Toughness Enhancement Research Articles

Crosslinking-induced compatibility and toughness enhancement in poly(lactic acid)/poly(3-hydroxybutyrate-co-4-hydroxybutyrate) blends with epoxidized soybean oil.

Polylactide (PLA) is inherently brittle and lacks ductility, which greatly restricts its range of applications. In order to address these issues, we blended PLA with biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), and introduced epoxidized soybean oil (ESBO) as a reactive modifier to enhance the properties of the PLA/P(3HB-co-4HB) blends. Furthermore, we used theoretical calculations, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Soxhlet extraction, differential scanning calorimetry (DSC), polarising optical microscopy (POM), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and mechanical testing to investigate the compatibility, crystallization behavior, microstructure, thermal and mechanical properties of the PLA/P(3HB-co-4HB)/ESBO blends. The mechanisms underlying these properties were analyzed in detail. ESBO was found to form cross-linking grafts between PLA and P(3HB-co-4HB), strengthening interfacial bonding and thereby enhancing compatibility. The in situ formation of graft copolymers resulted in finer, more uniform dispersion of P(3HB-co-4HB) and ESBO droplets within the PLA matrix, further improving interfacial adhesion and overall material compatibility. With the addition of 5 wt% ESBO, the tensile strain at break of PLA/P(3HB-co-4HB)/ESBO films increased from 114.6 % to 453.3 %, while the notched impact strength improved from 3.75 kJ∙m-2 to 8.75 kJ∙m-2, compared to PLA/P(3HB-co-4HB) films. However, excessive ESBO slightly decreases the mechanical performance of the material.

Carbon nanotubes at bilayer in-plane graphene/hBN with interlayer twist angles abnormally enhance its interlayer stress transfer.

A possibility of unprecedented architecture may be opened up by combining both vertical and in-plane heterostructures. It is fascinating to discover that the interlayer stress transfer, interlayer binding energy, and interlayer shear stress of bi-layer Gr/hBN with CNTs heterostructures greatly increase (more than 2 times) with increase the numbers of CNTs and both saturate at the numbers of CNTs= 3, but it causes only 10.92% decrease in failure strain. By analyzing the crack propagations and Von-Mises stress, we find that this abnormal enhancement in interlayer stress transfer and toughness originates from the localization of the stress fields arising from misfit dislocations and their out-of-plane deformations at the joints of CNTs and B-Gr/hBN heterostructures. Our discoveries hold great importance in comprehending the mechanical interfacial characteristics of bi-layer Gr/hBN and are anticipated to spark a great deal of curiosity in investigating its novel physics and potential uses.

Multiscale Structural Strong yet Tough Triboelectric Materials Enabled by In Situ Microphase Separation

AbstractLightweight green polymer materials with exceptional toughness, high strength, and excellent ductility represent ideal candidates for enabling next‐generation sustainable flexible electronics. However, the conflicting properties of material strength and toughness present a significant challenge in achieving an optimal combination of both attributes. In this study, a strong yet tough polymeric triboelectric material is prepared by constructing a multiscale reinforced network based on a nonsolvent‐induced microphase separation strategy. The synergistic enhancement of strength and toughness is achieved by reinforcing non‐covalent interactions within the polymer and constructing nanofibrous networks. The resulting triboelectric materials exhibited remarkable fracture toughness (78.6 MJ m−3), high tensile strength (42.5 MPa), an improvement in triboelectric output (71%), and promising recyclability. The integrated triboelectric wearable sensor maintained robust output signals. This study provides a novel solution for coordinating the conflicts between strength and toughness in heterogeneous polymer materials, showing significant potential in expanding their applications in flexible electronics and self‐powered sensing technologies.

Recycled PET Packaging Materials of Improved Toughness— Importance of Devitrification of the Rigid Amorphous Fraction

AbstractDegradation, a common problem faced during the processing of recycled poly(ethylene terephthalate) (PET), leads to significant embrittlement of the products, as a result of which the material loses its applicability. Increased crystallization rate of the short chains of recycled PET and obstructed mobility of the amorphous phase are the main causes of enhanced brittleness. In this research, a straightforward method is proposed for improving the toughness of recycled PET products, namely the devitrification of the rigid amorphous phase by thermal annealing, which results in enhanced molecular mobility in the amorphous fraction, thereby promoting ductile deformation. The effects of thermal annealing conditions are comprehensively evaluated on the microstructure and macroscopic properties, i.e., impact resistance, of recycled PET films. The perforation energy value of the recycled PET film is found to increase to its threefold, reaching a value higher than 18 J mm−1, as a result of 10 s thermal treatment at 120 °C. Differential scanning calorimetry, dynamic mechanical analyses, and thermally stimulated depolarization current measurements provide evidence for the devitrification of the rigid amorphous fraction under these conditions, which is the key to efficient enhancement in toughness.

Characterization of modified resin-based carbon fiber composite

Abstract This paper investigated the improvement of toughness and mechanical properties in resin castings. The results suggested that the resin system met the film-forming requirements for hot-melt film immersion technology when the toughening agent was added at a content of 6 parts. The resin casting demonstrated a substantial enhancement in impact toughness while maintaining its heat resistance. The impact strength was elevated by 48%, and there was a concurrent increase in bending strength of over 4%. Based on the results of resin system, the mechanical performance of type I, II and III carbon fiber composites was investigated. Finally, the interface of composite was analysed. The results indicated that the mechanical performance of type I composite was comparable to that of type III. The tensile strength of type I was 2761 MPa, with a modulus of 176 GPa. The bending strength measured at 2189 MPa, with a modulus of 162 GPa. Additionally, the shear strength was recorded at 98 MPa, while the impact toughness reached 282 kJ/m2. Furthermore, the compressive strength was determined to be 1.03 GPa. It was worth noting that the carbon fiber exhibited excellent bonding performance with the resin following the mechanical properties test.

Synergistic enhancement of low-temperature strength and toughness in poly(boron-urethane) elastomers via π-π stacking and hydrogen bonding

Synergistic enhancement of low-temperature strength and toughness in poly(boron-urethane) elastomers via π-π stacking and hydrogen bonding

Enhancement of toughness and gas barrier properties of PLA‐based films through bio‐based isosorbide dioctate: Synthesis, characterization, and application

AbstractPolylactic acid (PLA), as a bio‐based biodegradable material, has high tensile strength and modulus, but its low flexibility and poor barrier properties limit its application in packaging. In this study, Pullulan polysaccharide (Pullulan) and chain extenders (ADR4468) were selected to improve the properties of PLA‐based films. The ratio of PLA/Pullulan/ADR4468 was optimized by studying the mechanical and barrier properties of films. Then isosorbide dioctate (SDO), a kind of bio‐based plasticizer, was synthesized and added into PLA/Pullulan (4 wt%)/ADR4468 (0.8 wt%) system to study the effect of SDO content on the properties of films. A film with 15 wt% SDO showed elongation at a break of 79.7% while retaining a tensile strength of 30.6 MPa. With 20 wt% SDO, water vapor permeability and oxygen permeability of PLA/Pullulan/ADR/SDO film were reduced by 12.7% (2.95 × 10−14 kg m/(m2 s Pa)) and by 20.6% (1.95 × 10−3 cm3 m/ (m2 d Pa)), respectively, compared with that of PLA/Pullulan/ADR films. This study fills the research gap between PLA and Pullulan blends, broadens the application scenarios of new bio‐based plasticizers, and provides a method for improving the toughness and barrier properties of PLA. The films prepared in this study have potential applications in the green‐packaging field.Highlights The synthesis and characterization of isosorbide dioctate. The modified compatibility of PLA and Pullulan by ADR 4468. The optimization of the content of PLA/Pullulan/ADR 4468 film. The improvement of toughness and barrier properties of film by SDO.

Harnessing the potential of coal-derived graphene oxide/epoxy nanocomposites: Enhancing thermal conductivity and fracture toughness

The choice of precursor material significantly influences the properties of graphene oxide (GO), thereby providing its adaptability across diverse applications. Coal, with its distinctive molecular structure characterized by graphene-like domains and aliphatic side chains, as well as abundant impurities and heteroatoms featuring specific functional groups, emerges as a promising precursor. Employing a recently developed facile one-pot process for synthesizing semianthracite coal-derived GO (AC-GO), we have, in this study, explored its potential as a nanofiller in an epoxy matrix, resulting in AC-GO-enriched nanocomposites. The main purpose of the project was to introduce AC-GO within the epoxy matrix to enhance its thermal conductivity and fracture resistance by enhancing interfacial interactions. Our findings indicate remarkable enhancements in thermal conductivity (0.646 Wm-1K-1 at 1.0 wt% loading) and fracture toughness (6.7 MPam1/2 at 0.8 wt% loading) within AC-GO loaded nanocomposites, with these improvements being 255 % and 215 %, respectively, over those for the epoxy matrix. Remarkably, they surpass those achieved with graphite-derived GO (Gr-GO) by approximately 112 % and 76 %, respectively. Enhancing thermal conductivity and fracture toughness in epoxy nanocomposites is vital for effective heat dissipation and durability, making them ideal for high-performance electronics, aerospace, and automotive applications. These improvements can be attributed to the enhanced interactions between oxygen moieties located at the periphery of AC-GO and the fundamental epoxy-amine hardener system within the resin formulation, fostering electron acceptor–donor interactions. Furthermore, we introduce a new figure of merit (FOM) that accurately captures the combined role of thermal conductivity and fracture toughness. It is shown that this FOM can serve as a useful design tool for selecting an optimal nanofiller loading for targeted applications. The findings of our paper highlight the versatility and unique attributes of AC-GO, offering promising opportunities for applications in the industrial engineering, owing to their outstanding interfacial properties.

Deformation and fracture of lithosphere-inspired polymeric multi-layer composites

Inspired by the diversity of structures and patterns inherent in the earth's lithosphere, this study endeavors to enhance the interplay between stiffness and toughness through the introduction of a new class of polymeric multi-layer composite materials termed by the authors as "lithomers". Structured single-edge notched bending specimens were fabricated using a combination of additive manufacturing and casting, employing two different methacrylate-thiol resins. The outer layers exhibit a stiff and brittle characteristic, while the layer in between is compliant in nature. Three types of lithomers with wave-like structures and one with a rectilinear structure were investigated regarding their stiffness and toughness in a 3-point bending setup. The results were compared with those of a pure stiff matrix material. The findings revealed that fracture toughness increased regardless of the interlayer's shape compared to the pure matrix material. Correspondingly, this enhancement in fracture toughness correlated with a reduction in stiffness. The most balanced results in terms of stiffness and fracture toughness were achieved, with the lithomer having a wave-like structure in its initial stage. It exhibited a roughly 27 times improvement in fracture toughness with a moderate decrease in stiffness of approx. 1/5 compared to the pure matrix material.

Research on Compression Failure Characteristics and Damage Constitutive Model of Steel Fiber-Reinforced Concrete with 2% Copper-Coated Fibers Under Impact Load.

This study systematically investigates the mechanical properties of plain concrete (PC) and 2% steel fiber reinforced concrete (SFRC) under both static and dynamic loading conditions, utilizing advanced mechanical testing equipment and dynamic impact testing methods. The strain rate range studied spans from 10-4 s-1 to 483.12 s-1. Under static loading conditions, the maximum bearing capacity and energy absorption capacity of 2% SFRC are 2.16 times and 3.83 times greater than those of PC, respectively, indicating a significant enhancement in toughness and resistance to failure. Under dynamic loading conditions, the energy absorption capacity of SFRC increases to 6.36 times that of PC. The impact failure behavior of SFRC was analyzed using the split-Hopkinson pressure bar-digital image correlation (SHPB-DIC) method, revealing that the failure was primarily driven by splitting tension. The failure process was subsequently categorized into four distinct stages. At high strain rates, the dynamic enhancement factor, peak stress, and peak strain of SFRC exhibit a linear increase with strain rate, whereas the energy absorption capacity increases in a nonlinear manner. This study presents a simplified viscoelastic constitutive model with four parameters and develops a damage-based viscoelastic constitutive model with seven parameters, demonstrating its broad applicability. The findings offer both theoretical insights and experimental evidence to support the use of SFRC under high strain rate conditions.

Investigation of Inclusions and Associated Dislocation Configurations in 4H-SiC Wafers through Synchrotron X-Ray Topography and Ray-Tracing Simulation

Silicon carbide (SiC) is a wide bandgap semiconductor that steadily replacing the application of conventional semiconducting materials such as silicon-based devices. Its superior properties such as larger bandgap, higher electron saturation velocity and thermal conductivity [1, 2] enables devices to be more effective and efficient with smaller volume, higher dielectric strength, and lower energy loss [3-5]. The prerequisite of expanding SiC devices industry is to achieve steady manufacture of large-scale, high-quality, polytypic stable SiC substrate wafers. Therefore, understanding the nature and origins of crystallographic defects within SiC is a major research pursuit since those can induce degradation that challenges device reliability while achieving high performance [6]. Synchrotron X-ray topography (XRT) [7, 8] is a powerful non-destructive characterization technique that generate high-resolution X-ray images of the internal structure of a crystal. Crystallographic defects and structural features are then revealed as topographic contrast features that can be identified applying contrast formation mechanisms. Extensive studies have been conducted to observe various dislocation configurations, stacking faults, and low-angle grain boundaries using this approach. In this study, optically observable hexagonal features on a 6-inch 4° off-axis 4H-SiC substrate wafer are investigated through synchrotron XRT in both transmission and grazing-incidence geometries. These hexagonal features are identified as inclusions as correlated topographic contrasts reveal the generation of large strain fields associated with them. Indentation behavior is found to be induced by the presence of inclusions as both regular (9keV) and high energy (18keV) grazing-incidence topographs show arrays of opposite-signed threading edge dislocation (TED) pairs expand from inclusions along <11-20> directions, which is the evidence of the generation of prismatic loop. Basal plane dislocation (BPD) half loops are also observed associated with inclusions. Using ray-tracing simulation technique based on orientation contrast mechanism [9, 10], contrasts of inclusion at different depth and associated dislocations can be simulated and compared to X-ray topographic images. This will provide insights on the behavior of inclusions embedded in SiC as well as the activation of associated dislocations.Reference:[1] Matsunami, H., Current SiC technology for power electronic devices beyond Si. Microelectronic Engineering, 2006. 83(1): p. 2-4.[2] Codreanu, C., et al., Comparison of 3c SiC, 6h SiC and 4H SiC MESFETs performances. Materials Science in Semiconductor Processing, 2000. 3: p. 137-142.[3] Xie L., et al Enhancement of toughness of SiC through compositing SiC–Al interpenetrating phase composites. Nanotechnology, 2020 31 135706[4] Lin K., et al Enhanced mechanical properties of 4H-SiC by epitaxial carbon films obtained from bilayer graphene. Nanotechnology, 2020 31 195702[5] Shen G., et al, Synthesis, characterization and field-emission properties of bamboolike β-SiC nanowires. Nanotechnology, 2006 17 3468–72.[6] Neudeck, P.G., Electrical Impact of SiC Structural Crystal Defects on High Electric Field Devices. Materials Science Forum, 2000. 338-342: p. 1161-1166.[7] Tanner, B.K. and D.K. Bowen, Synchrotron X-radiation topography. Materials Science Reports, 1992. 8(8): p. 371-407.[8] Lang, A.R., The early days of high-resolution X-ray topography. Journal of Physics D: Applied Physics, 1993. 26(4A): p. A1.[9] Huang, X.R., et al., Superscrew dislocation contrast on synchrotron white-beam topographs: an accurate description of the direct dislocation image. Journal of Applied Crystallography, 1999. 32(3): p. 516-524.[10] Dudley, M., X.R. Huang, and W. Huang, Assessment of orientation and extinction contrast contributions to the direct dislocation image. Journal of Physics D: Applied Physics, 1999. 32(10A): p. A139.Figure 1: (a) Optical image showing hexagonal features on the upper region of a 4° off-axis 4H-SiC substrate wafer; (b) synchrotron white beam X-ray topograph recorded in 11-20 transmission geometry for the same region, showing the strain contrast induced by those hexagonal features; (c) synchrotron monochromatic beam X-ray topograph recorded in 11-28 grazing-incidence geometry for the same region, showing contrast of some hexagonal features (marked with blue arrows); (d) enlarged optical image of the hexagonal feature; (e) enlarged 11-28 grazing-incidence synchrotron X-ray topograph showing TED slip bands induced by a hexagonal feature; (f) enlarged 22-4,16 grazing-incidence synchrotron X-ray topograph showing TED slip bands induced by a hexagonal feature. Figure 1

Melamine-based biomass-containing P/N synergistic flame retardants confer superb flame retardancy and toughness to epoxy resins

Epoxy resin (EPs) coatings for aircraft need to have good flame retardant properties and toughness. On the other hand, to meet the needs of sustainable development, EPs also have high environmental friendliness and low cost requirements. In light of this, a one-pot approach was used to create a bio-based phosphorus‑nitrogen synergistic flame retardant (MDV) employing DOPO, vanillin, and MA as raw materials. The results showed that MDV can give EP superb flame retardancy and toughness. With the addition of 3 wt% MDV, the tensile and flexural strengths of EP composites increased by 13.6 % and 14.5 %, respectively, and the impact strength increased from 13.9 KJ/m2 to 43.1 KJ/m2. The excellent toughness enhancement comes from the fact that the structure of MDV itself can preferentially consume and dissipate energy when counteracting external impacts. In addition, MDV/EP also has excellent flame retardant properties, showing good self-extinguishing capability off fire in tests. Compared with pure EP, the total heat release (THR) and peak heat release rate (PHRR) of 7-MDV/EP composites were reduced by 45.3 % and 64.5 %, respectively. Mechanistic analyzes showed that the segregation of the condensed phase and the gas-phase flame-retardant effect both originated from the P/N synergistic effect, which was the source of the excellent flame-retardant effect of MDV/EP.

Fabrication of dense Cf/SiC ceramic matrix composites using 3D printing and PIP with short carbon fibre as a toughening material

ABSTRACT To achieve weight reduction, toughness enhancement, and the fabrication of complex structures in SiC composites, a combination of SLS and PIP processes was used. Silicon carbide powder served as the matrix material, while short carbon fibres were used for toughening, resulting in dense Cf/SiC ceramic matrix composites. The effects of varying carbon fibre sizes and contents on the microstructure and mechanical properties of Cf/SiC composites were examined. Results indicated that adding 8% carbon fibre increased the fracture toughness of Cf/SiC composites by 33.33%. Further increases in carbon fibre content showed minimal effects on fracture toughness. Based on experimental results and finite element simulations, toughening mechanisms, including fibre pull-out, fibre debonding, and crack deflection, were further elucidated. Consequently, Cf/SiC composites with complex structures, such as turbine specimens and lattice structures, were successfully fabricated.

Extending interfacial toughness and thermal cycling lifetime of thermal barrier coatings via interfacial 3D pattern

AbstractWeak interface bonding is a critical factor that compromises the long‐term durability of the thermal barrier coatings. To mitigate this, we introduce an innovative interface‐strengthening approach by integrating four types of 3D patterns at the top coat/bond coat interface using the laser cladding technique. Tensile tests demonstrate a significant enhancement in interfacial bonding strength, increasing by over 139.2% from 21.6 ± 1.7 MPa for conventional thermal barrier coatings without patterns to 51.67 MPa for the patterned coatings. Moreover, the thermal cycling lifetime has been extended by 41%, from 1026 ± 25 cycles for the conventional coating to 1936 ± 164 cycles for the patterned coating. This enhancement in interfacial toughness and thermal cycling lifetime is primarily because of the blocking and deflection effects of 3D patterns on interfacial crack propagation. Besides, the geometric parameters of the patterns play a crucial role in determining the failure behavior of the thermal barrier coatings. This strategy presents a practical solution for the development of durable thermal barrier coatings and provides the valuable insights for the optimization of other heterogeneous interfaces.

An investigation on workability and strength on compression of GPC with addition of different aspect ratio glass fibers

The heating of limestone and other materials to high temperatures to produce Ordinary Portland cement (OPC), a key component in concrete releases of carbon dioxide CO2 which makes the construction industry a notable contributor to greenhouse gas emissions. The search for more sustainable alternatives has led to the exploration of alkali-activated materials as a replacement for OPC. Alkali-activated materials are a class of binders that can be used in concrete production without the need for traditional cement. These materials often include industrial by-products such as fly ash, GGBFS (sometimes also called GGBS) (Ground Granulated Blast Furnace Slag), and other waste materials. The development and adoption of alkali-activated materials represent a promising avenue for reducing the environmental impact of the construction industry. On-going research and collaboration are crucial to addressing technical challenges and promoting the widespread use of these alternative binders. The exploration and utilization of alternative materials such as GGBFS, fly ash, and geopolymer concrete play a crucial role in mitigating the environmental impact of the construction industry, particularly in terms of reducing CO2 emissions and utilizing industrial by-products effectively. A good concrete mix is obtained from combination of different size of aggregates. Addition of fibers plays a crucial role in enhancing the tensile strength of concrete. Similar synergy of addition of different aspect ratio of optimum dosages fibers as of different size of aggregates may improve strength and ductility of concrete. Short fibres can stop the propagation of micro-cracks with enhancement of toughness, and long fibres can stop the propagation of macro-cracks. From the aforementioned perspective, it is preferable to add the same volume of fibre with a different aspect ratio to improve the pre- and post-cracking performance of concrete. It also aids in boosting maximal strength.This study aims in preparing geopolymer concrete with graded glass fibres in order to investigate improvement the strength in compression and workability.

Fabrication and Enhanced Flexibility of Starch-Based Cross-Linked Films.

The development of sustainable materials has driven significant interest in starch as a renewable and biodegradable polymer. However, the inherent brittleness, hydrophilicity, and lack of thermoplasticity of native starch limit its application in material science. This study addresses the limitations of native starch by converting it to dialdehyde starch (DAS) and cross-linking with polyether diamines via imine bonds. The effects of Jeffamine molecular weights (D-2000, D-400, and D-230) and mole ratios on the mechanical, thermal, and structural properties of starch-based films were examined. The cross-linked DAS/Js films exhibited significant enhancements in flexibility and toughness. Specifically, DAS/J2000 at a 0.03 mol ratio achieved a tensile strength of 62.9 MPa. In comparison, DAS/J400 at a 0.5 mol ratio demonstrated 126.2% elongation at break, indicating the balance between cross-linking density and chain mobility. X-ray diffraction (XRD) analysis revealed reduced crystallinity and tighter molecular packing with increased cross-linking. Dynamic mechanical analysis (DMA) indicated a decrease in Tg with an increasing mole ratio, reflecting enhanced molecular mobility. The results underscore the potential of optimized cross-linking conditions to produce starch-based films with properties that contribute to developing sustainable biopolymer materials.

Self-healing effect on the impact-resistance of hybrid stitch toughening CFRP composites: Experimental and numerical study

The self-healing effect on the impact-resistance has been investigated for hybrid stitch toughening CFRP composites using multiscale modeling. The stitches made of the healing agent, poly ethylene-co-methacrylic acid (EMAA), facilitate the repair of delamination damages via a self-healing process. The other stitches, fabricated from carbon fiber, contribute to the enhancement of interlaminar toughness. Considering the local structural features adjacent to the stitches, an equivalent fiber-embedded laminate (EFEL) cell is established to characterize the mesoscale behavior. A modified constitutive model is developed to accurately describe the deformation modes of the EFEL cell. Subsequently, a macroscale model is constructed by directly extending the EFEL cells. The self-healing of the impact-resistance is numerically explored through multiple low-velocity impact (LVI) tests. The proposed modeling approach enables a prediction error less than 8.4% and the computation time of approximately 17.3 h (1036 min), demonstrating the high accuracy and efficiency. After the self-healing process, the peak impact forces of the LVI specimens increase, while decreases in absorbed energy are observed. Moreover, the healed specimens exhibit fewer damaged elements and a smoother damaged surface compared with the unhealed ones. It demonstrates that the EMAA healing agent possesses the capability to improve the impact-resistance of hybrid stitch toughening CFRP composites.

Microstructure and property alterations and toughening mechanism of cast TC4 alloy by solid state treatment with low-density DC electric field

In this paper, the impact of low-density DC electric field treatment (LDCT) on the microstructure and mechanical properties of cast TC4 titanium alloy (CTC4) was investigated. The findings indicate that the driving force for the current provided by LDCT enhances the texture of CTC4. When the current density is sufficiently high, the induced recrystallization effect weakens the texture, leading to an isotropic state. The polygonization of grain boundaries in the LDCT state CTC4 has been identified, along with the emergence of a secondary α phase due to recrystallization. Additionally, this study highlights the phenomenon of preferential nucleation and growth occurring at the grain boundaries. LDCT induces a grain refinement effect in the CTC4 material, whereby the average grain size of the LDCT3 sample decreases from 31.05 μm in the untreated sample to 28.93 μm. The observed reduction in dislocation density in the LDCT states is believed to result from the diffusion of impurity atoms and vacancies. The observation of dislocation plugging at the inner grain boundary of the LDCT3 sample suggests that the electron wind promotes dislocation slip toward the grain boundary. Furthermore, the simultaneous enhancement of strength and toughness in the LDCT state of the CTC4 alloy has been achieved. The LDCT3 sample demonstrates superior performance, exhibiting noteworthy increases of 7.7%, 22.0%, and 10.9% in tensile strength, elongation, and fracture energy, respectively, compared to the untreated sample. The significant role of non-thermal effects in LDCT and the mechanism of atomic diffusion induced by this effect are discussed. The origins of dislocation motion and phase transition are elucidated from the perspective of atomic diffusion.

Competitive reaction behavior and formation mechanism of reactively spark plasma sintered TiB2-TiC composite ceramics with tunable compositions

TiB2-TiC composite ceramics with tunable compositions (70 wt% < TiB2 < 100 wt%) were fabricated by the reactive spark plasma sintering (SPS) technique using Ti, B4C, and TiB2 as raw materials. The effects of sintering temperature and holding time on the densification, electrical, and mechanical properties of composite ceramics were investigated. Additionally, the competitive reaction behavior of the Ti-B4C-TiB2 ternary system and the formation mechanism of TiB2-TiC composite ceramics were systematically highlighted, respectively. The TiB2-TiC composite ceramics successfully obtained 98.9 % relative density, 8.0 ± 0.3 μΩ∙cm electrical resistivity, and 6.8 ± 0.2 MPa∙m1/2 fracture toughness at the sintering temperature of 1800 °C, pressure of 35 MPa, and holding time of 5 min. As the sintering temperature was increased in the Ti-B4C-TiB2 ternary system, competitive reactions occurred not only between Ti and B4C as well as between Ti and TiB2 reactants, but also between B4C and in-situ generated TiC, accompanied by the formation of TiB and free carbon in the system. The enhancement of fracture toughness could be attributed to the generation of TiB. Meanwhile, the establishment of a conductive network, which was promoted by the presence of free carbon, resulting in significant reduction in electrical resistivity. However, as a consequence of the deformation and dissociation of the free carbon, a reduction in the load-bearing cross-section resulted in a corresponding reduction in the flexural strength of the composite ceramic.

Effects of Different Austenitizing Times on the Microstructure and Properties of Cr‐Ni‐Mo‐V Series High‐Strength Steels

Herein, the effects of varying austenitizing times on the microstructure and mechanical properties of Cr‐Ni‐Mo‐V series high‐strength steel are investigated, discussing the mechanisms that enhance strength and toughness. By controlling the austenitizing duration, the microstructure during subsequent heat treatments is improved, leading to enhanced overall mechanical properties. The experimental steel undergoes treatments at different austenitizing times, and the microstructure is characterized using optical microscopy, energy‐dispersive spectroscopy, field emission scanning electron microscopy, and X‐ray diffraction. Mechanical properties are assessed through tensile testing, impact testing, and microhardness measurements. The results indicate that, when comparing an austenitizing time of 1 to 1 h and 15 min, the ultimate tensile strength decreases by 10%, microhardness reduces by 78.2 HV, elongation increases by 1.39 times, and toughness improves by 80%. The enhancement in toughness is primarily attributed to the synergistic effect of tempered martensite and bainite within the microstructure. Fracture morphology analysis reveals that variations in austenitizing time affect carbide distribution, accelerate carbide dissolution, decrease the crack growth zone, and enhance toughness. This study provides valuable insights for designing Cr‐Ni‐Mo‐V series high‐strength steels with optimal strength‐toughness synergies.