Kinetics of interlayer formation on polycrystallineα-Al2O3/copper-titanium alloy interface

Copper-titanium alloys are known to wet an alumina surface. Traditionally, contact angles are used as measurable parameters to monitor the progress of wetting. Contact angle is a measure of the thermodynamic equilibrium at the interface. For reactive wetting systems, it is well known that the interfacial properties vary as a function of time. In the present study, kinetics of reaction were studied by monitoring the rate of interfacial phase formation. An immersion apparatus was built for this purpose. The extent of reaction was measured both by a simple surface compositional analysis and by interfacial reaction layer thickness measurements. The reaction layer exhibited a parabolic growth with an associated activation energy of 180 to 230 kJ/mole. A speculative growth mechanism is proposed based on the experimental observations and the information available in the literature.     

Influence of interfacial reaction rates on the wetting driving force in metal/ceramic systems

The wetting of copper-silicon alloys of various compositions on vitreous carbon substrates at 1423 K was studied by the sessile drop method. The morphology and chemistry of products of interfacial reactions between silicon and carbon were characterized by scanning electron microscopy (SEM), electron probe microanalysis, and high-resolution optical profilometry. In addition to measurements of contact angles and spreading kinetics in the reactive Cu-Si/Cv system, similar measurements were performed for the nonreactive Cu-Si/SiC system. It was found that the reaction rate has no effect on the final contact angle, which is nearly equal to the thermodynamic contact angle of the alloy on the reaction product. These findings appear to be valid for a wide range of interfacial reaction rates and for different types of interfacial reactions.     

A determination of interfacial energy and interfacial composition in CuPb and CuPbX alloys by solid state wetting measurements

Solid state wetting studies have been used to measure interfacial energies and also to estimate interfacial composition. The approach is applicable to systems where one phase forms partially wetting islands on a substrate of the other phase, and requires that the compositions of all surfaces be carefully monitored so as to allow surface energies to be corrected for adsorption effects. The CuPb interface was studied by this technique with the wetting of Pb islands on polycrystalline Cu, CuAg and CuAu polycrystalline alloys. The results show that Au lowers the CuPb interfacial energy, indicating the presence of Au segregation at the interface, whereas Ag does not change the interfacial energy. Both of the above results are also correctly predicted, quanlitatively, by a simple nearest neighbor bond model used in conjunction with the regular solution approximation. Studies of Pb on monocrystalline (001)- and (111)-oriented substrates of Cu have been carried out. These yield values of 926 and 1016 mJ/m² for the two interfacial energies, respectively. Similar studies of Pb on (001)Cu-5 at.% Au, and (111)Cu-8 at.% Au yield interfacial energies of 889 and 959 mJ/m², respectively, indicating interfacial excesses of Au of 0.22 and 0.34 monolayers at those interfaces.     

Wettability and interfacial behaviour of NdF3-LiF-Nd2O3 on TiB2-based ceramics

Wettability of TiB2-based ceramics by NdF3-LiF-Nd2O3 melt was studied using sessile drop technique in this paper. Wetting ex-periment was carried out under inert atmosphere at 1050 ℃. Chemical reactions which occurred on the solid-liquid interface and solid-gas interface during wetting process were discussed by thermodynamic calculations combined with X-ray diffraction (XRD) patterns. Micromorphoiogy and element distribution of fracture surface at the interfacial region of solid/liquid system were analyzed by scanning elec-tron microscope (SEM) equipped with energy dispersive spectrometry (EDS). Contact angles of the drop were determined as a function of time in order to describe the wetting process, and wetting phenomenon was interpreted fi'om a viewpoint of interface structure. The results showed that wetting was a dynamic wetting process with characteristics of reactive wetting. Penetration and oxidization phenomena during the experiment had great effect on wetting process.     

Influence of melt carbon and sulfur on the wetting of solid graphite by Fe-C-S melts

The interfacial phenomena between carbonaceous materials such as graphite, coke, coal, and char and Fe-C-S melts are important due to the extensive use of these materials in iron processing furnaces. However, the understanding of the interfacial phenomena between these kinds of carbonaceous materials and molten iron alloys is far from complete. In this study, graphite was selected as the solid carbonaceous material because its atomic structure has been well established. The sessile drop method was adopted in this investigation to measure the contact angle between solid graphite and molten iron and to study the interfacial phenomena. The influence of carbon and sulfur content in Fe-C-S melts on the wettability of solid graphite has been investigated at 1600 °C. The melt carbon content was in the range of 0.13 to 2.24 wt pct, and the melt sulfur content was in the range of 0.05 to 0.37 wt pct. X-ray energy-dispersive spectrometer (EDS) analysis was conducted on an HITACHI S-4500 scanning electron microscope to detect composition distribution at the interfacial region. It was found that contact of solid graphite with Fe-C-S melts will result in a nonequilibrium reactive wetting. It involved carbon transfer from the solid to the liquid and iron transfer from the liquid to the solid. The Fe-C-S melts exhibited relatively poor wetting when the reactions were absent. The mass transfer between solid graphite and Fe-C-S melts was observed to strongly enhance the wetting phenomena. It is proposed that the decrease of system free energy corresponding to the mass transfer reactions strongly influences the formation of the interface region and results in the progressive spreading of the wetting line. The composition and thickness of the graphite/iron interfacial layer was dependent on the intensity of mass transfer across the interface. The resulting change in the interfacial energy γ _ls is a strong function of mass transfer, and it varies in accordance with time of contact. The influence of carbon content on the wetting phenomena could only be seen at in the initial stages, whereas the influence of sulfur on the wettability was found when the system approached equilibrium. Therefore, the interfacial tension in its equilibrium condition at the graphite/Fe-C-S melt interface was determined only by the extent of sulfur adsorption at this interface.     

Influence of ash on mass transfer and interfacial reaction between natural graphite and liquid iron

The interfacial reaction is a factor that plays an important role in governing the rate of many metallurgical processes. In the direct iron smelting process, interfacial reactions of carbonaceous materials, such as coals, with molten iron is one of the key factors that dictate the rate of carbon transfer from the carbonaceous materials into molten iron and establish a carbon concentrated melt to reduce iron oxide in the slag phase. In the current investigation, wetting of natural graphite, which contains 8.8 pct ash, by iron was studied in a horizontal tube furnace at 1600 °C using the sessile drop approach to establish a fundamental understanding of the influence of ash on interactions between graphite and iron. The mass-transfer phenomena between the solid substrate and the iron droplet were studied by withdrawing the assembly at different time intervals. After the wetting experiment, the contacting surface of the iron droplet was observed by a field emission scanning electron microscope (FESEM). The components of the interfacial layer formed during the experiment were examined by energy dispersive spectroscopy (EDS). The change in the carbon and sulfur contents of the droplet at different time intervals during the wetting experiment was analyzed by a LECO carbon and sulfur analyzer. It was found that the formation of an ash interfacial layer between the carbonaceous materials and the liquid iron has a strong influence on the mass transfer and interfacial reaction. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Reactive wetting of SiO<Subscript>2</Subscript> substrates by molten Al

The reactive wetting behavior of SiO₂ substrates by molten Al was investigated at temperatures between 800 °C to 1250 °C in a purified Ar-3 pct H₂ atmosphere of about 0.11 MPa using an improved sessile drop method. The time dependence of the changes in contact angle and droplet geometry was monitored and the wetting kinetics was identified. The initial equilibrium or quasi-equilibrium contact angles are generally larger than 90 deg and do not significantly vary with temperature. The subsequent remarkable decrease in the contact angle mainly results from the progressive decrease in the droplet volume rather than the advance of the solid-liquid interfacial front. The significant effect of temperature on the wetting kinetics is essentially related to its effect on the reaction and molten Al penetration progress. For systems with a considerable decrease in the droplet volume during reactive wetting, a criterion for evaluation of the true wetting improvement was proposed.     

Interface attachment kinetics in alloy solidification

The current status of our understanding of nonequilibrium interface kinetics during solidification is reviewed. Measurements of solute trapping and kinetic interfacial undercooling during rapid alloy solidification are accounted for by the continuous growth model (CGM) without solute drag. Disorder trapping has been predicted and observed in the rapid solidification of ordered intermetallic compounds. In systems that undergo either solute or disorder trapping, a transition from short-range diffusion-limited to collision-limited growth occurs, which originates in the reduced driving free energy for the formation of such metastable materials, resulting in three orders of magnitude change in the interface mobility. Applications to cellular and dendritic growth are discussed. A correlation is presented for estimating the diffusive speed—the growth rate necessary for substantial solute trapping—for alloy systems in which it has not, or cannot, be measured. The raw data for Si(Bi) solute trapping measurements to which many models have been compared are presented in the Appendix.     

Work of Adhesion in Al/SiC Composites with Alloying Element Addition

In the current work, a general methodology was proposed to demonstrate how to calculate the work of adhesion in a reactive multicomponent alloy/ceramic system. Applying this methodology, the work of adhesion of Al alloy/SiC systems and the influence of different alloying elements were predicted. Based on the thermodynamics of interfacial reaction and calculation models for component activities, the equilibrium compositions of the melts in Al alloy/SiC systems were calculated. Combining the work of adhesion models for reactive metal/ceramic systems, the work of adhesion in Al alloy/SiC systems both before and after the reaction was calculated. The results showed that the addition of most alloying elements, such as Mg, Si, and Mn, could increase the initial work of adhesion, while Fe had a slightly decreasing effect. As for the equilibrium state, the additions of Cu, Fe, Mn, Ni, Ti, and La could increase the equilibrium work of adhesion, but the additions of Mg and Zn had an opposite effect. Si was emphasized due to its suppressing effect on the interfacial reaction.     

Fluid Oscillation in the drop tower

An interfluid meniscus oscillates within a cylindrical container when suddenly released from earth's gravity and taken into a microgravity environment. Oscillations damp out from energy dissipative mechanisms such as viscosity and interfacial friction. Damping out of the oscillations by the latter mechanism is affected by the nature of the interfacial junction between the fluid-fluid interface and the container wall. Perfluoromethylcyclohexane and isopropanol in glass were the materials used for the experiment. The wetting condition of the fluids against the wall changes at the critical wetting transition temperature. This change in wetting causes a change in the damping characteristics. This paper is based on a presentation made in the symposium “Experimental Methods for Microgravity Materials Science Research” presented at the 1988 TMS-AIME Annual Meeting in Phoenix, Arizona, January 25–29, 1988, under the auspices of the ASM/MSD Thermodynamic Data Committee and the Material Processing Committee.     

Four wetting phases in AIN/AI and AIN Composites/AI systems,models of nonreactive,reactive, and composite systems

The contact angles between molten aluminum and samples of A1N and A1N composites were measured to establish a way of estimating the wetting of nonreactive systems, reactive systems, and composite systems. The experiments were conducted using an improved sessile drop technique which prevented the oxidation of the aluminum. By plotting the results on a logarithmic time scale, it was found that the contact angle value for A1N containing Y₂O₃ as a sintering agent progressed through four phases (I: original-wetting phase, II: quasiequilibrium phase, III: interfacial-reaction-wetting phase, and IV: equilibrium phase), while the contact angle of purified A1N progressed through only two phases, I and IV. Phase III in the sample containing Y₂O₃ was caused by the interfacial reactions; the wetting speed in phase III (interfacial-reaction-wetting speed) and the value of the contact angle in phase IV (equilibrium wettability) depend on the interfacial reactions. The contact angle for A1N composite also progressed through the four phases. The contact angle of phase II (original wettability) conformed to Cassie’s law, whereas the contact angle of phase IV depended on the condition of the interface. However, Cassie’s equation should be applicable throughout phases II through IV when the condition of the interface is understood. Also, the mechanism of the interfacial reaction wetting was explained using Cassie’s equation by taking into account the ratio of area of components at the interface in phase III. Formerly Graduate Student, Department of Materials Science and Engineering, Waseda University.     

Dynamic reactive wetting and its role in hot dip coating of steel sheet with an Al-Zn-Si alloy

The effect of substrate preheat temperature on the dynamic wetting of 55Al-43.4Zn-1.6Si hot dip coating melts on low-carbon steel substrates has been investigated. An experimental apparatus based on the sessile drop technique was developed, which allowed the substrate to be preheated to a different temperature than that of the droplet. The initial wetting and spreading of the molten metal droplet on the substrate was recorded at 1000 frames per second using a high-speed digital camera. Wetting was improved (ϑ decreased from 120 to 25 deg) as the substrate preheat temperature was increased from room temperature and approached the droplet temperature, beyond which the improvement in wetting was negligible. Immersion experiments using a thermocouple instrumented substrate dipped into a coating bath were performed for various substrate preheat temperatures. Interfacial heat fluxes and interfacial resistances were calculated from the temperature responses. The “minimum” interfacial resistance was decreased by an order of magnitude (1 × 10⁻⁴ to 2 × 10⁻⁵ m² K/W) as the substrate preheat temperature was increased from room to bath temperature. The reduction in interfacial resistance was related to the improvement of the initial wetting and the increase in mass transfer of iron atoms from the substrate across the interface. There was an apparent increase in the minimum interfacial resistance for substrate temperatures greater than the bath temperature. This was due to the increased rate of alloy layer formation and the exothermic nature of the Fe-Al interfacial reactions. The significance of these findings was discussed with respect to the mechanism of alloy layer formation at the interface during the initial stages of solid-liquid contact. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Ti—Cu—Nb合金钎料的制备及其在SiC表面润湿性的研究

采用真空电弧熔炼法制备Ti-50Cu-SNb（质量分数）合金钎料。根据DSC曲线确定出合金钎料的熔化温度为980～1050℃;通过能谱（EDS）和x射线衍射（XRD）分析得出钎料化学组成主要为Cu3Ti2和CuTi2,Nb元素以固溶体的形式存在于钛铜合金中;通过改良后的座滴法研究了钎料在1000、1050和1100℃下润湿角度的变化情况。实验表明在高温下钎料对基体均有很好的润湿作用;在钎料与SiC基体反应界面,主要生成物TiSi促进了润湿过程的进行。     

钾离子电池合金负极与电解液界面作用的研究进展

近年来,钾离子电池（KIBs）因钾元素丰度高、氧化还原电位低等优势受到越来越多的关注.负极是电池的重要组成部分之一,直接影响着电池的安全性、稳定性和能量密度.其中,合金负极基于多电子反应机制能够提供较高的理论比容量,有望提升全电池的能量密度.此外,其储钾电位远离了金属钾的沉积/析出电位,保证了电池的安全性.然而,（去）合金化过程中剧烈的体积波动会引起电极材料的破裂和粉化,进而导致容量快速衰减.优化电解液构筑稳定的电极–电解液界面是一种切实有效稳定合金负极结构的方法,主要包括：调控固体电解质膜的组分、调节钾离子的溶剂化结构、利用溶剂对电极的化学吸附作用等.它具备工艺简单、成本低廉等优点.本文综述了近年来钾离子电池合金负极与电解液界面作用的相关研究进展,总结了电解液的优化策略,分析了合金负极的储钾机制和电化学性能,重点阐述了合金负极与电解液的界面作用机制,并对未来钾离子电池电解液的发展提供了新的见解与思路.     

Wetting of ceramic particulates with liquid aluminum alloys: Part II. Study of wettability

Wetting phenomena in ceramic particulate/liquid Al-alloy systems were investigated experimentally using a new pressure infiltration technique developed by the authors. Studies were performed on two different ceramic particulates, SiC and B₄C, with four different liquid aluminum alloy matrices, pure Al, Al-Cu, Al-Si, and Al-Mg. Five major variables tested to study wetting phenomena in ceramic/Al-alloy systems were holding time, melt temperature, alloying element, gas atmosphere, and particulate. Metal: ceramic interfaces were investigated with optical microscopy, SEM, EPMA, and Auger Electron Spectroscopy (AES) in order to understand better the wetting process. The threshold infiltration pressure decreased with, temperature as well as with pressurization time for all the ceramic/metal systems. A strong correlation was found between the alloying effect on the threshold pressure and the free energy of formation of oxide phase of the alloying element. More reactive alloying elements were more effective in improving wettability. In air atmospheres, the threshold pressure usually increased markedly as a result of a thick oxide layer formation on the liquid front. Compacts of B₄C particulates showed lower threshold pressures than those of SiC, particulates. Fracture occurred in a generally brittle manner in infiltrated SiC, specimens. AES element profiles on the fracture surfaces showed fast diffusion of Si, and pile-up of C at the metal∶SiC boundaries which promoted fracture through the carbon-rich layer. The fracture surfaces of infiltrated B₄C specimens indicated plastic deformation, hence a more ductile failure mode.     

Solid-State wetting of graphite by Pb and Pb-Ni alloys

Equilibrium segregation of Ni to the interface of solid Pb/graphite was studied using a solid-state wetting approach. Increasing amounts of Ni, ranging from 0 to 0.2 wt pct Ni, added to Pb were found to systematically lower the contact angle. No significant surface concentration of Ni was found at the Pb surface. The reduction of the contact angle was therefore attributed entirely to the lowering of the interfacial energy by interfacial adsorption of Ni. The amount of Ni at the interface was determined using the Gibbs adsorption isotherm. The presence of excess Ni at the interface was confirmed qualitatively by crater-edge profiling studies performed using a scanning Auger microprobe (SAM). All the experiments were performed under ultrahigh vacuum (UHV) to reduce the effects due to surface adsorption of impurities.     

On the estimation of the solid liquid interfacial energy of glassy alloys as a function of temperature and structure

An attempt has been made to find out a model based on homogeneous nucleation principle to estimate solid liquid interfacial energy as a function of temperature and structure for a number of glassy alloy systems. Easy estimation of interfacial energy is stemmed from the availability of thermal and viscosity data for glassy alloys. Good match has been found in the interfacial energies with the reported values.     

Chemical thermodynamics as a predictive tool in the reactive metal brazing of ceramics

Thermodynamics have long been applied to our understanding of the reactive wetting phenomena in metal-ceramic joining. We postulate the existence of a “solvent effect” due to the interaction between the reactive element addition and the brazing alloy. This effect plays a significant role in reactive wetting. By taking this effect into account, more realistic reactivities of different reactive element additions into a given brazing base alloy are predicted. Irreversible thermodynamics are also used to characterize the driving forces for reactive metal-ceramic joining.     

Influence of Zn Coating on Interfacial Reactions and Mechanical Properties During Laser Welding-Brazing of Mg to Steel

To investigate the influence of Zn coating on the joining of magnesium alloy AZ31?to Zn-coated steel, dissimilar metal joining both with and without Zn coating was performed by the laser welding-brazing (LWB) process. Welding characteristics including joint appearance, identification of interfacial reaction layers, and mechanical properties were comparatively studied. The results indicated that the presence of Zn coating promoted the wetting of liquid filler wire on the steel substrate. Heterogeneous interfacial reaction layers formed along the interface between the Mg alloy and Zn-coated steel, whereas no distinct reaction layer and increased concentration of Al were identified at the interface between the Mg alloy and noncoated steel. The maximum tensile-shear strength of Mg/steel lap joint with Zn coating reached 180?N/mm, which was slightly higher than that achieved without Zn coating (160?N/mm). Failure of joint in both cases occurred at the interface; however, the fracture mode was found to differ. For Zn-coated steel, the crack propagated along the Mg-Zn reaction layer and Fe-Al phase, with little Mg-Zn reaction phases remaining on the steel side. As for noncoated steel, some remnants of the seam adhered to the steel substrate.