Interface Decohesion Research Articles

Smart Binders for Silicon Based Composite Electrode in Li-Ion Batteries

Silicon is one of the most promising alloying anode materials for Li-ion batteries thanks to its high specific and volumetric capacity. In comparison with the commercially available graphite, silicon delivers 10 times higher specific capacity (up to 3600 mA.h.g-1) and 3 times higher volumetric capacity ( up to 2200 mA.h.cm-3) [1]. However, silicon suffers from high volumic expansion upon lithiation (up to 280 %). It induces the pulverization of the micrometric silicon particle, the perpetual solid electrolyte interface renewal and decohesion between constitutive elements of the electrode, drastically reducing its lifespan [2].To tackle those issues we propose the formulation of composite electrode with improved binder. It is composed of carboxymethyl cellulose sodium salt (NaCMC, as a binding network) and zinc sulfate dissolved in a pH 3 buffer solution (composed of citric acid and potassium hydroxide). The originality and improvement comes from the use Zn2+ ions as coordination agents, binding to carboxylate groups from the CMC and citric acid. Among benefits, we believe that the coordination helps to mitigate the stress inside the electrode because of the improved reticulation of the network, thus improving its resilience [3]. To support this hypothesis, we provide physico-chemical characterizations of the binder as well as the electrochemical performances of our electrodes. [1] M.N. Obrovac, V.L. Chevrier, Alloy Negative Electrodes for Li-Ion Batteries. Chem. Rev. 2014, 114, 11444-11502. [2] A. Etiemble, A. Tranchot, T. Douillard, H. Idrissi, E. Maire, L. Roué., Evolution of the 3D Microstructure of a Si-Based Electrode for Li-Ion Batteries Investigated by FIB/SEM Tomography, J. Electrochem. Soc. 2016,163, A1550-A1559 [3] D. Mazouzi, R. Grissa, M. Paris, Z. Karkar, L. Huet, D. Guyomard, L. Roué, T. Devic, B. Lestriez, CMC-citric acid Cu(II) cross-linked binder approach to improve the electrochemical performance of Si-based electrodes. Electrochim. Acta 2019, 304, 495-504.

Role of tempering cooling rate on impact toughness of 2CrMoV weld metal

Abstract

Decohesion of a rigid flat punch from an elastic layer of finite thickness

Interfacial bond strength is a crucial mechanical property of solid adhesive joints that plays an important role in a wide range of applications. A common way of quantifying mechanical strength of an adhered interface is to measure the apparent adhesion strength by finding the maximum pulling force in a tensile bond test and dividing it by the area. Despite the simplicity of this method, there is growing evidence suggesting that the measured quantity is not necessarily an intrinsic attribute of the interface but depends on thickness of the adhesive film and size of the interface. In this work, the critical pull-off force of a flat rigid punch adhered to an elastic film of finite thickness is studied via asymptotic analysis as well as finite element (FE) simulations. The decohesion behavior is found to be governed by two dimensionless parameters η and φ: the former represents the deformation of the interface relative to the interaction distance of interfacial forces, while the latter denotes a correction factor due to finite thickness of the film. As η changes from 0 to infinity, the interface decohesion would take place from uniform detachment (DMT-like) to crack-like propagation (JKR-like). The transition behavior can be well described by an empirical solution, which suggests a new rational procedure to consistently characterize the intrinsic adhesion properties of an adhered interface from tensile bond tests. Finally, the general empirical solution and the adhesion characterization procedure are directly validated by a series of experiments via detaching a stainless-steel flat punch from adhesive Polydimethylsiloxane (PDMS) films. This work not only offers a clear and explicit solution to capture the transition behavior of interface decohesion but also provides a guideline for modulating adhesion performance via geometry rather than chemistry of the adhesives.

Effect of austenite stability on the fracture micromechanisms and ductile-to-brittle transition in a medium-Mn, ultra-fine-grained steel for automotive applications

This work reports on the tensile and Charpy impact behaviour of a high-strength, ultra-fine-grained, medium-manganese steel with a ferrite + austenite microstructure. The mechanical stability of austenite was varied by varying the test temperature, while keeping all other microstructural features constant. By lowering the tensile test temperature, austenite decomposition into martensite occurred earlier, inducing strong work hardening, decreasing tensile elongation and triggering ferrite–martensite interfacial decohesion. Under impact testing, the material exhibited a broad transition in absorbed energy and in thickness reduction at fracture initiation. A continuous transition in fracture mechanism, from fully ductile to fully interfacial fracture, occurred with lowering the test temperature. Besides chemically induced weakening of ferrite–austenite interfaces, the temperature-dependent mechanical stability of retained austenite, as well as the strength of the ferrite phase, is thought to control local stresses at interfaces between ferrite and freshly formed martensite. It thus drives the extent of interfacial microcrack initiation and propagation before blunting and development into voids.

Metallurgical modeling of intergranular HAZ liquation cracking during laser welding newly developed crystallography-dependent aerospace materials. Part II: Grain boundary alloying segregation of microstructure modification

Metallurgical modeling of the nonequilibrium grain boundary segregation was coupled with a nonequilibrium weld pool solidification to numerically analyze the contributing factors to liquation cracking resistance. The effect of the welding conditions, material composition, and average grain size on the kinetics of the grain boundary segregation in the Inconel 718-type nickel-based superalloy during laser welding were optimized. The grain boundary segregation of boron near the fusion boundary is of particular interest, and is closely correlated to the intergranular heat-affected zone (HAZ) liquation cracking. It is indicated that the low heat input, fine-grained material and full penetration contribute to the reversible desegregation of boron and suppress the grain boundary segregation of boron to significantly minimize the segregation-induced grain boundary liquation and improve the weldablity. The subsolidus temperature due to nonequilibrium weld pool solidification is capable of ameliorating the segregation kinetics to reduce the HAZ grain boundary segregation. Intergranular HAZ liquation cracking is evitable with a crack-free weld without using filler wire. The grain boundary segregation decreases and the threshold tensile stress of solid-liquid interfacial decohesion across the intergranular liquid film simultaneously increases in the recrystallized HAZ during the weld shape change from partial penetration to full keyhole penetration. Furthermore, the numerical analysis results are verified indirectly by the experiment results of the total crack length. In addition, this metallurgical modeling is also applicable for the alloying segregation behavior prediction of other nickel-based superalloys with similar metallurgical properties.

Computational micromechanical modeling of transverse tensile damage behavior in unidirectional glass fiber-reinforced plastic composite plies: Ductile versus brittle fracture mechanics approach

A detailed micromechanical finite element analysis methodology is presented to predict the transverse tensile (fiber perpendicular) failure behavior of a unidirectional (UD) glass fiber-reinforced plastic composite ply. In order to understand the constituent-level stress–strain and damage behavior, finite element analysis is accomplished using representative volume element (RVE) that consists of random fiber distribution as observed in the microscopic image of an actual composite ply. For modeling the fiber/matrix interface failure behavior, cohesive zone module (cohesive surface/cohesive element) of Abaqus® is used. In order to capture the epoxy matrix stiffness and strength degradation, the following two different approaches are used: (i) initially, the linear Drucker–Prager plasticity model in combination with a ductile fracture criterion is used; (ii) later, a brittle failure approach such as the quadratic normal stress criterion within the framework of eXtended finite element method is used. From the detailed micromechanical analysis of the RVE, it is observed that the initial damage in the RVE occurs in the form of fiber/matrix interface decohesion. With increasing tensile load, interface crack propagates and creates a stress concentration region in the matrix material, adjacent to the crack tip. Further load application causes both interface crack tip and matrix stress concentration to move away from the load application direction. As soon as the interface crack tip reaches approximately 60° to 70° away from the load application direction, the conjunction of the matrix damage with the interface crack leads to the RVE final failure. The predicted average stress–strain curves from the above-mentioned two different epoxy matrix failure criterions (ductile and brittle) correlate very well with the experimental results, indicating that the brittle failure behavior of a UD fiber-reinforced plastic composite ply under transverse tensile load is mainly controlled by the fiber/matrix interface properties.

An FFT-based spectral solver for interface decohesion modelling using a gradient damage approach

This work presents a fast Fourier transform (FFT) based method that can be used to model interface decohesion. The inability of an FFT solver to deal with sharp interfaces discards the use of conventional cohesive zones to model the interfacial mechanical behaviour within this framework. This limitation is overcome by approximating sharp interfaces (e.g. grain/phase boundaries) with an interphase. Within the interphase, the background plastic constitutive behaviour is inherited from the respective adjacent grains. The anisotropic kinematics of the decohesion process is modelled using a damage deformation gradient that is constructed by mapping the opening strains (in normal and tangential modes) to the associated projection tensors. The degradation (damage) of the interfacial opening resistances is modelled via a dimensionless nonlocal damage variable that prevents localisation of damage within the interphase. This nonlocal variable results from the solution of a gradient damage based regularisation equation within the interphase subdomain. The damage field is constrained to the interphase region by applying a relatively large penalisation on the damage gradients inside the interphase. The extent of nonlocality ensures that the damage is largely uniform in the direction perpendicular to the interphase, thus making its thickness the theoretical lengthscale for dissipation. To achieve model predictions that are objective with respect to the interphase thickness, scaling relations of the model parameters are proposed. The numerical performance is shown for a uniform opening case and then for a propagating crack. Finally, an application to an artificial polycrystal is shown.

Plastic deformation and fracture behaviors in particle-reinforced aluminum composites: A numerical approach using an enhanced finite element model

A microstructure-based comprehensive finite element model, which incorporated the deformation/fracture of the matrix alloy, fracture of the particle and decohesion of interface, was built to predict the effects of particle size and shape on the plastic deformation and fracture behaviors in particle-reinforced metal matrix composites. The effect of particle size on the yield strength and work hardening rate of the matrix alloy was demonstrated. When the particle diameter is <10 µm, the fracture of the matrix alloy near the interface dominates the failure mechanism of the composite, whereas changed to particle fracture with particle diameter >10 µm. A cohesive zone model was also included in order to predict interfacial failure behavior. It was noted that SiC/Al interface exhibits a high interfacial bonding strength and the interfacial decohesion was caused by crack propagation from the particle to the interface. The simulation results are in good agreement with the experiment tensile test results in the SiCp/6061Al composite.

Microstructure and mechanical properties of a high-Zn aluminum alloy prepared by melt spinning and extrusion

High-Zn aluminum casting alloys usually contain coarse dendrites, network eutectoid structure and casting defects which deteriorate the mechanical properties seriously. In order to overcome these problems, the combination of melt spinning and extrusion was explored for microstructure modification in this work. A high-Zn aluminum alloy (Al–27Zn-1.5Mg-1.2Cu-0.08Zr) was prepared by melt spinning and extrusion. The results show that the melt spun alloy mainly consists of micro-sized network-like grain boundary (GB) η-MgZn2 structure (η phase) and disc-like precipitates (GP-zone, η′-phase and η-precursor) embedded into fine α-Al grains with high solute atomic concentration. After extrusion, the grain size of α-Al is further refined due to the recrystallization, and primary network GB η-phase structures are transformed to granular η particles. Moreover, the extrusion induces the precipitation of nano-sized η′-phase, η-precursor and Zn phases. As a result, the alloy exhibits a high tensile strength of 485 MPa and a reasonable elongation of 5.2%. The contributions of grain boundary, dislocation, solid solution and precipitate strengthening to the yield strength are calculated according to the microstructure analysis, and it is found that precipitation strengthening is the main strengthening mechanism in this alloy. Fracture analysis shows that micro-cracks preferentially occur at α-Al/η phase interfaces due to interfacial de-cohesion, and propagate along the GBs.

Analysis of high-temperature flexural behaviour of copper–alumina micro- and nanocomposites

Copper (Cu)-based composites were studied for their high-temperature mechanical response. Copper is a high temperature–high strength material when combined with harder reinforcements, which find applications in engine components. High-temperature flexural testing of copper–alumina (Al2O3) micro- and nanocomposites fabricated by powder metallurgy was carried out at temperatures of 100 and 250°C. The composition of micro- and nanocomposites varied as 5, 10 and 20 vol.% and 1, 3 and 5 vol.%, respectively. The variation in the flexural strength of the composites at high-temperature testing is reported and compared with the ambient test values here, and, subsequently, deformation mechanisms of the composites are discussed. Fractography was performed to predict the mode of failure. The ductile mode of failure in microcomposites is contradictory to quasicleavage in nanocomposites. Nanocomposites show higher flexural strength at 100°C compared to microcounterparts. Interfacial de-cohesion and particle pull out are the results of the thermal gradient across the matrix to the reinforcement.

Ballistic Response of a FCC-B2 Eutectic AlCoCrFeNi2.1 High Entropy Alloy

An AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA), comprising of FCC phase and a high volume fraction of plate and irregularly shaped BCC-ordered intermetallic B2 domains, was subjected to normal impact by spherical Tungsten–Carbide projectiles. Depending on projectile velocity, the impacted AlCoCrFeNi2.1 plates were partially penetrated (at the lowest velocity of 803 m/s), plugged (intermediate velocity of 1159 m/s), and fully penetrated (highest velocity of 1388 m/s). Electron microscopy was utilized to characterize the residual damage or deformation features in the recovered specimens. Failure in the partially penetrated conditions was dominated by interfacial decohesion at the plate-like B2 and FCC interfaces. At higher velocities where plugging occurred, failure was dominated by crack formation in regions containing adiabatic shear band. These results indicated a transition in failure modes as a function of projectile velocities, where the FCC-B2 microstructure dominate failure at lower velocities, while such microstructural features do not influence dynamic failure at higher velocities.

Superior tensile fracture strength of hot isostatically pressed TiC–steel metallic composite fabricated by a novel infiltration

A metallic composite having TiC particle content as high as ~47 vol% in a cold work tool steel matrix was successfully fabricated by a novel infiltration process. The penetration of the liquid steel reached geometrically complex regions, such that no interfacial flaw was observed. The interface between the ferrite matrix and TiC was semicoherent with a faceted morphology consisting of low-index planes of each phase. Owing to these characteristics of the interface, neither interfacial decohesion nor cracking was observed after the tensile fracture. The initial failure occurred in the TiC particle by a {100} cleavage fracture. The cracks formed from each fractured TiC particle interlinked forming a major crack. The hot-isostatically pressed composite exhibited 16% higher strength (919 MPa) than the as-infiltrated composite (791 MPa). The fracture strength of the composite largely depended on the degrees of suppression of the TiC cracking and its propagation. The residual stresses pertaining to the TiC and steel matrix were measured by X-ray diffraction. They were not significant factors responsible for the increased fracture strength of the hot-isostatically pressed composite. The increased strength of the hot-isostatically pressed composite could be explained in terms of the mutually interactive influences of the load transfer mechanism, matrix toughening, reduced TiC contiguity, and M7C3 carbide bridging TiC particles.

Recipe for improving the impact toughness of high-strength pearlitic steel by controlling the cleavage cracking mechanisms

Achieving superior impact toughness in high-strength pearlitic steels is extremely desirable and challenging due to the brittle character of the intervening cementite lamellae. Besides the ‘Hall-Petch’ type lamellar strengthening, a systematic understanding of various micro-toughening mechanisms through cleavage cracking resistance is essential to develop an integrated microstructure for toughness improvement. In this study, both thermal as well as thermo mechanical processing routes were adopted to correlate the processing and microstructural parameters with the mechanical properties. The prime contribution of pearlite nodule size refinement towards improving the impact toughness is discussed in terms of frequent cleavage crack deflection at the nodule boundaries. Other microstructural parameters controlling the toughness are the pearlite morphology (lamellar or spheroidized), interlamellar spacing and the cementite lamellae orientation with the crack path. It appears that both spheroidized and fine lamellar pearlite are more effective crack arresters than their coarse lamellar pearlite counterparts. Besides, the variation of crack growth resistance with the pearlite lamellae orientation and the ferrite-cementite interface (habit) plane is also presented, relating to the mechanism of interface decohesion.

Compressive failure of fiber composites containing stress concentrations: Homogenization with fiber-matrix interfacial decohesion based on a total Lagrangian formulation

Compression failure by fiber kinking limits the structural applications of fiber composites. Fiber kinking is especially prevalent in laminates with holes and cutouts. The latter behavior is characterized by strain localization in the matrix material and fiber rotations. To study fiber kinking on the level of the individual constituents, a homogenization of fiber composites is presented. It is based on a total Lagrangian formulation, making it independent of fiber rotations. It accounts for the microstructure of the composite, including fiber-matrix interfacial decohesion, and enables all types of material behavior of the constituents. The response of each constituent of the composite is modeled separately and the global response is obtained by an assembly of all contributions. The model is implemented as a user-defined material model (UMAT) in ABAQUS and used for multiscale modeling of notched unidirectional plies subjected to compression. The model performs well in agreement with a finite element model of an explicit discretization of the microstructure and literature results. The simulations predict the formation of a kink band in near 0-degree plies and show that the open-hole compression strength is sensitive to fiber-matrix interfacial decohesion. The present work suggests a convenient and computationally efficient tool for simulating the elastic-plastic behavior of fiber composites on the fiber-matrix level and predicting the compressive strength of laminates.

Intercritical annealing temperature dependence of hydrogen embrittlement behavior of cold-rolled Al-containing medium-Mn steel

The present investigation attempts to evaluate the influence of intercritical annealing temperature (TIA) on the hydrogen embrittlement (HE) of a cold-rolled Al-containing medium-Mn steel (Fe-0.2C-4.88Mn-3.11Al-0.62Si) by using electrochemical hydrogen-charging, slow strain rate tensile test and scanning electron microscope. The results show that an excellent combination of strength and ductility (the product of ultimate tensile strength and total elongation) up to ∼53 GPa·% was obtained for the specimen intercritically annealed at an intermediate temperature of 730 °C, whereas the HE index increases significantly with an increase in TIA up to 850 °C. Being different from the typical dimple ductile fracture for the uncharged specimen, the hydrogen-charged specimen exhibits a mixed brittle interface decohesion and ductile intragranular fracture mode in the crack initiation region and the brittle fracture fraction increases with increasing TIA. Both the stability and amount of austenite play a critical role in governing the HE behavior of TRIP-assisted medium-Mn steel. Thus, it is suggested that suitable TIA should be explored to guarantee the safety service of automotive parts made of this type of steel in addition to acquiring excellent mechanical properties.

Effect of Ferrite/Martensite Phase Size on Tensile Behavior of Dual-Phase Steels with Nano-Precipitation of Vanadium Carbides

This study investigates the effect of ferrite/martensite phase size and dispersion of nano-precipitates in ferrite on strength, ductility, and fracture behavior of dual-phase (DP) steels. Dispersion of nano-precipitates in ferrite improves the strength with keeping sufficient uniform elongation and post-uniform elongation, while decrease in ferrite/martensite phase size has a little effect on the increase in strength in the phase size range investigated. However, the refinement of phase size significantly improves the post-uniform elongation and reduction in area. It is concluded therefore that a simultaneous combination of refinement of ferrite/martensite phase size and dispersion of nano-precipitation in ferrite is effective to significantly improve the strength and strength–post-uniform elongation in DP steels. Quantitative analysis of void formation reveals that fracture by martensite cracking is a primary fracture mechanism in coarse phase-sized DP samples, while ferrite/martensite interface decohesion becomes a dominant fracture mechanism in fine phase-sized DP samples. It is suggested that the refinement of phase size is a promising strategy to change the fracture behavior from brittle to ductile manner, leading to an enhancement of local deformability after the necking.

Acoustic emissions during tensile test of DC06 and HCT600X

AbstractIn this paper the acoustic emission behaviour during tensile tests of the materials DC06 and HCT600X is studied. Two steels with different characteristics (mild deep‐drawing steel DC06 and high‐strength steel HCT600X) are consciously chosen to show the influence of the material properties on the generated acoustic emissions. The acoustic emission behaviour and the corresponding signals differ clearly from each other. In addition, the effect of the strain rate as well as the rolling direction (0°, 90°) on the acoustic emission behaviour is investigated. Both parameters have a significant influence on the resulting acoustic emissions during tensile deformation. Furthermore, a new criterion based on the acoustic emission parameter FCOG (centroid frequency) for detection of damage beginning in dual‐phase steels is developed. The criterion supports the assumption that during tensile deformation of dual‐phase steels two failure mechanisms, ferrite/martensite interface decohesion and martensite phase fracture, exist.

Temperature-Dependent Interfacial Debonding and Frictional Behavior of Fiber-Reinforced Polymer Composites

As fiber-reinforced polymer matrix composites are often cured from stress-free high temperature, when subjected to ambient temperature, both the mismatch of the coefficient of linear thermal expansion between the fiber and the matrix and the dependence of material properties on temperature will influence the interfacial behavior. Thus, it is necessary to provide an insight into the mechanism of temperature effects on the thermomechanical properties and behaviors along the interface. In this work, we conducted microbond tests of the glass fiber–epoxy material system at controlled testing temperature (Tt). A modified interface model is formulated and implemented to study the interfacial decohesion and frictional sliding behavior of microbond tests at different Tt. With proper cohesive parameters obtained, the model can predict temperature-dependent interfacial behaviors in fiber-reinforced composites. Both the slope of the peak force as well as the measured force at the stage of frictional sliding decrease with Tt in a wide range of the length of microdroplet-embedded fiber (le). The interfacial shear strength (IFSS) keeps almost constant at Tt ≤ 40 °C and decreases with le when temperature is above 40 °C. The average frictional stress (τfAverage) along the interface increases with le when temperature is below 80 °C but is almost constant when temperature is above or equal to 80 °C. Overall, in the same range of le, τfAverage is greater when Tt is at low temperature.

Influence of Fiber Distribution and Interfacial Strength on Transverse Compressive Strength of Unidirectional Composites

The representative volume element(RVE) of the computational micromechanics is established with random fiber distribution being generated by random sequential expansion algorithm. The plasticity of matrix and interfacial decohesion are simulated by using Drucker-Prager model and cohesive zone model respectively. The effects of the random fiber distribution and interfacial strength on the transverse compressive strength of unidirectional composites are analyzed. The results show that the random fiber distribution is a factor to cause the instability of the transverse compressive strength. Meanwhile, the matrix plastic shear damage and non interfacial damage is dominated in compression failure. Therefore, the RVE model without interface element adopted can clearly predict the compressive strength and the damage process of unidirectional composites, which contributes to simplify the modeling without considering the value of interfacial parameters.

Experimental investigation and simulation on stress rupture behavior of a Ni-based DS superalloy affected by initial elastic-plastic multi-axial stress state

In this study, the stress rupture behavior of a Ni-based directionally solidified (DS) superalloy affected by initial elastic-plastic multiaxial stress state at 850 °C has been investigated. Smooth and three types of U-shape notched plate specimens have been adopted. The notch effect on stress rupture lives is exhibited as notch softening, and there is a positive correlation between the degree of notch softening and theoretical stress concentration factor. Scanning electron microscopy (SEM) observation is conducted to reveal failure mechanism. For both smooth and notched specimens, thickness dependence on crack initiation due to the changed crack tip stress state is exhibited. The initiation of microcracks is mainly caused by interfacial decohesion at the carbide/matrix interface, non-uniform deformation field at eutectic/matrix interface and stress concentration around cavities. The plastic fiber zone of smooth plate is located in the intermediate region, which is occurred throughout a wide region near notch root of notched specimen. Finally, a finite element analysis (FEA) is performed based on the transverses elastic viscoplastic constitutive model with the Kachanov-Rabotnov damage rule. The simulation results show that the effect of notch softening is due to the fact that the redistributed tensile stress is higher than the value of net section stress in a very wide region.