Improvement Of Mechanical Properties Research Articles

Interfacial engineering reaction strategy of in-situ Cr23C6/CoCrFeNi composites with network structure for high yield strength

CoCrFeNi high-entropy alloy (HEA) has distinctive properties such as high hardness and good corrosion resistance, however, its low strength or poor yield strength at room temperature limits its wide-range applications in industry. Herein, Cr23C6 particles reinforced CoCrFeNi composites with graphene nanoplates as a precursor were fabricated using in-situ reaction spark plasma sintering and cold rolling annealing processes. Results showed that the microstructure of the CoCrFeNi HEA and their composites were face-centered cubic structures before and after annealing, and Cr23C6 particles were precipitated inside the matrix during SPS. The precipitated Cr23C6 particles exerted strong pinning forces to migrate dislocations and grain boundaries, effectively refining the grains during the annealing process. After cold rolling, Cr23C6/CoCrFeNi composites showed a typically banded deformation structure. After annealing, fine equiaxed grains were distributed around the deformed grains, and the proportion of equiaxed grains was increased with the annealing time. The yield strength (YS) of Cr23C6/CoCrFeNi composites was significantly higher than that of CoCrFeNi alloy after cold rolling and annealing. When annealed for 20 min, the YS and elongation of Cr23C6/CoCrFeNi composites with 0.3 wt% graphene addition were 1100 MPa and 6 %, respectively. The YS was 68.2 % higher than that of the CoCrFeNi alloy. We have identified that the improvement of mechanical properties of Cr23C6/CoCrFeNi composites is mainly attributed to grain refinement, dislocation strengthening, precipitation strengthening, and load transfer strengthening, among which dislocation strengthening plays a major role.

Microstructure and mechanical properties of Mg-Nd-Zn-Zr alloy fabricated by TIG-based wire – Arc directed energy deposition with pulsed current

In this study, the Mg-Nd-Zn-Zr alloy thin-wall specimens were prepared by tungsten inert gas (TIG) based wire-arc directed energy deposition (WA-DED) with different pulsed currents. The arc characteristics of different pulsed current frequents were observed. The microstructures, and mechanical properties of as-deposited (AD), 5 Hz, 10 Hz, 15 Hz, and 20 Hz specimens were systematically analyzed and evaluated. The uniformly equiaxed crystals with random grain orientations and intergranular network Mg-Nd-Zn eutectics were found in the WA-DED fabricated Mg-Nd-Zn-Zr alloy thin-wall specimens. No significant voids were found. The microstructures were regulated, and the mechanical properties were improved by adjusting the pulsed current frequency. The 10 Hz specimen had the optimal microstructure with an average grain size of 10.35 μm. Concurrently, the 10 Hz specimen exhibits excellent strength-ductility synergy and isotropic, benefiting from the finely equiaxed crystals. The average microhardness of the 10 Hz specimen was 68.51 HV0.2, and the ultimate tensile strengths in the building and traveling directions were 223 MPa and 229.7 MPa, respectively, and the yield strengths in the building and traveling directions were 138.3 MPa and 145.3 MPa, respectively. Notably, the elongations in the building and traveling directions of the 10 Hz specimen were 16.8 % and 17.4 %, respectively. The local strain evolution and fracture surfaces of AD and 10 Hz specimens in the building and traveling directions were observed. The mechanisms of grain refinement and mechanical properties improvement were revealed.

Changes in Microstructure and Mechanical Properties of Goryeo Dynasty Bronze Vessels with Manufacturing Process

Bronze vessels are manufactured using casting and forging techniques, and various microstructures can be observed depending on the manufacturing process. In this study, we confirmed mechanical properties and microstructural evolution in the manufacturing process by observing the microstructures and composition analysis of 18 bronze vessels in the Goryeo Dynasty excavated from historical sites. The results show that 13 of the bronze vessels were manufactured using a Cu-Sn alloy with a Sn content of 20 to 24 wt%. The α phase and β(M) phase were observed, indicating that hot forging and quenching treatment were performed after casting. 3 bronze vessels were produced from a Cu-Sn-Pb alloy, and considering that the α phase and α+δ phase were observed, it could be seen that the process was completed by slow cooling after casting. The correlation between the type of bronze vessel and the manufacturing process has not been confirmed, except of ewer. It was confirmed that various microstructures were created depending on the manufacturing process and that the mechanical properties also changed. Bronze vessels composed of the α phase and α+δ phase due to the casting process had lower Vickers hardness values compared to bronze vessels that showed the quenched β(M) or γ phase. Electron backscatter diffraction (EBSD) phase analysis and kernel average misorientation (KAM) were performed using six bronze vessels composed of α and β(M) phases. The results showed that the factors affecting hardness were the ratio of the β(M) phase and the KAM value. However, it could not be confirmed to what extent the ratio of the β(M) phase and KAM value affected the improvement in mechanical properties.

Study on the hydration characteristics and mechanical properties of recycled powder-slag powder-cement system

This study systematically investigated the influence of different blending ratios of recycled powder and slag powder on hydration heat evolution and mechanical properties. Various modern microscopic testing techniques were employed to quantitatively characterize hydration products and microstructures, revealing their hydration mechanisms. The results indicate that both recycled powder and slag powder can accelerate the early hydration rate. When recycled powder and slag powder are co-blended, their early hydration rate and cumulative heat release surpass those of specimens with single additions of recycled powder. Moreover, the mechanical properties in the later stage are superior to those of specimens with single additions of recycled powder. At 60d, the PRS70–1–2 in the multi doped recycled powder and slag powder system even exceeds that of the uni doped SL system, but is much higher than that of the uni doped RP system，the compressive strength of the multi doped recycled powder and slag powder system increased by 25.5 %, 37.1 % and 36.9 %, respectively, compared with that of the uni doped RP system. Specimens with single additions of recycled powder and slag powder have a relatively high proportion of harmful and very harmful pores. At 28d, the porosity of the multi doped recycled powder and slag powder system decreased by 19.2 %, 24.2 % and 14.8 %, respectively, compared with that of the uni doped RP system. However, when recycled powder and slag powder are co-blended, the proportion of harmful and very harmful pores decreases, while the proportion of less harmful and harmless pores increases. This leads to an overall reduction in porosity and an improvement in mechanical properties.

The Anti/Deicing Performance of the Low Interfacial Toughness Coating Is Enhanced: Induced Ice Crack Generation and Its Extension.

The low interfacial toughness of the material surface is important for crack initiation and expansion of the ice layer as it remains an effective method for large-scale deicing. However, there are challenges, such as a large critical icing size and incomplete shedding of the ice layer. Adjusting the interfacial forces to make the ice more prone to cracking, expanding, and shedding is advantageous in addressing the problem of anti-icing failure in materials with low interfacial toughness. Therefore, we propose a deicing strategy that combines porous PDMS (polydimethylsiloxane) coatings with low interfacial toughness and piezoelectric vibration. A series of hydrophobic porous PDMS coatings with different porosities were prepared on the surface of an aluminum alloy substrate through curing and phase separation. The elastic modulus of the coatings decreased from 1465 to 509 kPa as the coating porosity increased, revealing the mechanism behind the improvement in mechanical properties. The key to promoting ice fracture on porous PDMS coatings lies in the synergistic effect of the out-of-plane shear stress and microcracks at the solid-ice interface. This work focuses on exploring the characteristics of interfacial forces by combining the intrinsic mechanical properties of coatings with external forces, providing new insights for designing low interfacial toughness anti-icing materials.

Characterisation of AZ31/TiC composites fabricated via ultrasonic vibration assisted friction stir processing

In this study, the effect of ultrasonic vibration during Friction Stir Vibration Processing (FSVP) on the microstructure and mechanical behaviour of AZ31/TiC surface composites was investigated. Specifically, Titanium Carbide (TiC) particles were introduced as a reinforcement (15 vol%) into the magnesium alloy AZ31 using both Friction Stir Processing (FSP) and FSVP. Comprehensive examinations were carried out to analyse the microstructure, hardness, and tensile behaviour of the resulting composites. The study revealed significant improvements in mechanical properties due to the application of ultrasonic vibration during FSP. Firstly, the stir zone region was found to be free from voids, enhancing material flow and promoting even dispersion of TiC powders within the matrix. Secondly, refinement of grains was observed due to dynamic recrystallization and the pinning effect imposed by TiC particles, leading to the formation of more dislocations in the composite and indicating a considerable alteration in the material’s structure. Importantly, the vibration during FSP introduced an auxiliary energy source, resulting in a remarkable enhancement in both hardness and tensile strength. Compared to the AZ31/15 vol% TiC FSP composite, the composites produced via FSVP exhibited a grain size reduction of about 64% and improvements in hardness and ultimate tensile strength (UTS) of about 55% and 21%, respectively. Notably, these improvements were achieved without compromising the ductility of the composite, which remained at appreciable levels.

Preparation of Cf/Si3N4 composites based on vat photopolymerization combined with precursor infiltration and pyrolysis

AbstractThe development of vat photopolymerization (VPP) 3D printing technology has created the conditions for the fabrication of complex structured Si3N4 ceramics. However, Si3N4 ceramics produced through VPP often lack sufficient mechanical properties, which limiting their applications. This study introduces short carbon fibers (Cf) into the VPP‐Si3N4 ceramics, combined with the polymer infiltration and pyrolysis (PIP) process, to prepare Cf/Si3N4 composites. The effect of Cf content on slurry preparation, green part printing, and mechanical properties of the Cf/Si3N4 composites was systematically investigated. The results indicate that Cf significantly enhances the mechanical properties of Cf/Si3N4 composites. At 6 wt.% Cf content, the samples exhibit the highest strength and fracture toughness, reaching 183.2 MPa and 6.2 MPa·m1/2, respectively, representing increases of 29.7% and 92.3% compared to samples without Cf. The improvement in mechanical properties is partly due to the ‘pinning effect’ of Cf, which enhances interlayer bonding strength in the printed green parts, positively impacting the overall mechanical properties of the composites. Additionally, inherent toughening mechanisms of Cf, such as fiber pull‐out, crack deflection, and crack bridging, further enhance the composite's mechanical properties. This study confirms the feasibility of using Cf to enhance the mechanical properties of VPP‐Si3N4 ceramic.

Effect of wall thickness on the precipitation behavior, microstructure, electrical conductivity and mechanical properties of copper alloy prepared by electron beam powder bed fusion

Electron beam powder bed fusion (EB-PBF) is one of the most promising technologies for preparing thin-walled copper alloy, because copper alloy have a high energy absorption rate for electron beam, and high preheating temperature can reduce the solidification temperature gradient and reduce the deformation of thin-walled parts. At present, there are few reports on the systematic research work on the EB-PBF of thin-walled CuCrZr alloy parts, and it's impossible to effectively supervise the production of complex thin-walled CuCrZr alloy parts. This work aims to investigate the effect of thickness on the microstructure and mechanical properties of CuCrZr alloy produced by EB-PBF. As the wall thickness decreases from 5.0 mm to 0.3 mm, the grain sizes of the XY and YZ planes decreased from 20.4 μm and 43.1 μm to 14.5 μm and 21.5 μm respectively, and the texture intensity decreased from 16.04 and 23.57 to 7.62 and 10.99. The analysis showed that Cr2O3 nanoprecipitates were precipitated in situ in the sample, and their average size decreased from 65.8 nm to 21.6 nm. Due to the reduction in grain and nanoprecipitate size, the performance of thin-walled samples is significantly enhanced, with yield strength (YS) increasing from 112 MPa to 165 MPa and conductivity increasing from 71.7 %IACS to 86.1 %IACS. Finally, the main contributions to the YS of specimens with different wall thicknesses was discussed. Precipitation strengthening and dislocation strengthening are the main strengthening mechanisms in thin-walled samples, and the gradual refinement of nano-precipitates is the main reason for the improvement of mechanical properties as the wall thickness decreases.

Super Tough PA6/PP/ABS/SEBS Blends Compatibilized by a Combination of Multi-Phase Compatibilizers.

Development of multi-component blends to prepare high-performance polymer materials is still challenging, and is a key technology for mechanical recycling of waste plastics. However, a multi-phase compatibilizer is prerequisite to create high-performance multi-component blends. In this study, POE-g-(MAH-co-St) and SEBS-g-(MAH-co-St) compatibilizers are prepared via melt-grafting of maleic anhydride (MAH) and styrene (St) dual monomers to polyolefin elastomer (POE) and poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS), respectively. Subsequently, these compatibilizers are utilized to compatibilize the PA6/PP/ABS/SEBS quaternary blends through melt-blending. When POE-g-(MAH-co-St) and SEBS-g-(MAH-co-St) are added, respectively, both can promote the distribution of the dispersed phases, significantly reducing the dispersed phase size. When adding 10 wt% POE-g-(MAH-co-St) and 10 wt% SEBS-g-(MAH-co-St) together, compared to the non-compatibilized blend, the fracture strength, fracture elongation, and impact strength surprisingly increased by 106%, 593%, and 823%, respectively. It can be attributed to the hierarchical interfacial interactions which facilitate gradual energy dissipation from weak to strong interfaces, resulting in the improvement of mechanical properties. The synergistic effect of the enhanced phase interfacial interactions and toughening effect of elastomer compatibilizer achieved simultaneous growth in strength and toughness.

Hybrid siloxane oligomer: A promising consolidant for the conservation of powdered tremolite jade artifacts

Jade has played a pivotal role in the political, economic, cultural, and technological development of ancient societies. However, numerous tremolite jade artifacts unearthed from archaeological sites exhibit various deterioration patterns due to natural weathering and human activities. Among these, powdering is the most detrimental form of degradation, significantly affecting the physical characteristics of artifacts, as well as archaeological research and museum exhibitions. This paper develops a novel hybrid siloxane oligomer as a potential consolidant for powdered tremolite jade artifacts and compares it with traditional consolidants, including acrylic resin and ethyl silicate. Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and X-ray fluorescence (XRF) analyses show that the jade samples used in the experiment are predominantly composed of tremolite. Various techniques are employed to evaluate and compare the effectiveness of the three consolidants, including color variation tests, open porosity tests, contact angle measurements, peeling tests, hardness tests, ultra-depth-of-field microscopy, and scanning electron microscopy (SEM). The novel hybrid siloxane oligomer demonstrates superior consolidation effects, with consolidated samples showing significant improvements in mechanical properties, reaching a Leeb hardness of 163 HL, while maintaining color variations within acceptable limits (ΔE = 3.87). The results demonstrate the potential of the novel hybrid siloxane oligomer in consolidating powdered tremolite jade artifacts.

Novel food preservation strategy using sprayed PVA/chitosan-based coatings activated by macroemulsions of chamomile essential oil adsorbed on activated carbon.

Active films based on polyvinyl alcohol (PVA) and chitosan (CS) were developed by encapsulating chamomile essential oil using an emulsification process, followed by adsorption onto activated carbon (AC) to stabilize the oil droplets. Microscopic analysis showed that the average size of the micelles was between 0.1 μm and 1.5 μm. The micelles obtained were incorporated into PVA/CS film formulations with different concentrations of chamomile essential oil (5 %, 10 %, 15 % w/w), and the optical, physical, mechanical, antibacterial, and antioxidant properties as well as the release rate of the encapsulated oil were studied to test their application in food packaging. The SEM images showed a homogeneous dispersion of the EO in the polymer matrix containing AC, due to the formation of hydrogen bonds, which is confirmed by the FTIR results and is accompanied by an increase in the viscosity of the film-forming solutions, a decrease in the crystallinity and an improvement in mechanical properties by an increase in elongation at break (15.95 ± 0.10 to 47.02 ± 0.06 %) of the films produced. In addition, some properties of the PVA/CS films were increased by the addition of EO-AC, notably thickness (0.097 ± 0.12 to 0.144 ± 0.01 mm) and opacity (1.632 ± 0.11 to 8.266 ± 0.12), while the water absorption rate and solubility of the films decreased. PVA/CS-EO-AC films exhibit good antioxidant and antibacterial activity against E. coli and S. aureus, high barrier properties (UV-blocking) and a controlled release of bioactive molecules contained in EO. The PVA/CS/EO-AC coating reduced the weight loss of the tested apples to (3.31 ± 0.29 %) compared to apples packaged in polyethylene film, and maintained their appearance after 3 weeks of storage. These results offer the possibility of reducing food waste through this new coating strategy based on the encapsulation of EO.

A comparative study on tribological and mechanical behavior of as-cast and aged Mg-6Gd-2Ag-0.6Zr alloy at elevated temperatures

The effects of aging treatment on the mechanical and tribological behavior of Mg-6Gd-2Ag-0.6Zr alloy were investigated. Shear punch testing and hot hardness measurements were conducted to evaluate the mechanical properties of the alloys at various temperatures of 25–350 °C. The aging treatment enhanced the mechanical behavior of the alloy, resulting in increases in hardness and ultimate shear strength by about 53–64% and 11–22%, respectively, at various temperatures. Dry sliding wear tests were carried out under the normal loads of 5, 20, 40, and 60 N within a temperature range of 25–325 °C using a Pin-on-disk tribometer against AISI52100 steel disks. Despite the improvements in mechanical properties, the aging treatment reduced wear resistance by about 45% under a normal load of 5 N at various wear temperatures. However, as the normal load was increased to 60 N the aged alloy showed about 11–23% lower wear rate at various temperatures. The characterization of the wear surfaces also showed that the oxidation wear became more dominant as the normal load and the wear temperature increased. Under higher normal loads of 40 and 60 N, a 54–88% greater transfer of magnesium oxides was observed on the steel disk, which reduced the contact between the steel disk and the magnesium alloy pin.

Fabrication and characterization of nacre-inspired metal/ceramic composites containing AlN nanowhiskers

Nacre-like composites prepared by infiltrating ice-templated porous ceramic-scaffolds with molten metal phases have successfully imitated the strengthening and toughening mechanisms of nacre at different lengthscales from macro to micro, but have not yet been able to replicate the nanoscale toughening mechanisms of nacre, which limits the further improvement in mechanical properties of the nacre-inspired composites. To resolve this issue, we prepared nacre-inspired Al/SiC composites containing AlN nanowhiskers by in-situ growth of whiskers during the spontaneous infiltration process of Al-10 wt%Mg alloy into an ice-templated porous SiC skeleton. It was found that the oxidation of the SiC skeleton had a significant impact on the growth of AlN nanowhiskers, as well as the phase composition and mechanical properties of the composites. When the skeleton was oxidized at 1100 °C in air for 2 h, the composite exhibited a large number of AlN whiskers and the optimal phase composition, while the flexural strength and fracture toughness of the composite reached their maximum values. The strengthening and toughening mechanisms, such as plastic deformation, crack deflection, multiple cracking, crack bridging, crack branching, and delamination, caused by the lamellar structure were observed. It was also found that the pull-out and bridging of the AlN whiskers provided strengthening and toughening effects at the nanoscale for the nacre-like composites.

Enhanced mechanical properties of the surface-modified CNTs reinforced 2195 aluminum-based composite

Carbon nanotubes (CNTs) reinforced aluminum-based composites exhibit characteristics such as low density, high specific strength, and high specific stiffness, making them promising materials for applications in aerospace, automotive lightweighting, and other fields. The dispersion of CNTs in the aluminum matrix and the strength of the interface between CNTs and the aluminum matrix are crucial for the preparation of CNTs reinforced aluminum-based composites. In this study, CNTs were surface-modified with partial coating of Al2O3, and then the CNTs reinforced 2195 aluminum-based composite (2195/CNT composite) were prepared using a combination of melting-casting process and hot extrusion. The tensile strength, yield strength, and elongation of the aged 2195/CNT composite reached 697 MPa, 590 MPa, and 11.3%, respectively, demonstrating a significant improvement in mechanical properties compared to 2195 alloy prepared under the same conditions. CNTs were primarily present at grain boundaries, and a small amount of glow stick-like Al4C3 phase was found near the CNTs. The formation of glow stick-like Al4C3 phase was attributed to the segregation of solute elements at the interface in the alloy. First-principles calculations revealed that solute elements tended to segregate at the interface closer to the aluminum matrix. Moreover, the segregation of Cu and Ag elements at the interface could enhance the cleavage energy of the Al4C3/Al interface, while the segregation of Mg elements reduced the cleavage energy of the interface. This study also analyzed the reinforcement mechanisms involved in the 2195/CNT composite.

Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

An ultra-high strain rate (104 s-1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650°C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

Targeted CRISPR regulation of ZNF865 enhances stem cell cartilage deposition, tissue maturation rates, and mechanical properties in engineered intervertebral discs

Cell and tissue engineering based approaches have garnered significant interest for treating intervertebral disc degeneration and associated low back pain due to the substantial limitations of currently available clinical treatments. Herein we present a clustered regularly interspaced short palindromic repeats (CRISPR)-guided gene modulation strategy to improve the therapeutic potential of cell and tissue engineering therapies for treating intervertebral disc disease. Recently, we discovered a zinc finger (ZNF) protein, ZNF865 (BLST), which is associated with no in-depth publications and has not been functionally characterized. Utilizing CRISPR-guided gene modulation, we show that ZNF865 regulates cell cycle progression and protein processing. As a result, regulating this gene acts as a primary titratable regulator of cell activity. We also demonstrate that targeted ZNF865 regulation can enhance protein production and fibrocartilage-like matrix deposition in human adipose-derived stem cells (hASCs). Furthermore, we demonstrate CRISPR-engineered hASCs ability to increase GAG and collagen II matrix deposition in human-size tissue-engineered discs by 8.5-fold and 88.6-fold, respectively, while not increasing collagen X expression compared to naive hASCs dosed with growth factors. With this increased tissue deposition, we observe significant improvements in compressive mechanical properties, generating a stiffer and more robust tissue. Overall, we present novel biology on ZNF865 and display the power of CRISPR-cell engineering to enhance strategies treating musculoskeletal disease. Statement of significanceThis work reports on a novel gene, ZNF865 (also known as BLST), that when regulated with CRISPRa, improves cartilagenous tissue deposition in human sized tissue engineering constructs. Producing tissue engineering constructs at human scale has proven difficult, and this strategy presents a broadly applicable tool to enhance a cells ability to produce tissue at these scales, as we saw an ∼8–88 fold increase in tissue deposition and significantly improved biomechanics in large tissue engineered intervertebral disc compared to traditional growth factor differentiation methods. Additionally, this work begins to elucidate the biology of this novel zinc finger protein, which appears to be critical in regulating cell function and activity.

Hydration mechanism and potential as solid-state electrolytes in sodium chloride-magnesium phosphate composite

This study explores the feasibility of NaCl based magnesium phosphate cement (NaCl-MPC) composites as a solid electrolyte for energy storage applications by analyzing the physical, mechanical, hydration and electrochemical properties of composites. The results indicated that the incorporation of NaCl greatly improved the mechanical properties and ionic conductivity of composites, demonstrating enhanced electrochemical stability, making it a promising energy storage material. NaCl induced complex physical and chemical interactions within the MPC system by facilitating the filling of micropores and microcracks, providing the additional nucleation sites and converting intermediate products into struvite. NaCl also reacted chemically in the MPC system to produce small amounts of hazenite crystals. These effects ultimately led to the densification of the microstructure of MPC and significantly improved its mechanical properties. Generally, the improvement of ionic conductivity of solid electrolytes compromises their mechanical properties. However, the NaCl-MPC composites in this study showed significant improvement both in ionic conductivity and mechanical properties, highlighting their potential for advanced energy storage applications.

Design of epoxy composites via molecular orbital modulation and enhanced π-πF interactions achieving synchronous improvement of electrical and mechanical performance

The stacked aromatic rings in bisphenol A epoxy resins provide good mechanical properties and thermal stability while leading to the transport of conjugated delocalized electrons, which dramatically affects the insulation properties of the material. This contradiction leads to performance bottlenecks in epoxy-based encapsulation materials, further limiting the development of high-voltage semiconductor devices. In this study, fluorophenyl-modified epoxy monomers (FPMEPs) are designed to enrich the intermolecular interactions in an aromatic system while inhibiting the charge transport process, thereby solving the contradiction between the electrical and mechanical properties. Firstly, FPMEP with high insulation properties was designed by theoretical calculations and then synthesized by highly selective click chemistry. The fluorophenyl modulates the molecular orbitals of epoxy monomers and acts as a deep trap to inhibit charge injection and transport processes. Further, the π-πF stacking between the aromatic system and fluorophenyl enhances the interaction of the matrix molecules and solves the dispersion problem of fluorinated graphene (FG) fillers. The FPMEP/FG composites thus exhibit a considerable improvement in electrical and mechanical properties (breakdown strength of 39.8 kV/mm, dielectric loss of 0.011@50 Hz, tensile strength of 68.8 MPa, and adhesive strength of 2.15 MPa), and demonstrate good water repellency and aging durability. This matrix-filler synergistic modification strategy provides new insights into the design of insulation material.

Tailoring the microstructure and mechanical properties of wire arc additively manufactured Ti6Al4V alloy by in-situ microalloying with modified nanocarbon

Carbon alloying is a validated strategy for enhancing the mechanical properties of titanium alloys prepared by wire arc additive manufacturing (WAAM). However, achieving uniform carbon distribution, particularly nanocarbon, in the melt pool via the brushing method is challenging, which limits the improvement of mechanical properties. In this paper, nanocarbon was modified by nitric acid hydrothermal treatment and added into the Ti64 melt pool during the WAAM. The distribution of modified nanocarbon in the melt pool was characterized, and the microstructure and mechanical properties of the nanocarbon-alloyed titanium alloy deposits were studied. The findings revealed that the surface of modified nanocarbon generated oxygen-containing functional groups, which enhanced its dispersion in the melt pool. The addition of 0.1–0.3 wt% modified nanocarbon induced no pores in the deposits compared to unmodified ones. The tensile strength of the deposited alloys was continually enhanced with increasing modified nanocarbon content, while the elongation had a peak value. The Ti64 with 0.1 wt% nanocarbon exhibited a balanced comprehensive performance with an ultimate tensile strength (UTS) of 981 MPa coupled with an elongation of 8 %. The achievement of the balanced mechanical performances was attributed to the refinement of α-Ti and solid solution strengthening of nanocarbon. When 0.3 wt% nanocarbon was added, the UTS increased to 1012 MPa but the elongation sharply decreased to 4.5 % due to the precipitation of TiC.

Improvement in mechanical properties of extruded Mg alloy through shape control of extrusion billet

This study proposes controlling the billet shape to enhance dynamic recrystallization (DRX) behavior and improve the mechanical properties of AZ31 alloy extrudates. Billets with two shapes—conventional cylindrical (non-tapered) and cone-shaped (tapered)—were used to compare DRX behavior and mechanical properties of the extrudates. The results indicate that the greater and more uniform deformation induced by compressive stress between the container wall and the tapered billet results in greater amounts of geometrically necessary dislocations (GNDs) and deformation twins at the beginning of the extrusion. These crystallographic features, along with a higher deformation degree, increase the DRX fraction from 81% for the non-tapered extrudate to 89% for the tapered extrudate. Consequently, the tapered extrudate exhibits a simultaneous improvement in yield strength (168–184 MPa) and elongation (25%–29%) compared to the non-tapered extrudate. Grain size reduction, texture weakening, and strain hardening by residual strain in unDRXed grains contribute to the improvement in mechanical properties of the tapered extrudate. The proposed tapered billet extrusion process offers a pathway to producing high-performance Mg alloy extrudates without additional processes such as pre-deformation or die-angle utilization.