Temperature Coefficient Of Surface Tension Research Articles

Thermocapillarity transition-induced unconventional thermal behavior and dilution in laser welding of metals with dissimilar sulfur content

An enhanced three-dimensional transient Thermal-Fluid-Dilution model, integrating a sub-model that accounts for surface tension, is proposed to investigate the unconventional thermal behavior and dilution induced by the surface-active element (sulfur) during the laser joining process of 304SS with higher sulfur content and pure nickel with lower sulfur content. Surface tension is modeled as a function dependent on local temperature and the concentration of the surface-active element (sulfur) at the free surface. The temperature and sulfur-dependent surface tension initially generate an unconventional driving force, subsequently leading to the transitions of heat transfer, flow pattern, and species dilution. Specifically, the inclusion of the sulfur effect results in a redistribution of larger surface shear stress along the transition boundary, causing unconventional flow behavior. The temperature coefficient of surface tension (TCST) is the coexistence of TCST (-) and TCST (+), leading to a novel flow pattern with combined inward-outward flows. Moreover, the anomalous flow exhibits observed phenomena such as the rotation of the major axis (RA) and center line shift (CLS) within the melt pool, showing more reasonable simulated melt pool dimensions when accounting for the sulfur effect. Additionally, the dilution model integrated with the unconventional flow pattern presents a more uniform concentration distribution compared to the conventional dilution. Finally, the simulated distribution of alloy elements is validated effectively by experimental data obtained from Energy Dispersive Spectrometer (EDS) analysis.

Issledovanie vzaimodeystviya ekzogennykh nanofaz oksida alyuminiya s olovom i sur'moy v rasplavakh kobal'ta.II. poverkhnostnoe natyazhenie i plotnost'

The surface tension and density of Co-Sn and Co-Sb melts with introduced Al2O3 nanoparticles (dmid = 41 nm) were studied by the large drop method. A related change in the structural properties of the metal, in particular the inversion of the surface tension temperature coefficient, has been revealed. The influence of Co+ (Al2O3-Sn/Sb) ensembles formed on the density of melts is considered in the framework of the metallic melts quasi-chemical theory. So, if for the Co-Sn-Al2O3 system, looseness, as a rule, decreases, then in the Co-Sb-Al2O3 system, on the contrary, it increases. This indicates a different influence of the ensembles Co+(Al2O3-Sn) and Co+ (Al2O3-Sb) on the change in the cluster structure of the melt and its surface properties.

Impact of sulfur content on thermo-capillarity and melt pool dynamics in laser powder bed fusion of 316L powders

A three-dimensional numerical model is developed to investigate the influence of sulfur content on the transitions of thermo-capillarity and flow dynamics during laser powder bed fusion (LPBF) of 316L powders. The impacts of variations in sulfur contents on thermal behaviors involving heat transfer and solidification characteristics, thermo-capillarity transition, as well as the spatial and directional transitions in flow dynamics, are analyzed through mechanistic modeling techniques. It is observed that transient thermal behaviors, including melt pool profile, track morphology, and solidification processes, are significantly influenced by the contained sulfur concentration. High sulfur concentrations tend to result in finer microstructures and equiaxed grains. Through simulations, it is noted that the transition in the sign of temperature coefficient of surface tension (TCST) is more easily observable in low-sulfur level but disappears as the sulfur concentration is extremely low (0.0001%) With sulfur content increasing, a more homogenized velocity distribution is observed, accompanied with heightened flow complexity denoted by the emergence of additional branch flows and vortices. These findings offer valuable insights into the underlying physics of melt pool dynamics in the LPBF process and present a potential approach for process optimization.

Investigations on dross formation susceptibility in laser fusion cutting of different stainless steel compositions with emphasis on minor element effects

The problem of variable susceptibility to dross formation or cast-to-cast variations in the performance of solid-state laser fusion cutting of 2 mm stainless steel sheets is investigated. The conducted study considered five different steel batches that each fully meets the material specifications of AISI 304 steel but show variations in minor element concentrations, particularly with respect to the sulfur content. Based on the hypothesis that the dross formation phenomenon correlates with surface tension and viscosity of the melt, the general melt flow behavior of the batches was first characterized by complementary experimental and simulative investigations. This combined approach allowed for a qualitative distinction of batches with a primary negative or positive temperature coefficient (NTC/PTC) of surface tension. Subsequent cutting experiments on qualitatively different batches with variations in cutting speed and gas pressure give evidence that an experienced wider processing window for dross-free cuts relates to PTC batches. However, these batches showed more irregular cut edge topography with slightly increased roughness values. It is consequently concluded that proper quality management in laser cutting of different batches of a material needs to consider the real composition of the materials being cut.

Role of Surface-Active Element Sulfur on Thermal Behavior, Driving Forces, Fluid Flow and Solute Dilution in Laser Linear Welding of Dissimilar Metals

Understanding heat and mass transfer and fluid flow in the molten pool is very helpful in the selection and optimization of processing parameters, and the surface-active element has an important effect on the heat and mass transfer in laser welding of dissimilar metals. A three-dimensional (3D) numerical model coupled with a sub-model of surface tension, which considers the influence of local temperature and the concentration of surface-active element sulfur at the gas/liquid surface, is used to analyze the thermal behavior, driving forces, fluid flow, and solute dilution during laser linear welding of 304SS and Ni. The relationship between surface tension, driving forces, and the temperature coefficient of surface tension with the spatial distribution of temperature and the surface-active element sulfur is quantitatively analyzed. The simulation results show that the molten pool is fully developed at 45 ms, and the collision of inward and outward convection, with the maximum velocity reaching 1.7 m/s, occurs at the isotherm with a temperature between 2200 K and 2500 K. The temperature-gradient term and concentration-gradient term of surface shear stress play different roles in different positions of the free surface. The local sulfur concentration changes the temperature sensitivity of the surface tension at different sides of the free surface and further determines the transition of convection. Complex fluid flow promotes solute dilution, and the distribution of solute becomes uniform from the front to the rear of the molten pool. The Ni element is transferred to 304SS mainly at the rear side. The work provides theoretical support for the control of joint quality by changing the content of surface-active elements in dissimilar welding.

Marangoni flow patterns of molten pools in multi-pass laser cladding with added nano-CeO2

Adding rare-earth elements has been proven to modify the microstructure and enhance the mechanical properties of the laser cladding layer. However, the effect of such elements on the flow pattern in molten pools has not been extensively determined, especially for multi-pass laser cladding. The surface tension of T15 high speed steel and nano-CeO 2 mixed powders is measured using the sessile drop method. Comparing the results from the high-speed photography of the molten pool flow and the multicomponent multiphase flow model, various Marangoni flows driven by surface tension are elucidated, and the cross-section of the multi-pass cladding is further analyzed. The surface tension increases with increasing CeO 2 content. When CeO 2 is less than 0.6 wt%, the surface tension monotonically increases with increasing temperature, and the molten pool flows inward. When CeO 2 is greater than 0.6 wt%, the surface tension decreases at high temperatures, and the molten pool exhibits double flows. In multi-pass laser cladding, the inclination of the molten pool increases on adding CeO 2 . Consequently, the inclined angle of the cladding pass interface increases, and the fusion line on the substrate tends to be straightened. At 0.9 wt% CeO 2 , the added powders remain at the center of the molten pool because of a low velocity, creating a low-temperature zone. The temperature coefficient of surface tension demonstrates a positive–negative–positive distribution from the center to the surrounding pool surface, thus forming an outflow. The solidus point of the cladding alloys is lower than that of the substrate, resulting in a small indentation at the remelted region between passes, which increases the interfacial zone. • Flow in multi-pass molten pool changes from inward to outward with CeO 2 addition. • Surface tension curve drops at high temperature with CeO 2 composition above 0.6 wt%. • A low velocity and temperature zone forms in the center of molten pool at 0.9 wt% CeO 2 . • Fusion interface matching with experiments is dominated by flow and solidus point.

Molar Volume and Surface Tension of Liquid Bi\u2013Cu Alloys

Bi–Cu alloys may potentially be used for thermal energy storage or as a catalyst for methane pyrolysis. For application research and simulations, it is necessary to know the reliable thermophysical properties of liquid alloys. Density of liquid Bi–Cu alloys (25, 50, 75 at. pct Cu) was measured with dilatometric method over the 971 K to 1500 K range. Density decreases linearly with temperature for all compositions. The molar volume calculated from measured densities shows positive excess molar volume. Surface tension was measured with maximum bubble pressure method over the 1125 K to 1500 K range. The data fitted with linear equations show that while the surface tension of 25 at. pct Cu decreases and that of 50 at. pct Cu alloy does not vary with temperature, the surface tension of 75 at. pct Cu alloy increases with temperature. The present results are confronted with literature data and several model calculations, part of which were performed in Pandat, and the reasons for positive excess molar volume and surface tension temperature coefficient are explained in terms of thermodynamics of Bi–Cu solutions.

Evolution of molten pool morphology and prediction of inclined cladding layer morphology

Laser cladding is a process in which multiple physical fields and multiple factors are coupled. Metal particles are fed into the melt pool to form a cladding layer through melting and solidification. The temperature and flow field in the melt pool affect the pool morphology, especially for inclined surface cladding, which ultimately affects the shape quality. In this study, based on a combination of experiments and simulations, the influence of the melt pool flow on the melt pool morphology in the laser cladding process is studied, the influence of the substrate sulfur concentration on the flow field is analyzed, and a prediction model for the morphology of the inclined clad layer is established. The results showed that the variation of the sulfur concentration on the melt pool surface significantly affected the Marangoni convection in the melt pool, which influenced the melt pool morphology. As the sulfur content decreased, the melt pool morphology evolved through three stages: circular arc melt pool morphology, bowl melt pool morphology, and double arc melt pool morphology. The melt pool morphology after solidification was between the melt pool morphologies produced by positive and negative values of the surface tension temperature coefficient. The model prediction results and the experimental results were in good agreement, and the relative errors of the width, height, and depth of the molten layer were within 8%. The agreement of the molten layer offset was poor, and the maximum relative error was 8.2%, which was because the effects of the powder and protective gas on the melt pool were neglected. The model can predict the values of the width, height, offset, and depth of the melt of the clad layer with the inclination of the substrate within an error range of 10%, which provides theoretical guidance for the study of the inclined formation mechanism and the optimization of the process parameters.

Fluid flow and solute dilution in laser linear butt joining of 304SS and Ni

Laser linear welding combined with advanced auto-control technology is a promising joint method of dissimilar metals. In this study, an improved three-dimensional model was developed to investigate the thermal behavior, fluid flow and concentration dilution during laser linear dissimilar welding of 304 stainless steel and nickel. The fluid flow and solidification behavior were presented in a 3D view to deeply study the thermal behavior and convection characteristics inside the melt pool. The relationship between dynamic characteristics and concentration dilution was studied numerically and experimentally, and the effects of welding speed, temperature coefficient of surface tension (TCST) and dynamic viscosity on mass transfer were also investigated. Larger cooling rate (GR) and smaller morphology parameter (G/R) were found at top area of the weld pool (WP). Elements from SS (Cr and Fe) were mainly mixed at front side, but Ni was mainly diluted at middle part. Resulting from the Marangoni convection, all the elements were mainly mixed at top area and then transported to the bottom. The redistribution of the species was also observed at each side, resulting in a relatively uniform distribution at each side. Nevertheless, the effects of welding speed, TCST and dynamic viscosity on solute dilution were simulated and proved non-negligible. Differences of solidification and dilution phenomenon were also observed between liner welding and spot welding. It was demonstrated the obtained results in this work provided a vital perspective in comprehending the heat and mass transfer phenomenon inside the melt pool during welding and additive manufacturing process.

Interaction of exogenous refractory nanoparticles of Al2O3 and MgAl2O4 with nonferrous metal impurities in iron melts

The exogenous refractory nanoparticles is proposed for refining iron-based melts from nonferrous metal impurities. Investigated the heterophase interaction of Al2O3 and MgAl2O4 nanoparticles with Sb/Sn/Cu and showed that the degree of removal of nonferrous metal impurities was in the Fe-Sb system up to 30 rel.%, in the Fe-Sn system up to 29 rel. % and in the Fe-Cu system up to 23 rel. %. The existence of refractory nanoparticles in a liquid metal was proved by studying the structural properties of the melt. In the melts, after the introduction of the nanoparticles, inversion of the temperature coefficient of surface tension is observed, as well as multidirectional change depending on the nature of the nanoparticles and the holding time during interfacial interaction. Decompression and compression of the melts after the introduction of nanoparticles and the multidirectional nature of the dependences of properties indicate a possible change in the cluster structure of liquid metal.

Density and Surface Tension of Fe-Cu Melts

Fe-Cu alloys are used as structural materials for manufacture of large machine parts subjected to shock loads. Fe-Cu alloys have a higher corrosion resistance in a humid atmosphere and in salt solutions than cast steel. Fe-Cu alloys have high enough damping characteristics. Upon cooling the Fe-Cu melts is stratified into two phases before crystallization which in field of gravity are separated by density. It is possible to suppress delamination and obtain a material with structure of a “frozen emulsion” by heating melt to the temperature T* determined for each composition by a specific way. In this paper, we studied surface tension of liquid alloys of Fe-1wt.% Cu, Fe-20wt.% Cu, and Fe-30wt.%Cu in order to determine the temperature T*. For the melt of Fe-20wt.% Cu value T*=1670°C is highest. It is confirmed by results of measuring temperature dependence of surface tension. Temperature dependence of the surface tension Fe-Cu melts is characterized by a positive value of the temperature coefficient of surface tension dσ/dT which is abnormal for metal melts. Experimental data on the density, the surface tension of Fe-Cu liquid alloys have of independent metrological importance for practical foundry.

Numerical modelling of fluid flow and weld penetration in activated TIG welding

This research work emphasis on understanding the weld pool development while carrying out Activated Tungsten Inert Gas (A-TIG) welding by employing Computational Fluid Dynamics (CFD). The influence of temperature coefficient of surface tension (∂γ/∂T) and the concentration of oxygen, the main surface active component on weld bead geometry is studied. A three-dimensional (3D) numerical model has been developed for A-TIG welding process with varying oxygen levels employing ANSYS Fluent for 316LN stainless steel. The general conservation equations consisting mass, energy and momentum were solved in order to acquire the temperature and velocity fields with oxygen levels varying from 50 to 300 ppm in weld pool. The impact of driving forces particularly buoyancy and Marangoni on the weld pool convection were examined. The simulation confirmed that the weld bead shape was influenced mainly by Marangoni convection consecutively dependent on the oxygen content in the weld metal in the course of A-TIG welding. The addition in oxygen content changes the surface tension temperature coefficient ∂γ/∂T from negative to positive gradient causing inward flow. It was found that minor oxygen content in the molten pool until 150 ppm exhibited outward flow and with higher oxygen content beyond 150 ppm exhibited an inward flow. The oxygen content in the weld bead without flux and with flux was found to be 69 and 336 ppm respectively for the type 316LN stainless steel plates welded by A-TIG welding. The simulated weld bead profile was validated by comparing with the experimentally obtained weld bead profile. There was excellent agreement between the two weld bead profiles.

Surface and interfacial properties of Fe-C-O-Cr alloys in contact with alumina

In this paper, temperature and concentration dependencies on density and surface tension of liquid Fe-C-O-Cr alloys (1.93 - 4.80 wt.% Cr) were investigated in high-temperature resistance observation furnace by a sessile drop method during heating from liquidus temperature to 1600?C. The interfacial characteristics (interfacial tension, wetting angle, work of adhesion, and spreading coefficient) of liquid alloy/alumina system were also determined depending on temperature. The effect of temperature and chromium content on surface and interfacial properties was proven in case of all examined alloys. Based on the fact that the content of surface-active elements such as oxygen (up to 195 ppm) and sulfur (up to 545 ppm) was higher, the influence of activities of both mentioned elements on surface tension of alloy samples was assessed. Particular attention was paid to the dependence of the surface tension temperature coefficient on oxygen and sulfur activity.

Simulation on the Marangoni flow and heat transfer in a laser-heated suspended droplet

In this study, the Marangoni flow and heat transfer inside a laser-heated water droplet suspended in the immiscible oil phase is numerically investigated. It is shown that the Marangoni flow is induced by non-uniform temperature distribution across the droplet interface caused by the localized heating source. Effects of the laser power, laser beam size and surface tension temperature coefficient are investigated. Simulation results show that the temperature rising rate and average temperature rising linearly increase with laser power due to more heat generated by photothermal effect and the Marangoni flow is intensified due to larger interface temperature gradient. With increasing laser beam diameter, the temperature distribution becomes more uniform due to more uniform laser energy distribution. The Marangoni flow is reverse when the surface tension temperature coefficient changes from the positive to the negative and vice versa, resulting in the transformation of the Marangoni flow and temperature distribution.

Neural network modelling on temperature coefficient of surface tension and its usage in melting point prediction of nanosized metal particles

Temperature coefficient of surface tension is a very important parameter to calculate phase diagrams of nanoparticle metal systems. In this paper, neural network calculation was for the first time used to evaluate the temperature coefficient. It shows that the constructed neural network can predict the temperature coefficient values for 37 metals, with the deviation from the averaged experimental measurements smaller than 25%. Furthermore, the neural network predictions were compared with the calculated values by using an empirical equation and it shows a better performance.

Theoretical calculation of surface tension and its temperature coefficient associated with liquid Cu–Ti alloys

ABSTRACTIn this work, the surface tension of Cu–Ti binary liquid alloys is calculated in the framework of Eyring theory as a function of composition and temperature. It is observed that for all investigated alloys the surface tension can be described by a linear function of the temperature with negative slope, and the temperature coefficient of surface tension decreases as Ti-content of the alloys increases linearly. The obtained theoretical results are compared to the experimental data available in the literature as well as to the theoretical results evaluated by using four models, such as the compound formation model, the quasi-chemical approximation for regular solutions, ideal solution model and Butler model treated in literature frequently.

Influence of particle size on electrochemical thermodynamics of Nano-Au electrodes: Mechanism, factors, range and degree

There is a significant effect of particle size on electrochemical thermodynamics of nano-metal electrodes, it is still unclear, however, the mechanism, factors, range and degree of the effect. Herein, in theory, we derived the relations of the electrochemical thermodynamic quantities and the size of nanoparticles which constituted the nano-metal electrodes, discussed the mechanism and the influencing factors. Experimentally, nano-Au with different radii (0.9–37.4 nm) made as nano electrodes to research the size dependence of electrochemical thermodynamic quantities. Combining the results of theory and experiments, discussed the influencing regularities, range and degree. The regularities obtained from these experiments are consistent with the theoretical relations. The research results show that particle size has pronounced effect on electrochemical thermodynamic quantities. Both the Eo and the lnKo decrease with the particle size decreasing, while other electrochemical thermodynamic quantities increase. These effects should be attributed to partial molar surface area, surface tension and its temperature coefficient. Thereinto, partial molar surface area and surface tension are the major influencing factors for Eo, Ko, ΔrGm and ΔrHm, partial molar surface area and temperature coefficient of surface tension are for (∂E/∂T)p, ΔrSm and Qr,m. For Au nanoparticles, as the radius exceeds 10 nm, the major factor is partial molar surface area, there exist linear relationships between the electrochemical thermodynamic quantities and reciprocal of radius. However, as the radius is less than 10 nm, the effects of surface tension and its temperature coefficient gradually hold the main positon with the radii decreasing, respectively; as well as there are no linear relationships. Our research offer significant fundamental insight on the size-dependent electrochemical thermodynamics, and can greatly impact future exploration and application of nano-metal electrodes.

Size-Dependent Thermodynamics and Kinetics of Adsorption on Nanoparticles: A Theoretical and Experimental Study.

Owing to their excellent adsorption properties compared with those of the corresponding bulk materials, nanoparticles have been widely applied in many fields. Their properties depend on the thermodynamics and kinetics of adsorption, which depend on the particle size. In this paper, we present universal theories of the thermodynamics and kinetics for nanoadsorption that have been developed over the past few years. Theoretically, we have derived relationships between the adsorption thermodynamic properties and the particle size, as well as those between the adsorption kinetic parameters and the particle size. Moreover, we discuss the regularities and mechanisms of influence of the particle size on the thermodynamics and kinetics of adsorption. Experimentally, taking the adsorption of methyl orange on nano-CeO2 in aqueous solution as a system, we have studied the size-dependent thermodynamics and kinetics of the system, and the size dependences were confirmed to be consistent with the theoretical relationships. The results indicate that particle size has a significant effect on the thermodynamic properties and kinetic parameters of adsorption: with decreasing particle size of nano-CeO2, the adsorption equilibrium constant K⊖ and the adsorption rate constant k increase, while the molar Gibbs free energy of adsorption Δads Gm⊖, the molar adsorption entropy Δads Sm⊖, the molar adsorption enthalpy Δads Hm⊖, the adsorption activation energy Ea, and the adsorption pre-exponential factor A all decrease. Indeed, ln K⊖, Δads Gm⊖, Δads Sm⊖, Δads Hm⊖, ln k, Ea, and ln A are each linearly related to the reciprocal of particle size. Furthermore, thermodynamically, Δads Gm⊖ and ln K⊖ are influenced by the molar surface area and the difference in surface tensions, Δads Sm⊖ is influenced by the molar surface area and the difference in temperature coefficients of surface tension, and Δads Hm⊖ is influenced by the molar surface area, the difference in surface tensions, and the difference in temperature coefficients of surface tension. Kinetically, Ea is influenced by the partial molar surface enthalpy of the nanoadsorbent, ln A is influenced by the partial molar surface entropy, and ln k is influenced by the partial molar surface Gibbs energy. The theories can quantitatively describe adsorption behavior on nanoparticles, explain the regularities and mechanisms of influence of particle size, and provide guidance for the research and application of nanoadsorption.

On the effect of temperature coefficient of surface tension on shape and geometry of weld beads in hot wire gas tungsten arc welding process

S304HCu stainless steel is inevitable materials in super heater and reheater tubes in steam power boiler industries. The major challenge in welding of T92 steel and S304HCu stainless steel is the selection of the appropriate filler wire and establishing welding procedures especially in dissimilar welding such that the weld joints meet the service requirements at high temperatures. This present work is aimed to study the effect of welding current and wire feed rate on weld bead geometry produced with hot wire gas tungsten arc welding (HW-GTAW) process using different filler wires of 0.8mm diameter viz., ERNiCrFe-7A (IN 52M) and ERNiCrCoMo-1 (IN 617) on S304HCu stainless steel tubes. These weld bead depositions were made at hot wire current of 30A with two different welding currents viz., 130A and 110A at a constant wire feed rate and travel speed. From the results, it is established that temperature distribution and the presence of surface active elements are the causes for the formation of weld beads in different shapes.

Surface-active element transport and its effect on liquid metal flow in laser-assisted additive manufacturing

During laser-assisted additive manufacturing, the transport phenomena, solidification behavior, and melt pool geometry are affected by base-metal sulfur content and oxygen present in the atmosphere. The role of these surface-active elements during metal-based additive manufacturing is not well understood. In this study, the mass transport of sulfur and its effect on liquid metal convection (Marangoni flow) are examined by using an improved 3D transient heat transfer and fluid flow numerical model. An improved surface tension model is proposed to take into account the influence of sulfur content and temperature at the surface of melt pool. The sulfur mass transport equation is combined with the other conservation equations. The results show that the sulfur redistribution leads to transitional Marangoni flow. The powder addition into the melt pool results in the dilution of sulfur in the melt pool. Increase in mass flow rate and energy input results in decreased temperature coefficient of surface tension. When temperature coefficient of surface tension changes sign from positive to negative, the flow motion transition from inward flow to outward flow occurs. Two predominant types of flow pattern lead to two types of fusion boundaries of deposited track.