Superior Comprehensive Mechanical Properties Research Articles

Achieving enhanced strength-ductility synergy in Mg-6Zn-1Mn alloy by introducing deformable Ti particles

The Mg-based composites have been considered as an efficacious method to enhance the strength of Mg matrix. How to concurrently augment the strength and ductility of the Mg matrix composites remains a pivotal concern. In this work, Mg-6Zn-1Mn (ZM61) composites, reinforced with varying contents of deformable Ti particles, were successfully manufactured employing a method of semi-solid stirring coupled with ultrasonic treatment, subsequently followed by hot extrusion. The outcomes demonstrated marked enhancement in strength and ductility of composites. The interfacial reaction between Ti and Mg matrix minimized the precipitation of MgZn2 and α-Mn in the matrix. Ti particles boosted the dynamic recrystallization (DRX) behavior effectively. The TEM characterizations revealed that MgZn2 nucleated on the Ti particle and Mn diffusion layer was formed in the Ti particle. The 2Ti/ZM61 composite achieved superior comprehensive mechanical properties, marked by the YS of 288 MPa, the UTS of 383 MPa, and the elongation to 22.1%. The augmented strength was primarily owning to the grain boundary strengthening and the mismatch coefficient of thermal expansion (CTE) between Ti and Mg. The synergistic deformation of Ti particles was the main reason of improving the ductility.

In-situ formed TiCx reinforced Ti composites derived from polyzirconocarbosilane precursor: Synthesis, characterization and mechanical properties

Discontinuously reinforced titanium (Ti) matrix composites (DRTMCs) strengthened by in-situ TiCx particles are synthesized via pyrolysis of polyzirconocarbosilane (PZCS) and pressureless sintering. The Ti matrix reacts with the pyrolysis product of PZCS to form TiCx particles, which effectively refine the α-Ti grains and create a clean, well-bonded semi-coherent interface. A notable orientation relationship is observed between the TiCx and α-Ti phases: (111)TiCx||(101¯1)Ti and [1¯10]TiCx||[12¯10]Ti. The Ti-2PZCS composite demonstrates a significant reduction in average grain size, from 101.5 μm in pure Ti to 39.49 μm, coupled with superior comprehensive mechanical properties: an ultimate tensile strength of 710 MPa, a yield strength of 588 MPa, and an elongation of 9.5 %. The enhanced strength of Ti/PZCS composites is mainly due to grain refinement, solid solution strengthening, and load transfer mechanisms. This study introduces a novel approach for fabricating high-performance Ti composites, highlighting the potential for advanced material applications.

Mechanical properties and thermal shock resistance of TiB2‒B4C composite ceramic tool materials at microscopic scale

AbstractA finite model incorporating microstructure was developed to investigate the thermal shock resistance of TiB2‒B4C composite ceramic cutting tool materials. Numerical simulations were conducted to analyze changes in the transient temperature field and thermal stress field during the thermal shock process. TiB2‒B4C composite ceramic tool materials were fabricated using discharge plasma sintering technology. With different B4C contents, different sintering temperatures and holding times as study variables, optimization of the sintering process parameters and ceramic material components was achieved through testing the mechanical and microscopic morphology of the ceramics. Thermal shock water quenching experiments were performed, and the strength‐decay method was employed to assess the thermal shock resistance of TiB2‒B4C ceramics. The findings indicate that the optimal sintering conditions are temperature of 1700°C and holding time of 5 min. The TiB2‒B4C ceramic material containing 20 vol% B4C exhibits superior comprehensive mechanical properties and thermal shock resistance, and its relative density, fracture toughness, hardness, and flexural strength were 99.3%, 6.8 MPa m1/2, 22.8 GPa, and 598 MPa, respectively. The critical thermal shock temperature difference falls within the range of 400°C‒500°C.

Effect of Phenolic Resin Coating Thickness on Mechanical Properties and Corrosion Resistance of Metal Materials

In the realm of petrochemical and other industries, metal materials face threats such as impact and high-temperature electrochemical corrosion. Consequently, there has been significant attention towards organic coatings that effectively attenuate impact forces while simultaneously providing a barrier against corrosive agents. The thermosetting phenolic resin 2130, known for the facile curing process, exceptional thermal stability, water resistance, corrosion resistance, and superior mechanical properties post-curing, finds extensive applications in the field of coatings. To address the challenge of depositing a complete and uniform resin coating on complex workpieces, coatings with varying thicknesses on the surface of 304 stainless steel were deposited via rotary evaporation combined with long-term low-temperature drying. The relationship between coating thickness and mechanical properties, as well as corrosion resistance, was investigated and analyzed through a comprehensive approach involving mechanical testing, electrochemical analysis, and long-term service weight loss assessment. The results demonstrated that the coatings deposited on the metal surface exhibited excellent integrity and compactness. Moreover, an increase in coating thickness led to a significant reduction in material corrosion rate. The coatings exhibited excellent substrate adhesion and flexibility, thereby providing effective protection against impact on the metal substrate. The relationship between the thickness of the coating and the surface roughness was evident, while the flexibility of the coating first increased and then decreased with the increase of coating thickness. When the coating thickness was 7 μm, the maximum surface roughness of the coating measured 0.44 μm. Under these conditions, the impact toughness of the coating reached the peak, exhibiting a ductile fracture mode and showcasing superior comprehensive mechanical properties. The findings of this study will offer theoretical support for the investigation and formulation of resin coatings in subsequent industrial production.

Seeding ductile nanophase in ceramic grains.

Transgranular brittle fracture is the dominant failure mode of brittle materials, including ceramics and ceramic matrix composites. However, strengthening these materials without sacrificing their toughness has been a big challenge. In this study, an innovative approach is proposed to achieve coordinated strengthening and toughening of ceramics-based composites by introducing specific ductile coherent nanoparticles into ceramic grains. As an example, the WC-Co cemented tungsten carbides were used to demonstrate how this brittle material can achieve ultrahigh strength without losing toughness by seeding metallic nanoparticles inside WC grains. The mechanisms for inducing the formation and modulating the amount, size, and distribution of such nanophase within the ceramic grains were disclosed. The fraction of transgranular ruptures of the brittle ceramic phase was reduced significantly due to the presence of the ductile coherent in-grain nanoparticles. Both the strength and strain limit of the cemented carbides were remarkably increased compared to their counterparts reported in the literature. The coordinated strengthening and toughening strategy proposed in this work is applicable to a broad range of ceramics and ceramic matrix composites to obtain superior comprehensive mechanical properties.

Enzyme-Mineralized PVASA Hydrogels with Combined Toughness and Strength for Bone Tissue Engineering.

Enzymatic mineralization is an advanced mineralization method that is often used to enhance the stiffness and strength of hydrogels, but often accompanied by brittle behavior. Moreover, the hydrogel systems with dense networks currently used for enzymatic mineralization are not ideal materials for bone repair applications. To address these issues, two usual bone repair hydrogels, poly(vinyl alcohol) (PVA) and sodium alginate (SA), were selected to form a double-network structure through repeated freeze-thawing and ionic cross-linking, followed by enzyme mineralization. The results demonstrated that both enzymatic mineralization and double-network structure improved the mechanical and biological properties and even exhibited synergistic effects. The mineralized PVASA hydrogels exhibited superior comprehensive mechanical properties, with a Young's modulus of 1.03 MPa, a storage modulus of 103 kPa, and an equilibrium swelling ratio of 132%. In particular, the PVASA hydrogel did not suffer toughness loss after mineralization, with a high toughness value of 1.86 MJ/m3. The prepared hydrogels also exhibited superior biocompatibility with a cell spreading area about 13 times that of mineralized PVA. It also effectively promoted cellular osteogenic differentiation in vitro and further promoted the formation of new bone in the femur defect region in vivo. Overall, the enzyme-mineralized PVASA hydrogel demonstrated combined strength and toughness and great potential for bone tissue engineering applications.

Ti-PEEK interpenetrating phase composites with minimal surface for property enhancement of orthopedic implants

Bioinspired interpenetrating phase composites (IPCs) present a promising strategy for augmenting the mechanical properties of materials, thereby synergistically enhancing the strength and fracture toughness of orthopedic implants. In this study, Ti6Al4V-PEEK IPCs were fabricated by pressing molten PEEK into additively manufactured Ti6Al4V scaffolds designed using minimal surface structures. The mutual spatial interpenetration and strong binding between Ti and PEEK were confirmed through CT detection and SEM analyses, revealing the presence of continuous constituents within biomimetic architectures. Due to interpenetration promoting interaction and efficient stress transfer of the two phases, IPCs enhances toughness and energy absorption by over 291% and 309% respectively while maintaining bone-compatible elastic modulus and higher strength. The mechanisms underlying stress dispersion, crack propagation resistance, and prolonged stress plateau period of IPCs were investigated through the utilization of digital image correlation (DIC) and finite element simulation techniques. Among the various types of IPCs investigated, Gyroid IPCs exhibit superior comprehensive mechanical properties, thereby facilitating the development of customized IPCs aimed at ensuring long-term stability in orthopedic implantation scenarios.

Hot-work die steel with superior mechanical properties at room and high temperatures prepared via a combined approach of composition design and nanoparticle modification

Hot-work die steel with excellent strength and toughness can improve the precision of the die and prolong its service life. However, this is very difficult to achieve because of the opposing relationship between strength and plasticity. In this paper, we propose a combined approach of composition design and nanoparticle modification to overcome this difficulty. A novel hot-work die steel with reinforced trace nano-(TiC–TiB2) was fabricated using a traditional method. It had an improved microstructure, which consists of fine martensitic laths with high dislocation density, abundant small precipitates, and small and dispersed residual austenite. This expected microstructure improved the work hardening and uniform deformation ability of the steel, resulting in superior comprehensive mechanical properties. The yield strength and impact toughness of the novel hot-work die steel at room temperature were 1464 MPa and 597 J/cm2, respectively, increases of 121 MPa and 265 J/cm2, respectively, compared to the values for advanced and widely used traditional H13 steel. In particular, the impact toughness of the novel hot-work die steel at room temperature was approximately 42.5% and 33.0% higher than the impact toughness of H13 containing 0.01 and 0.02 wt% nanoparticles, respectively. Furthermore, the yield strength, ultimate tensile strength, and elongation of novel hot-work die steel at 500 °C were 1078 MPa,1103 MPa, and 40.4%, respectively, increases of 85 MPa, 86 MPa, and 4.2%, respectively, compared to values of the blank that was used in this work. This work shows new prospects for the development of hot-work die steel with excellent strength and toughness.

Microstructure, texture evolution and mechanical properties of a large-scale multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

A large-scale Mg-6.2Gd-3.7Y-0.9Zn-0.3Zr-0.3Ag (wt.%) magnesium component with the dimension of 480 × 250 × 160 mm3 was fabricated via direct-chill (DC) casting, homogenization and multidirectional forging (MDF). The evolution of the microstructure, texture and uniaxial tensile properties during MDF process were comprehensively investigated. 2.5%, 5.6% and 10.9% anisotropy were obtained in the MDF alloy subjected to 9, 18 and 27 passes, respectively. The MDF alloy subjected to 27 passes tensile along FD exhibits superior comprehensive mechanical properties, with a yield strength (TYS) of 292 MPa, ultimate tensile strength (UTS) of 384 MPa and elongation of 9.0%. Interdendritic Mg5(Gd, Y, Zn) phases dissolved after homogenization, with the precipitation of intragranular lamellar 14H long period stacking ordered (LPSO) phases from α-Mg matrix. During the MDF process, intragranular lamellar LPSO phases were initially kinked, suppressing dynamic recrystallization (DRX) behavior in the first 9 passes, and subsequently partially dissolved. Dynamic precipitation of Mg5(Gd, Y) and ultrafine LPSO phase were also induced by MDF. With the cumulative deformation of MDF, increased volume fraction of Mg5(Gd, Y) phases, enhanced texture and refined α-Mg grains are likely responsible for the improved mechanical properties via MDF. We also found that prismatic <a> slip is activated in the deformed grains with the c-axis around FD and multiple slip is activated in the other deformed grains during the MDF process. This paper provides a superior MDF processing route to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

Toughening Ceramic-Based Composites by Homogenizing the Lattice Strain at Phase Boundaries.

Ceramic-based composites generally have low fracture toughness, and toughening these materials without sacrificing their hardness has been a big challenge. This study presents an approach for toughening ceramic-based composites by modulating the strain partition and stress distribution in phase-boundary regions. A new concept of homogenizing the lattice strain to achieve high fracture toughness in ceramic-based composites is proposed based on the collective lattice shear of martensitic phase transformation. The strategy was demonstrated by ZrO2-containing WC-Co ceramic-metal composites as a prototype. The crystal planes along the WC/ZrO2 martensitic transforming phase boundaries exhibited significantly larger and uniform lattice strains compared with conventional dislocation pile-up phase boundaries with highly localized lattice strains. The homogeneous strain and stress distributions across interfaces enabled the composite to have simultaneously high fracture toughness and hardness. The "homogenizing the lattice strain" strategy proposed in this work is applicable to a broad range of ceramic-based composites to achieve superior comprehensive mechanical properties.

Development of Fe-Mn-Si-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large recovery strain by laser powder bed fusion

This work systematically studied the effect of volumetric energy density E on the densification, microstructures, tensile mechanical properties, and shape memory performance of a Fe-Mn-Si-Cr-Ni shape memory alloy (SMA) fabricated by laser powder bed fusion (L-PBF). An E of 90–265 J/mm3 is suggested to fabricate the Fe-Mn-Si-Cr-Ni SMA with minor metallurgical defects and a high relative density of above 99%. The increase in E can promote the formation of the primary γ austenite and the solid phase transformation from the primary δ ferrite to the γ austenite, which helps to achieve a nearly complete γ austenitic microstructure. The increase in E also contributes to fabricating the Fe-Mn-Si-Cr-Ni SMA with superior comprehensive mechanical properties and shape memory performance by L-PBF. The Fe-Mn-Si-Cr-Ni SMA with a combination of good ductility of around 30%, high yield strength of above 480 MPa, an ultrahigh ultimate tensile strength of above 1 GPa, and large recovery strain of about 6% was manufactured by L-PBF under a high E of 222–250 J/mm3. The good shape memory effect, excellent comprehensive mechanical properties, and low cost of Fe-Mn-Si-Cr-Ni SMAs, as well as the outstanding ability to fabricate complex structures of L-PBF technology, provide a solid foundation for the design and fabrication of novel intelligent structures.

Correlation between secondary γ′ and high-temperature tensile behavior of a powder metallurgy nickel-based superalloy EP962NP

A powder metallurgy nickel-based superalloy EP962NP was subjected to solid solution treated and cooled in four media (water, oil, air and furnace) followed by aging treatment to investigate the correlation between secondary γ′ (γs′) and tensile properties of the experimental alloy at 750 °C. Results show that the size of γs′ increases sharply with the decreasing cooling rate, and morphologies of γs′ depend on the cooling regime and present various characteristics including spherical, rod-shaped, cubic, etc. By implementing the heat treatment process of solid solution treatment (1210 °C/2 h, air cooling/AC) and two-step aging treatment (i.e., 870 °C/8 h, AC + 760 °C/16 h, AC), superior comprehensive mechanical properties can be obtained with ultimate tensile strength, yield strength and elongation of 1251 MPa, 1079 MPa and 13.3%, respectively, due to the high density of stacking faults. Interaction between γ′ and dislocations indicates that the deformation mechanism of the alloy exhibits stacking faults on (1‾11‾) [121] and microtwins, which depends on the size of γs′. The increasing size of γs′ precipitates drives a transition in the dominant deformation mechanism from stacking faults shearing to microtwinning.

Mechanism of enhanced ductility of Ti–6Al–4V alloy components deposited by pulsed plasma arc additive manufacturing with gradient-changed heat inputs

Titanium alloys deposited by high-energy-density beam additive manufacturing (AM) technologies possess higher strength and lower ductility in the as-built condition. To improve the ductility of the as-built deposited components, this study employed the pulsed plasma arc AM（PPAM） technology with a gradient-changed heat input strategy to study the effect of microstructure evolution on the mechanical properties. The results indicate that the grain evolution in the height direction of the thin-walled Ti–6Al–4V alloy components is affected by the pulse stirring and cooling gradient. These two factors lead to three modes of nucleation growth at the solid–liquid interface of the solidification front and prevents coarsening microstructure growth along a single direction. After being deposited by multiple thermal cycles under the high pulse frequency process, the deposited microstructure decomposed to form a dispersed nano secondary α phase, which benefits the growth along the close-packed plane {10 1‾ 1}at the platelet colony α or the grain boundary direction. Consequently, the average elongation rate (A) of 12.7 ± 1% and area reduction rate (Z) of 56.5 ± 2% were higher than the forging standard, and the average tensile properties were also commensurate with the forging strength. This result is because the secondary α phase precipitates and grows along the same orientation to form a fine platelet α phase, which is advantageous for being slipped during the stretching process and enhances the plasticity. Thus, the thin-walled components of the as-built specimens fabricated via PPAM exhibit superior comprehensive mechanical properties.

Superior Comprehensive Mechanical Properties of a Low-Carbon Medium Manganese Steel for Replacing AISI 4330 Steel in the Oil and Gas Industry.

A low-carbon medium manganese steel (0.12C-3.13Mn) containing Cr, Ni, Mo, V, and Cu elements was designed to replace the AISI 4330 steel applied in the oil and gas industry. The mechanical properties, microstructures, and fatigue crack growth rate were comparatively analyzed using uniaxial tension tests, microstructure characterization, and compact tension with fatigue crack growth characterization. The results showed that the ductility and -40 °C impact energy of 0.12C-3.13Mn steel were better than AISI 4330 steel (from 115 J to 179 J), while the yield strength of 957 MPa of the former was lower than the latter of 1060 MPa after being subjected to the same tempering process. The microstructure of 0.12C-3.13Mn steel was composed of a mixture of tempered martensite, reversed austenite, and nanosized precipitation particles, while the microstructure of S4330 steel contained ferrite and large-size Fe3C with lath and near-spherical morphologies. Compared to Cr-rich Fe3C, (V, Mo)C and Cu-rich particles have smaller sizes and, thus, provide more strengthening increment, leading to a higher yield ratio. The impressive fatigue-resistance property was obtained in 0.12C-3.13Mn steel because the threshold value was 5.23 MPa*m1/2 compared to the value of 4.88 MPa*m1/2 for S4330 steel. Even if the fatigue crack grew, the stress intensity factor range of 0.12C-3.13Mn steel was obviously wider than that of AISI 4330 steel due to the presence of reversed austenite and secondary cracks. Overall, the AISI 4330 steel could be replaced with the designed 0.12C-3.13Mn steel due to the similar strength and better ductility, low-temperature toughness, and fatigue-resistance property.

Exceptional strength-ductility synergy of additively manufactured CoCrNi medium-entropy alloy achieved by lattice defects in heterogeneous microstructures

• Giant strengthening in SLMed CoCrNi alloys by subsequent deformation and annealing. • CoCrNi alloy delivers yield strength of 1161.6 MPa and strain of 31.5%. • The refined hierarchical microstructure and lattice defects result in high strength. The selective laser melting (SLM) with subsequent cold rolling and annealing is used to produce high-density lattice defects and grain refinement in the CoCrNi medium-entropy alloys (MEAs). The superior comprehensive mechanical properties have been achieved in the as-SLMed CoCrNi alloy after rolling and annealing. The as-SLMed alloys delivered the yield strength of 693.4 MPa, the ultimate tensile strength of 912.7 MPa and the fracture strain of 54.4%. After rolling with 70% reduction in thickness and annealing at 700 °C for 2 h. the yield strength, ultimate tensile strength and fracture strain reached 1161.6 MPa, 1390.8 MPa and 31.5%, respectively. The exceptional strength-ductility synergy is mainly attributed to the refined hierarchical microstructures with coarsening grains at a level of 30 µm and ultrafine grains at a level of 1 µm, and the heritage of dislocation-formed sub-grains and other lattice defects. This investigation demonstrates that the SLM with subsequent rolling and annealing is beneficial to fabricate high strength and ductile MEAs with single face-centered cubic (fcc) structure.

Towards ultrastrong and ductile medium-entropy alloy through dual-phase ultrafine-grained architecture

• Novel V 0.5 Cr 0.5 CoNi medium-entropy alloy with fully-recrystallized dual-phase UFG architecture. • Formation of local chemical ordered structure in HCP solid solution and the significant strengthening effects. • Ultrahigh yield strength of 1476 MPa and promising uniform elongation of 13.2% at room temperature. Advanced materials with superior comprehensive mechanical properties are strongly desired, but it has long been a challenge to achieve high ductility in high-strength materials. Here, we proposed a new V 0.5 Cr 0.5 CoNi medium-entropy alloy (MEA) with a face-centered cubic/hexagonal close-packed (FCC/HCP) dual-phase ultrafine-grained (UFG) architecture containing stacking faults (SFs) and local chemical order (LCO) in HCP solid solution, to obtain an ultrahigh yield strength of 1476 MPa and uniform elongation of 13.2% at ambient temperature. The ultrahigh yield strength originates mainly from fine grain strengthening of the UFG FCC matrix and HCP second-phase strengthening assisted by the SFs and LCO inside, whereas the large ductility correlates to the superior ability of the UFG FCC matrix to storage dislocations and the function of deformation-induced SFs in the vicinity of the FCC/HCP boundary to eliminate the stress concentration. This work provides new guidance by engineering novel composition and stable UFG structure for upgrading the mechanical properties of metallic materials.

Effect of VC addition on the microstructure and properties of TiC steel-bonded carbides fabricated by two-step sintering

The effect of VC addition on microstructure, mechanical properties and high-temperature oxidation behavior of the TiC steel-bonded carbides, fabricated by two-step sintering, were examined by SEM, EDS, and XRD. The results show that an appropriate amount of VC enables the TiC steel-bonded carbide to further refine the hard phase particles while maintaining high density. When the VC addition amount is not higher than 0.8 wt%, the hard phase particles are gradually refined with the increase of VC content. The added VC is mainly distributed in the rim phase around the hard phase particles, which inhibits the dissolution and precipitation of TiC and thus refines the grains. When the VC addition amount reaches 1.2 wt%, the excess VC raises the possibility of particle agglomeration or segregation, which will coarsen the rim phase and degrade the mechanical properties. Overall, TiC steel-bonded carbides with 0.8 wt% VC possesses superior comprehensive mechanical properties. Moreover, when TiC steel-bonded carbides are oxidized at a constant temperature of 750 °C, their high-temperature oxidation behavior follows a parabolic law. The oxidation rate is mainly controlled by the surface chemical reaction rate in the early stage and the oxygen ion diffusion rate in the later stage.

Spark plasma sintering of WC-VC0.5 composites with exceptional mechanical properties and high-temperature performance

WC-based composites, especially WC-Co, are generally considered representative of cermets with widespread commercial applications. The remarkable toughening enhancement is achieved in WC-Co cermets, however, the incorporation of metallic binders invariably results in a serious deterioration of both hardness and thermal stability. Here we synthesized WC-VC0.5 composites with exceptional combination of high hardness and fracture toughness and high-temperature hardness. Conspicuously, the composite of WC with 5 wt.% VC0.5 sintered at 1750 °C shows superior comprehensive mechanical properties of high microhardness of 26.2 ± 0.5 GPa and toughness of 9.2 ± 0.2 MPa·m1/2. WC-VC0.5 composites possess excellent high-temperature hardness, and the hardness of WC-5 wt.% VC0.5 at 700 °C is still over 20 GPa. These excellent properties are attributed to high densification in addition to high-dose stacking faults caused by vacancy defects and twinned structure. Our study may offer a promising pathway towards the design and synthesis of next-generation advanced composites for applications in demanding industrial environments, especially high-temperature applications.

Mechanical Behavior of Single and Bundled Defect-Free Carbon Nanotubes

ConspectusSuperstrong materials can be utilized in many fields such as bulletproof vests, airframes, suspension bridges, flywheel energy storage, etc. As one of the strongest materials, carbon nanotubes (CNTs) can potentially be used to fabricate superstrong fibers. However, the tensile strength of CNTs is impaired a lot by defects, and the CNT fibers prepared so far have strengths much lower than that of a single CNT, showing a “size effect”. The conventional study of solid mechanics is usually based on the assumption that materials contain defects. Defect-free ultralong CNTs can hopefully help us avoid the “size effect” of nanomaterials and produce superstrong CNT fibers. They would also provide a system for the study of the mechanical behavior of ideal solids with a nonlocalized “quantum stress singularity”.In this Account, we discuss our recent studies on the mechanical behavior of defect-free single CNTs and CNT bundles. First, we introduce the defect-free structure of ultralong CNTs, which is one type of ideal solid. Second, we review the investigation of the static tensile properties and dynamic fatigue resistance and their temperature-dependence of single centimeters long defect-free CNTs. The results showed that defect-free CNTs have superior comprehensive mechanical properties, including superstrength, -toughness, and -durability. Different from traditional materials, the fatigue lifetime and fracture of CNTs are dominated by the first single-bond-sized defect (quantum stress singularity), showing “superbrittleness”. Third, by using a gas flow focusing in situ synthesis method as well as a synchronous tightening and relaxing strengthening strategy, we successfully fabricated CNT bundles with tensile strengths approaching that of single CNTs and showed that the “size effect” can be avoided. In addition, the advantages and promising future of using CNTs in flywheel energy storage are discussed. Finally, we provide our perspectives on the challenges and future directions in this field.

Investigation on in situ silica dispersed in natural rubber latex matrix combined with spray sputtering technology

Abstract In this study, different processes are performed for the preparation of natural rubber latex (NRL)/silica composites. A novel approach is to use spray sputtering technology combined with in situ method to improve the dispersion of silica in rubber latex matrix and further improve the properties of vulcanizates. Results show that in situ silica in rubber matrix prepared from NH4Cl and Na2SiO3 has better Payen effect than other processes. Meanwhile, when the in situ silica reached 10 phr in the rubber matrix, the dosage can suitably match the dispersion capacity of the spray sputtering process with superior comprehensive mechanical properties. Compared with the traditional precipitation method, the tensile strength and tear strength of the silica/NR composites prepared by spray sputtering technology combined with in situ method were increased by 34.7% and 19.7%.