Higher Interfacial Strength Research Articles

Microscopic impacts of ultrasonic vibration on interfacial strength of SiCp/Al composites

SiCp/Al composites are used in aerospace and deep-space exploration equipment because of their extremely high strength and thrust-to-weight ratios; however, the differences in the properties of the reinforcement and matrix materials in this type of composites have restricted their applications. The ultrahigh-frequency vibration characteristics of ultrasonic vibration processing technology can effectively solve the above bottlenecks, but the effect of high-frequency vibration on the interfacial properties of SiCp/Al composites is still unclear. The effects of ultrasonic vibration on the interface strength of composites were analyzed from a microscale perspective by means of single particle push-out Molecular Dynamics (MD) simulations and tests under different conditions. The results show that the interface strength is negatively correlated with particle size but positively correlated with ultrasonic amplitude, with a maximum increase of about 51% relative to no ultrasound. Brittle-plastic transition was observed on the surface of particles with high interface strength, and lateral microcracks due to stress concentration were present on the surface of particles with low interface strength. Higher strains and grain refinement were obtained for larger amplitudes, and stacking faults and tangle dislocations appeared on the side of the interface layer close to the Al matrix. The results provide potential insights to improve the micromechanical and mechanical properties of SiCp/Al composites, enhance the longevity of the materials, and realize the sustainable use of resources by expanding the efficient, precise, and clean machining of such materials.

Enhancing dielectric property and multi-interface polarization of poly(vinylidene fluoride)/Ni-embedded CaCu3Ti4O12 fibers composites tailored by magnetic field

In the realm of advanced electrical equipment and systems, polymer nanocomposites possess significant application value due to their excellent dielectric properties. Metal@ceramic fillers with a core-shell structure can enhance the dielectric constant (ε′) of polymer nanocomposites; however, their application is limited by the high dielectric loss (tanδ). A magnetic field tailoring strategy is introduced in this article to significantly improve the dielectric properties of poly(vinylidene fluoride) (PVDF) composites. Magnetic CaCu3Ti4O12–Ni (CN) composite fibers are formed by embedding Ni nanoparticles within CaCu3Ti4O12 (CCTO) fibers. Furthermore, the CN fibers are horizontally orientated in the PVDF matrix by tailoring the optimal magnetic field to 1.0 T–150 ℃. This results in a significant increase in the ε′ of 25, which is 92 % and 194 % higher than that of a CN fiber without magnetic field treatment and pure PVDF, respectively, while maintaining a low tanδ of 0.08. Experimental and simulation results indicate that the magnetic orientation tailoring enhances the multi-interface polarization, especially the inner interfacial polarization (△Pin) at the CCTO/Ni interfaces, dominantly improving dielectric performance, as evidenced by the high interfacial polarization strength, △ε2 ∼ 141.51, the low activation energy, Ea ∼ 0.81 eV, and the large △Pin ∼ 1.06×104 μC/m2. This magnetic orientation tailoring strategy offers a new paradigm and significant guidance for the development of polymer dielectrics with exceptional dielectric properties.

Delamination free forming of novel high interface strength metal-polymer laminates

A new class of metal-polymer-laminates, fabricated using wire mesh and “steel-chips” interlayer, is shown to have significantly high interface strength. A finite element model, calibrated using tensile, lap shear, and peel tests, is used to predict the deformation and failure of the laminates. Formability of the developed laminates is studied using the limiting-dome-height tests. The metal-polymer-laminates do not delaminate in any of the tests. A complete shift of forming-limit-curve towards biaxial-tension region is observed in strain-based forming limit diagram for the polymer side. Strain-path independent forming-limits are plotted in stress space, to negative the effect of non-proportional strain histories.

A super-toughened polyethylene naphthalene (PEN) enabled by polyacrylate elastomer with low crosslink density and reactivity

In elastomer toughening of polyester plastics, both the particle size distribution of the elastomer and the interfacial strength between the elastomer and matrix are key factors for toughness. In this work, bi-functional polyacrylate elastomers with controllable crosslinking density and reactivity were designed for enhancing the toughness of polyethylene naphthalene (PEN) matrix. Firstly, the elastomers with crosslinked structure possess increased melt viscosity and endowed wide particle size distribution, which contribute to the construct of thin matrix ligament and make PEN matrix more susceptible to shear-yield. Secondly, the high interfacial strength between elastomer and matrix can facilitate the transfer of external stress from PEN matrix to the elastomer, protecting the matrix from destroying. The resulted PEN blends exhibit an excellent impact resistance of 45.20 kJ/m2 and a high tensile toughness of 3.586 MJ/m3, which are 21.73 times and 47.81 times higher, respectively, than the virgin PEN. The present work may provide an effective approach for designing polyester blends with enhanced impact resistance and tensile toughness.

Simultaneous improvement in the elastic and fracture properties of graphene-epoxy nanocomposites–a computational perspective

The incorporation of stiff nano-additives (such as graphene) into a relatively soft polymer material (such as epoxy) usually leads to an improvement in elastic properties (i.e., Young's modulus) at the expense of fracture properties (i.e., tensile strength and toughness). Despite over a decade of research in polymer nanocomposites, we still lack a clear understanding of their structure-property relationships, which limits us from enhancing both elastic and fracture properties concurrently. Here, we performed large-scale reactive molecular dynamics simulations to study the deformation and fracture of model graphene/epoxy systems under uniaxial tension. A computationally efficient reactive force field was developed for graphene-epoxy system, allowing covalent bond formation, and breaking, which is crucial to model cross-linking in model epoxy as well as fracture. It was found the mechanical properties of the nanocomposite are very sensitive to the strength of the graphene-epoxy interface. As expected, elastic modulus increases with the interfacial strength. However, there appears to be an optimal interfacial strength to enhance the tensile strength and toughness. This is due to stress concentration occurring near the graphene edges at high interfacial strength, which leads to premature fracture. We show that by appropriately selecting an intermediate interface strength, one can simultaneously improve the ultimate tensile strength, toughness and the Young's modulus of the nanocomposite epoxy at ultra-low (∼0.2 % by weight) loading fraction of graphene additives. Our findings highlight the critical importance of properly engineered additive-matrix interfacial strength to develop high-performing polymer nanocomposites that are concurrently stiff, strong as well as tough.

Unlocking the Potential of CO2 Capture: A Synergistic Hybridization Strategy for Polymeric Hydrogels with Tunable Physicochemical Properties.

Unlocking CO2 capture potential remains a complex and challenging endeavor. Here, a blueprint is crafted for optimizing materials through CO2 capture and developing a synergistic hybridization strategy that involves synthesizing CO2-responsive hydrogels by integrating polymeric networks interpenetrated with polyethyleneimine (PEI) chains and inorganic CaCl2. Diverging from conventional CO2 absorbents, which typically serve a singular function in CO2 capture, these hybrid PEAC hydrogels additionally harness its presence to tune their optical and mechanical properties once interacting with CO2. Such synergistic functions entail two significant steps: (i) rapid CO2-fixing through PEI chains to generate abundant carbamic acid and carbamate species and (ii) mineralization via CaCl2 to induce the formation of CaCO3 micro-crystals within the hydrogel matrix. Due to the reversible bonding, the PEAC hydrogels enable the decoupling of CO2 through an acid fumigation treatment or a heating process, achieving dynamic CO2 capture-release cycles up to 8 times. Furthermore, the polyethyleneimine-acrylamide-calcium chloride (PEAC) hydrogel exhibits varying antibacterial attributes and high interfacial adhesive strength, which can be modulated by fine-tuning the compositions of PEI and CaCl2. This versatility underscores the promising potential of PEAC hydrogels, which not only unlocks CO2 capture capabilities but also offers opportunities in diverse biological and biomedical applications.

Microstructure and mechanical properties of heterogeneous-gradient composite plates with a sphere-array interlayer prepared using explosive welding

Composite structures with high strength and controllable fragments driven by implosions are valuable in weaponry. This study explored a technical approach to preparing heterogeneous-gradient composite plates with a sphere-array interlayer using explosive welding. TA1 and Q235B steel plates with various spherical grooves were employed as the flyer and base plates, respectively. The spherical grooves were filled with Q235 steel balls. Composite plates were formed by a single explosion using the parallel method, and the parameters adopted in the experiment were within a weldable window. The performance of the TA1/Q235 steel balls/Q235B composite plate was studied through microstructural observations and mechanical property testing. The results indicated that the two embedded spherical structure schemes (with steel balls protruding or not protruding from the plane of the base plate) created effective metallurgical bonding interfaces between the two plates and at the top of the spheres. Surface flatness plays a crucial role in forming wavy interfaces. The composite plates embedded with non-protruding spheres exhibited better mechanical properties, higher interface strength, and a more regular, wavy interface than those embedded with protruding spheres. The ultimate tensile strength of the composite plate containing a sphere with a diameter of 2 mm was similar to that of an intact composite plate. The fracture surfaces of the specimens embedded with spheres exhibited ductile and quasi-cleavage fracturing in the tensile and impact-toughness tests. The structure of the composite plates embedded with non-protruding spheres provides a strategy for preparing multifunctional warhead shells.

Development of Hot-Wire Laser Additive Manufacturing for Dissimilar Materials of Stainless Steel/Aluminum Alloys

The formation of brittle intermetallic compounds (IMCs) at the interface between dissimilar materials causes considerable problems. In this study, a multi-material additive manufacturing technique that employs a diode laser and the hot-wire method was developed for stainless steel/aluminum alloys. An Al-Mg aluminum alloy filler wire (JIS 5183-WY) was fed on an austenitic stainless-steel plate (JIS SUS304) while varying the laser power and process speed and using paste-type flux and flux-cored wire. The effects of laser power and process speed on phenomena during manufacturing and IMC formation were investigated. Finally, the wall-type multilayer specimens were fabricated under optimized conditions. The suppression of IMC formation to a thickness of less than 2 μm was achieved in the specimens, along with a high interfacial strength of over 120 MPa on average.

Reversibly stable and highly stretchable transparent polymer nanocomposite adhesives using hierarchical spring-like molecular nanobridges

For the development of stretchable optoelectronic devices, optically transparent composite adhesives should afford reversible stretchability and high optical transmittance as well as strong interfacial adhesion. However, simultaneous achievement of these essential prerequisites for advanced stretchable optical composite adhesives remains challenging. Herein, we offer an unprecedented approach for the fabrication of reversibly stretchable and optically transparent polymer nanocomposite adhesives based on the construction of hierarchical elastic molecular nanobridges between rigid-flexible hybrid nanoparticles and matrix resin. Photoreactive flexible poly(propylene glycol) (meth)acrylate chains were chemically combined with a rigid nano-silica core to form rigid and flexible hybrid nanoparticles. Subsequently, multiple elastic molecular nanobridges between the embedded hybrid nanoparticles and acrylate resin matrix were constructed inside the polymer composite through UV curing, which results in a stretchable interconnection that allows efficient repeated stretching and recovery of stretchable polymer nanocomposite adhesives. The newly fabricated nanocomposite adhesive film with a low content of rigid-flexible hybrid nanoparticles afforded an excellent reversible stretchability and outstanding cyclic elastic durability, and simultaneously maintained high optical transparency (95.1%) and interfacial adhesion strength (21.5 N/25 mm) of the film compared to those of conventional optical adhesive film.

Synergistically improving interface behavior by designing physical twisting structure and “rigid-flexible” interface layer on ultra-high molecular weight polyethylene (UHMWPE) fiber surface

The application limitations of Ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced composites in different fields can be attributed to their surface chemical inertness and weak interfacial adhesion. Herein, we developed a novel method for preparation of a stable biomimetic layer surface treatment, via the combination use of physical twisting structure and “rigid-flexible” interface layer. Unlike the conventional methods under special conditions, in this method, the UHMWPE fibers were converted into twisting structure, and the efficient nanoparticle deposition facilitated on the fiber surface in the presence of reductive dopamine coating. Moreover, the multi-structured synergy promotes the roughness of the T-UHMWPE fiber, which improves the interface bonding strength of the fibers-reinforced composites. The effectiveness of the modified treatment was evaluated by Fourier transform infrared spectroscopy (FT-IR), microscopic confocal laser Raman spectrometer (Raman), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), contact angle and surface free energy. The surface morphology and interfacial properties of the treatment was evaluated using field emission scanning electron microscopes (FE-SEM) and energy dispersive spectrometry (EDS). The experimental results demonstrated that the interfacial shear strength (IFSS) of the modified T-UHMWPE was improved by 218 %, compared with those of the unmodified UHWMPE fibers. This innovative approach, combining physical twisting structure and “rigid-flexible” interface layer, would provide a valuable potential for the preparation of advanced UHMWPE reenforced composites with high interfacial bond strength.

Laser metal deposition of titanium on stainless steel with high powder flowrate for high interfacial strength

Direct joining of titanium and stainless steel 316 L with a strong interface is very challenging due to the formation of the brittle intermetallic compounds FeTi and Fe2Ti in the intermixing zones and to the high residual stress induced by the mismatch of the thermal expansion coefficients. In this bimetallic directed energy deposition study, firstly, deposition of Ti on stainless steel was carried out using conventional process parameter regime to understand the interfacial cracking susceptibility and then a novel high powder flowrate approach is proposed for controlling the dilution and constraining the intermetallic phases forming at the interface. The influence of high temperature substrate preheating (520 °C) on the cracking susceptibility and interface strength was also investigated. The deposited Ti samples and their interfaces with the 316 L substrate were characterized with optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy to investigate the geometry, microstructures and chemical compositions in relation to the cracks. The high powder flowrate deposition of Ti on stainless steel 316 L results in an extremely thin dilution region (~ 10 μm melt pool depth in the substrate) restricting the formation of the intermetallic phases and cracks. The ultimate shear strength of the interfaces of the crack free sample was measured from cuboid deposits and the highest measured strength is 381 ± 24 MPa, exceeding the weaker base material pure Ti. The high interfacial strength for high powder flowrate deposition is due to the substantial attenuation and shadowing of the laser beam by the in-flight powder stream as demonstrated by the high-speed imaging resulting in an extremely small dilution region.

Effect of thermal-mechanical conditions on strength of silanized Al alloy/CFRTP hybrid joint made by thinning-controlled hot pressing

The strength of thermal-assisted joined metal and carbon fiber-reinforced thermoplastics (CFRTP) is dependent on physical and chemical interactions at the joining interface, which are strongly influenced by heat and pressure. Currently, there is a lack in deep research on effect mechanism of changeable pressure on the joining quality, limiting the joining condition optimization of the thermal-assisted joining process. In this study, an improved hot-pressing joining process with added thinning displacement control was adopted to study the effect of the joining pressure on the structure and strength of the interface between a silane-treated Al alloy and three CF-Polyamide-6 (CF/PA6). A high-strength, thinning-controlled lapped joint of Al and CF/PA6 could be realized by the proposed process, regardless of the fiber volume fractions in CF/PA6. At temperatures above the melting point of PA6, higher pressure typically resulted in higher interface strength. However, as the temperature approached the decomposition temperature, the joints under higher pressure tended to exhibit lower strength. The underlying mechanism of the interface strength variation with pressure was investigated by analyzing the effects of the joining conditions on the chemical reaction conditions, the resolidified-resin structure near the interlayer, and the existence of defects. These findings lay the foundational groundwork for future endeavors in metal/composite joining, offering potential benefits for industrial applications and environmental sustainability in the automotive sector.

Effect of expansive agent on the mechanical properties of carbon-fibre-reinforced cement-based composites

Improving the flexural strength of a cement-based composite (CBC) reinforced with chopped carbon fibre (CF) while maintaining good workability is highly attractive for building high-rise large-span structures. A sulfoaluminate-based expansive agent (EA) was used to optimise the mechanical properties of CBCs reinforced with chopped CF by improving the fibre–matrix interfacial properties. The results of single-fibre pull-out tests showed that the interfacial frictional bond strength was improved by up to 51% owing to the addition of the EA, whereas the chemical debonding energy remained nearly unchanged. The effects of various concentrations of EA on the strength of cement pastes containing various lengths and volume fractions of CF were then investigated. The results indicated that, benefitting from the EA-induced high interfacial bond strength, the flexural strength and fluidity of the CF-reinforced cement paste could be further optimised. For example, utilising the EA, the flexural strength could be improved by 28% for a cement paste containing 0.5% CF of length 15 mm.

Anti-friction gold-based stretchable electronics enabled by interfacial diffusion-induced cohesion

Stretchable electronics that prevalently adopt chemically inert metals as sensing layers and interconnect wires have enabled high-fidelity signal acquisition for on-skin applications. However, the weak interfacial interaction between inert metals and elastomers limit the tolerance of the device to external friction interferences. Here, we report an interfacial diffusion-induced cohesion strategy that utilizes hydrophilic polyurethane to wet gold (Au) grains and render them wrapped by strong hydrogen bonding, resulting in a high interfacial binding strength of 1017.6 N/m. By further constructing a nanoscale rough configuration of the polyurethane (RPU), the binding strength of Au-RPU device increases to 1243.4 N/m, which is 100 and 4 times higher than that of conventional polydimethylsiloxane and styrene-ethylene-butylene-styrene-based devices, respectively. The stretchable Au-RPU device can remain good electrical conductivity after 1022 frictions at 130 kPa pressure, and reliably record high-fidelity electrophysiological signals. Furthermore, an anti-friction pressure sensor array is constructed based on Au-RPU interconnect wires, demonstrating a superior mechanical durability for concentrated large pressure acquisition. This chemical modification-free approach of interfacial strengthening for chemically inert metal-based stretchable electronics is promising for three-dimensional integration and on-chip interconnection.

First-principles comparative study on diamond/carbide combinations: Interfacial adhesion and bonding nature

Joining diamond and metal is vital to expand their application scope in electronic and military industries. A metallic carbide layer will be inevitably introduced on diamond to ensure strength and wettability, its tight interfacial adhesion with diamond needs to be satisfied in priority. Here, the bonding characteristics of diamond(001)/carbide(001) interfaces were comparatively studied through first-principles calculations, wherein six experimentally possible carbides MxCy (TiC, Cr3C2, V8C7, Mo2C, ZrC, and WC) were employed. By evaluating the thermal stability, activity, and mechanical properties of bulk MxCy, as well as the corresponding interface energy and adhesion work, three outstanding interface structures (with Cr, W, and Ti) were yielded. Further analysis of electronic structures showed the interfacial bonding originated from M–C bonds and stronger CC covalent bonds. Besides, bonding strength was found to be significantly related to interfacial charge density and orbital hybridization. Overall, Cr might be the preferable carbide former with high interfacial stability and strength. This study provided atomic insights into the tailoring of diamond/carbide combination with superior interfacial compatibility to develop high-performance diamond devices.

Temperature-Immune, Wide-Range Flexible Robust Pressure Sensors for Harsh Environments.

Flexible pressure sensors possess vast potential for various applications such as new energy batteries, aerospace engines, and rescue robots owing to their exceptional flexibility and adaptability. However, the existing sensors face significant challenges in maintaining long-term reliability and environmental resilience when operating in harsh environments with variable temperatures and high pressures (∼MPa), mainly due to possible mechanical mismatch and structural instability. Here, we propose a composite scheme for a flexible piezoresistive pressure sensor to improve its robustness by utilizing material design of near-zero temperature coefficient of resistance (TCR), radial gradient pressure-dividing microstructure, and flexible interface bonding process. The sensing layer comprising multiwalled carbon nanotubes (MWCNTs), graphite (GP), and thermoplastic polyurethane (TPU) was optimized to achieve a near-zero temperature coefficient of resistance over a temperature range of 25-70 °C, while the radial gradient microstructure layout based on pressure division increases the range of pressure up to 2 MPa. Furthermore, a flexible interface bonding process introduces a self-soluble transition layer by direct-writing TPU bonding solution at the bonding interface, which enables the sensor to achieve signal fluctuations as low as 0.6% and a high interface strength of up to 1200 kPa. Moreover, it has been further validated for its capability of monitoring the physiological signals of athletes as well as the long-term reliable environmental resilience of the expansion pressure of the power cell. This work demonstrates that the proposed scheme sheds new light on the design of robust pressure sensors for harsh environments.

First-Principles Computation of Microscopic Mechanical Properties and Atomic Migration Behavior for Al4Si Aluminum Alloy

In this paper, the interfacial behavior and the atom diffusion behavior of an Al4Si alloy were systematically investigated by means of first-principles calculations. The K-points and cutoff energy of the computational system were determined by convergence tests, and the surface energies for five different surfaces of Al4Si alloys were investigated. Among the five surfaces investigated for Al4Si, it was found that the (111) surface was the surface with the lowest surface energy. Subsequently, we investigated the interfacial stability of the (111) surface and found that there were two types of interfaces, the Al/Al interface and the Al/Si interface. The fracture energies and theoretical strengths of the two interfaces were calculated; the results show that the Al/Al interface had the highest interfacial strength, and the calculation of their electronic results explained the above phenomenon. Subsequently, we investigated the diffusion and migration behavior of Si atoms in the alloy system, mainly in the form of vacancies. We considered the diffusion of Si atoms in vacancies of Al and Si atoms, respectively; the results showed that Si atoms are more susceptible to diffusive migration to Al atomic vacancies than to Si atomic vacancies. The results of the calculations on the micromechanics of aluminum alloys, as well as the diffusion migration behavior, provide a theoretical basis for the further development of new aluminum alloys.

Influence of the Surface State on the Interfacial Bonding Strength of the Cold-Rolled Brass/Carbon Steel Composite.

To improve the interfacial bonding of dissimilar composites, the interaction mechanism between the surface state and severe plastic deformation to strengthen the interfacial bonding strength was revealed. In this study, the different surface states of the steel strip were designed by louver blade grinding (LBG) and diamond bowl grinding (DBG), and the cold-rolled composite method was developed to prepare the brass/carbon steel composite strips. The results show that the steel surface after DBG has a large roughness of 9.79 μm, a hard hardening layer of 6.2 GPa, and high cleanliness of 1.34 atomic % oxygen content, while that after LBG has a roughness of 1.31 μm, a hardening layer of 4.2 GPa, and an oxygen content of 2.37 atomic %. The large roughness promotes the breaking of the hardening layer; the hardening layer is beneficial to obtain sufficient interfacial stress to expose the fresh metal; and the high cleanliness reduces the barrier to the fresh metal and contributes to the bonding of the fresh metal. The interface of the cold-rolled brass/carbon steel composite strip after LBG and DBG is mechanical bonding and metallurgical bonding, respectively. In the process of the cold-rolling composite, large shear deformation occurs at the interface of brass and steel, resulting in a high concentration of vacancy and dislocation defects, which provides a channel for interdiffusion of atoms at the interface. Under the diffusion driving force provided by the cold-rolling shear deformation heat, a nanodiffusion layer with a thickness of 60 nm and high interfacial bond strength was formed.

Design optimization of high interface strength metal–polymer–metal sandwich panels

Design optimization of high interface strength metal–polymer–metal sandwich panels

TiC–Fe gradient coating with high hardness and interfacial adhesion strength on cast iron prepared by in-situ solid-phase diffusion method

The improvement of comprehensive properties including hardness, toughness, wear, and adhesion strength of the coating-substrate system, especially avoiding the trade-off between the hardness and adhesion strength, is strongly required for various applications. Herein, an effective strategy is proposed, by in-situ solid-phase diffusion method, to fabricate a novel TiC–Fe gradient coating with high hardness and interfacial adhesion strength on cast iron. The eveloped coating was composed of equiaxed TiC particles and α-Fe phase. The microstructure was graded in TiC size and volume fraction. The formation of the graded microstructure was attributed to the nucleation-growth process controlled by diffusion of the carbon concentration gradient. The TiC volume fraction in the coating was as high as 95%. The phase interface (TiC/TiC interface and TiC/α-Fe interface) and the coating/substrate interface exhibited excellent interfacial bonding at the atomic scale. The novel gradient coating could simultaneously achieve high hardness (23.9 ± 1.3 GPa), high elastic modulus (265.7 ± 9.4 GPa), and excellent adhesion strength (>225 ± 10 MPa). Apparently, in-situ solid-phase diffusion method may provide a new route to fabricate TiC–Fe gradient coatings with high-volume fraction on steel/iron, capable of capable of exhibiting elevated hardness, high elastic modulus, excellent interfacial adhesion strength, and superior wear resistance.