Papers by Keyword: Interface Energy

Abstract: Using a first-principles methodology we have investigated the interfacial and bonding characteristics of the Al(001)/Fe (0-11) interface. The Al/Fe interface model was developed using a face-to-face matching method. Among many possible interface structures, the Al (001)/ Fe(0-11) orientation relation gave the minimum lattice misfit along the a and b directions (a=b= -0.47%). Hence, this interface structure provided the minimum energy value and was used for this study. To predict the interface strength and stability, the work of separation and interfacial energy were calculated. Here, all systems were calculated under exactly the same conditions (k-point mesh, cutoff energy, lateral lattice strain etc). In order to predict the bonding nature at the interface, charge density difference plot was evaluated, which showed charge gain at the interface. The aim of this study is to describe the adhesive behavior between Al and Fe, provide some insights about strength and stability of this interface structure for galling, and provide reference interface system for Al/Fe welding.

Abstract: In this paper, highly scattered fine-scale Ni-Nb base glassy particles were successfully produced by wet milling method. The Al-based metal matrix composites (MMC) comprising pure Al matrix and different amounts of Ni-Nb glassy powder reinforcement were fabricated by powder metallurgy, and their mechanical properties were examined by compression tests at room temperature. It’s proved that only the 2.5 to 5 wt.% addition of the glassy reinforcements enhanced significantly the yield strength of pure Al from 120 to near 200 MPa, while keeping considerable plastic deformation before the fracture strain at about 25%. These results showed that the highly scattered fine-scale glassy particles were efficient reinforcements in fabricating high-performance Al based MMC. The high yield strength of such composites blended with the low mass fraction of glassy particulates was roughly analyzed using Orowan shear model. Finally, the ductile fracture characteristics of the composites were analyzed by evaluating the Ni-Nb glassy/Al metallic interface energy.

Abstract: To evaluate the interface strength of externally bonded fiber-reinforced polymer (FRP) composites to concrete structures, the method of the Linear Elastic Fracture Mechanic (LEFM) model is simply used. The parameters defining the material properties, describing bond action of the FRP-concrete interface is used , which was got recently by Obaidat from three-dimensional (3D) finite-element simulation results. Both the fracture energy and shear strength of the interface are determined by a function of concrete compressive strength and the adhesive shear stiffness, the maximum transferable load is predicted by LEFM interface bond-slip model. Comparison between the predicted and the experiment results shows good agreement and a certain degree of safe estimation.

Abstract: Cu precipitation in steel has been investigated numerous times. Still, a consistent simulation of the nucleation, growth and coarsening kinetics of Cu precipitates is lacking. Major reason for this is the fact that Cu precipitation involves complex physical interactions and mechanisms, which go beyond the classical precipitation models based on evaporation and absorption of precipitate-forming monomers (atoms). In the present work, we attempt a comprehensive modeling approach, incorporating coalescence results from Monte Carlo simulation, prediction of the nucleus composition based on the minimum energy barrier concept, diffusion enhancement from quenched-in vacancies, dislocation pipe diffusion, as well as the transformation sequence of Cu-precipitates from bcc-9R-fcc. Our simulations of number density, radius and phase fraction coincide well with experimental values. The results are consistent over a large temperature range, which is demonstrated in a TTP-plot.

Abstract: An ab initio study was carried out on interface energies at coherent interfaces between bcc Fe and MXs (NaCl structure, M = Ti, Zr, Hf, V, Nb, Ta, X=C, N). The interface energies have positive values for carbides and nitrides of group IVB metals (Ti, Zr, Hf), while they have negative values for carbides and nitrides of group VB metals (V, Nb, Ta). Influence of bond energy was estimated using the discrete lattice plane/nearest neighbor broken bond (DLP/NNBB) model. It was found that the dependence of interface energy on the type of carbides and nitrides was closely related to changes of the bond energies between Fe, M and X(=C, N) atoms before and after formation of the interfaces Fe/MX.

Abstract: A calculation of the interface energy for the Ni-Al binary alloy, including the inter-phase boundary (IPB) energy and the anti-phase boundary (APB) energy, has been performed using the Cluster Variation Method (CVM) with the tetrahedron approximation within the temperature range of 600°C~1300°C. The calculated IPB energies range between 8 and 13 mJ/m2, while the APB energies range between 24 and 46 mJ/m2. Additionally, the dependence of the average composition and the order parameter on distance with the compositionally diffuse interfacial regions has been computed. The calculation also shows the width of the diffuse IPB increases with the temperature linearly.

Abstract: Poly(ethylene terephthalate) films were exposed under argon plasma glow discharge and induced polymerization of acrylic acid (AA) in order to introduce carboxylic acid group onto PET (PET-AA) assisting by ultroviolet radiation. Hirudin-immobilized PETs were prepared by the grafting of PET-AA, followed by chemical reaction with hirudin. The surface structure of the treated PET is determined by X-ray photoelectron spectroscopy (XPS). The wettability and surface free energy, interface free energy of the films is investigated by contact angle measurement. Platelet adhesion evaluatiion is conducted to examine the blood compatibility in vitro. Scanning electron microscopy (SEM) and optical microscopy reveal that the amounts of adhered, aggregated and morphologically changed platelets are reduced on hirudin-immobilized PET films.

Abstract: The valence electron structure of GP Zone in Al-Zn alloy was calculated according to the Empirical Electron Theory(EET). The result of valence electron structure was further applied to analyze the interface energy between GP Zone and matrix. The reason that the GP Zones were formed even at the highest quenching speed and the hardness was stably ascended as soon as GP zones were formed and reached the maximum before the precipitation of metastable phase, was that the amoumt of the strongest covalent bond in the GP Zone was far more than that in α-Al cell and the Al atom in GP Zone was easily prone to forming covalent bond with Zn atom. It was an easy and effective method to apply the EET theory with the hardball model to calculation of interface energy.