Surface Melting Research Articles

The organization of subglacial drainage during the demise of the Finnish Lake District Ice Lobe

Abstract. Unknown basal characteristics limit our ability to simulate the subglacial hydrology of rapidly melting contemporary ice sheets. Sediment-based landforms generated beneath Late Pleistocene ice sheets, together with detailed digital elevation models, offer a valuable means of testing basal hydrology models, which describe the flow and dynamics of water in the subglacial system. However, to date no work has evaluated how well process-based subglacial hydrology models represent the hypothesized conditions associated with glaciofluvial landform formation in the palaeo setting. Previous work comparing model output to geomorphological evidence has typically done so using models that do not resolve subglacial processes and instead express likely subglacial water pathways. Here, we explore the ability of the Glacier Drainage System model (GlaDS), a process-based subglacial hydrology model, to represent the genesis conditions associated with a specific glaciofluvial landform termed “murtoos”. Distinctive triangular landforms found throughout Finland and Sweden, murtoos are hypothesized to form 40–60 km from the former Fennoscandian Ice Sheet margin within a “semi-distributed” system at the onset of channelized drainage in small cavities where water pressure is equal to or exceeds ice overburden pressure. Concentrating within a specific ice lobe of the former Fennoscandian Ice Sheet and using digital elevation models with a simulated former ice surface geometry, we forced GlaDS with transient surface melt and explored the sensitivity of our model outcomes to parameter decisions such as the system conductivity and bed topography. Our model outputs closely match the general spacing, direction, and complexity of eskers and mapped assemblages of features related to subglacial drainage in “meltwater routes”. Many of the predictions for murtoo formation are produced by the model, including the location of water pressure equal to ice overburden, the onset of channelized drainage, the transition in drainage modes, and importantly the seasonal sequence of drainage conditions inferred from murtoo sedimentology. These conclusions are largely robust to a range of parameter decisions, and we explore seasonal and inter-annual drainage behaviour associated with murtoo zones and meltwater pathways. Our results demonstrate that examining palaeo basal topography alongside subglacial hydrology model outputs holds promise for the mutually beneficial analyses of palaeo and contemporary ice sheets to assess the controls of hydrology on ice dynamics and subglacial landform evolution.

Ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surface and its tribological properties

Due to the poor tribological properties, the applications of titanium alloy are restricted. Both laser texturing and surface coating are effective methods to enhance the tribological properties of titanium alloy surfaces. Hence, this study proposed a new ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surfaces to improve its tribological properties by modifying titanium alloy’s surface composition and micro-nanostructures in one step. A polymer film (polyimide, PI) was selected as the carbon source preplaced on the titanium alloy (Ti-6Al-4 V, TC4) surface. On the one hand, under ultrafast laser (picosecond 355 nm laser) irradiation, the laser-induced photothermal effect led to the carbonization of the polymer film and the formation of the pyrolytic carbon coating on the titanium alloy surface. Pyrolytic carbon also reacted with titanium alloy to form titanium carbides. On the other hand, ultrafast lasers also led to the melting and ablation of the titanium alloy surface, creating micro-nanostructures with interlocking micro-holes and micro-bumps. The coefficient of friction (COF) and wear rate of the titanium alloy surfaces were significantly reduced due to the synergistic effects of carbon coating and micro-nanostructures. It showed great significance in improving the tribological properties and the surface treatment of metallic materials.

Level-Set Method Based Predictive Modelling to Track the Evolution of Surface During Pulsed Laser Surface Melting

Abstract The objective of this study is to investigate the evolution of surface geometry during pulsed laser surface melting (pLSM) via level-set method-based interface tracking numerical framework. Existing models to track surface geometry are inaccurate and computationally expensive. Therefore, they have limited use in gaining understanding of the surface evolution during pLSM. A numerical model, integrating the level-set approach, fluid flow and heat transfer dynamics, is detailed in this paper. The muti-phase numerical model achieves accurate tracking of interface for a single pulse by implementing the volumetric laser heat source on the moving interface by modifying the Berr-Lambert's law. The accuracy of the single pulse model is confirmed by comparing its Peak-to-Valley Height (PVH) to experimental data. The deviation in PVH is limited to about 15%, with a maximum Root Mean Square Error (RMSE) of ∼0.24 μm, highlighting the model's reliability. Additionally, the evolved surface of a single pulse from the model is replicated over an area with dedicated overlaps to generate the predicted textured surface with reasonable accuracy. Some inaccuracies in the predicted surface roughness values were observed because the textures were generated based on single pulse geometry computed on an initially flat surface. Nonetheless, the results highlight a significant development in numerical frameworks for pLSM and can be used as a tool to gain deeper insights into the process and for process optimization.

Study on the wetting characteristics of liquid-Al/ SiO2 interface with Si content in liquid-Al

Aiming to address the issue of aluminum slag adhering to the interior walls of vacuum lifting ladles in the aluminum electrolysis industry, Molecular dynamics simulations are employed to investigate the wetting behavior and adhesion characteristics of aluminum droplets on silica surfaces. Our findings indicate that with an increase in silicon content within the droplets, wetting diminishes and complete wetting of the silica substrate by aluminum droplets is not achieved. The presence of silicon reduces both the melting point temperature and surface tension of aluminum droplets, leading to a significant increase in contact angle and a corresponding decrease in wettability. Moreover, an elevated silicon content within molten aluminum droplets substantially decreases their interaction energy with the substrate surface. The virtual wall method is applied to examine average separation force and work of separation for detaching aluminum droplets from the substrate, revealing that adhesion characteristics are predominantly governed by mutual adhesive forces. This paper presents an atomic-level analysis elucidating how silicon as an alloying element influences adhesion between liquid aluminum and solid surfaces.

Antarctic ice-shelf meltwater outflows in satellite radar imagery: ground-truthing and basal channel observations

Abstract Ice shelves regulate the flow of the Antarctic ice sheet toward the ocean and its contribution to sea-level rise. Accurately monitoring the basal and surface melting of ice shelves is therefore essential for predicting the ice sheet's response to climatic warming. In this study, we utilize Sentinel-1A synthetic aperture radar satellite imagery combined with shipboard measurements of water temperature and salinity to investigate the presence of surficial meltwater plumes along the Antarctic coastline. Our approach reveals a strong correlation between areas of pronounced low radar backscatter extending from ice shelves and significant decreases in water temperature and salinity, suggesting meltwater-enriched ocean waters. We propose that the low radar backscatter signature of meltwater outflows is caused by stable stratification of the upper water column, driven by density contrasts from buoyant, low-salinity meltwater and surface current shear that reduce Bragg scattering waves. The resulting smooth water surfaces were observed adjacent to the surface expression of deep basal channels, documented in a helicopter survey along part of the Bellingshausen Sea ice edge. We present high-temporal resolution satellite radar as a tool for identifying meltwater release from beneath ice shelves, capable of all-weather, day-and-night imaging.

Generation of multiply charged metal ions in a high current short pulse vacuum arc

We have studied the plasma composition of a high current short pulse vacuum arc discharge with different cathode materials: lanthanum, gadolinium, lead, silver, and tin. We find that for optimal vacuum arc discharge parameters – arc current pulse duration about 2 μs and amplitude about 3 kA – the maximum ion charge state is 11+ and mean ion charge state from 7.8+ for tin to 9.6+ for lanthanum. The mean ion charge state for different materials depends on the discharge voltage and the energy required for ionization to maximum charge state. The cathode surface heats to a temperature of 700 °C–1100 °C in the course of the arc current pulse, depending on the cathode material, and the cathode surface of low melting point metals such as lead and tin melts to a depth of 5 μm and 10 μm, respectively. Surface melting does not lead to change in plasma ion composition, since the ion flux from the cathode considerably exceeds the evaporated atom flux.

Supraglacial lake evolution and its drivers in Dronning Maud Land, East Antarctica

Abstract Supraglacial lakes on Antarctic ice shelves can have far-reaching implications for ice-sheet stability, highlighting the need to understand their dynamics, controls and role in the ice-sheet mass budget. We combine a detailed satellite-based record of seasonal lake evolution in Dronning Maud Land with a high-resolution simulation from the regional climate model Modèle Atmosphérique Régional to identify drivers of lake variability between 2014 and 2021. Correlations between summer lake extents and climate parameters reveal complex relationships that vary both in space and time. Shortwave radiation contributes positively to the energy budget during summer melt seasons, but summers with enhanced longwave radiation are more prone to surface melting and ponding, which is further enhanced by advected heat from summer precipitation. In contrast, previous winter precipitation has a negative effect on summer lake extents, presumably by increasing albedo and pore space, delaying the accumulation of meltwater. Downslope katabatic or föhn winds promote ponding around the grounding zones of some ice shelves. At a larger scale, we find that summers during periods of negative southern annular mode are associated with increased ponding in Dronning Maud Land. The high variability in seasonal lake extents indicates that these ice shelves are highly sensitive to future warming or intensified extreme events.

Cermet coatings obtained by electric spark alloying to increase service life of dental instruments

The article presents the results of our study of protective cermet coatings obtained by the method of electric spark alloying on a dental instrument (excavator) using SHS (self-propagating high-temperature synthesis) electrodes based on TiC-NiCr. The influence of discharge energy during electric spark alloying on the roughness, thickness, and proportion of the TiC carbide phase in the cermet coating has been established. It has been shown that during electric spark alloying, the material of the used SHS electrode and the surface of the substrate melt, their convective mixing occurs, and during crystallization, coatings are formed that consist of a strengthening phase TiC and iron-based solid solutions: Fe9.64Ti0.36, F1.88C0.12, and Cr-Ni-Fe-C. It has been found that the maximum size of TiC grains is formed on the surface of the cermet coating, and as they approach the substrate, their size decreases to less than 10 nm. It has been found that the microhardness of the surface of the resulting cermet coatings increased to 6.2 times compared to the microhardness of the original metal base, which was 2 GPa. The results of scanning electron microscopy and energy dispersive analysis of the surface of samples with and without cermet coating before and after corrosion tests are presented. The influence of disinfectants (2 and 100 % Trilox, Wendelin, MegaDes-ortho) on the corrosion resistance of samples with and without developed protective cermet coatings at room and elevated temperatures up to 50 °C and their exposure for 120 h has been established.

Effect of energy density on down surface characteristics of AlSi10Mg alloy fabricated via selective laser melting

The correlation between surface roughness and energy density in the down surface area of AlSi10Mg alloy manufactured by selective laser melting was analyzed. This study investigated the relationship between the contour melt pool shape and surface roughness in the down surface area across an energy density range of 10–150 J/mm³. As the energy density increased, the contour melt pool in the down surface area became more stable, which significantly influenced surface roughness. Low energy density resulted in the unstable formation of the contour melt pool, leading to a deterioration in surface quality, whereas high energy density promoted the stable formation of the melt pool. Sufficient energy density is essential for the complete formation of the contour melt pool on the down surface, which plays a crucial role in reducing surface roughness. However, within the energy density range where the contour melt pool is fully formed, keyhole defects may occur, and it can be anticipated that these defects may worsen at energy densities exceeding the critical threshold.

An investigation of rapid surface melting in nanowires

The investigation into virtual melting phenomena in nanowires holds significant relevance owing to its profound impact on material durability under extreme loading conditions. Thus, the exploration of this pivotal plastic deformation mechanism is undertaken utilizing the phase-field methodology. Employing a monolithic solver, we solve the coupled highly nonlinear time-dependent Ginzburg–Landau equation and dynamic elasticity equation. Our analysis encompasses the consideration of surface tension stress in conjunction with a coherent solid–liquid interface subjected to uniaxial transformation strain, thereby unveiling intriguing facets of melting phenomena. The investigation delves into the influence of transformation strain, kinetic coefficient, and temperature on the thickness of the solid–liquid interface and its corresponding velocity. This analysis is conducted through meticulous comparison with existing experimental data and analytical solutions. Moreover, employing the phase-field method yields precise descriptions of the system kinetics, capturing virtual melting phenomena in both pristine and flawed nanowire configurations.

تأثير استعمال ليزر النيوديميوم ياك (Nd-YAG) على البنية الدقيقة وصلابة سطح الفولاذ AISI1012

The unique characteristics of the laser beam such as directionality, monochromaticity, and brightness make it a very important tool in the surface treatment engineering. The concentrated heat in the laser beam can be precisely directed toward the processed region on the surface. The laser beam power, beam size, and scanning velocity are easily controlled during the different processing methods. Laser surface modifications of metallic materials, such as laser surface melting, laser surface alloying, and laser cladding are some of the most important methods to improve the mechanical properties of the processed layer on the surface. A pulsed Nd-YAG laser surface melted specimens of low carbon steel with a maximum power of 90W at different processing parameters. The rapid melt and solidification of the treated layer produced a refinement in the microstructure. The original microstructure of this steel (Ferrite + Pearlite) has been transformed to new phases of martensitic and bainitic structures. The melted layer consists of the melted pool, the heat affected zone, and the substrate. The maximum hardness of the laser melted layer is more than 400 HV. The effect of different lasers such as high power CW CO2 laser on the mechanical properties and corrosion resistance of steel alloys will be carried out in future studies. Keywords: Nd-Yag Laser, Laser surface treatment, Microstructure and hardness of AISI1012 steel

Beyond symmetry: Investigating asymmetric melt pool evolution in multi-pulse laser surface melting

A numerical investigation is carried out to explore the intricacies of multi-pulse pulsed laser surface melting (pLSM) to understand its impact on surface evolution. A finite-element-based multi-phase model with temperature-dependent properties is employed to track the interface for multiple laser pulses. Examining various overlap spacings and conducting a comparative analysis of the number of pulses, the study focuses on the exclusive influence of overlapping in surface texture generation. Notably, the assumption of an initially flat surface eliminates the effects of the initial surface roughness to provide unique insights completely based on multi-pulse dynamics. While the first pulse on a flat initial surface resulted in a symmetric surface evolution, asymmetric melt pools were observed in the second pulse and subsequent pulses. The asymmetry results from non-uniform cooling and melt pool flows influenced by the surface evolved in the first pulse. The topography-driven surface tension from the first pulse made the trailing peak solidify slower than the leading peak. The asymmetry was significant for smaller overlaps between the two pulses and reduced as the overlap increased. Further, an increase in the number of laser pulses promotes the generation of identical asymmetric surface features. In conclusion, the study demonstrates the importance of the developed model in accurately predicting the surface evolution influenced by topography-driven surface tension and that single pulse axisymmetric models are insufficient.

Surface energy balance closure over melting snow and ice from in situ measurements on the Greenland ice sheet

Abstract Accurately quantifying all the components of the surface energy balance (SEB) is a prerequisite for the reliable estimation of surface melt and the surface mass balance over ice and snow. This study quantifies the SEB closure by comparing the energy available for surface melt, determined from continuous measurements of radiative fluxes and turbulent heat fluxes, to the surface ablation measured on the Greenland ice sheet between 2003 and 2023. We find that the measured daily energy available for surface melt exceeds the observed surface melt by on average 18 ± 30 W m−2 for snow and 12 ± 54 W m−2 for ice conditions (mean ± SD), which corresponds to 46 and 10% of the average energy available for surface melt, respectively. When the surface is not melting, the daily SEB is on average closed within 5 W m−2. Based on the inter-comparison of different ablation sensors and radiometers installed on different stations, and on the evaluation of modelled turbulent heat fluxes, we conclude that measurement uncertainties prevent a better daily to sub-daily SEB closure. These results highlight the need and challenges in obtaining accurate long-term in situ SEB observations for the proper evaluation of climate models and for the validation of remote sensing products.

Study of the features of concentration inhomogeneities during the on ground-based processing of the space experiment of the Ge(Ga) crystals growth

The article presents the results of the preparation and ground testing of the space experiment for growing Ge (Ga) crystals, planned on board the multifunctional laboratory module as part of the ISS RS. Under the conditions simulating microgravity, the features of the formation of concentration inhomogeneity in the form of growth bands when growing crystals under various thermal conditions (in the presence or absence of a free melt surface (Marangoni convection)), as well as when changing technological parameters (variations in growth rate) were investigated. Based on the obtained results of metallographic and electrophysical studies, conclusions were made about the peculiarities of the influence of the technological parameters of the crystallization process on the structural perfection of the grown crystals under microgravity conditions

Remote Forcing for a Circulation Pattern Favorable to Surface Melt over the Ross Ice Shelf

Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasigeostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño–related sea surface temperature (SST) anomalies in the tropical central–eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to the Ross Sea. The northerly flow toward the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS. Significance Statement During austral summer, surface melt occurs over the Ross Ice Shelf, accelerates ice loss, and poses ice-sheet destabilization risks in a warming world. The northerly wind anomaly over the Ross sector provides strong poleward heat and moisture transport and is favorable for the surface melt. This wind anomaly is influenced by two remote forcings, El Niño and heating anomaly over western Australia, through generating Rossby wave trains from the tropics and subtropical Australia. This study reveals a previously unexplored relationship that atmospheric heating over western Australia influences large-scale circulation, contributing to surface melt.

Structure and Wet-Sliding Characterization of a Laser Powder Bed Fusion Ti-6Al-4V Biomedical Alloy: Effect of Laser Surface Modification

The effect of laser modification on the structure and wet (Simulated Body Fluid)-sliding behaviour of a Laser Powder Bed Fusion alloy Ti-6Al-4V was studied. The scanning of 400 W fiber laser with a speed of 10 mms –1 led to a surface melting with an increase in hardness (780–820 HV) and 20%-decrease in wear. Under the scanning speeds of 40–60 mms –1 the surface was refined almost without melting to provide a 7–8% increase in hardness/wear resistance accompanied by a decrease in the friction coefficient

Femtosecond Laser Ablation and Delamination of Functional Magnetic Multilayers at the Nanoscale.

Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences.

Versatile fluidity test model for cast superalloys and comparison between IN718 and IN939

A spiral fluidity test model of superalloys with 10 mm in height and 3 mm in thickness was designed to evaluate the fluidity of two distinct Ni-based superalloys IN718 and IN939. The factors influencing fluidity are ascertained through comparative analysis utilizing methodologies such as JMatPro, differential scanning calorimetry and high-temperature confocal laser scanning microscopy. The results show that under identical testing conditions, the fluidity of the IN939 superalloy surpasses that of the IN718 superalloy. When subjected to the same temperature, the melt viscosity and surface tension of IN939 superalloy are considerably reduced relative to those of IN718 superalloy, which is beneficial to improving the melt fluidity. Furthermore, the liquidus temperature and solidification range for the IN939 superalloy are both smaller compared with those of the IN718 superalloy. This condition proves advantageous in delaying dendrite coherency, thereby improving fluidity.

The impact of LSM pretreatment on the growth behavior, electrical insulation and corrosion resistance properties of PEO coating on 6061 aluminum alloy

This work reported the influence of laser surface melting (LSM) pretreatment on the growth behavior, electrical insulation and corrosion resistance of plasma electrolytic oxidation (PEO) film on 6061 aluminum alloy. It is found that the LSM pretreatment refines the surface structure of original Al metal, generating defects that store excessive energy, thereby enhancing reaction kinetics and phase transition during the PEO process. By LSM pretreatment, uniform electrical discharge and film growth can be obtained, resulting in fewer defects and lower porosity in PEO layers. Additionally, a large amount of columnar crystals comprising of SiO2 phase are observed, which transformed from the SiO32− deposited on the surface, and the LSM pretreatment significantly improves the electrical insulation, corrosion resistance, and substrate adhesion of following PEO layer. Under the same PEO treatment duration, the breakdown voltage of coating increased by 100 V, and icorr decreased from 3.26 × 10−4 to 9.13 × 10−6 A cm−2. It is expected that the combination of LSM and PEO processes can not only enhance the surface properties of Al metal, but also expand the practical application of aluminum alloy in high-power electronic devices and related fields.

Interaction of contour and hatch parameters on vertical surface roughness in laser powder bed fusion

In Laser Powder Bed Fusion (L-PBF), surface roughness is pivotal for controlling the mechanical and functional performances, as well as the geometrical accuracy of the final product. This study extensively investigated the interactions of hatch and contour processing parameters, along with contour offset distance, on vertical surface roughness for 316L stainless steel in L-PBF. Melt pool morphology and surface arithmetic average roughness (Sa) were quantified using confocal microscopy, while scanning electron microscopy was employed to interpret the detailed microstructure of surface features. Under low volumetric energy density (VED) hatch conditions (e.g., 66.7 J/mm3), varying the contour offset distance has a negatable effect on the surface roughness when the contour VED is lower than 121.6 J/mm3, remaining relatively smooth surfaces dominated by bare melt tracks with sparely attached partially melted particles. Increasing the hatch or contour VED (e.g., 166.7 J/mm3), dross formation, identified by the microstructural differences and explained by the melt pool instability and migration, is inevitable, which dictates the surface roughness with higher Sa values. The larger contour offset distance further promotes the dross occurrence with irregularity and increases Sa. Employing a low contour VED with an appropriate offset distance and adopting the contour-first scan strategy was demonstrated as an effective solution to reduce the dross formation. Through the analysis of melt pool behavior, surface topography, and microstructure, this study elucidates the mechanisms governing dominant surface characteristics under the combined influence of hatch and contour parameters. It lays the foundation for precise control of surface roughness without altering hatching parameters, enabling the tailored manipulation of performance in additively manufactured structures.