Molecular Dynamics Study on Interfacial Energy and Atomic Structure of Ag/Ni and Cu/Ni Heterophase System

The results of molecular dynamics calculations on the interfacial energies and atomic structures of Ag/Ni and Cu/Ni interfaces are presented. Calculation on Ag/Ni interfaces with low-index planes shows that those containing the (111) plane have the lowest energies, which is in agreement with the experiments. Comparing surface energy with interfacial energy, it is found the order of the interfacial energies of Ag/Ni and Cu/Ni containing the planes fall in the same order as solid-vapor surface energies of Ag, Cu and Ni. In this MD simulation, the relaxed atomic structure and dislocation network of (110)_Ag||(110)Ni interface are coincident to HREM observations.

The effect of interfacial energy anisotropy on planar interface instability in a succinonitrile alloy under a small temperature gradient

The morphological stability of a planar interface with different crystallographic orientations is studied under a small positive temperature gradient using a transparent model alloy of succinonitrile. Novel experimental apparatus is constructed to provide a temperature gradient of about 0.37 K/mm. Under this small temperature gradient, the planar interface instability depends largely on the crystallographic orientation. It is shown experimentally that the effect of interfacial energy anisotropy on planar interface stability cannot be neglected even in a small temperature gradient system. Higher interfacial energy anisotropy leads the planar interface to become more unstable, which is different from the stabilizing effect of the interfacial energy on the planar interface. The experimental results are in agreement with previous theoretical calculations and phase field simulations.

Controlling upconversion through interfacial energy transfer(IET):Fundamentals and applications

Photon upconversion has received substantial attention owing to its great promise in broad applications from bioimaging to other frontier fields like display,upconversion laser,information security and anticounterfeiting.A smart control and manipulation of the upconversion luminescence has always been a key topic,however,to date the most efficient mechanism for upconversion nanoparticles remains the energy transfer upconversion and recently reported energy migration mediated upconversion.Recently,we found that the interfacial energy transfer(IET)is also an efficient approach for enabling and tuning photon upconversion of lanthanide ions.Moreover,it can be used for the mechanistic understanding of the interionic interactions such as energy transfer and energy migration on the nanoscale.In this review,the recent advances of the research on the IET are summarized,the principles for designing IET process and typical examples are discussed together with its applications in both mechanistic research and frontier information security.The challenges and perspectives for future research are also commented.

THEORETICAL CALCULATION OF SPECIFIC INTERFACIALENERGY OF SEMICOHERENT INTERFACE BETWEEN MICROALLOY CARBONITRIDES AND AUSTENITE

According to the misfitting dislocation theory,a method of theoretical calculation was devel- oped for the specific energy of the semicoherent interface between microalloy carbonitrides and austenite matrix.The calculating formulae were derived and the results were satisfactorily applied on the research works.

Atomistic calculations of surface and interfacial energies of Mg_(17)Al_(12)-Mg system

It is well known that precipitation hardening in magnesium(Mg)alloys is far less effective than in aluminum alloys.Thus,it is important to understand the surface and interfacial structure and energetics between precipitates and matrix.In upscale modeling of magnesium alloys,these energy data are of great significance.In this work,we calculated the surface and interfacial energies of Mg_(17)Al_(12)-Mg system by carefully selecting the surface or interface termination,using atomistic simulations.The results show that,the higher fraction of Mg atoms on the surface,the lower the surface energy of Mg_(17)Al_(12).The interfacial energy of Mg/Mg_(17)Al_(12)was calculated in which the Burgers orientation relationship(OR)was satisfied.It was found that the(011)P|(0002)Mg interface has the lowest interfacial energy(248 mJ/m 2).Because the Burgers OR breaks when{10¯12}twin occurs,which reorients the matrix,the interfacial energy for Mg_(17)Al_(12)and a{10¯12}twin was also calculated.The results show that after twinning,the lowest interfacial energy increases by 244 mJ/m^(2),and the interface becomes highly incoherent due to the change in orientation relationship between Mg_(17)Al_(12)and the matrix.

Penny-shaped interfacial crack between dissimilar magnetoelectroelastic layers

A penny-shaped interfacial crack between dissimilar magnetoelectroelastic layers subjected to magnetoelectromechanical loads is investigated,where the magnetoelectrically impermeable crack surface condition is adopted. By using Hankel transform technique,the mixed boundary value problem is firstly reduced to a system of singular integral equations,which are further reduced to a system of algebraic equations. The field intensity factors and energy release rate are finally derived. Numerical results elucidate the eects of crack configuration,electric and/or magnetic loads,and material parameters of the magnetoelectroelastic layers on crack propagation and growth. This work should be useful for the design of magnetoelectroelastic composite structures.

RAFTING PREDICTION CRITERION FOR NICKEL-BASE SINGLE CRYSTALS UNDER MULTIAXIAL STRESSES AND CRYSTALLOGRAPHIC ORIENTATION DEPENDENCE OF CREEP BEHAVIOR

Based on the relief of interfacial energy density by dislocation generation at the gamma - gamma ' interfaces, a rafting prediction criterion has been developed for nickel-base single crystals under multiaxial stresses. The diagrams of rafting have been presented, and confirmed by experimental results. The rafting process have been analyzed quantitatively by the relief of interfacial energy. The criterion has been applied to study the creep behavior. The example of creep life analysis shows that the criterion can be correlated greatly to the crystallographic orientation dependence of creep behavior. (Author abstract) 11 Refs.

THEORETICAL PREDICTION OF THE KINETICS CURVES OFPEARLITIC TRANSFORMATION IN HYPO-PROEUTECTOID STRUCTURAL STEELS

Supposing carbon contents of ferrite phases in pearlite precipitating from austenite in multicomponent steel at temperature T and in Fe-C ystem at T' are the same the pearlite formation temperature diference, can be calculated from the FeX phase diagrams and the equilibrium temperature Al. Using Tp and Fe-C binary thermodynamic model, the driving forces for phase transformation from austenite to pearlite in multicomponent steels have been successfully calculated. Through the combination of simplified Zener and Hillert's model for pearlite growth with Johnson-Mehl equation, using data from known TTT diagrams, the interfacial energy parameter and activation energy for pearlite formation can be determined and expressed as functions of chemical composition in steels by regression analysis. The calculated starting curves of pearlitic transformation in some commercial steels agree well with the experimental data.

EVOLUTION OF VOIDS IN DUCTILE POROUS MATERIALS AT HIGH STRAIN RATE

In the present work, a dynamic damage model in ductile materials under the application of dynamic general stresses loading is presented. The evolution equation of ductile voids has the closed form, in which work-hardening, the change of surface energy of voids, rate-dependent, inertial effects are taken into account. The expressions of critical stresses for the growth and compaction of voids are directly obtained from the evolution equations of voids. Numerical analysis of the model indicates that the growth of voids is sensitive to the strain rates. The voids grow quickly as the increase of strain rates. It is also shown that the influence of the inertial effects on the void growth is great at high loading rates. It appears to resist the growth of voids. In addition, a dynamic collapse model of ductile voids is also proposed, which can be applied to study the problems of compaction in powder and other materials.

Effect of interface anisotropy on tilted growth of eutectics:A phase field study

Interfacial energy anisotropy plays an important role in tilted growth of eutectics. However, previous studies mainly focused on the solid-solid interface energy anisotropy, and whether the solid-liquid interface energy anisotropy can significantly affect the tilted growth of eutectics still remains unclear. In this study, a multi-phase field model is employed to investigate both the effect of solid-liquid interfacial energy anisotropy and the effect of solid-solid interfacial energy anisotropy on tilted growth of eutectics. The findings reveal that both the solid-liquid interfacial energy anisotropy and the solid-solid interfacial energy anisotropy can induce the tilted growth of eutectics. The results also demonstrate that when the rotation angle is within a range of 30°-60°, the growth of tilted eutectics is governed jointly by the solid-solid interfacial energy anisotropy and the solid-liquid interfacial energy anisotropy;otherwise, it is mainly controlled by the solid-solid interfacial energy anisotropy. Further analysis shows that the unequal pinning angle at triple point caused by the adjustment of the force balance results in different solute-diffusion rates on both sides of triple point. This will further induce an asymmetrical concentration distribution along the pulling direction near the solid-liquid interface and the tilted growth of eutectics. Our findings not only shed light on the formation mechanism of tilted eutectics but also provide theoretical guidance for controlling the microstructure evolution during eutectic solidification.

A novel computational model for isotropic interfacial energies in multicomponent alloys and its coupling with phase-field model with finite interface dissipation

In this work,a novel computational model for the description of the temperature-and composition-dependent isotropic interfacial energy in multicomponent alloys was first developed in the framework of the CALculation of PHAse Diagram(CALPHAD)approach and implemented in a home-made code.By linking to the open-source code for interfacial energy calculation in alloys,OpenIEC,the databases for isotropicγ/liquid andγ/γ’interfacial energies in Ni-Al,Ni-Cr,Al-Cr,and Ni-Al-Cr systems were then efficiently established.After that,a direct coupling strategy between the current CALPHAD interfacial en-ergy database and the phase-field model with finite interface dissipation was proposed and applied to three-dimensional(3-D)phase-field simulations of the primaryγdendritic growth in both Ni-Al and Ni-Al-Cr alloys during isothermal solidification.The effect of the interfacial energy on the morphology,tip growth rate,and partitioning coefficients in primaryγdendrites of binary Ni-Al and ternary Ni-Al-Cr alloys was investigated by comprehensively comparing the phase-filed simulation results using the composition-/temperature-dependent interfacial energies with those using the constant value.It is an-ticipated that the presently developed CALPHAD model for interfacial energy is of general validity for different multicom ponent alloys and should be integrated with the phase-field model for quantitative simulation of their microstructure evolution.

Estimation of Nucleation Thermodynamical Parameters of La2Sr2xCuO4 (LSCO) and YBa2Cu2O7–δ (YBCO) Crystallizing from High Temperature Solution

The growth kinetics of LSCO and YBCO single crystals from high temperature solution of LSCO-CuO solute-solvent and YBCO-CuO solute-solvent systems has been investigated. Based on regular solution model and classical nucleation theory, the thermodynamical data investigated for the systems are used to determine the nucleation parameters: interfacial free energy, metastable zone-width, volume free energy, critical energy barrier for nucleation and radius of critical nucleus for LSCO and YBCO which leads to the understanding of the nucleation phenomena of LSCO and YBCO.

Peeling behavior and spalling resistance of CFRP sheets bonded to bent concrete surfaces

In this paper, the peeling behavior and the spalling resistance effect of carbon fiber reinforced polymer （CFRP） sheets externally bonded to bent concrete surfaces are firstly investigated experimentally. Twenty one curved specimens and seven plane specimens are studied in the paper, in which curved specimens with bonded CFRP sheets can simulate the concrete spalling in tunnel, culvert, arch bridge etc., whereas plane specimens with bonded CFRP sheets can simulate the concrete spalling in beam bridge, slab bridge and pedestrian bridge. Three kinds of curved specimens with different radii of curvature are chosen by referring to practical tunnel structures, and plane specimens are used for comparison with curved ones. A peeling load is applied on the FRP sheet by loading a circular steel tube placed into the central notch of beam to debond CFRP sheets from the bent concrete surface, meanwhile full-range load-deflection curves are recorded by a MTS 831.10 Elastomer Test System. Based on the experimental results, a theoretical analysis is also conducted for the specimens. Both theoretical and experimental results show that only two material parameters, the interfacial fracture energy of CFRP-concrete interface and the tensile stiffness of CFRP sheets, are needed for describing the interfacial spalling behavior. It is found that the radius of curvature has remarkable influence on peeling load-deflection curves. The test methods and test results given in the paper are helpful and available for reference to the designer of tunnel strengthening.

The Effect of Surface Properties of Biomedical Materials on Their Blood Compatibility

The effect of surface properties of six types of biomedical materials on their blood compatibility was investigated in this study. The surface roughness of biomaterials was determined by confocal laser scanning microscopy （CLSM）. The contact angle was observed by contact angle measurement （CAM）. Then the surface free energy （SFE） and interfacial free energy （IFE） were calculated by the contact angle value based on the Owens- Wendt （OW） theoretical model and Young＇ s equation. Meanwhile, hemolytic assay was employed to evaluate the haemolysis. The experimental results showed that the greater roughness was, the greater contact angle would be ; the less proportion of polar component in surface free energy （SFE） was, the lower haemolysis would be.

Calculation of solid-liquid interfacial free energy and its anisotropy in undercooled system

The solid-liquid interfacial free energy and its anisotropy are crucial quantities in determining the microstructure and mechanical properties of materials. However, most researches mainly concerned the solidliquid coexistence at melting point. In this work, two methods, the critical nucleus method （CNM） and the capillary fluctuation method （CFM）, were combined to get these quantities in undercooled system by molecular dynamics （MD） simulations. The melting point, Tolman length, interfacial free energy and its anisotropy were calculated, and good consistent results from these two methods are obtained. The results of interfacial free energy obtained by CNM and CFM are 103.79 and 102.13 mJ·m^-2, respectively, with the error 〈2%. Meanwhile, both of the methods provide the rank of interfacial free energy by γ7100〉 γ7120 〉 γ 7110 〉 γ112 〉 γ111. The results of the present study are also in good agreement with experimental data and computational data in the literature.

THEORETICAL PREDICTION OF PROEUTECTOID FERRITICTRANSFORMATION IN HYPO-PROEUTECTOID STRUCTRAL STEELS

Proeutectoid ferrite with carbon content xo precipitating from austenite in a multicomponent steel at temperature T is supposed to be equivalent to proeutectoid ferrite with the same carbon content precipitating from austenite in Fe-C binary system at temperature T'.is described as the temperature difference of proeutectiod ferrite formation, and can be calculated from the Fe-X diagrams and the equilibrium temperature A3. By introducing Tf and basing on the thermodynamic model for Fe-C binary alloy, the driving force for phase transformation from austenite to proeutectoid ferrite in multicomponent steels has been successfully calculated. Through the Johnson-Mehl equation and using the data hem known TTT diagrams, the relationship between the chemical composition and the intedecial edenly packeter as well as activation energy for proeutectoid ferrite formation can be calculated. The starting curves of proeutectoid ferritic transformation calculated in this way in some hypo-proeutectoid structural steels agree well with the erperimental data.

Mechanism of ferrite nucleation induced by Y_(2)O_(2)S inclusion in low carbon steel

To reveal the mechanism of ferrite nucleation induced by Y_(2)O_(2)S inclusion in steel,the work of adhesion,interfacial energy,structure stability and electronic properties of Fe(111)/YY_(2)O_(2)S(001)interfaces with various terminations were first investigated using the first-principles calculations.Secondly,the steels with and without yttrium were prepared,while the rare earth yttrium-based inclusions in low carbon steel were characterized using an electron probe micro-analyzer,and the grain size of steel was analyzed using a scanning electron microscope with electron backscattered diffraction.The results show that the bonding strength of Fe/Y_(2)O_(2)S interfaces with S-and Y-terminations is stronger than that of the interface with O-terminations.The Fe-hcp-S interfaces with S-termination have the highest work of adhesion(4.01 J/m2)and the lowest interface distance(1.323A).The Fe-hcp-S interface exhibits the highest stability,and its interfacial bonding force is mainly attributed to the strong hybridization of Fe-3d and S-2p orbitals in the energy range of-7.5-0 eV.Moreover,the interfacial energy of Fe-hcp-S is substantially lower than those of the ferrite(s)/Fe(L)interface and the ferrite-austenite interface,suggesting that Y_(2)O_(2)S inclusions in steel can efficiently promote ferrite nucleation.The experimental observations demonstrate that the ferrite grain size of steel containing 0.03 wt.% Y is much more refined than that of the steel without yttrium,and the average grain size of steel with and without Y is 102 and 258μm,respectively.This indicates that the results of our calculations match with experimental findings.

Can orientations of directionally solidified dual-phase Al_(2)O_(3)/YAG eutectics be induced by single-phase sapphire seeds?

Directionally solidified dual-phase Al_(2)O_(3)/Y_(3)Al_(5)O_(12)(YAG)eutectic ceramics(DSECs)typically exhibit strong anisotropy.To improve their properties,various single-phase sapphire seeds,including r-axis[1-102],m-axis[10-10],c-axis[0001],and a-axis[11-20],were used as seeds to induce the orientation of the Al_(2)O_(3)/YAG DSECs.The results showed that Al_(2)O_(3) in the eutectics could be governed by the sapphire seeds.The YAG in each induced eutectic had a specific growth direction endowed by Al_(2)O_(3) in the asinduced eutectics or the sapphire seed.Herein,we calculated the planar lattice misfits and interfacial strain energies of four crystallographic orientation relationships based on the constructed lattice models.It was elucidated the constraint of the sapphire seed caused YAG to grow following the rule of mini-mizing the interfacial strain energy.This revealed the reason why Al_(2)O_(3)/YAG DSECs orientation can be successfully induced.These results may provide a novel method for the design of high-performance eu-tectic ceramic materials.

CALTPP:A general program to calculate thermophysical properties

A program CALTPP(CALculation of ThermoPhysical Properties)is developed in order to provide various thermophysical properties such as diffusion coefficient,interfacial energy,thermal conductivity,viscosity and molar volume mainly as function of temperature and composition.These thermophysical properties are very important inputs for microstructure simulations and mechanical property predictions.The general structure of CALTPP is briefly described,and the CALPHAD-type models for the description of these thermophysical properties are presented.The CALTPP program contains the input module,calculation and/or optimization modules and output module.A few case studies including(a)the calculation of diffusion coefficient and optimization of atomic mobility,(b)the calculation of solid/liquid,coherent solid/solid and liquid/liquid interfacial energies,(c)the calculation of thermal conductivity,(d)the calculation of viscosity,and(e)the establishment of molar volume database in binary and ternary alloys are demonstrated to show the features of CALTPP.It is expected that CALTPP will be an effective contribution in both scientific research and education.