Super-high Strength Research Articles

The influences of functionalized carbon nanotubes as lubricating additives: Length and diameter

The super high strength, ductility and one-dimensional system of multi-walled carbon nanotubes (MWCNTs) make them become ideal additives for liquid lubricants. Although the MWCNTs have been added in kinds of lubricants, the influences of the length and diameter of the MWCNTs have not been studied systemically when they are used as lubricant additives. In this study, a series of MWCNTs with different diameter and length are modified by oxygen functional group and long-chain alkyl, and applied as additives of water and liquid paraffin (LP) respectively to investigate how the length and diameter of the MWCNTs influence their tribological properties. The results indicate that the short length MWCNTs samples showed better tribological properties than the long length MWCNTs samples, and the middle-diameter (10–20 nm) MWCNTs sample presented the best antiwear performance either in water or in LP. The established mechanisms are that the appropriate diameter (10–20 nm) and length (0.5–2 μm) make the MWCNTs-5 easier to enter the clearance of the friction pairs, play the role of rolling bearing between friction pairs, and fill in the cracks to mend surface damage of the friction pairs.

Thermo-Mechanical Treated High Strength AA-7xxx Aluminium Alloy by Cold and Cryo-Rolling Study their Mechanical Properties Corrosion and Microstructure Correlation

Thermo-mechanical treatment, in particular, cryo-rolling is a unique technique to produce super high strength AA-7xxx aluminium alloys with ultra-fine grained structure. In order to conduct the rolling at room temperature and cryo-temperature (liquid N2 (-190°C)), the AA-7xxx alloy ingot was rolled from 6mm to 1mm with 85% reduction in thickness. Optical microscopy, XRD, electron microscopy, hardness and tensile testing were conducted on the rolled alloy for understanding the phase changes and evaluating the mechanical properties. The alloy rolled at liquid nitrogen (LN2) exhibits very high strength with reasonable ductility. Corrosion behaviour of AA-7xxx series aluminium alloy various conditions in NaCl (3.5%) solution were investigated. Cold rolled and cryo rolled alloy exhibits better corrosion resistance than that of cast.

Investigation of characteristic and evolution of fine-grained bainitic microstructure in the coarse-grained heat-affected zone of super-high strength steel for offshore structure

E690 steel is a novel developed super-high strength steel for offshore structure. The microstructure-property relationship in the coarse-grained heat-affected zone of E690 steel subjected to high heat input welding with rapid cooling are studied, and the evolution of fine-grained bainitic microstructure is in-situly and crystallographically characterized. The results reveal that the fine-grained bainitic microstructure with abundant high angle grain boundaries is obtained in the coarse-grained heat-affected zone, attributing to rapid cooling. The formation of fine-grained bainite is attributed to extensive impingements and intersections of bainite sheaves forming via both primary nucleation and sympathetic nucleation. Abundant of high angle grain boundaries exist between the sheaves of bainite. The fine-grained bainitic microstructure with abundant of high angle grain boundaries in the coarse-grained heat-affected zone of this super-high strength steel contributes to excellent low temperature impact toughness.

Healable and Mechanically Super-Strong Polymeric Composites Derived from Hydrogen-Bonded Polymeric Complexes.

It is challenging to fabricate mechanically super-strong polymer composites with excellent healing capacity because of the significantly limited mobility of polymer chains. The fabrication of mechanically super-strong polymer composites with excellent healing capacity by complexing polyacrylic acid (PAA) with polyvinylpyrrolidone (PVPON) in aqueous solution followed by molding into desired shapes is presented. The coiled PVPON can complex with PAA in water via hydrogen-bonding interactions to produce transparent PAA-PVPON composites homogenously dispersed with nanoparticles of PAA-PVPON complexes. As healable materials, the PAA-PVPON composite materials with a glass transition temperature of ≈107.9 °C exhibit a super-high mechanical strength, with a tensile strength of ≈81 MPa and a Young's modulus of ≈4.5 GPa. The PAA-PVPON composites are stable in water because of the hydrophobic interactions among pyrrolidone groups. The super-high mechanical strength of the PAA-PVPON composite materials originates from the highly dense hydrogen bonds between PAA and PVPON and the reinforcement of in situ formed PAA-PVPON nanoparticles. The reversibility of the relatively weak but dense hydrogen bonds enables convenient healing of the mechanically strong PAA-PVPON composite materials from physical damage to restore their original mechanical strength.

Facile Fabrication of Room-Temperature Self-Healing, Mechanically Robust, Highly Stretchable, and Tough Polymers Using Dual Dynamic Cross-Linked Polymer Complexes.

The development of polymeric materials with a combination of excellent mechanical performance and room-temperature self-healing property is still a huge challenge. Here, we report a facile method for the fabrication of dual dynamic cross-linked polymer complexes that simultaneously possess multiple remarkable mechanical properties and room-temperature self-healability by simply mixing polymers that have complementary interactions in solutions. Thanks to the synergistic effects of electrostatic and hydrogen-bonding interactions within their networks, the complexes obtained a superhigh tensile strength of 27.4 MPa and toughness of 110.0 MJ/m3 when compared with other polymers that can self-heal at room temperature. More importantly, the complexes can repair a physical cut in an ∼90% relative humid environment at room temperature with a high healing efficiency of ∼96% because of the dynamic nature of the noncovalent interactions. This method is a simple, low-cost, and widely applicable strategy for the large-scale fabrication of room-temperature self-healing materials that possess superior and controllable mechanical performances.

High thermal conductivity of chain-aligned bulk linear ultra-high molecular weight polyethylene

It is difficult for bulk polymers to be used in the thermal management field because of their low thermal conductivity (TC). Considering that there have been few studies on the enhancement of TC for bulk polymers, we, in this work, used linear ultrahigh molecular weight polyethylene (LUHMWPE), which has a reduced number of branching, rather than conventional UHMWPE to successfully produce a high TC bulk polymer via utilizing solid state extrusion (SSE) to obtain a highly oriented structure. The high orientation of polymer backbone chains parallel to the extrusion direction and the increased crystallinity were responsible for the greatly improved TC. The oriented bulk LUHMWPE's thermal conductivity reached 4.7 W/mK, approximately 13 times that of its compression-molded sample, is also higher than the conventional UHMWPE prepared by SSE (3.0 W/mK). Moreover, it is found that the final thermal conduction performance of bulk LUHMWPE had a positive correlation with the extrusion draw ratio. The result of scanning electron microscopy shows that a number of nanofiberlike structures were formed during SSE, accounting for the super high tensile strength (120.4 MPa) of the bulks. The enhanced thermal conduction performance and high tensile strength make neat LUHMWPE a highly potential candidate to be used in electronic packaging areas.

Super-high-strength and formable medium Mn steel manufactured by warm rolling process

In this paper, we demonstrate the design and manufacture of super-high strength medium Mn steel with good ductility, via the combination of warm rolling and V alloying. This new strategy could produce not only the extensive precipitation of fine VC particles in both ferrite and austenite but also the bimodal size distribution of retained austenite (RA) grains. A substantial increase of yield strength up to 650 MPa was achieved after the intercritical annealing of this V-alloyed medium Mn steel without deteriorating ductility; whereas the calculated precipitation strengthening using the classical Ashby–Orowan theory is no more than 400 MPa. Quantifying possible strengthening mechanisms revealed that dislocation strengthening should make an additional contribution because recovery in austenite could be strongly retarded by the nanosized precipitates. In this V-alloyed steel, the coarse RA grains firstly transformed to martensite during yielding at the much higher stress threshold, followed by a significant work hardening due to dislocations multiplication, twinning-induced-plasticity (TWIP) and transformation-induced-plasticity (TRIP) in the ultrafine RA grains. The best combination of strength and ductility included 1.5 GPa ultimate tensile strength and 28% total elongation. This was achieved due to the sustainable TRIP and TWIP effects in the later straining stage resulting from the ultrafine austenite grains, the latter were reversely transformed from the recrystallized ferrite grains.

An Al–7Si alloy/cast iron bimetallic composite with super-high shear strength

A new composite technology is presented consisting of the surface pretreatment of cast irons, the hot-dipping in a Zn–0.2wt.% Bi melt and the Al/Fe composite process. The shear strength of Al/Fe (Al–7Si/cast iron) bimetallic composites fabricated by the technology is up to 32MPa that is far more than the shear property obtained by composite technology reported in literatures. The super-high shear strength is mainly attributed to the formation of a peculiar concave–convex interface (CCI) structure. The addition of 0.2wt.% bismuth into the zinc melt can promote the formation of Zn-rich regions at the surface layer of cast irons, leading to the formation of Al–Fe phases at these Zn-rich regions. Reducing the amount of Al–Fe phases appearing in the ferrite–graphite interface in cast irons can benefit improving the shear property of Al/Fe bonding interface. Further analysis of the stress state confirms that the CCI can enhance the shear strength of Al/Fe bonding interface.

A super high-strength Mg-Gd-Y-Zn-Mn alloy fabricated by hot extrusion and strain aging

A super high-strength wrought Mg-12.6Gd-1.3Y-0.9Zn-0.5Mn (GWZ1311M, wt%) alloy fabricated by hot extrusion and strain aging is developed. The strain before aging including cold rolling or cold rolling plus stretching results in strong work hardening and promotes the precipitation of γ' phase and chain-like structures during subsequent aging. While the grain sizes and texture components in different aged samples do not show essential difference, the number densities of both γ' phase and chain-like structures are much higher in strain-aged samples than those in the aged sample without pre-deformation. The enhanced formation of γ' phase and chain-like structures are associated with the higher dislocation density imparted by the cold deformation before aging. As a result, the GWZ1311M alloy after strain aging at 200 °C achieves super high tensile yield strength of 475 ± 8 MPa (only applying cold rolling before aging) and 543 ± 1 MPa (applying cold rolling plus stretching before aging), respectively. In contrast, the yield strength of peak-aged GWZ1311M alloy is only 410 ± 6 MPa after conventional aging at 200 °C. It is proposed herein that hot extrusion and strain aging, especially applying cold rolling plus stretching before aging, is an effective approach for developing high-strength Mg alloys.

Overcoming the strength-conductivity trade-off dilemma in carbon nanotube/aluminum-copper fibers by diffusion interface and chemical reaction interface

The carbon nanotube fiber has not shown its advantage and been widely used in many applications due to low conductivity. Depositing a metallic layer on the carbon nanotube fiber surface became an effective method. However, the strength of the carbon nanotube fiber decreases with increasing conductivity and coating thickness. Here, we deposited nanocrystalline metal coating on carbon nanotube fibers by magnetron sputtering. The coating consists of an ultrathin Al transitional layer and a Cu layer. After annealing, the Al atoms and Cu atoms diffused into the carbon nanotube fiber to form diffuse interface and chemical reaction interface, leading to the sliding resistance increase and contact resistance decrease between carbon nanotubes. As a result, the new composite fiber with a 2 μm thick Cu layer can exhibit a superhigh effective strength of 996 MPa and electrical conductivity of 2.6 × 107 S/m. This structure achieves both conductivity and strength increasing simultaneously.

Preparation of non-magnetic and ductile Co-based bulk metallic glasses with high GFA and hardness

Co(Fe,Ni)-based bulk metallic glasses (BMGs) characterized with super-high hardness and strength are generally brittle and strong magnetic, significantly undercutting their momentous applications as coating materials. Here we report Co92-xNi2Ta6Bx (x = 29–35) non-magnetic BMGs with a combination of appropriate plasticity and GFA, as well as superhigh hardness and strength. BMG Rods with maximum diameters up to 2.5 mm were fabricated by copper mold casting method. All alloys exhibit superhigh compressive fracture strength of 5.21–5.63 GPa, high hardness of 1290–1410 HV and plasticity of 1.2–3.5%. Besides, the amorphization can effectively decrease the magnetization and all the alloys show non-magnetic properties at glassy state. The partial crystallization in the high B content glassy alloys will not significantly change the non-magnetic or poor-magnetic feature. It is also found that the increase of B content can substantially improve the thermal stability of the glassy alloys and inhibit the formation of strong magnetic phases. These Co-based alloys are promising candidates for the future application of spray coating materials.

Ultrastiff, Tough, and Healable Ionic-Hydrogen Bond Cross-Linked Hydrogels and Their Uses as Building Blocks To Construct Complex Hydrogel Structures.

We report the ultrastiff and tough poly(acrylamide- co-acrylic acid)/Na-alginate/Fe3+ (P(AM- co-AA)/Na-alginate/Fe3+) hydrogel via the formation of hybrid ionic-hydrogen bond cross-linking networks. The optimal P(AM- co-AA)/Na-alginate/Fe3+ hydrogel possessed super high elastic modulus (∼24.6 MPa), tensile strength (∼10.4 MPa), compression strength (∼44 MPa), and toughness (∼4800 J/m2). The P(AM- co-AA)/Na-alginate/Fe3+ hydrogel was highly stable and maintained its superior mechanical properties in 0.5-2 M NaCl solution, aqueous solution with pH ranging from 4 to 10. The ionic cross-linking networks of the P(AM- co-AA)/Na-alginate/Fe3+ hydrogels can be locally and selectively dissociated by treating with aqueous NaOH solution with pH of 13 for 1 min and reformed by locally adding the additional Fe3+ solutions, making the hydrogels healable and cohesive. The healed hydrogels from the cutting surfaces can bear a tensile strength of up to 7.1 MPa. Various complex hydrogel structures can be constructed by using the P(AM- co-AA)/Na-alginate/Fe3+ hydrogels as building blocks via the adhesion of as-prepared hydrogels.

Investigation of an <inline-formula> <tex-math notation="LaTeX">${X}$ </tex-math> </inline-formula>-Band Long Pulse High-Power High-Gain Coaxial Multibeam Relativistic Klystron Amplifier

Increasing the output power of the microwave is one of the most important development directions for high-power microwave (HPM) technology. However, when the output power is increased, the radio frequency breakdown would occur owing to superhigh electric field strength. This problem limits the power handling capability of a single-HPM generator, and this problem becomes more serious for high-frequency bands and long pulse. One solution to overcome this problem is coherent power combining, and coherent power combining can achieve an equivalent power of the order of mymargin TW. The relativistic klystron amplifier (RKA) is a promising candidate for coherent power combing owing to its character of controllable frequency and steady phase. However, the radiation power of RKA quickly decreases when the source is scaled up to higher frequencies such as ${X}$ -band, and moreover, the multigigawatts long pulse radiation from RKA at the ${X}$ -band has not yet been obtained experimentally. In this paper, we present investigations into an ${X}$ -band coaxial multibeam RKA, The power handling capability was increased by introducing 20 electron drift tubes and a four gaps extended interaction output cavity. The amplitude uniformity of the multiple electron beams was improved by optimized the anode and cathode configuration. Then, a radiation power of 2.2 GW with pulsewidth of 120 ns is generated experimentally; the working frequency and amplifier gain are 9.4GHz and 50 dB, respectively.

Super-High-Strength and Formable Medium Mn Steel Manufactured by Warm Rolling Process

In this paper, we demonstrate the design and manufacture of super-high strength medium Mn steel with good ductility, via the combination of warm rolling and V alloying. This new strategy produced not only the extensive precipitation of fine VC particles in both ferrite and austenite but also the bimodal size distribution of retained austenite (RA) grains. A substantial increase of yield strength up to 650 MPa was achieved after the intercritical annealing (IA) of this V-alloyed medium Mn steel without deteriorating ductility; whereas the calculated precipitation strengthening using the classical Ashby-Orowan theory is no more than 400 MPa. Quantifying possible strengthening mechanisms revealed that dislocation strengthening should make an additional contribution because recovery in austenite could be strongly retarded by the nanosized precipitates. In this V-alloyed steel, the coarse RA grains firstly transformed to martensite during yielding at the much higher stress threshold, followed by a significant work hardening during successive deformation due to dislocations multiplication, twinning-induced-plasticity (TWIP) and transformation-induced-plasticity (TRIP) in fine RA grains. The best achieved combination of tensile properties included 1.8 GPa ultimate tensile strength, 1.0 GPa yield strength and 18% total elongation.

Microstructure and Properties of a Novel Cu–Ni–Co–Si–Mg Alloy with Super-high Strength and Conductivity

The Cu–4.5Ni–1.2Co–1.0Si–0.15Mg alloy with super-high strength and high electrical conductivity was designed, and a two-step thermo-mechanical treatment was applied to improve the mechanical and electrical properties of the alloy. The microstructure and properties of the alloy were investigated by transmission electron microscope observation, tensile test, hardness and electrical conductivity measurements. The results show that the final alloy treated by two-step thermo-mechanical process has a hardness of 329 HV, a yield strength of 1086 MPa, an elongation of 3.6%, and an electrical conductivity of 30.1%IACS, respectively. The nanoscale β-Ni3Si and δ-(Co,Ni)2Si precipitates form during the thermo-mechanical process, and the addition of the Co could promote the precipitation of δ-(Co,Ni)2Si particles. The orientation relationship (OR) between Cu matrix and the precipitates is: (022)Cu//(011)β//(010)δ and [100]Cu//[100]β//[001]δ. Comparing with the directly aging treatment and one step thermo-mechanical treatment, precipitates that form during the two-step thermo-mechanical process are much smaller and distributed more densely, resulting in the better comprehensive properties of the alloy.

Biomimetic Supertough and Strong Biodegradable Polymeric Materials with Improved Thermal Properties and Excellent UV‐Blocking Performance

AbstractThe preparation of biodegradable polymeric materials with both great strength and toughness remains a huge challenge. The natural spider silk exhibits a combined super high tensile strength and high fracture toughness (150–190 J g−1), attributing to the hierarchically assembled nanophase separation and the densely organized sacrificial hydrogen bonds confined in the nanoscale granules. Herein, inspired by natural spider silk, a facile strategy is reported for the preparation of nanostructured biomimetic polymeric material by incorporating biomass‐derived lignosulfonic acid (LA) as interspersed nanoparticles into a biodegradable poly(vinyl alcohol) (PVA) matrix. The fabricated PVA/LA nanocomposite film exhibits the world's highest toughness of 172 (±5) J g−1 among the PVA materials, as well as a powerful tensile strength of 98.2 MPa and a large breaking strain of 282%. The outstanding performance is attributed to the strain‐induced scattering of LA nanoparticles in the PVA matrix and the strong intermolecular sacrificial hydrogen bonds confined in the interphase. Moreover, after introducing the easily available green biomass LA, the prepared biomimetic polymer films show excellent ultraviolet‐blocking performance and good thermal stability. As both PVA and LA are biodegradable, this work presents an innovative design strategy for fully biodegradable robust polymeric materials with integrated strength and toughness.

Micro‐/Nanohoneycomb Solid Oxide Electrolysis Cell Anodes with Ultralarge Current Tolerance

AbstractAs a clean, efficient, and promising energy conversion device, solid oxide electrolysis cell (SOEC), which can achieve transformation from electricity to chemical fuels, has captured worldwide attention. A novel biomimetic honeycomb SOEC anode with super low tortuosity factor (≈1), ground‐breaking porosity (≈75%), and high structural strength, has been successfully fabricated by freeze casting and infiltrating. This honeycomb anode demonstrates ultralow polarization resistance (0.0094 Ω cm2, lower than any existing anodes reported so far) and high durability for hours at a large current density of 2.0 A cm−2 at 800 °C. These unique advantages are derived from the effective release of oxygen through the yttria‐stabilized zirconia honeycomb skeletons, and the exposure of active areas along the inner pore of the honeycomb structure after infiltrating La0.6Sr0.4CoO3±δ. Such a honeycomb electrode combines high electrical, chemical, and thermal stability under high temperatures and large current densities, demonstrating the feasibility of biomimetic structures for use in large‐scale and highly efficient energy conversion systems.

Efficient and scalable synthesis of highly aligned and compact two-dimensional nanosheet films with record performances

It is crucial to align two-dimensional nanosheets to form a highly compact layered structure for many applications, such as electronics, optoelectronics, thermal management, energy storage, separation membranes, and composites. Here we show that continuous centrifugal casting is a universal, scalable and efficient method to produce highly aligned and compact two-dimensional nanosheets films with record performances. The synthesis mechanism, structure control and property dependence of alignment and compaction of the films are discussed. Significantly, 10-μm-thick graphene oxide films can be synthesized within 1 min, and scalable synthesis of meter-scale films is demonstrated. The reduced graphene oxide films show super-high strength (~660 MPa) and conductivity (~650 S cm−1). The reduced graphene oxide/carbon nanotube hybrid-film-based all-solid-state flexible supercapacitors exhibit ultrahigh volumetric capacitance (407 F cm−3) and energy density (~10 mWh cm−3) comparable to that of thin-film lithium batteries. We also demonstrate the production of highly anisotropic graphene nanocomposites as well as aligned, compact films and vertical heterostructures of various nanosheets.

A two-class rotation transmission nanobearing driven by gigahertz rotary nanomotor

For a vehicle, its speed can be adjusted via a transmission system. In this study, we propose a model of two-class rotation transmission nanosystem to adjust the input rotation via a gigahertz rotary nanomotor. To obtain an efficient rotation transmission system, carbon nanotubes, which have super-high in-shell strength but extremely low inter-shell friction, are adopted to build the coaxially rotary components. Besides 200 GHz motor, the other two components are the rotor1 in the class-1 nanobearing, and the rotor2 in the class-2 bearing, respectively. Considering both the chirality and radii differences of the rotary components, 27 types of transmission models are built and tested via molecular dynamic simulations. When the transmission ratio of the rotational frequency of the rotor2 and the input frequency is between 0.1 and 0.9, a successful transmission system is obtained. According to the rotation transmission ratios (RTRs) of both rotors in each model, some conclusions are drawn for potential design of such nanodevice. Besides, temperature can also influence the output rotation of the rotor2. It implies another way to adjust the output rotation from the same transmission system.

A novel high-strength Al-based nanocomposite reinforced with Ti-based metallic glass nanoparticles produced by powder metallurgy

A novel Al-based composite reinforced with Ti-based metallic glass (MG) nanoparticles was fabricated by powder metallurgy through mechanical alloying combined with hot extrusion. During the ball-milling process, MG microparticles were refined into nanosized particles through severe plastic deformation. Hot extrusion of the milled powders resulted in a dense and uniform dispersion of the metallic glass nanoparticles in the Al-7075 matrix. This unique homogeneous structure led to a significant enhancement of strength without adversely affecting the plasticity, thus developing super-high specific yield strength. The yield strength increased from 297 MPa for Al-7075 matrix to 530, 610, 880, and 1014 MPa for the composites milled for 10, 15, 30, and 50 h, respectively. A critical analysis of the different factors contributing to the strength of the composites was carried out. Grain refinement, Orowan strengthening, and dislocation–dislocation interactions were demonstrated to be the most important contributors to the enhanced strength of the nanocomposite.