Interphase Interface Research Articles

Stress–strain prediction of dual phase steels using 3D RVEs considering both interphase hardness variation and interface debonding at grain boundaries

Stress–strain prediction of dual phase steels using 3D RVEs considering both interphase hardness variation and interface debonding at grain boundaries

Elastic equilibrium of spherical particle composites with transversely isotropic interphase and incoherent material interface

The rigorous analytical solution to the unit cell model of spherical particle composite with transversely isotropic interphase and incoherent material interface has been obtained by the multipole expansion method. To this end, a general expression of the displacement vector in spherical transversely isotropic solid in terms of the vector spherical harmonics has been derived. By accurate fulfillment of the contact conditions, the model boundary value problem is reduced to the linear algebraic system. The anisotropic interface model has been developed as the first order approximation of the transversely isotropic interphase. Relevance of this model to the theory of material interfaces and its applicability in the nanomechanics context is discussed. The developed model expands the theory of curved deformable interfaces of Gurtin et al. [Phil. Mag. A 78 (1998) 1093] on the incoherent interfaces between the dissimilar elastic materials and provides a certain insight into the interface elastic moduli. Taking incoherency of the nano level interfaces into account enables more realistic models and thus increases the predictive power the homogenization theory of nanostructured solids. The obtained accurate numerical data discover a significant effect of the interphase/interface anisotropy on the local stress and effective stiffness of spherical particle composite.

Quenching of graphene suspension photoluminescence with saturated hydrocarbons

This paper describes a study of quenching of graphene suspension (GS) photoluminescence upon formation of an interphase interface by a saturated hydrocarbon using n-octane (С8Н18) as an example. Based on the analysed photoluminescence spectra, structural analysis, and theoretical evaluations, the paper offers a model where octane molecules are attached at the edges of composite graphene sheets by the presence of functional oxygen-containing groups. It is assumed that in the formed structure quenching of photoluminescence relates to the Anderson electron density delocalisation effect.

Representative unit cell model of elastic spherical particle composite with interphase and/or general imperfect interface

We consider the representative unit cell (RUC) model of the elastic spherical particle composite with (a) interphase layer and (b) general imperfect interface in the form proposed by Bövik (1994). The rigorous analytical solution to both RUC model problems is obtained by the multipole expansion method in a unified manner. Fulfillment of the matrix-to-inhomogeneity elastic contact conditions reduces the boundary value problem to the linear algebraic system for multipole strengths and provides a highly efficient algorithm for numerical study. The proposed approach applies to all physically consistent models of imperfect interface including the nonlinear ones. In so doing, use of the vector spherical harmonics makes the solving procedure simple and straightforward. Comparison of the accurate numerical data obtained from the interphase and interface models confirms correctness of the Bövik model and illustrates its applicability limits in the multi-particle environment. The developed RUC model enables consideration of composite with the spherical particles of diverse size, properties, interphases and interface bonding, with an adequate account of interaction between the inhomogeneities. Comparison with the laboratory test data for syntactic foam shows that a careful modeling of microstructure is a prerequisite for reliable prediction of the effective elastic properties of composite.

Austenite to Ferrite Transformation in Fe – 9 %Cr Alloys. II. Determination of Growth Rates

The paper continues theoretical analysis of austenite to ferrite transformation in an Fe-9 %Cr alloy demonstrating a typical site-saturation behaviour under the condition of diffusionless growth of a phase. In the previous paper the K coefficient in the Avrami equations being the asymptotes of Calm’s solution of the site-saturation transformation kinetics was used that contained a constant activation energy indicating the small value of the work of critical nucleus formation. This approach permitted to determine activation energy of transformation that was found to be equal to about 300 kJ/mole. In the present paper a new method of finding Calm’s equation coefficients from bending point at isothermal curves plotted on double logarithmic scale is proposed. Actually this bending point is the intercept of the two above-mentioned asymptotes of the Cahn’s curve, and equating the formulae describing theses asymptotes allows to find the coefficients in question. Given the average austenite grain size, it permits to find numerical values of growth rates. The activation energy thus acquires the exact physical meaning of the energy barrier at the interphase interface; its value was found to be 286 kJ/mole, which is close to previous results. The growth rates were thus determined as a function of temperature and the TTT diagram for the alloy is calculated that shows close correspondence with experiment.

Dual-Functional Electrolyte Additives toward Long-Cycling Lithium-Ion Batteries: Ecofriendly Designed Carbonate Derivatives.

Long-term stability of the solid electrolyte interphase (SEI) and cathode-electrolyte interface (CEI) layers formed on anodes and cathodes is imperative to mitigate the interfacial degradation of electrodes and enhance the cycle life of lithium-ion batteries (LIBs). However, the SEI on the anode and CEI on the cathode are vulnerable to the reactive species of PF5 and HF produced by the decomposition and hydrolysis of the conventional LiPF6 electrolyte in a battery inevitably containing a trace amount of water. Here, we report a new class of cyclic carbonate-based electrolyte additives to preserve the integrity of SEI and CEI in LIBs. This new class of additives is designed and synthesized by an ecofriendly approach that involves fixing CO2 with functional epoxides bearing various reactive side chains. It was found that the cyclic carbonates of 3-(1-ethoxyethoxy)-1,2-propylene carbonate and 3-trimethoxysilylpropyloxy-1,2-propylene carbonate, possessing high capability for the stabilization of Lewis-acidic PF5, exhibit a capacity retention of 79.0% after 1000 cycles, which is superior to that of the pristine electrolyte of 54.7%. Moreover, TMSPC has HF-scavenging capability, which, along with PF5 stabilization, results in enhanced rate capability of commercial LiNi0.6Mn0.2Co0.2O2 (NCM622)/graphite full cells, posing a significant potential for high-energy-density LIBs with long cycle stability.

Failure Analysis of Unidirectional Ceramic Matrix Composite Lamina and Cross-Ply Laminate under Fiber Direction Uniaxial Tensile Load: Cohesive Zone Modeling and Brittle Fracture Mechanics Approach

The current research work presents the computational micromechanical analysis of the room temperature tensile failure behavior of unidirectional (UD) and cross-ply (0/90) ceramic matrix composites (CMCs). For computational micromechanical analysis, three-dimensional (3D) representative volume element (RVE) and multi-fiber multilayer RVE (M2 RVE) models are generated that are representative of the lamina and the laminate under investigation. The RVE and M2 RVE models are generated by replicating the fiber distribution, and the placement of the fibers observed in a microscopic image of an actual CMC laminate. The generated RVE models consist of the discrete representation of individual constituent phases of the CMC such as fibers, interphase, matrix, and the fiber–interphase interface region. Under the applied external tensile load, the fiber–interphase interface interactions are modeled using the cohesive elements that follow the bilinear traction separation law. The matrix, fiber, and interphase materials failure behavior is captured using a brittle cracking model. In order to validate the proposed numerical methodology, the predicted average stress–strain curve at the UD laminate level is compared to the experimental stress–strain curve reported in the literature. In addition, the observed different phases in the predicted stress–strain curve are validated with the literature data. Using the proposed numerical methodology, a detailed local stress–strain and damage analysis leads to an observation that the so-called ductile stress–strain behavior (kink in the stress–strain curve) of a CMC UD laminate under uniaxial fiber direction tensile loads is mainly caused by the matrix damage initiation. Apart from the SiC material properties such as strength and fracture energy, it is also observed that the RVE size influences the average strength and failure strain predictions using computational micromechanics.

Structure and properties of layer, surfaced on HARDOX 450 steel by boron containing wire

Analysis of structure phase states and properties of the layers formed on HARDOX 450 low alloy steel by welded-on wires with boron content of 4.5 and 6.5 % wt. was made by the methods of modern physical material science. In the initial state HARDOX 450 steel has the structure of tempered martensite, in the volume and along the boundaries of crystals of it the cementite particles are located. The particles located in the volume have acicular shape and those along boundaries are mainly round. The presence of extinction bend contours has been revealed, indicative of the curvature torsion of crystal lattice of the material’s portion. They originate and finish on the interfaces of martensite crystals. Scalar density of chaotically located dislocations and forming the netlike substructure is 6.2·1010 cm–2. The layer welded on HARDOX 450 steel has microhardness increasing by more than two-fold that of the base. Analysis of state diagrams of Fe – C, Fe – B, B – C systems and polythermal cross–sections in Fe – C – B system has shown that the rapid cooling of Fe23C6 – Fe23B6 alloys from liquid state would facilitate the formation of multiphase structural states. It is stated by the methods of transmission electron diffraction microscopy that the reasons for the high microhardness level of the surface layers are the following: formation of iron borides and crystals of ultafine-dispersion (up to 100 nm) packet martensite with high level (~1011 cm–2 ) of scalar density of dislocations; presence of nanodimentional particles of iron and boron carbides in the volume and on the boundaries of martensite crystals; high level of curvature torsion of crystal lattice of iron borides and α-phase grains, caused by the internal stress fields along interphase (interface of iron boride crystals and α-phase grains) and intraphase boundaries (interface of iron borides and martensite crystals packet). Increase in boron concentration from 4.5 to 6.5 % is accompanied by the sufficient increase (by 1.2 – 1.5 times) in hardness of welded layer. It is caused by the increase of dimensions and relative content of iron boride regions by 1.5 – 2.0 times.

Comparative study of CNC and CNF as additives in waterborne acrylate-based anti-corrosion coatings

Nanocomposite coatings are of great interest as barrier coatings since synergy effects between matrix and additive properties can be achieved. This, however, requires favorable additive-matrix interactions to provide a strong interphase (interface region). In this work we elucidate the properties of two environmentally benign nanocomposite coatings based on a waterborne acrylate formulation with additives from renewable sources, i.e. either cellulose nanocrystals, CNC; or, alternatively, cellulose nanofibrils, CNF. We focus on the corrosion protective properties of these coatings and discuss the reason why the nanocomposite with CNC displays favorable corrosion protection properties whereas that with CNF does not. To this end we utilized scanning electron microscopy, water contact angle measurement, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy techniques to investigate the microstructure, surface wetting, interactions between cellulosic materials and matrix as well as corrosion protective properties of both composite coatings.

Tailored interphase and thermal interface resistance of self‐assembled thermally reduced graphene oxide–polyamide hybrid/epoxy composites with enhanced thermal conductivity

ABSTRACTThermally reduced graphene oxide–polyamide (TrGO‐PA) hybrids were fabricated by self‐assembly between TrGO nanosheets and PA microparticles, and the dispersibility, interphase extension, and thermal conduction mechanism of TrGO‐PA/epoxy (EP) composites were investigated. Most of the oxygen‐containing functional groups of TrGO were removed, and a conjugated structure of graphene was recovered. TrGO was distributed evenly on the PA surface via electrostatic adsorption between TrGO and PA, which resulted in the inhibition of TrGO aggregation in the epoxy matrix. Compared with that of TrGO/EP and PA/EP composites, the thermal interface resistance (RTIM) of TrGO‐PA/EP composites was greatly decreased to 38.3 mm2 kW−1 and the thermal conductivity was improved to 0.268 W/(m K), which was attributed to the enhanced dispersibility of TrGO‐PA and the enlarged interphase in TrGO‐PA/EP composites. A schematic model of thermal conduction mechanisms was proposed based on the formation of contiguous thermal transfer pathways by bridged TrGO adsorbed on well‐dispersed PA microparticles in TrGO‐PA/EP composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47826.

Effect of the System Geometry on the Flow Stability of an Evaporating Liquid

In this paper, we study the exact stationary solution of the Oberbeck–Boussinesq equations describing the joint flow of a viscous heat-conducting liquid and the cocurrent flow of a gas-vapor mixture in a flat horizontal layer. The initial formulation of the problem takes into account mass transfer through the interphase interface due to evaporation, vapor diffusion in the gas phase in the presence of diffusion heat conduction, and a longitudinal temperature gradient at the solid impermeable boundaries of the channel. The effect of the layer thickness of working media on the characteristics of the main flow under conditions of equal thermal load on the channel walls was studied. Based on the linear theory, the stability of the exact solution is studied, typical forms of perturbations and their dynamics are determined with a change in the linear dimensions of a system, and neutral curves and maps of the instability regimes are plotted.

An effectively inhibiting lithium dendrite growth in-situ-polymerized gel polymer electrolyte

Polyacrylate polymer is a promising polymer matrix for gel polymer electrolyte (GPE) in lithium-ion batteries. Herein, in-situ polymerized poly(ethylene glycol phenyl etheracrylate) (PEGPEA) based GPE combined with 1 M LiPF6 in ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (EC/DMC/EMC, 1:1:1 in volume) solvents was introduced. The maximum recoverable strain of the in-situ polymerized PEGPEA-GPE was up to 99%. The outstanding interfacial compatibility between PEGPEA-GPE and the lithium electrode was also obtained. Surprisingly, lithium dendrite was effectively suppressed in charge-discharge cycling because of polymer-enhanced solid electrolyte interphase (SEI) and excellent contact interface. Furthermore, the PEGPEA-GPE exhibited wide electrochemical stability window up to 4.9 V versus Li+/Li, and achieved an ionic conductivity of 3.35 × 10−3 S cm−1 at 25 °C. When used as electrolyte, the Li[Ni0.5Co0.2Mn0.3]O2/PEGPEA-GPE/Li batteries showed high discharge capacity retention rate of 97.5% after 70 charge-discharge cycles and considerable discharge rate capability, i.e., 155 mAh g−1 0.2C, 142 mAh g−1 0.5C, 120 mAh g−1 1C, 60 mAh g−1 2C. These results demonstrate that this highly elastic in-situ polymerized PEGPEA-GPE is a potential electrolyte system for high-performance polymer electrolyte lithium-ion batteries and has excellent application prospects in wearable and flexible batteries.

Pulsed Laser Condensation of Dense Cubic ZnO with Unique Luminescence, Vibrations, and Interphase Interfaces

Dense ZnO with a high-pressure stabilized rocksalt (R)-type structure was fabricated by pulsed laser ablation of bulk wurtzite (W)-type ZnO under a rather high peak power density for a prolonged time in a vacuum. Such dynamic synthesis of R-ZnO relies on effective six-coordination of Zn with O atoms in a laser plume for homogeneous nucleation of R-besides the W-type structure with ZnO4 tetrahedra. The deposit on amorphous silica contains ca. 10% dense R-ZnO with internal compressive stress up to 22.5 GPa based on the X-ray lattice parameter. Transmission electron microscopic observations further indicated the polymorphic condensates are (011)R, (112̅0)W, and (0001)W faceted for mutual coalescence to reach specific crystallographic orientation relationships which are different from that due to R → W transformation, all with an energetically favorable three-dimensional match of lattice planes. The R-type islands up to 100 μm in size on silica substrate showed Raman bands at 800, 1380, and 1607 cm–1 and strong photoluminescence at 545 nm due to ZnO6 octahedra in the cubic crystal field.

Evolution of Microstructure and Mechanical Properties in Steels during Isothermal Holding in the Region of Bainitic Transformation Temperature in Dependence on Silicon Content

Under isothermal treatment conditions, bainite transformation involves decomposition of austenite into a nonequilibrium structure consisting of needles of super-saturated bainitic ferrite and carbide precipitates. Similarly to martensitic transformation, bainitic ferrite forms by shear mechanism. Owing to relatively low temperature, only interstitial elements, predominantly carbon, can migrate by diffusion. Depending on the transformation temperature, carbon migrates from ferrite and forms carbides, either within bainitic ferrite needles and at the interphase interface between bainitic ferrite and austenite, or only within bainitic ferrite needles. In conventional steels, bainite transformation continues until the decomposition of austenite phase is almost complete. If the steel contains enough silicon, carbide precipitation may be suppressed or even prevented altogether. In such case, carbon which diffuses from the needles of bainitic ferrite may enrich adjacent austenite areas. Depending on heat treatment conditions, the carbon-enriched austenite may become sufficiently stable to resist decomposition and remain in the microstructure.

Ab initio study of the likely orientation relationships of interphase and homophase interfaces in a two-phase HCP + BCC Mg-Li alloy

Density functional theory is employed to examine the properties of interfaces generated between the hexagonal close packed (HCP) α and body centred cubic (BCC) β phases in a Mg-8wt.%Li binary alloy. While there are four experimentally-observed and geometrically-predicted orientation relationships (OR) associated with these adjoining HCP and BCC structures, interfacial energy considerations govern the most likely choice of OR. Here, the Burgers OR was found to have the lowest interfacial energy and the largest work of separation. It was also shown that homophase β/β interfacial energies are much higher than the interfacial energy of the α/β phases exhibiting the Burgers OR as the preferred OR. The findings are consistent with the hypothesis that the energy of a preferred interface corresponds to a local minimum in the five-dimensional boundary geometrical phase space. In addition, it was revealed that occupied s bands of the local electronic density of states of atomic layers in the vicinity of the α/β interface exhibiting the Burgers OR shift towards lower electronic energies, thereby increasing the interface stability. The crystal orbital Hamiltonian population provided further quantitative evidence that such an interphase interface of Burgers OR represents the strongest covalent bonding, thereby indicating that chemical bonding constitutes an essential contribution to the interfacial energy. Hence, the simple association between geometrical parameters of an interface and interfacial energy is incomplete.

Experiments of methane gas solubility in formation water under high temperature and high pressure and their geological significance

ABSTRACTThe solubility of methane in formation water and water content in the coexisting gas phase were measured under the conditions of high temperature and high pressure, using an ultra-high-pressure fluid PVT system, where the experimental temperature reached up to 453 K and pressure reached up to 130 MPa. Experimental results show the following (1) The two phases of gas and liquid still exhibit an obvious interphase interface even under high temperatures and pressures. (2) When temperatures exceed 353 K, the solubility of methane in formation water increases as the temperature and pressure rise. The growth rate of solubility is faster under a relatively low temperature and pressure, and slower at a relatively high temperature and pressure, but the solubility will not increase without limit. In this experiment, the solubility of methane in formation water reached its peak when the temperature was at 453 K and the pressure at 130 MPa. (3) Water content in the coexisting gas phase increases as temperature rises, with a smaller increase at relatively low temperatures and a much greater increase at relatively high temperatures but decreases with the increasing pressure, more rapidly under low pressure and more slowly under high pressure. The solubility of methane in formation water and the water content in the coexisting gas phase are controlled by both temperature and pressure, but using classic calculation models, these two parameters under high temperatures and pressures are inconsistent with our experimental data. Therefore, the study is significant and highlights other possible effects on solubility and condensate water content. Additionally, an example from the Yinggehai Basin in the South China Sea, where the temperature and the pressure are high, demonstrates the influence of solubility and phase behaviour on natural gas migration, its formation and the distribution of gas reservoirs.

Micromechanics-based thermo-viscoelastic properties prediction of fiber reinforced polymers with graded interphases and slightly weakened interfaces

A three-dimensional (3D) micromechanical study is performed for effective viscoelastic properties prediction of fiber reinforced polymers (FRPs) containing elastic, transversely isotropic/isotropic ellipsoidal fibers surrounded by graded interphases, embedded in an isotropic, viscoelastic matrix. Based on mean-field homogenization theory, an improved double-inclusion model for FRPs considering graded interphase and imperfect interface is established. Applying two-step homogenization technology, elastic-viscoelastic corresponding approach and Time-Temperature Superposition Principle (TTSP), effective thermo-viscoelastic moduli of FRPs are obtained with respect to the grading and geometric parameters. By solving the interface damage tensors numerically, the mathematical errors in the previously used analytical expressions are avoided, and the entire prediction scheme is extended to fillers at any aspect ratio. Comparing the results for composites with 3D randomly dispersed fibers with existing semi-analytical solutions, the accuracy and efficiency of the proposed method is verified. Parameters analyses are conducted, which indicate that the established model and the proposed method should be of great help for predicting mechanical properties of FRPs and designing micro-composites.

Diversity and physiological and biochemical properties of heterotrophic bacteria isolated from Lake Baikal neuston

For heterotrophic microorganisms (44 strains) isolated-from the surface film of Lake Baikal, iden- tification was carried out and their. physiological and biochemical characteristics were determined. Com- pared to the water column, diversity of cultured heterotrophs was low, indicating formation of stable micro- bial communities at the air-water interphase interface. Heterotrophic bacteria isolated from the surface mi- crolayer exhibited the enzymatic activity comparable to that for strains form other biofilm associations. Deinococcusfi6us strain NA202 'vas the most active component of the community, capable of utilization of the broadest spectrum of mono- and disaccharides,'sugars, and amino acids. This strain possessed the highest diversity of extracellular enzymes and was the most resistant to UV radiation. The physiological and bio- chemical properties of this strain may-be responsible for its adaptation to survival in extreme conditions of the surface microlayer. Our results improve our understanding of occurrence of UV-resistant strains in freshwater ecosystems.

Clustering and precipitation processes in a ferritic titanium-molybdenum microalloyed steel

Atom Probe Microscopy has been performed on a titanium-molybdenum microalloyed steel after simulation of thermomechanical processing. The results reveal the evolution of clustering and precipitation reactions at the austenite/ferrite interphase interface during isothermal heat treatments of durations ranging between 300 s and 100 h. Shorter isothermal ageing times led to extensive solute clustering at the austenite/ferrite interface, which remained free of precipitates. For ageing times beyond 3600 s, high number densities of interphase nano-precipitates were observed along with extensive solute clustering. Beyond 100 h, there was little evidence of solute clustering at these austenite/ferrite microstructural interfaces, which were instead dominated by a dispersion of coarser nano-precipitates. Both the clusters and nano-precipitates formed during isothermal ageing possessed a disc shape morphology and the growth has taken place in the through thickness direction of the disc without much change in the aspect ratio. The size of clusters and nano-precipitates increased from ∼2 nm after 300 s to ∼15 nm after 100 h of isothermal ageing at 650 °C. The solute clusters contain mainly C, Ti and Mo atoms, while the stoichiometry of the nano-precipitates approached that of MC carbide as their size increased beyond ∼4 nm. It is proposed that Mo controls the process of precipitate growth, resulting in a fine and uniform dispersion of nano-precipitates and a high level of tensile strength after just 300 s ageing at 650 °C. Interestingly, the peak strength was achieved during the very early stages of the precipitation process.

A model for the compositions of non-stoichiometric intermediate phases formed by diffusion reactions, and its application to Nb3Sn superconductors.

In this work we explore the compositions of non-stoichiometric intermediate phases formed by diffusion reactions: a mathematical framework is developed and tested against the specific case of Nb3Sn superconductors. In the first part, the governing equations for the bulk diffusion and inter-phase interface reactions during the growth of a compound are derived, numerical solutions to which give both the composition profile and growth rate of the compound layer. The analytic solutions are obtained with certain approximations made. In the second part, we explain an effect that the composition characteristics of compounds can be quite different depending on whether it is the bulk diffusion or grain boundary diffusion that dominates in the compounds, and that “frozen” bulk diffusion leads to unique composition characteristics that the bulk composition of a compound layer remains unchanged after its initial formation instead of varying with the diffusion reaction system; here the model is modified for the case of grain boundary diffusion. Finally, we apply this model to the Nb3Sn superconductors and propose approaches to control their compositions.