Interfacial Adhesion Strength Research Articles

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.

Stochastic dynamics of substrate non-uniform stiffness affecting molecular adhesion in cell–substrate interface subjected to tensile loading

The mechanically heterogeneous extracellular matrix (ECM) or tissues widely exist in biological systems and are capable of significantly regulating directional cell migration. However, prior to whole cell movement, how the cell senses these cues from mechanical heterogeneities of the ECM or substrate remains unclear at the molecular bond level. To address this issue, we theoretically investigate interface adhesion between a non-uniform stiffness substrate and a rigid plate via a series of receptor–ligand bonds subjected to a tensile loading by integrating substrate surface deformation described by continuum mechanics approach into the stochastic events of bond dissociation and association govern by Markov processes. Interestingly, it is found that, during stretching adhesion interface, due to the large collective contact forces near the stiff edge of the adhesion area, the crack first develops at this stiff edge and then grows to another relatively soft adhesion edge until the completed detachment achieved, which is distinct from the cracks growing from both two edges to center of adhesion area in the case of uniformly elastic solid–solid or solid–fluid interface. Moreover, the lifetime of the bond cluster, interface adhesion strength, and the effect of inter-bond distance are examined, respectively. The corresponding mechanism of dependence of the lifetime and adhesion strength on the non-uniform stiffness of the substrate and inter-bond distance is also analyzed. These findings provide a detailed mechanistic understanding of the adhesion interface responding to the mechanical heterogeneities of the substrate at the molecular bond level.

Computational modeling and analysis of the interfacial debonding in copper/copper and copper/polyether-ether-ketone coatings deposited by cold spraying

Cold Spraying (CS) is a promptly developing solid-state additive material deposition technique that is frequently used for high-value metallic component repair. The purpose of this research is to investigate the interfacial adhesion strength of cold-sprayed copper (Cu) coatings deposited on Cu and polyether-ether-ketone (PEEK) substrates for repair applications. In light of this, we propose a computational framework that accounts for both of the two main failure mechanisms, i.e., failure at the Cu/Cu interface caused by plasticity and damage initiation and failure at the Cu/PEEK interface due to brittle crack. Towards this end, different damage models are employed to describe the ductile damage of bulk materials, and a large deformation Cohesive Zone Model (CZM) is developed to model Cu/Cu interface debonding, allowing for stable calculations under large interfacial deformation. The Virtual Crack Closure Technique (VCCT) is used to simulate brittle debonding failure of the Cu/PEEK coating. The threshold stresses for coating debonding, found experimentally, are successfully compared to the numerical predictions. Such debonding modeling techniques might be useful for predicting coating behavior and bonding strength in cold spraying under various loading situations and material combinations.

TiC–Fe gradient coating on pure titanium fabricated by in-situ solid-phase diffusion: toward superior hardness and interfacial adhesion strength

Protective hard coatings can significantly improve the bottleneck problem of low hardness and poor wear resistance on titanium alloy surface. However, hardness and adhesive strength usually exhibit an inverse relationship, which greatly limits its widespread use. In this work, TiC–Fe gradient coating with high hardness and adhesion was successfully fabricated by in-situ solid-phase diffusion method (ISDM) on pure titanium at 1000 °C for 2 h. The average thickness of the coating was approximately 5 μm, and the volume fraction of TiC in the coating was greater than 95 vol%. The grain size of TiC gradually increased from 200 nm at the coating surface to 2 μm towards the substrate. The phase interface and the coating/substrate interface exhibited excellent interfacial bonding at the atomic scale. The novel TiC–Fe gradient coating can simultaneously achieve superior hardness (42.9 ± 2.6 GPa) and elastic modulus (557.4 ± 10.3 GPa) that is mainly dominated by in situ synthesised high volume fraction TiC, as well as high adhesion strength (>225 ± 10 MPa). The increased adhesion strength was attributed to the excellent macro/micro interfaces and gradient transition of the microstructure. The use of ISDM to fabricate TiC–Fe gradient coating on titanium alloy may provide a new strategy to improve the comprehensive properties including hardness, elastic modulus, interfacial adhesion strength, and wear resistance for wider applications.

Enhancing the interfacial adhesion of PET and silicone rubber by plasma-assisted coupling agent treatment

The poor interfacial adhesion between silicone rubber and polyethylene glycol terephthalate (PET) affects the safety and durability of fabric-rubber products in service. In this study, a low-cost and simple atmospheric plasma surface treatment device is used to treat the surface of polyester fabric continuously, followed by coating KH570 onto the fabric surface. The adhesion strength of fabric-rubber interface is successfully enhanced by this method. The peel strength of the specimens treated with this bonding process reaches 3.92 N/mm and 5.73 N/mm in the warp and weft directions, respectively, which are 5.16 and 7.44 times of untreated fabric samples, superior to commercially-available silicone rubber adhesive. In addition, the bonding mechanism of the interface is characterized by Fourier transform infrared spectra (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and water contact angle test. This study provides a practical and environmentally friendly method for fabricating fabric silicone rubber materials with high interfacial performances.

Interfacial Adhesion Property of Asphalt Binder with Calcium Alginate Carrier of Asphalt Rejuvenator.

Recently calcium alginate has been successfully applied to encapsulate asphalt rejuvenator, which can protect asphalt rejuvenator from early leakage and release asphalt rejuvenator when triggered by specific factors such as cracks. The interfacial adhesion property of asphalt binder with calcium alginate carrier is of great importance to its actual performance. In this paper, the molecular model of the interface region between asphalt binder and calcium alginate was established, and molecular dynamics simulations were performed on it to investigate the molecular interaction at the interface region. By extracting and processing the data during the simulation process, the interfacial adhesion behavior was expounded using the spreading coefficient (S), permeation depth and permeation degree. Furthermore, the interfacial adhesion strength was evaluated by adopting the interfacial adhesion work. Results showed that the value of S was greater than 0, implying that asphalt binder could wet the surface of calcium alginate. Saturate had the highest value of permeation degree, followed by resin, aromatic and asphaltene. However, asphalt binder could not infiltrate into the interior of TiO2, only accumulating and spreading on the surface of TiO2. The interfacial adhesion work of unaged and aged asphalt binder to calcium alginate was -114.18 mJ/m2 and -186.37 mJ/m2, respectively, similar to that of asphalt-aggregate interface. The van der Waals interactions contributed the most to the formation of the interfacial adhesion strength. In addition, a certain degree aging of asphalt binder and addition of titanium dioxide in the calcium alginate carrier were helpful to enhance the interfacial adhesion strength.

Origin and stability of the core-shelled Y–Ti–Zr–O nano-oxides in oxide-dispersion-strengthened ferritic alloys

Quaternary Y–Ti–Zr–O nano-oxides form in preference to other ternary nano-oxides in Y+Ti+Zr micro-alloyed FeCr- oxide-dispersion-strengthened (ODS) ferric alloys. In this study, bulk substitution and interfacial segregation were calculated from the first-principles to explore the formation and stability of core-shelled Y–Ti–Zr–O nano-oxides. Our results were validated with previous electron microscopic characterizations. The major findings that were obtained are as follows. Quaternary Y–Ti–Zr–O nano-oxides are most likely formed as a consequence of Zr substitution of Ti in Y–Ti–O nano-oxides. Ti segregation from the matrix interior to the Y2Ti2O7 interface is a self-limiting process, and the resulting Ti-shell at Y2Ti2O7 nano-cores can hardly be thermally stable. In contrast, the Y2(Ti,Zr)2O7 nano-core due to Zr substitution can strongly trap the Zr-substituted Ti at its interface. The resulting Ti-shell can be more stable at high Zr-content Y2(Ti,Zr)2O7 nano-cores but will reduce the interface adhesion strength. The gained insights help to clarify the experimental observations and achieve a better understanding of micro-alloying effects and mechanisms in FeCr-ODS ferric alloys.

High Performance and Multifunction Moisture-Driven Yin-Yang-Interface Actuators Derived from Polyacrylamide Hydrogel.

High actuation performance of a moisture actuator highly depends on the presence of a large property difference between the two layers, which may cause interfacial delamination. Improving interfacial adhesion strength while increasing the difference between the layers is a challenge. In this study, a moisture-driven tri-layer actuator with a Yin-Yang-interface (YYI) design is investigated in which a moisture-responsive polyacrylamide (PAM) hydrogel layer (Yang) is combined with a moisture-inert polyethylene terephthalate (PET) layer (Yin) using an interfacial poly(2-ethylhexyl acrylate) (PEA) adhesion layer. Fast and large reversible bending, oscillation, and programmable morphing motions in response to moisture are realized. The response time, bending curvature, and response speed normalized by thickness are among the best compared with those of previously reported moisture-driven actuators. The excellent actuation performance of the actuator has potential multifunctional applications in moisture-controlled switches, mechanical grippers, and crawling and jumping motions. The Yin-Yang-interface design proposed in this work provides a new design strategy for high-performance intelligent materials and devices.

Thermal shock resistance and failure mechanisms of high temperature resistant radar and infrared compatible stealth coatings

The compatibility stealth coatings for aircrafts application have attracted widely concerns recently in aerospace engineering. In this work, the high temperature resistant radar and infrared compatible stealth coating (HRISC) system was prepared first, which mainly consisted of seven layers, such as low-emissivity layer, thermal barrier ceramic layer 1/2 (TBC1, TBC2), lossy layer, matching layer, etc. And then, the microstructures and thermal shock behaviors of HRISC system was determined. Results showed that the microstructures obviously changed after cyclic thermal shock tests. The horizontal cracks extended at the interface, leading to the matching layer and above detaching from the HRISC system after 70 thermal shock cycles. The numerical simulations showed that the interface of matching layer and TBC1 was under the highest stress state and prone to failure. In addition, the residual interfacial adhesion strength of the HRISC system after thermal shock tests was tested. The results showed that the failure position was at the interface between the matching layer and TBC1, and the interfacial adhesion strength decreased obviously with the increase of thermal shock cycles. All these can provide reference for the design and failure analysis of HRISC system in engineering application.

Grain-boundary/interface structures and scatterings of ruthenium and molybdenum metallization for low-resistance interconnects

Ruthenium and molybdenum are of great potential to replace copper for use as the next-generation interconnect metallization. Important parameters including their intrinsic resistivity, grain-boundary reflectivity and interface permeability need to be carefully examined. Hence in this study, ruthenium and molybdenum films with various thicknesses were prepared on different substrates by physical vapor, chemical vapor and atomic layer depositions. The microstructure, chemical compositions, bonding configurations and interfacial adhesion were characterized, and the electrical resistivities with scaling was examined using the Fuchs-Sondheimer and Mayadas-Shatzkes models. Experimental results indicate that the grain-boundary reflectivity was strongly influenced by the structure coherency and impurity (oxygen) segregation. Thermal annealing facilitated defect elimination and structure recovery, lowering the intrinsic resistivity and the grain boundary reflectivity. Strong interface bonding caused serious interface diffuse scattering, and an inverse proportional relationship between interfacial adhesion strength and interface permeability was suggested, which was dominated by the electronegativity of the metals.

Interfacial Click Chemistry Enabled Strong Adhesion toward Ultra‐Durable Crack‐Based Flexible Strain Sensors

AbstractFlexible strain sensors, particularly crack‐based ones, have evoked great interests in recent years because of their excellent sensitivity and promising applications in health monitoring and human‐machine interactions. However, the poor durability originated from the weak interfacial bonding between fragile conductive layer and stretchable elastic substrate makes it difficult to meet the needs of practical use. Herein, a strategy enabled by interfacial click chemistry is proposed for effectively enhancing the adhesion strength (τ), thereby improving the durability of the flexible strain sensors. It is found that the strong interfacial adhesion can bear larger cyclic shear force, effectively suppress the crack propagation of the conductive layer, and prevent the conductive layer from peeling off, thus stabilize the conductive path under specific strain during cyclic test, resulting in excellent durability. Moreover, the device durability (number of stable cycles, i.e., Cn) is found to linearly depend on τ, based on which “durability‐adhesion coefficient (CDA)” is defined. So far it is known, this is the first report to quantitatively establish the relationship between interfacial adhesion strength and cycling durability of crack‐based strain sensors, providing a new viewpoint for future design of flexible devices with high reliability.

First-principles insights into micro-alloying roles of Zr in Cu–Cr–Zr alloys

Interface has been often neglected in exploring micro-alloying mechanisms in polycrystalline Cu–Cr–Zr alloys. In this study, interface structure modeling and first-principles calculations were carried out to explore the segregation behaviors of micro-alloying element Zr at nano-Cr particle interfaces and a series of low-Σ (Σ ≤ 11) Cu grain boundaries (GBs) in Cu–Cr–Zr alloys. The segregation effects on interface adhesion strength were also evaluated. Our results suggested that Zr can substitute the top-most Cu atoms at most nano-Cr particle interfaces (those with the Nishiyama–Wassermann orientation relation) with the maximal coverage of 1/3 ML. The segregation to other nano-Cr interfaces with the Kurdjumov–Sachs orientation relation is, however, energetically forbidden. At almost all the low-Σ GBs (except the Σ3 (111) only), Zr segregation can be consistently favored up to a full coverage (1 ML), which can improve the GB binding by ∼30%. Based on these results, the multi-fold benefits of Zr micro-alloying were discussed.

Tissue-Adhesive Decellularized Extracellular Matrix Patches Reinforced by a Supramolecular Gelator to Repair Abdominal Wall Defects.

Implantation of surgical meshes composed of synthetic and biological materials has been applied for abdominal wall defect repair. Despite many efforts, there are no reliable meshes that fully satisfy clinical requirements because of their lack of biodegradability, mechanical strength, and tissue-adhesive properties. Here, we report biodegradable, decellularized extracellular matrix (dECM)-based biological patches to treat abdominal wall defects. By incorporating a water-insoluble supramolecular gelator that forms physical cross-linking networks through intermolecular hydrogen bonding, dECM patches were reinforced to improve mechanical strength. Reinforced dECM patches possessed higher tissue adhesion strength and underwater stability compared with the original dECM because of enhanced interfacial adhesion strength. In vivo experiments using an abdominal wall defect rat model showed that reinforced dECM patches induced collagen deposition and the formation of blood vessels during material degradation, and the accumulation of CD68-positive macrophages was suppressed compared to nonbiodegradable synthetic meshes. Tissue-adhesive and biodegradable dECM patches with improved mechanical strength by a supramolecular gelator have enormous potential for use in the repair of abdominal wall defects.

Mode I fracture toughness of glass fibre reinforced thermoplastic composites after UV and atmospheric plasma treatments

In the present paper, the mode I fracture toughness properties of a thermoplastic composite resin reinforced with glass fibres are experimentally evaluated. The neat resin is initially characterized in terms of static and mode I fracture toughness properties. Then three sets of panels are manufactured and tested: reference panels made of untreated glass fibres and the thermoplastic resin; UV treated glass fibres reinforced thermoplastic panels and plasma treated glass fibres reinforced thermoplastic panels. The effect of the treatment on the interfacial adhesion strength between fibres and matrix is characterized by a push-out test. An overall increase of the interfacial strength leads to an overall decrease of the composite mode I fracture toughness evaluated by Double Cantilever Beam (DCB) tests. Optical and Scanning Electron Microscopy images of the fracture surfaces are acquired and used to obtain a better interpretation of the fracture mechanisms.

The Connection Between Electromigration Resistance and Thin-Film Adhesion and Their Degradation With Temperature

Growth of voids driven by electromigration in current carrying metal thin films is a common mode of failure in microelectronic devices. Studies have shown that electromigration driven void growth rate in such devices is inversely related to the interface adhesion strength between the current carrying metal thin films and the passivation layers on top of the metal films. In this paper, we characterize the degradation in electromigration resistance with temperature in metallic thin films with passivation and argue on a general mathematical form for connecting the electromigration resistance to adhesion strength. Test structures with thin film Cu metal lines are designed and fabricated for performing electromigration experiments and characterizing the void growth rate. Tests are carried out on devices with Cu thin film having TiN and SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> as passivation layers, over a range of current densities and temperatures. The growth rates of the voids in the Cu lines undergoing electromigration are analyzed using classical models from literature. The experimental observations on void growth rate with increase in current density and temperature are validated by comparing the data to those from prior literature. The void growth is also simulated and the void interface is tracked using an explicit boundary tracking computational technique. It is observed that the contribution of interface adhesion strength to electromigration resistance decreases with increase in temperature. That is, the experiments suggest that the passivation layers cease to provide resistance to electromigration with increasing temperature. Based on the test results, we develop a general form of a mathematical model to describe the degradation in electromigration resistance with metal film adhesion to the passivation layer.

Adjusting the interfacial adhesion via surface modification to prepare high-performance fibers

Ultra-high molecular weight polyethylene (UHMWPE) fiber is a new kind of high-performance fiber. Due to its excellent physical and chemical characteristics, it is widely used in various fields. However, the surface UHMWPE fiber is smooth and demonstrates no-polar groups. The weak interfacial adhesion between fiber and resin seriously restricts the applications of UHMWPE fiber. Therefore, the surface modification treatments of UHMWPE fiber are used to improve the interfacial adhesion strength. The modified method by adding nanomaterials elucidates the easy fabrication, advanced equipment and proper technology. Thus, the progress of UHMWPE nanocomposite fibers prepared via adding various nanofillers are reviewed. Meanwhile, the effects of other various methods on surface modification are also reviewed. This work advances the various design strategies about nano technologies on improving interfacial adhesion performance via treatment methodologies.

Preparation of Highly Stable Polymer Microstructure with Enhanced Adhesion Strength by Pushpin-like Nano/Microstructure Array.

This polymer microstructure expands more available application, which is a milestone for the development of micro-electro-mechanical system devices towards intelligence and multifunction. Poor interface bonding between the polymer and Si or metal is a particular problem, which restricts the application and promotion of polymer materials. In this study, a transition strengthening layer is proposed to obtain a highly stable polymer microstructure by enhancing the interfacial adhesion strength. The transition strengthening layer is activated by a pushpin-like nano/microstructure array with micromachining technology. Given its good graphical qualities and compatibility, epoxy negative photoresist SU-8 is applied to evaluate the strengthened capabilities of the pushpin-like nano/microstructure array. The microstructure of SU-8 is prepared by the same processes, and then the adhesion strength between the SU-8 microstructure and various activated substrates is tested by the thrust tester. It was determined that SU-8 with an activated pushpin-like microstructure array possessed a highly stable adhesion ability, and its adhesion strength increased from 6.51 MPa to 15.42 MPa. With its ultrahigh stable adhesion ability, it has been applied in fabricating three typical microstructures (hollow square microstructure, gradually increasing adjacent periodic microstructure, and slender strip microstructures) and large-area SU-8 microstructures to evaluate the feasibility of the transition strengthening layer and repeatability and universality of the microfabrication processes. The drifting and gluing phenomenon are avoided by this method compared with the traditional design. The proposed pushpin-like nano/microstructure array is promising in enhancing the stability of polymer microstructures with a substrate.

Interfacial adhesion strength between FDM-printed PLA parts and surface-treated cellulosic-woven fabrics

PurposeThe purpose of this study is to investigate surface treatments and fiber types on adhesion properties polylactic acid (PLA) three-dimensional (3D) parts printed on woven fabrics.Design/methodology/approachThe cotton, flax and jute fabrics were exposed to alkali, hydrogen peroxide, stearic acid and ionic liquid treatments to modify surface characteristics before PLA 3D printing. The modification efficiency was assessed with Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM) analyses. Then, fused deposition modeling (FDM) printer and PLA filament were used for 3D printing onto the untreated and treated fabrics. The adhesion strength between the fabrics and PLA 3D parts were tested according to DIN 53530 via universal tensile tester.FindingsThe fabric structure is effective on adhesion force and greater values were observed for plain weave fabrics. Maximum separation forces were obtained for alkali pretreated fabrics among jute and cotton. Hydrogen peroxide treatment also increased adhesion forces for jute and cotton fabrics while decreasing for flax fabrics. Stearic acid and ionic liquid treatments reduced adhesion forces compared to untreated fabrics. Treatments are effective to alter adhesion via changing surface chemistry, surface morphology and fabric physical properties but display different effects related to fabric material.Originality/valueThis study provides experimental information about effects of different fiber types and surface treatments on adhesion strength of PLA 3D parts. There is limited research about comprehensive observation on 3D printing on cellulosic-woven fabrics.

Atomistic investigation on adhesive strength of coupling agents to aluminum

For the adhesion of aluminum, which is of great importance in multimaterialisation, this paper focused on silane coupling agents as one of dominant factors. Amino, mercapto and EP silanes were employed as typical examples, then the atomistic adhesion mechanism was clarified through first-principles calculations and verified in continuum mechanics by tensile tests and finite element analysis. First-principles calculations revealed that the interfacial adhesive strength is governed by stiffness and occurrence of necking, even in atomistic stress-strain relationships. It was also found that stiffness correlates with the deformation mode of the molecular structure, and that necking occurs between the weakest bonds with small bond population and are determined by the interatomic local strain. Interfacial debonding occurred in both first-principles calculations and tensile tests, and the first-principles calculated values of interfacial adhesive strength were in qualitative agreement with the interfacial maximum stress values obtained by finite element analysis based on the breaking load during tensile tests of butt-bonded round bar specimens. Based on these results, this paper summarized effectiveness, applicable conditions and challenges of upscaling method from quantum mechanics to continuum mechanics.

Simple stitch-assisted carbon fiber-aluminum laminates via out-of-autoclave process

Fiber–metal laminates (FMLs) are hybrid materials that provide the advantages of both metal and fiber-reinforced polymer composite (FRP) such as improved damage tolerance and impact strength, particularly in aerospace and automotive applications. However, the production of FMLs remains expensive because the manufacturing process is performed in an autoclave. In addition, delamination failure due to low interfacial adhesive strength between the metal and fiber layer is a problem that must be solved to improve the mechanical properties of FMLs. In this study, simple stitch-assisted carbon fiber-aluminum laminates were developed using vacuum-assisted resin transfer molding (VARTM). The FMLs produced through vacuum-assisted resin transfer molding were stitched with aramid fibers through holes on Al sheets for the resin flow associated with the VARTM. The mechanical properties of the FMLs were investigated by impact and compression after impact tests as well as double cantilever beam and flexural tests. The stitching effectively improved the interfacial strength and toughness owing to the anchoring between the aluminum and carbon fiber layers, thus preventing delamination crack propagation. As a result, the stitched FML with significantly improved interfacial adhesive and toughness was developed by the VARTM process, which will accelerate the application of FML to various lightweight structures.