Triple Line Region Research Articles

Dynamic wetting and spreading mechanisms of SAC305 with added Au elements in the laser jet weld ball bonding process

The lead-free solder SAC305 has inferior wetting properties compared to conventional leaded solders, which deteriorates the weld quality. In this study, Au coatings with varying thickness were applied to improve its wettability and the influencing mechanism was investigated. The results indicated that the wetting angle (WA) and spreading area (SA) increased and then decreased with increasing thickness of the Au coating. The minimum value of WA and maximum value of SA were 25.4° and 8.7 mm2, respectively, when Au coating thickness was 50 nm. The analysis of the interfacial microstructure revealed that the generation of AuSn4 in the triple line region would significantly improve the wettability of Sn alloys. However, when the Au coating thickness reach up to 75 nm, the dense intermetallic compound (IMC) (Cu, Ni)6Sn5 was generated and the wettability of Sn alloys was reduced. The effect of the interfacial compounds on wettability depended on the change of energy consumption mechanism during wetting. The main energy consumption mechanism changed from adsorption of elements to a reaction-controlled, which reaction wetting dominated when the Au coating thickness was greater than 50 nm. This study will provide a deep understanding of wetting behavior and a valuable insight for optimizing solder wetting processes.

Dynamic wetting and spreading mechanisms regulated by elemental Ni in a Mg/steel immiscible system during laser processing

Magnesium alloys (Mg) and steels are immiscible as they do not react with each other and are virtually insoluble in the liquid state. This feature hinders their joining either by fusion welding or brazing, thus limiting the application of this dissimilar pair in the automotive and aerospace industries. The metallurgical bonding of these dissimilar metals will only be achieved by another alloy element as transitional interlayers. The introduction of Ni is generally considered an effective way to solve the aforementioned joining difficulties. Here, Ni coating was introduced on the steel surface via electroplating, and the wetting and spreading behaviors of the Mg alloy over the Ni coated steel substrate during laser processing were investigated. The influence by the amount of Ni on the wetting and spreading behaviors was comprehensively studied for the first time by evaluating the role of the thickness of Ni coating. With the introduction of Ni, the Mg atoms were more likely to move toward the Fe substrate, being the dominant factor in the spreading process from viscosity to adsorption and desorption. However, the excessive addition of Ni transformed the dominant spreading mechanism to reaction-controlled. The analysis of the interfacial microstructure revealed that α-Mg + Mg2Ni generated in the triple line region and played an essential role in the wetting process. Moreover, the formation of dense Mg2Ni intermetallic compound due to excessive Ni element diminished the spreading. This paper elucidates the regulation mechanism for alloying elements in the Mg/steel immiscible system during laser processing to further expand the lightweight applications based on improved process efficiency and product quality.

Comprehensive correlation for the prediction of the heat transfer through a single droplet in dropwise condensation regime

Numerical simulations have been performed to determine the conduction heat transfer in a sessile droplet for a large range of dynamic contact angle θ and Biot number B i . The substrate is set at a constant and uniform temperature, while a convective heat transfer is set at the liquid–vapor interface. In such a configuration, the heat flux is concentrated in the triple line region, so that numerical results can become inaccurate as the Biot number increases. A reference case in which the heat flux can be determined analytically has thus be established to derive an empirical criterion on the local mesh refining needed to obtain accurate numerical results. To consolidate the results obtained with a finite elements code, calculations have been performed with a completely independent tool using Monte Carlo method on a set of cases. A correlation has then been derived from the numerical results data with a maximum deviation of less than 4% in the considered range of θ and B i , that covers conditions encountered in all the studies dealing with dropwise condensation of pure vapor. Comparisons with other laws available in literature have then been performed, evidencing some important discrepancies. • Available correlations lead to huge discrepancies when they are compared to each other. • Elements of the mesh must be smaller than the inverse of the local Biot number. • An unbiased correlation is provided to calculate the conduction thermal resistance. • In dropwise condensation this law is valid whatever the Biot number and contact angle.

Influences of Si and Ti on the wettability and reactivity of Al/graphite system at 900 °C

The effects of Si and Ti alloying elements and their concentrations on the wettability and reactivity of the Al/graphite (Al/Cg) system at 900 °C were studied by improved sessile-drop methods combined with thermodynamic and kinetic analyses. The Al/Cg system was not wettable, with an initial contact angle of 132°. However, the subsequent interfacial reaction to generate Al4C3 improved the wettability, despite the rate was relatively slow. The Si addition weakened the formation of Al4C3 at the interface, thus slightly worsening the wettability when its addition amount was less than 12 wt.%; whereas, when the Si addition reached 20 wt.%, the interfacial reaction product transformed from Al4C3 to SiC and a SiC + Al4C3 composite layer was formed at the triple line, resulting in substantial improvement in the wettability. On the other hand, a continuous composite layer of TiCx + Al4C3 covering the triple-line region was formed when 1–3 wt.% Ti was alloyed with Al. With the increase in the Ti content, the proportion of TiCx product in the composite layer increased and the wettability improved significantly. The reaction and spreading kinetics of the Al–Ti/Cg system were mainly controlled by the diffusion of Ti from the drop bulk to the triple line.

Wetting of liquid aluminum alloys on pure titanium at 873-973 K

The wetting behaviour of Al alloys (i.e., 6061 Al and 4043 Al alloys) on the surface of pure titanium was studied by sessile drop method at temperatures of 873–973K under high vacuum with ˜10−4 Pa. All wetting processes were divided into two stages: in the nonlinear stage, the formation of a compact intermetallic layer (Ti7Al5Si12) blocked the mass transfer at solid/liquid (S/L) interface and deteriorated wetting, while the formation of loose phase (Al3Ti) at triple line region can removed the oxide film and improved wettability. The wetting activation energy (56kJ/mol for a 6061Al/Ti system, and 71kJ/mol for a 4043Al/Ti system) corresponded to the sum of the difference in surface energy per molar area between α-Ti and TiO2 (27.2kJ/mol), and the Gibbs energy of formation for Al3Ti (30kJ/mol) or the decomposition energy for Ti7Al5Si12 (48kJ/mol). In the near-linear stage, the droplet spread on the surface of intermetallic compound (IMC). The spreading dynamics for 6061 alloy satisfied the Jiang’s empirical equation, and for 4043 alloy satisfied the viscous dissipation-limited model. The interfacial reaction had little effected on a droplet spreading, while the viscous friction drove the spread of 4043 alloy on precursor film in the near-linear stage.

Polarity effects on the wettability and interfacial chemistry at Cu–YSZ interface by applying a direct current

The application of a direct current, regardless of its polarity, can significantly improve the wettability of ZrO2–8mol% Y2O3 (YSZ) by molten Cu at 1373K, and this effect was more pronounced when YSZ was connected to cathode. The mechanisms for the wetting improvement varied with the change in the current polarity. When YSZ was connected to the cathode, the oxygen ions in the YSZ body driven by the external electric power moved to the solid–liquid interface and dissolved into liquid Cu, forming OCu clusters. As a consequence, the solid–liquid interfacial energy and liquid surface tension were greatly reduced and wettability improved. On the other hand, when YSZ was connected to anode, the improvement in the wettability was mainly driven by the formation of nonstoichiometric zirconia and metallic Zr at the interface. Nevertheless, the newly formed ZrO2 at the triple line region inhibited further spreading of liquid front.

Self-induced Marangoni flow in evaporating alcoholic solutions

Abstract The self-induced Marangoni convection in alcoholic solutions is the subject of the present experimental investigation. Pure ethanol and its mixtures with 5%, 10% and 20% in weight of water are presented and discussed. In particular, Marangoni flow in horizontal pipes from 100 to 1000 μm inner diameter is studied. Vortex spinning frequency, average particle tracers velocity and evaporation rate are measured and discussed. The evaporation rate increases and the evaporation flux decreases at bigger tube sizes in line with previous investigations; pure ethanol has higher evaporation rate and flux than ethanol/water mixtures. The spinning frequency and the average tracer particles velocity decrease for increasing water content in the mixtures. All of these findings are due to evaporative cooling effect which is higher at the meniscus wedge (where the triple-line region is found) than at the meniscus center; this causes a difference in temperature between the wedge and the center that generates a gradient of surface tension driving vigorous Marangoni convection, that has been reported and analyzed. The experimental results are explained on the basis of a numerical model including evaporation, vapor diffusion, heat and mass transfer from the liquid to the surrounding ambient and the Marangoni effects.

Onset of Marangoni convection in low viscosity silicon oil inside a heated capillary tube

In the present experimental investigation the onset of Marangoni convection inside a heated capillary tube filled with low viscosity silicon oil is presented and discussed. The 1 cSt viscosity silicon oil used evaporates spontaneously at ambient temperature. The evaporation of silicon oil inside the 1 mm internal diameter tube is not uniform, being larger near the meniscus triple line region than in the centre; this creates gradients of temperatures (which have been measured by InfraRed thermography) and therefore of surface tension. For the unheated tubes this gradient of surface tension is found to be not big enough to set a convection motion (Marangoni convection) which was reported by one of the present authors in previous studies using alcohols. With increasing power supplied to the tube by an electric heater, the Marangoni convection sets in and strengthens at increasing powers till the pinned meniscus detaches from the tube mouth and recedes inside the capillary.

Experimental investigation of mesoscale crack front triple line

The aim of this paper is to investigate the mesoscale behavior and structure of an adhesive near the fracture front of an asymmetric joint consisting of carbon fiber/epoxy resin composites bonded with a relatively soft, epoxy adhesive. A single cantilever beam fracture test at constant separation rate gave steady-state crack propagation, details of which were followed by digital image correlation (DIC). A deformed, triple line region was found between the adhesive, air, and the composite, somewhat resembling a “wetting ridge,” as found with a liquid meniscus in contact with a soft solid. Importantly, the partially separated bondline layer took part in (non-unidirectional) load transfer between adherends (and thus energy dissipation), contrary to common assumptions where the separated bondline is assumed no longer to play a structural role. A simple model, based on the Flamant contact mechanics approach, is proposed and compared with both a finite element solution and experimental data extracted from image correlation. The model points out the importance of two length scales: process zone extent and adhesive thickness, both being known to affect global properties of bonded structures.

Reactive Wetting Processes and Triple-Line Configuration of Sn-3.5Ag on Cu Substrates at Elevated Temperatures

Reactive wetting processes of molten Sn-3.5Ag on Cu substrates at elevated temperatures were investigated by the sessile drop method. Equilibrium contact angles of Sn-3.5Ag on Cu substrates are 36.5°, 32.9°, 25.25°, and 32.1° at 523 K, 573 K, 623 K, and 673 K, respectively, indicating that the contact angle does not decrease monotonically with increasing temperature. It is also found that the maximal triple-line mobility does not increase linearly with temperature. The complicated temperature effects on the equilibrium contact angles and triple-line mobility are attributable to the fact that Cu substrates dissolve easily in the liquid solder, hindering solder spreading. A description of the equilibrium state helped explain the triple-line region of the Sn-3.5Ag/Cu joint. The calculated results, based on the experimental values of tension balances along each of the three interfaces, show good agreement with the theoretical analysis. The present results are of practical interest for composite lead-free solder preparations and joining of Sn-3.5Ag to Cu substrates.

Modeling the early stages of reactive wetting

Recent experimental studies of molten metal droplets wetting high-temperature reactive substrates have established that the majority of triple-line motion occurs when inertial effects are dominant. In light of these studies, this paper investigates wetting and spreading on reactive substrates when inertial effects are dominant using a thermodynamically derived diffuse interface model of a binary three-phase material. The liquid-vapor transition is modeled using a van der Waals diffuse interface approach, while the solid-fluid transition is modeled using a phase field approach. The results from the simulations demonstrate an O(t(-1/2)) spreading rate during the inertial regime and oscillations in the triple-line position when the metal droplet transitions from inertial to diffusive spreading. It is found that the spreading extent is reduced by enhancing dissolution by manipulating the initial liquid composition. The results from the model exhibit good qualitative and quantitative agreement with a number of recent experimental studies of high-temperature droplet spreading, particularly experiments of copper droplets spreading on silicon substrates. Analysis of the numerical data from the model suggests that the extent and rate of spreading are regulated by the spreading coefficient calculated from a force balance based on a plausible definition of the instantaneous interface energies. A number of contemporary publications have discussed the likely dissipation mechanism in spreading droplets. Thus, we examine the dissipation mechanism using the entropy-production field and determine that dissipation primarily occurs in the locality of the triple-line region during the inertial stage but extends along the solid-liquid interface region during the diffusive stage.

Marangoni-driven instabilities of an evaporating liquid-vapor interface

Marangoni-driven instabilities of a liquid-vapor interface of ethanol formed in a horizontally oriented capillary tube of 600 microm diameter are described. Instabilities of the interface are reported as well as instabilities of the liquid flow underneath the meniscus. The experimental results consist of visual observation of the interface, microscale particle image velocimetry measurements of the liquid flow and ir temperature measurements of the interface. The instabilities are found in both the flow structure and the interfacial temperature which present a periodic oscillatory pattern with a characteristic frequency of about 5 Hz. The interface also oscillates periodically, having a characteristic frequency of about 1.4 Hz. The differential evaporative cooling along the extended meniscus in the triple-line region produces a temperature difference which sustains the liquid-thermocapillary Marangoni-driven convection. A linear stability analysis based on a one-sided model, modified to take into account evaporation, is used to show that the self-induced temperature difference at the triple-line region is responsible for the observed interfacial instabilities. The instabilities in the flow pattern are due to competition between the surface tension driving force and gravity and are also found to be influenced by the meniscus instabilities.

Self-organised marangoni motion at evaporating drops or in capillary menisci – thermohydrodynamical model

Thermocapillary convection has been observed both in capillaries and at the surface of evaporating sessile droplets. The present paper aims to give a model of the onset of these convective patterns. The model accounts for the self-induced surface gradient of temperature linked to the stronger mass transfer observed near the triple line region. The role of the apparent contact angle is also evidenced. Dimensionless quantities such as the Marangoni number and the partition coefficient are the key factors of the present analysis. The calculations show that for the same environmental conditions the convection can be influenced by the geometrical considerations. Indeed, the calculated Marangoni numbers are found to be greater in the capillary than in the drop for a wetting contact angle of less than π /4 ; for an angle greater than π /4 , the results are inverted.

Characterization of local texture in a moderately deformed polycrystalline AlSi-alloy

Polycrystalline material of various grain sizes of AlSi-alloy containing second-phase particles have been deformed at room temperature in axisymmetric compression. The variation in crystallographic orientation in the as-deformed material was obtained by the Electron Back Scattered Pattern (EBSP) technique in SEM. “Random” and cumulative long range misorientation gradients have been quantified within the matrix (M) and at heterogeneities such as the grain boundary (GB), the triple line region (TL) and in the vicinity of large second phase particles (P) in material compressed to equivalent plastic strains of 0.2 and 0.4. It is shown that the misorientation gradient increases differently in different regions with increasing strain. Maximum values were found in regions expected to be more strained than average in order to accomodate imposed constraint from neighbouring grains or from the presence of large second phase particles. An important feature of the deformed structure seems to be the cumulative rotation of the lattice about an axis close to the 〈111〉-axis in regions with large misorientations.