Effect of travelling magnetic field on interface morphology in directionally solidified Sn-Cd alloy

The diversity of interface morphologies is observed for directionally solidified Sn-0.65%Cd alloy under a travelling magnetic field （TMF） in the 4 mm-diameter sample. Under an upward TMF, planar and cellular interface morphologies transform alternately with increasing magnetic flux density （B≤10.3 mT）. The interface morphology transforms from shallow cellular to deep cellular morphology under a weak downward TMF （B=3.2 mT）. When the magnetic flux density increases further, both sides of the interface morphology appear to be slightly inconsistent, but they roughly tend to be planar under a strong downward TMF （BS10.3 mT）. The interface instability may be attributed to the flow driven by the TMF. Moreover, the shape of interface appears to be almost flat under an upward TMF, but deflective under a downward TMF.

Effect of interface morphology on the mechanical properties of titanium clad steel plates

Interface morphology has important influence on the bond quality of titanium clad steel plates. The mechanical properties of titanium clad steel plates with wavy and straight interfaces were investigated by tensile-shear tests and bending tests. The interface morphology of the plates was examined by optical microscopy （OM） and scanning electron microscopy （SEM）. The experimental results show that the shear strength of a wavy interface is higher than that of a straight interface. A wavy interface is the guarantee for obtaining high shear strength to provide a greater shear resistance. During the maerobending process, cracks appear in the swirl of the wave tip and ferrotitanium intermetallies. For in-situ observing the bending process by SEM, the wave tip of a wavy interface and the massive ferrotitartium intermetallies of a straight interface are places where cracks initiate and propagate. The results are the same as those observed in the macrobending process. Became of high hardness, the wave tip and the massive ferrotitanium intermetallies are hard in terms of compatible deformation.

Effect of electric current on stability of solidification interface morphology

Based on theoretical analyses, the effect of electric current density on stability of solidification interface morphology of QAl 4 alloy was studied experimentally. The results show that the experimental results agree well with the theoretical analyses, and the following conclusions can be drawn: the increase of electric current density improves the stability of the solidification interface morphology under the condition of no convection of the liquid metal. Otherwise this convection will slow down the trend of solidification interface developing to stability caused by increasing electric current density.

Bonding interface morphology of keyholeless friction stir spot welded joint of AZ31B Mg alloy and DP600 galvanized steel

Because the bonding interface of dissimilar metal joint between AZ31 B Mg alloy and DP600 galvanized steel by keyholeless friction stir spot welding(KFSSW)is permanent bonding,the interface morphology cannot be directly observed.If the joint is separated by external force,the original features of bonding interface of joint will be destroyed,which has influence on the accuracy for observation and analysis of the result.In this paper,the coordinates of the key point at the interface of every cross-section at intervals of 0.2 mm were measured and connected into an outline.The outline of all interfaces makes up the three-dimensional morphologies of bonding interface between AZ31 B Mg alloy and DP600 steel by KFSSW,which was constructed by Solidworks software to restore the real mechanical bonding state of joint.Combined with the microhardness analysis of cross-section and results of in-situ tensile test,the unique bonding state and morphology of Mg and steel in the welded joint were confirmed.

Effects of Ca(Y)-Si modifier on interface morphology and solute segregation during directional solidification of an austenite medium Mn steel

The austenite medium Mn steel modified with controlled additions of Ca, Y, Si were directionally solidified using the vertical Bridgman method to study the effects of Ca（Y）-Si modifier on the solid-liquid （S-L） interface morphology and solute segregation. The interface morphology and the C and Mn segregation of the steel directionally solidified at 6.9 μtrn/s were investigated with an image analysis and a scanning electron microscope equipped with energy dispersive X-ray analysis. The 0.5wt% Ca-Si modified steel is solidified with a planar S-L interface. The interface of the 1.0wt% Ca-Si modified steel is similar to that of the 0.5wt% Ca-Si modified steel, but with larger nodes. The 1.5wt% Ca-Si modified steel displays a cellular growth parttern. The S-L interface morphology of the 0.5wt% Ca-Si＋1.0wt% Y-Si modified Mn steel appears as dendritic interface, and primary austenite dendrites reveal developed lateral branching at the quenched liquid. In the meantime, the independent austenite colonies are formed ahead of the S-L interface. A mechanism involving constitutional supercooling explains the S-L interface evolution. It depends mainly on the difference in the contents of Ca, Y, and Si ahead of the S-L interface. The segregation of C and Mn ahead of the S-L interface enhanced by the modifiers is observed.

Numerical simulation of TBCs residual stresses by the growth of TGO on typical interface morphology

The effect of TGO （ thermally grown oxide ） growth based on typical interface morphology on residual stresses distribution in thermal barrier coatings was analyzed by ABAQUS software. TGO oxidation kinetics, the relationship between TGO thickness and thermal cycles number, and typical morphology including sinusoid , cone and groove were considered in the calculation process. 13 FEM （finite element method） models with different TGO thickness based on uniform interface morphology were established for analysis. The calculation results show that TCC （ top ceramic coating ） /TGO and TGO/BC （bond coating） interface residual stresses are affected significantly by inter）hce morphology and TGO thickness, both of which increase significantly with TGO growth ; the stress level in TCC/TGO interface is greater than that of TGO/BC interface ; each morphology peak exhibits tensile stress while each valley exhibits compressive stress in TCC/TGO interface; stress concentrates in such locations as each morphology center with sharp angle and the stress reaches the maximal value at the tip of each angle.

Interfacial morphology evolution in directionally solidified Al-1.5%Cu alloy

The solid-liquid interracial morphology evolution was investigated in directional solidification （DS） of Al-1.5%Cu alloy （mass fraction）. The results show that the solidified microstructural evolution is gradual other than sharp, and the microstructure patterns are interesting and diversiform at the pulling rate ranging from 30 μm/s to 1500 μm/s. Indeed, dendrite to cell transition follows this sequence： dendrites→→banded cellular dendrites→elongated cells and part of dendrites→main elongated cells and little dendrites. Moreover, the present microstructure is not normal microstructure as we saw before. Further, according to the experimental phenomenon, the dendrite to cell transition was studied theoretically. Dendrite tip shape is an important parameter to characterize the dendrite to cell transition. As the dendrite to cell transition is far from equilibrium solidification, non-equilibrium solidification is taken into consideration in calculation. Finally, it is speculated that the dendrite to cell transition would occur at the minimum tip radius.

INTERFACE MORPHOLOGIES AND MICROSTRUCTURES DURING DENDRITE-TO-CELL TRANSITION AT HIGH GROWTH RATE

The interface morphologies and microstruetures of the directionally solidified Ni-5wt-% Cu alloy during dendrite-to-cell transition at high growth rates have been investigated with a newly developed apparatus for unidirectional solidification with the temperature gradient at the solid/liquid interface higher than 1000 K/cm.The results show that in the vicinity of dendrite-to-cell transition point,the well developed sidebranches become shrivelled with the increase of growth rate and disappear at the dendrite-to-cell transition,and the primary spacing decreases simultaneously.Moreover,the length of mushy zone decreases greatly dur- ing the dendrite-to-cell transition.Cells obtained at high growth rates have very similar morphologies to those at low growth rates,but with much smaller cell spacings and unsmoothed cell walls which may be attributed to the different stability conditions of the cell walls at low and high growth rates respectively.

Mathematical Modelling of Particle Movement Ahead of the Solid-liquid Interface in Continuous Casting

Whether the particle will be trapped by the solid-liquid interface or not is dependent on its moving behavior ahead of the interface, so a mathematical model has been developed to investigate the movement of the particle ahead of the solid-liquid interface. Based on the theory for the boundary layer, the fluid velocity field near the solid-liquid interface was obtained, and the trajectories of particles were calculated by the equations of motion for particles. In this model, the drag force, the added mass force, the buoyance force, the gravitational force, the Saffman force and the Basset history force are considered. The results show that the behavior of the particle ahead of the solid-liquid interface is affected by the physical property of the particle and fluid flow. And in the continuous casting process, if it moves in the stream directed upward or downward near vertical solid-liquid interface or in the horizontal flow under the solid-liquid interface, the particle with the diameter from 5 um to 60um can reach the solid-liquid interface. But if it moves in horizontal flow above the solid-liquid interface, only the particle with the diameter from 5 um to 10 um can reach the solid-liquid interface.

Microstructure and fractal characteristics of the solid-liquid interface forming during directional solidification of Inconel 718

The solidification microstructure and fractal characteristics of the solid-liquid interfaces of Inconel 718,under different cooling rates during directional solidification,were investigated by using SEM. Results showed that 5 μm/s was the cellular-dendrite transient rate. The prime dendrite arm spacing (PDAS) was measured by Image Tool and it decreased with the cooling rate increased. The fractal dimension of the interfaces was calculated and it changes from 1.204310 to 1.517265 with the withdrawal rate ranging from 10 to 100 μm/s. The physical significance of the fractal dimension was analyzed by using fractal theory. It was found that the fractal dimension of the dendrites can be used to describe the solidification microstructure and parameters at low cooling rate,but both the fractal dimension and the dendrite arm spacing are needed in order to integrally describe the evaluation of the solidification microstructure completely.

INTERFACE MORPHOLOGIES AND SOLUTE SEGREGATION OF Al-Li ALLOY 8090 DURING UNIDIRECTIONAL SOLIDIFICATION

The solid-liquid interface morphology and solute segregation behaviour of AI-Li alloy 8090 during unidirectional solidification were studied by the liquid metal quenehing method under varied processing conditions.When solidification rate,R<O.13 or>O.75 mm/min (temper- ature gradient,G_L=130℃/cm),the structure revealed of planar or dendritic interface respectively.With the increase of R,the interface morphology becomes cellular from planar gradually,within a narrow range.And the greater the R,the,finer the dendrite.Segregation of element Cu and impurity elements Fe and Si are quite severe,the interface morphology markedly influences on solute segregation.During solidification at coarse dendrite interface, their segregation ratios are rather great and solidified structure is coarse.

Apparent Active Adsorption Force at a Solid-Liquid Interface with Active Adsorption

The paper presents a new relationship between the three surface tensions on the solid-liquid-vapor interface, γ_(sl)-γ_(sv)+γ_(lv)cosθ=βin order to understand the wetting on the liquid-solid interface in the case of active adsorption.The authors suggest a new force“apparent active adsorption force”βto take part in the balance at the three interface lines of contact in the solid-liquid-vapor phases,its dimen- sion isβ=Σα_iRT(Γ_i^(sl)-Γ_i^(sv)+Γ_i^(lv)cosθ),and its direction is dependent on the sign of β,whenβis a positive, the direction is agree with surface tension of the sol- id-vapor interface γ and vice versa.

Vacuum deposited film growth,morphology and interfacial electronic structures of 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT)

Interfaces play critical roles in electronic devices and provide great diversity of film morphology and device performance.We retrospect the substrate mediated vacuum film growth of benchmark high mobility material 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene(C8-BTBT)and the interface electronic structures.The film growth of C8-BTBT molecules is diversified depending on the substrate-molecule and molecule-molecule interactions.On atomic smooth substrates C8-BTBT film grows in layer-by-layer mode while on coarse substrate it grows in islands mode.The initial molecular layer at dielectric,semiconductor and conductive substrates displays slight different lattice structure.The initial molecule orientation depends on the substrate and will gradually change to standing up configuration as in bulk phase.C8-BTBT behaves as electron donor when contacting with dielectric and stable conductive materials.This usually induces a dipole layer pointing to C8-BTBT and an upward bend bending in C8-BTBT side toward the interface.Although it is air stable,C8-BTBT is chemically reactive with some transition metals and compounds.The orientation change from lying down to standing up in the film usually leads to decrease of ionization potential.The article provides insights to the interface physical and chemical processes and suggestions for optimal design and fabrication of C8-BTBT based devices.

Effects of external stress aging on morphology and precipitation behavior of θ'' phase in Al-Cu alloy

The exposure of Al-5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ＂ phase were investigated by transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and first principle calculation. The size of the θ＂ phase precipitated plates in stress-aging （453 K, 6 h, 50 MPa） is 19.83 nm, which is smaller than that of those present （28.79 nm） in stress-flee aging （453 K, 6 h）. The precipitation process of θ＂ phase is accelerated by loading external stress aging according to the analysis of DSC results. The apparent activation energy for the external stress-aging is 10% lower than the stress-free one. The first principle calculation results show that the external stress makes a decrease of 6% in the interface energy. The effects of the stress on aging process of the alloy are discussed on the basis of the classical theory. The external stress changes the morphology and precipitation behavior of θ＂ phase because the critical nucleation energy is decreased by 19% under stress aging.

Nanostructured lubricant additives for titanium alloy:Lubrication by the solid-liquid interface with Coulomb repulsion

In this work,the advantage of Coulomb repulsion in the intermolecular forces experienced by molecules on the solid–liquid nanosized contact interface is taken,and the superior friction-reducing property of Cu_(3)(PO_(4))2·3H_(2)O(CuP)oil-based additives has been confirmed for titanium alloy.Three-dimensional(3D)CuP nanoflowers(CuP-Fs)with a strong capillary absorption effect are prepared to achieve the homogeneous mixing of solid CuP and lubricating oil.Lubrication by CuP-Fs additives for titanium alloy,friction coefficient(COF)can be reduced by 73.68%,and wear rate(WR)reduced by 99.69%.It is demonstrated that the extraordinary friction-reducing property is due to the repulsive solid–liquid interface with low viscous shear force originating from Coulomb repulsion between polar water molecules in CuP and non-polar oil molecules.However,any steric hindrance or connection between this repulsive solid–liquid interface will trigger the adhesion and increase the viscous shear force,for example,dispersant,hydrogen bondings,and shaky adsorbed water molecules.Besides,the lamellar thickness of CuP and the molecular size of lubricant both have a great influence on tribological properties.Here the lubrication mechanism based on interface Coulomb repulsion is proposed that may help broaden the scope of the exploration in low-friction nanomaterial design and new lubricant systems.

Ultrafast laser-chemical modification hybrid fabrication of hydrostatic bearings with a superhydrophobicity solid-liquid interface

Oil film vortex severely reduces the stability of hydrostatic bearings. A solid-liquid interface with drag and slip properties can weaken the oil film vortex of the bearing. Here, a combined picosecond laser ablation and chemical modification method is proposed to prepare surfaces with microbulge array structure on 6061 aluminum alloy substrates. Because of the low surface energy of the perfluorododecyltriethoxysilane modification and the bulge geometry of the microbulge array structure, the surface shows excellent superhydrophobicity. The optimum contact angle in air for water is 164°, and that for oil is 139°. Two surfaces with “lotus-leaf effect” and “rose-petal effect” were obtained by controlling the processing parameters. The drag reduction properties of superhydrophobic surfaces were systematically investigated with slip lengths of 22.26 and 36.25 μm for deionized water and VG5 lubricant, respectively. In addition, the superhydrophobic surface exhibits excellent mechanical durability and thermal stability. The proposed method provides a new idea for vortex suppression in hydrostatic bearings and improves the stability of bearings in high-speed operation.

Recent Advances to Understand Morphology Stability of Organic Photovoltaics

Organic photovoltaic devices are on the verge of commercialization with power conversion efficiencies exceeding 10 % in laboratory cells and above 8.5 % in modules. However, one of the main limitations hindering their mass scale production is the debatable inferior stability of organic photovoltaic devices in comparison to other technologies.Adequate donor/acceptor morphology of the active layer is required to provide carrier separation and transport to the electrodes. Unfortunately, the beneficial morphology for device performance is usually a kinetically frozen state which has not reached thermodynamic equilibrium. During the last 5 years, special efforts have been dedicated to isolate the effects related to morphology changes taking place within the active layer and compare to those affecting the interfaces with the external electrodes. The current review discusses some of the factors affecting the donor/acceptor morphology evolution as one of the major intrinsic degradation pathways. Special attention is paid to factors in the nano- and microscale domain.For example, phase segregation of the polymer and fullerene domains due to Ostwald ripening is a major factor in the microscale domain and is affected by the presence of additives, glass transition temperature of the polymers or use of crosslinkers in the active layer. Alternatively, the role of vertical segregation profile toward the external electrodes is key for device operation, being a clear case of nanoscale morphology evolution. For example, donor and acceptor molecules actually present at the external interfaces will determine the leakage current of the device, energy-level alignment, and interfacial recombination processes. Different techniques have been developed over the last few years to understand its relationship with the device efficiency. Of special interest are those techniques which enable in situ analysis being nondestructive as they can be used to study accelerated degradation experiments and some will be discussed here.

Formation, Evolution and Final Structure of Interface in 2024Al Joints Fabricated by Explosive Welding

The wavy interface for similar or the same metal explosive welding（EXW） and the universal mechanism of wavy interface formation in EXW were studied in this work. Based on a new established model, it was deduced that the evolution frequencies of the instability were constrained in a limited range. Then experiments of identical metal EXW were performed and welding interfaces were characterized for examining the final morphology. By calculating the fractal dimensions and multifractal spectra of welding interface, the fractal characteristics of interface were revealed and a quantitative description was achieved for EXW interface structure. Thus, the formation, evolution and final morphology of wavy interface were systemically researched.

Interfacial phase formation of Al-Cu bimetal by solid-liquid casting method

The solid-liquid method was used to prepare the continuous casting of copper cladding aluminium by liquid aluminum alloy and solid copper, and the interfacial phase formation of Al-Cu bimetal at different pouring temperatures(700, 750, 800 oC) was investigated by means of metallograph, scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) methods. The results showed that the pouring temperature of aluminum melt had an important influence on the element diffusion of Cu from the solid Cu to Al alloy melt and the reactions between Al and Cu, as well as the morphology of the Al-Cu interface. When the pouring temperature was 800 oC, there were abundant Al-Cu intermetallic compounds(IMCs) near the interface. However, a lower pouring temperature(700 oC) resulted in the formation of cavities which was detrimental to the bonding and mechanical properties. Under the conditions in this study, the good metallurgical bonding of Al-Cu was achieved at a pouring temperature of 750 oC.

Interface evolution of a particle in a supersaturated solution affected by a far-field uniform flow

The effect of far-field uniform flow on the morphological evolution of a spherical particle in a supersaturated solution affected by a far-field uniform flow is studied by using the matched asymptotic expansion method. The analytical solution for the interface shape, concentration field, and interface velocity of the particle growth shows that the convection induced by the far-field uniform flow facilitates the growth of the spherical particle, the upstream flow imposed on the particle enhances the growth velocity of the interface when the flow comes in, the downstream flow lowers the growth velocity of the surface when the flow goes out, and the interface morphology evolves into a peach-like shape.