTT and LDH assays. Surface hardness was measured with Vicker's Microhardness tester and surface roughness was measured with a profilometer. CHX was used as the control group. BN-NS, BA-S, and SB-S showed antibacterial and antibiofilm activity against all cariogenic bacteria. BN-NS and SB-S demonstrated much lower cytotoxicity compared to CHX, while BA-S exhibited similar cytotoxicity. SB-S caused an increase in enamel surface hardness (p = 0.017), whereas no significant changes were observed in surface roughness or hardness in the other groups (p > 0.05). BN-NS and SB-S showed antibacterial effects and antibiofilm activity on all tested cariogenic bacteria. BN-NS and SB-S showed lower cytotoxicity than CHX, and their effects on enamel and composite resin surfaces were similar to the control group. Further studies are needed to support the use of BN-NS and SB-S as alternatives to CHX. BN-NS and SB-S are promising alternatives to the antibacterial agent CHX, which is known to be cytotoxic.

In vitro evaluation of dye penetration and dentin microhardness after laser irradiation using photon-induced photoacoustic streaming and shock wave enhanced emission photoacoustic streaming tips compared to ultrasonic activation

The purpose of this study was to compare the penetration of methylene blue (MB) dye after laser irradiation using PIPS (photon-induced photoacoustic streaming) and SWEEPS (shockwave enhanced emission photoacoustic streaming) methods compared to Passive ultrasonic irrigation (PUI) and to study their effect on dentin microhardness. A total of 44 single-rooted human teeth which were extracted for orthodontic or periodontal reasons were used. The teeth were decapitated to standardize roots to 12 mm in length. Canals were prepared up to size #30.6% and divided randomly into four groups (n = 11/group) according to the method of NaOCl activation: Group I: Er: YAG laser activation with PIPS tip; Group II: Er: YAG laser activation with SWEEPS tip; Group III: passive ultrasonic irrigation (PUI) and Group IV: conventional needle irrigation (CI). MB dye was injected then teeth were sectioned horizontally into coronal, middle and apical sections. Penetration depth/area percentages were measured using stereomicroscopy. Coronal specimens were further subjected to Vickers microhardness testing. Data were statistically analyzed. SWEEPS and PIPS activation methods provided higher dye penetration depth and area percentages compared to PUI with no statistically significant differences between all test groups. However, all test groups showed statistically significant differences with the CI (control) group. SWEEPS activation provided higher microhardness values with statistically significant differences with the other groups. Laser irrigant activation using PIPS and SWEEPS is comparable to PUI concerning MB dye penetration. However, SWEEPS preserved dentin microhardness significantly which can be beneficial for the long-term prognosis of root canal treated teeth.

The Microstructure, Hardness and Density Investigation of Mg Composites Reinforced with Nanoclay

Magnesium (Mg) stands out as a prevalent material in engineering, finding essential utility as a biomaterial due to its unique combination of low density, stiffness, high damping capacity, superior bending resistance, and impressive specific strength. Despite its high reactivity and somewhat inadequate mechanical properties for rigorous engineering applications, the incorporation of reinforcing nanoparticles has shown significant potential in enhancing the performance of magnesium-based composites. This study investigates the microstructure evaluation, hardness, and density of magnesium composites reinforced with nanoclay using a powder metallurgy approach. Nanoclay was preferred as a reinforcement element at weight percentages of 1%, 3%, 5%, and 7%. The densities of the composites were measured using the Archimedean principle, revealing that the addition of nanoclay generally increases the density of the composites due to the higher density of nanoclay compared to pure magnesium. However, the composite with 5% nanoclay exhibited a lower density than the one with 3% nanoclay, likely due to agglomerations leading to increased internal voids. Surface preparation for Vickers hardness testing involved sanding with 600, 1000, and 2000 mesh sanders, followed by polishing with 6μ and 3μ diamond suspensions. Hardness measurements, conducted using an AOB Vickers microhardness tester, indicated that the highest hardness value was observed in the composite with a 7% weight percentage of nanoclay, demonstrating that nanoclay addition enhances hardness. However, the composite with 3% nanoclay showed lower hardness compared to other reinforced composites. Optical images of the structures revealed metallographic spots indicative of contamination. These findings contribute to the understanding of the structural and mechanical behavior of nanoclay-reinforced magnesium composites, highlighting the potential for optimizing such materials for various applications in automotive, aerospace, and medical fields.

The antibiofilm effect and mechanism of silver nanowire-modified glass ionomer cement against multi-species oral biofilm

BackgroundTo investigate the antibiofilm effect and mechanism of the silver nanowire (AgNW)-modified glass ionomer cement (GIC) against multi-species oral biofilm, and to examine the mechanical and biochemical properties of this novel GIC material.MethodsConventional GIC was incorporated with different concentrations of AgNW and silver nanoparticles (AgNP). Multi-species biofilms of Streptococcus mutans, Streptococcus sobrinus, Lactobacillus fermentum, and Lactobacillus rhamnosus were cultured for 72 h on GIC specimens. Scanning electron microscopy (SEM) was adopted to examine the accumulation of biofilm on GIC surfaces. A live/dead assay was performed to assess the viability of bacteria. Extracellular polysaccharides (EPS) were labelled with Alexa Fluor 647-labelled dextran conjugate and then observed by a confocal laser scanning microscope (CLSM). The D/L-Lactic Acid Assay Kit was used to evaluate the lactic acid production of the multi-species biofilms. Compressive strength, surface roughness, hardness, and wettability were measured by a universal testing machine, an atomic force microscope (AFM), a Vickers microhardness tester, and a contact angle meter, respectively. Colour stability and fluoride release of GIC specimens were assessed by VITA Easyshade® V and ion chromatography. Cell counting kit-8 (CCK-8) was used to study cytotoxicity.ResultsSEM images showed that fewer biofilms were accumulated on the AgNW-GIC surfaces. The live/dead assay showed that the ratio of live bacteria was significantly lower in AgNW-GIC groups than in conventional GIC (5.8% vs. 100%, p < 0.0001). The EPS production was significantly less in AgNW-GIC groups compared to conventional GIC (p < 0.0001). There is no difference between groups regarding lactic acid production and fluoride release. The mechanical strength including compressive strength, surface roughness, hardness, and wettability were comparable between groups. The colour change between AgNW-GIC and conventional GIC was much milder than that between AgNP-GIC and conventional GIC. The results of cytotoxicity showed no significant differences in cell viability between groups.ConclusionsThis study demonstrated that AgNW-GIC had an excellent antibiofilm effect against multi-species oral biofilm, comparable mechanical and biochemical properties, and did not significantly affect the colour stability of GIC. The antibiofilm mechanism of AgNW-GIC may be related to inhibiting the viability and EPS production of bacteria.

In Situ Synthesis of MoSi2-SiC Composites by Two-Step Spark Plasma Sintering

The effect of different SiC doping content on the properties of MoSi2-based composites was analyzed in this study. The MoSi2-SiC composites were fabricated in situ by the SPS technique, utilizing self-synthesized carbon-containing Mo powder and Si powder as raw materials. A two-step sintering process was employed to ensure the formation of a uniform and dense composite structure. The microstructures and mechanical properties of these composites with various compositions were characterized. The results show that the composites were primarily composed of MoSi2, SiC, and a minor proportion of MoSiC phase. The introduction of SiC as a second phase was found to considerably enhance the mechanical properties of the MoSi2 matrix material. In particular, the MoSi2-26mol.%SiC sample exhibited Vickers hardness, fracture toughness, and flexural strength values of 16.1 GPa, 6.7 MPa·m1/2, and 496 MPa, respectively, corresponding to increases of 33%, 24%, and 28% compared to the pure MoSi2 material.

Mechanical and degradation behavior of Mg-1%Sn-x%HAp composite for biomedical application

Metal implants are preferred for orthopedics due to their strength and durability. A biodegradable metal with a density similar to bone, magnesium (Mg) is being considered for medical implants. This study examines the mechanical and corrosive properties of Mg-1%Sn-x%HAp composites with weight percentages of 0, 2, 5, and 7. Mechanical alloying is used to fabricate the composites. Adding hydroxyapatite (HAp) improves corrosion resistance and biocompatibility characteristics. SEM, XRD, and electrochemical tests were used for characterization. The results showed that adding HAp improved composite mechanical properties and corrosion resistance. SEM and EDS confirmed that Sn and HAp were uniformly distributed in Mg. Additionally, the XRD found α-Mg, Mg2Sn, and CaSn3 phases are present in the composite. Density, hardness, compressive and polarization test were performed to analyze the mechanical and chemical properties of the composite pallets. The Mg-1%Sn-2%HAp composites have a density of 1.744 g/cm³, close to human cortical bone. Hydroxyapatite (HAp) increased Vickers hardness by 26% in the Mg-1%Sn-7%HAp composite compared to the alloy. The Mg-1%Sn-7%HAp composite has 121.14 MPa ultimate compressive strength due to greater HAp content. This enhancement increased brittleness and decreased compressive strain. Electrochemical corrosion studies showed that the Mg-1%Sn-2%HAp composite had the lowest corrosion rate (0.28568 mm/year) and current density (12.502 µA/cm²). Due to a protective apatite layer and Sn-based oxides, the composite exhibits good corrosion resistance. The Mg-1%Sn-2%HAp composite showed good mechanical properties and corrosion resistance as a biodegradable orthopedic implant material.

Role of dysprosium substitution on microscopy architecture, structural stability, and crack propagation mechanism in Bi-2212 engineering ceramics

Abstract This study achieves a strong link between microscopy architecture and fundamental characteristics including electrical conductivity, superconducting, and key mechanical design properties of Bi2.1-xDyxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic structures with different dysprosium molar ratio ranges of 0.00 ≤ x ≤ 0.10. The Dy/Bi substituted Bi-2212 ceramics are characterized by scanning electron microscopy (SEM), electrical resistivity (ρ-T), Electron Dispersive x-ray (EDX) investigations, and microindentation Vickers hardness (Hv) tests. Powder x-ray diffraction (XRD) experimental inspection is also studied to support SEM and Hv results. All experimental findings show significant improvement with an increase in the Dy impurity molar ratio to x = 0.01. On this basis, the Bi2.09Dy0.01Sr2.0Ca1.1Cu2.0Oy ceramic structure exhibits the lowest resistivity of 8.95 mΩ.cm at 300 K and transition width of 4.75 K, and the highest T c o n s e t of 85.00 K and T c o f f s e t of 80.25 K. Additionally, XRD examinations show that optimum Dy ion substitution in the Bi-2212 system stabilizes the high superconducting phase by improving crystallinity, crystallite size, grain orientation distributions, texturing, and interlayer interactions. In contrast, excessive substitution severely deteriorates crystallographic properties. Further, SEM images reveal that the presence of optimum Dy impurity enhances the crystallinity, couplings between the adjacent layers, homogeneous surface appearance, and microstructure. Moreover, the key mechanical design features and stability of the durable tetragonal phase improve significantly for x = 0.01. As a result, the material exhibits superior mechanical properties, including a microhardness of 0.5556 GPa, fracture toughness of 0.5390 MPa.m1/2, elastic modulus of 45.5389 GPa, shear modulus of 18.2156 GPa, yield strength of 0.1852 GPa, and resilience of 0.3766 MPa under a 0.295 N load.

The impact of bleaching using 15% carbamide peroxide on surface properties of CAD-CAM composite structures

This study aims to evaluate the effects of the home bleaching method on the surface microhardness and surface roughness of both polished and unpolished CAD-CAM resin composite materials. A polymer-infiltrated ceramic network (PICN) block, Enamic (VE), along with four resin composite blocks (RCB) (Grandio [GN], Lava™ Ultimate [LV], BRILLIANT Crios [B], and Cerasmart [CS]), were prepared to dimensions of 14 mm × 12 mm × 2 mm and were categorized into unpolished and polished groups (n = 4). Microhardness measurements were conducted using a Vickers microhardness tester (300 gf load for 20 s) at various time points: before home bleaching, after home bleaching with 15% Opalescence for 8 h and for 56 h, 24 h after bleaching, and one month after bleaching. Surface topography was examined using a stylus contact profilometer (n = 4) and a scanning electron microscope (n = 3) at ×40 k magnification. Control specimens from each group were also measured. Data were analyzed using one-way ANOVA, Tukey’s post hoc test, two-way ANOVA and an independent t-test. The polished samples demonstrated a decrease in hardness after 8 h of bleaching, with the most significant reduction observed in VE, followed by GN, LV, CS, and BR. Significant differences were noted between all materials except for CS and LV. After 56 h, VE exhibited the greatest decrease in hardness, followed by GN, LV, BR, and CS, with significant differences between all materials except BR and CS. In the unpolished group, VE showed the highest reduction in hardness after 8 h of bleaching, followed by LV, GN, BR, and CS. After 56 h, the order was VE, LV, GN, CS, and BR, with significant differences observed between all materials except BR and CS. Similar trends in hardness reduction were observed at 24 h and 1 month post-bleaching. Additionally, hardness was significantly reduced after polishing for all materials. Overall, the reduction in hardness was significantly influenced by the type of material, the time, and the interaction between these factors (p < 0.05). Home bleaching using 15% carbamide peroxide significantly decreased microhardness. This effect was more pronounced in unpolished groups and with prolonged exposure. Further studies are recommended to determine the suitable concentration and duration of 15% carbamide peroxide application to ensure its use is safe for CAD-CAM materials.

Advancing Thermoelectrics in Lead‐Free Rhombohedral GeTe via Interfacial Engineering With MXene

AbstractLead‐containing GeTe‐based thermoelectric (TE) materials exhibit outstanding performance, but the toxicity of lead (Pb) limits their practical applications. Lead‐free GeTe‐based TE materials present a promising alternative for environmentally sustainable and scalable applications. Here, Bi doping is used to reduce the majority carrier concentration in GeTe, combined with uniform incorporation of nanoscale layered MXene via high‐energy ball milling. This approach significantly enhances the structural symmetry of GeTe, while MXene further reduces carrier concentration and improves carrier mobility. Consequently, the Ge0.93Bi0.07Te‐0.6 mass% MXene sample achieves an impressive average power factor of ≈28.40 µW m−1 K−2 across 303–603 K. Moreover, point defects, multilayer nanostructures, and grain boundaries reduce thermal conductivity to ≈1.04 W m−1 K−1 at 603 K. A maximum ZTmax of ≈2.1 at 603 K, an average ZTavg of ≈1.1, and a Vickers microhardness of ≈ 236.75 Hv are obtained. In particular, a high power density of ≈1.54 W cm−2 and a maximum conversion efficiency of ≈7.5% at a temperature difference of 300 K are achieved in a 7‐pair TE module. These outcomes represent the highest performance levels for lead‐free GeTe‐based materials. This work uncovers a straightforward method to enhance the structural symmetry of GeTe‐based compounds, providing insights for advancing lead‐free TE technologies.

Evaluation of the impact of acidic medications and fluoride-containing mouthwash on the enamel surface using quantitative light-induced fluorescence, microhardness, and scanning electron microscopy: an in vitro study

BackgroundDue to their acidic nature, certain medications can have deleterious effects on tooth enamel. Fluoride is a popular method for reversing these effects. Therefore, this study aimed to assess the impact of acidic medications, specifically anti-asthmatic drugs and vitamin C tablets, on enamel surfaces and to investigate the effects of fluoride following drug exposure.MethodsAn in vitro experimental study was conducted on ninety-six healthy human posterior teeth. Forty-eight samples were tested for surface demineralization via quantitative laser fluorescence (QLF), and the other forty-eight samples were tested for enamel microhardness via a Vickers hardness tester. The samples were divided into six groups: (i) Group DW_NF- samples immersed in distilled water with no fluoride exposure; (ii) Group DW_F- samples immersed in distilled water with intermittent fluoride exposure; (iii) Group VC_NF- samples treated with vitamin C only; (iv) Group VC_F- samples treated with vitamin C and fluoride mouthwash; (v) Group SB_NF- samples exposed to salbutamol inhaler with no fluoride exposure; (vi) Group SB_NF- samples exposed to salbutamol inhaler followed by fluoride exposure. For the evaluation of surface morphology by scanning electron microscopy (SEM), two random samples used for QLF from each group were taken. The Wilcoxon signed-rank test, Kruskal‒Wallis test, and post hoc test were applied as appropriate. The p value was set at 0.05.ResultsFollowing exposure to medication, significantly higher QLF values were observed in Group VC_F and Group SB_F than in Group DW-NF (control group) (p = 0.15 and 0.004, respectively). The difference in the QLF values was significantly greater in Group VC_NF than in the control group DW-NF, indicating greater demineralization with acidic medications (p = 0.034). Significant changes in surface microhardness were detected in Group VC_F compared with the control group (p = 0.024). Qualitative analysis of SEM images revealed erosion at the enamel surface in all groups except the control group, with the most prominent erosion in the vitamin C- and fluoride-treated groups (VC_F group).ConclusionThis study demonstrated the erosive potential of vitamin C tablets on enamel surfaces. Furthermore, the use of acidic fluoride mouthwash immediately after exposure to acidic medication exacerbates enamel demineralization.

Prediction of coating layer thickness and surface hardness in electric discharge coating process using RSM, ANN, and ANFIS with ANOVA optimization

Electric discharge coating (EDC) process is one of the unique and notable surface modification processes that enhance the surface properties of substrates. The coating layer thickness and surface hardness developed by the coating process are the predominant reason for substrate protection and performance enhancement. To enhance the coating efficiency and develop the desired output, optimization of input parameters and forecasting of output parameters was required. In this work, Mg alloy substrates are coated with Cu–Ni green compact electrodes by an EDC process. During the EDC process peak current ( I), pulse duration ( Ton), and compaction load for the electrode ( L) are major influencing parameters of coating layer thickness which are considered as input parameters. The coating layer thickness and surface hardness of the coating substrate were estimated by an optical microscope and Vickers hardness tester, respectively, and also considered as a response. The observed data were analyzed and optimized through analysis of variance (ANOVA) and response surface morphology (RSM) which provides a static relationship between the input parameter and response. Additionally, a prediction model was developed with a machine-learning approach. Two different tools namely artificial neural network (ANN) and, adaptive neuro-fuzzy inference system (ANFIS), were employed for accurate prediction of the model. From the ANN and ANFIS analysis regression coefficient (R) values were 0.97991 and 0.9912, respectively. The present study provides machine-learning capabilities and supports optimizing the input parameter to the target output in the EDC process.

Effect of Minor Reinforcement with Ultrafine Industrial Microsilica Particles and T6 Heat Treatment on Mechanical Properties of Aluminum Matrix Composites

This study examines the use of ultrafine (~128 nm) microsilica (composed of a mixture of amorphous and microcrystalline silicon dioxide phases) particles, an industrial waste product, as a reinforcing material to create aluminum matrix composites (AMCs) via ultrasonic-assisted stir casting followed by T6 heat treatment. This study aimed to improve the mechanical properties of pure aluminum, which has insufficient strength for most engineering applications. The main objective of this study is to develop environmentally and economically efficient AMCs with improved properties, namely, the balance between strength and ductility, for further application in caliber rolling processes. Attention is also paid to minor reinforcements using a low concentration of microsilica (~0.36%wt), which minimizes the problems with the wettability of the reinforcing material particles. The composites reinforced with ultrafine microsilica exhibited enhanced mechanical performance, including a 59.7% increase in Vickers microhardness and a significant improvement in tensile strength, reaching 73 MPa. Additionally, T6 heat treatment synergistically improved ductility to 60.3% elongation while maintaining high strength, achieving a balanced performance suitable for forming processes. The study results confirm that using microsilica as a reinforcing material is an effective way to improve the performance of aluminum alloys, while minimizing costs and solving environmental problems.

Two‐dimensional layered MoS2/lignin as additives for epoxy composites with improved mechanical and tribological properties

AbstractThe MoS2/lignin hybrid material was successfully synthesized and incorporated into an epoxy resin to fabricate composite coatings. The results demonstrate that MoS2 is uniformly attached to the surface of lignin sheets. Compared to adding lignin alone, the MoS2/lignin hybrid‐epoxy resin (EP) composite coatings exhibited enhanced friction‐reducing and wear‐resistant properties. Specifically, the 1 wt% MoS2/lignin hybrid displayed excellent dispersion and high interfacial compatibility within the resin matrix, leading to a 66.7% increase in Vickers hardness, a 27.5% increase in tensile strength, and a 73.9% improvement in char yield. Furthermore, the friction coefficient and wear rate were reduced by 63.2% and 75.8%, respectively. As a uniformly dispersed hybrid structure, the MoS2/lignin material can endure higher loads, autonomously repair defects, and form a stable and complete transfer film on the worn surface, demonstrating synergistic friction‐reducing and wear‐resistant effects within the epoxy resin matrix. Integrating MoS2 into a two‐dimensional material can provide a practical reference for designing polymer‐based hybrid materials with outstanding comprehensive properties.Highlights The MoS2/lignin hybrid material was successfully synthesized. MoS2 is uniformly attached to the surface of lignin sheets. The hybrid significantly enhances friction‐reducing and wear‐resistant properties. Vickers hardness increased by 66.7%, and tensile strength increased by 27.5%. The friction coefficient was reduced by 63.2%, and the wear rate was reduced by 75.8%.

Fabrication and Characterization of Vapor Gown Carbon Fiber/304L Matrix Stainless Steel Composite by Spark Plasma Sintering

In this paper, VGCF/304L stainless steel composite was prepared using spark plasma sintering (SPS) with 2 vol.% nanocarbon fiber. Then, phase content, grain size, and mechanical properties were evaluated. The results showed that the Vickers hardness of 304L sintered stainless steel and the composite prepared by SPS under the condition of 950 °C for 10 min were 244 HV and 310 HV, respectively, which is an increase of about 27.0%. The yield strength ascended from 587.1 MPa to 890.2 MPa, registering an increase of approximately 51.6%. Concurrently, the ultimate tensile strength rose from 821.5 MPa to 1064.7 MPa, with an approximate increase of 29.6%. This method for improving the mechanical properties of stainless steel is expected to be widely adopted for producing fiber-reinforced metal matrix composites with excellent overall performance.

Critical raw material-free multi-principal alloy design for a net-zero future

Refractory High-Entropy Alloys (RHEAs), such as NbMoTaW, MoNbTaVW, HfNbTaZr, Re0.1Hf0.25NbTaW0.4, Nb40Ti25Al15V10Ta5Hf3W2, TixNbMoTaW (x = 0, 0.25, 0.5, 0.75 and 1), and 3d transition metal HEAs such as Al10.3Co17Cr7.5Fe9Ni48.6Ti5.8Ta0.6Mo0.8W0.4 have demonstrated superior performance compared to traditional superalloys, particularly in high-temperature applications for engine components. However, the development of these alloys often depends on critical raw materials (CRMs) such as Ta, W, Nb, Hf, and others. The reliance on critical raw materials (CRMs) not only generates substantial emissions during recycling processes but also imposes considerable risks across global supply chains, hindering the pursuit of Net-zero ambitions. In this pioneering work, we unveil an inventive approach to inversely predict novel multicomponent alloy compositions, meticulously crafted to eliminate CRMs while achieving hardness levels comparable to those of CRM-containing multi-principal element alloys (MPEAs). A robust machine learning (ML) model was developed using a computational database of 3,608 entries, covering unary and binary materials from the Thermo-Calc 2024a software. Among various ML models, the Extra Trees Regressor (ETR) exhibited superior performance and was integrated with metaheuristic optimization techniques to identify novel MPEA compositions. The Cuckoo Search Optimization (CSO) method produced reduced-CRM MPEAs that closely matched Thermo-Calc predictions, with an error margin below ± 20%. To assess the efficacy of these reduced-CRM MPEAs, we compared the hardness of newly synthesized MPEA with CRM-containing counterparts reported in the literature, particularly those with high-risk critical raw materials like Niobium (Nb) and Tantalum (Ta). For example, the CoCrFeNb0.309Ni alloy, which includes CRMs Nb and Co exhibits a Vickers hardness of 480 HV. In contrast, our proposed composition, Ti0.01111NiFe0.4Cu0.4 achieves a comparable hardness of 488 HV without using a CRM. Our objective was not to develop high hardness alloy but to facilitate the development of reduced-CRM multi-principal element alloys (R-CRM-MPEAs). We validated our computational approach through the experimental synthesis of an FCC-phase alloy, Al6.25Cu18.75Fe25Co25Ni25. Thermo-Calc evaluation and ML model predictions of the Vickers hardness showed excellent agreement with the experimental hardness values, which lends credence to our approach. In conclusion, this study provides a robust framework for accelerating the discovery of novel R-CRM-MPEAs, effectively addressing challenges related to supply chain vulnerabilities, import dependence, and related environmental concerns.

Microstructural and mechanical properties of boron carbide (B4C) coated RDSO wear plate sample

In this research, a comparative investigation was carried out on the microstructural and mechanical characteristics of boron carbide (B4C) coated RDSO (Research design & standard organization, India) approved steel sample and uncoated RDSO steel samples intended for applicable as wear plates of ballast cleaning machines which is a railways track maintenance machine. Wear plates of ballast cleaning machines are subjected to extreme abrasion & impact stresses because they directly come in contact with railways ballast. Microstructural examinations were performed using scanning electron microscopy (SEM) and optical microscope to characterize the coating’s homogeneity, adhesion, and interfacial bonding with the steel substrate. Mechanical tests, including hardness testing, tensile strength, and wear tests, were conducted to understand the coated sample’s performance compared to the uncoated counterpart. Results indicated that the average micro-hardness values, 428 ± 10 HV and 302 ± 10 HV was obtained using Vickers hardness test done on the samples B4C coated RDSO sample and uncoated RDSO sample respectively. The average coefficient of friction (COF) for the carbide-coated sample was 0.33 under a 10 N load, while the uncoated sample had a COF of 0.64. This demonstrates that the carbide coating greatly improves wear performance. This comparative analysis suggests that B4C-coated steel is a promising railways for wear plate applications in ballast cleaning machines, providing increased lifespan and better performance.

Effects of Mo2C on Microstructures and Comprehensive Properties of Ti(C, N)-Based Cermets Prepared Using Spark Plasma Sintering

Ti(C, N)-based cermets are problematic in practical production applications due to their brittleness. To improve this defect, Ti(C, N)-based cermets were prepared under different sintering environments using a spark plasma sintering (SPS) device with different contents of Mo2C and 25 wt.% of nano tungsten carbide as additives. By means of microstructural analysis and comprehensive performance tests, the Ti(C, N) cermet with 6 wt.% Mo2C content showed the best comprehensive performance when sintered at 1450 °C under a pressure of 25 MPa with a holding time of 16 min. The density of this metal-ceramic was 6.27 g/cm3, the Vickers hardness was HV 2731, and the fracture toughness was 10.1 MPa·m1/2, which increased the density by 15%, the hardness by 63%, and the fracture toughness by 84% compared with the ceramic without added Mo2C. Densification of cermets can be promoted using SPS. The moderate addition of Mo2C can improve the wettability between the bonded phase and the hard phase, and its joint action with tungsten carbide can promote the formation of a ring structure and inhibit the growth of core-structure grains to enhance the toughness of the ceramic.