Melting Layer Research Articles

High Aspect Ratio Structuring of Glass with Ultrafast Bessel Beams.

Controlling the formation of high aspect ratio void channels inside glass is important for applications like the high-speed dicing of glass. Here, we investigate void formation using ultrafast Bessel beams in the single shot illumination regime. We characterize the morphology of the damages as a function of pulse energy, pulse duration, and position of the beam inside fused silica, Corning Eagle XG, and Corning Gorilla glass. While a large set of parameters allow for void formation inside fused silica, the operating window is much more restricted for Eagle XG and Gorilla glass. The transient formation of a molten layer around voids enables us interpreting the evolution of the morphology with pulse energy and duration.

Structure of GaN grown from vapour phase on a seeded layer of gallium melt formed on a boron nitride ceramic substrate

In this study, two empirical models for the growth of millimetre–thick GaN material with either highly ordered textured or polycrystalline structure on a ceramic substrate by Hydride Vapour Phase Epitaxy (HVPE) are considered. It is suggested that the specific type of the structure of GaN is determined at the nucleation stage and depends on the character of the wetting of the surface of the substrate by the liquid gallium melt.

Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less.

Modification of steel surface layer by electroslag surfacing using compounds with high melting point

The authors have studied the effect of alloying on the structure, microhardness and abrasive wear resistance of electroslag surfacing layers on low-alloy structural steel 09G2S. For modification, mixtures of Si3 N4 + FeSi2 + Si powders obtained in the Department of Structural Macrokinetics of the Tomsk Scientific Centre SB RAS by the method of SHS synthesis, as well as powder compositions based on TiC, were used. A molten electrode was made of low-alloy steel St3, on which modifying compositions Si3 N4 + FeSi2 + Si were poured out, in the first case, and modifying compositions Si3 N4 + FeSi2 + Si, located below, in the second case. Metallography and X-ray microanalysis methods were used to determine the structure and to analyze the composition of the deposited layers, heat-affected zone (HAZ) and the base metal, on the basis of which assumptions were made about the nature of the formation of coating properties – hardness and wear resistance. It is shown that the main influence on the wear resistance is exerted by structure of the surfacing metal. There is a positive effect of modifying coatings by alloying materials with the alloys Si3 N4 + FeSi2 + Si + St3 and TiC + St3. In the molten layer, many new crystallization centers are released in the form of dispersed TiC particles. Dispersed TiC particles with a high melting point (3180 °C) are the first to fall out of the melt and not only serve as multiple crystallization centers, but also prevent the growth of austenitic grains, which ensures the formation of dispersed structure. The coatings contain TiC carbide particles, as well as inclusions of other phases. At the same time, an increase in hardness of the deposited layer containing titanium carbide inclusions is observed in direction of the boundary with the base. Wear resistance of the layer increases when a TiC-based coating is formed. The obtained data can be used to create deposited layers on the metal surface with high resistance against abrasive wear.

Comparison of Bright Band Radar from GPM and MRR Observation in West Sumatera

The Bright band (BB) observation can be used as an indication of the melting layer height. Measurement of BB from Normal Scan (NS) on Global Precipitation Measurement (GPM) had been compared with Micro Rain Radar (MRR), which is installed in Kototabang, West Sumatera (0.23° S; 100.32°E; 865 m above sea level). The GPM data were collected from December 2014 to June 2018 and compared with MRR observation from January 2012 to August 2016. The BB values from these instruments were compared with those recommended by the International Telecommunication Union Recommendation (ITU-R) P.839. The BB from GPM and MRR showed slightly diurnal and seasonal variations. BB observations from GPM and MRR show good agreement with slight diurnal and seasonal variations differences. BB observations are more similar when the intensity of solar radiation is lower, i.e., at night (18.00-24.00 LT) until early morning (00.00-06.00 LT). Furthermore, MRR showed a slight bimodal pattern in the seasonal variation, while GPM did not. Thus, the seasonal variation in the observation of both instruments is different. The most significant difference from the seasonal variation was observed in the summer season (June-August (JJA)). The mean BB of the two instruments is lower than the Freezing Height Level (FHL) value calculated from the ITU-R model. However, many BB from the two instruments (>36 %) have a BB altitude higher than FHL. Thus, the constant assumption of FHL in West Sumatera for the rain attenuation estimation of microwaves may not be appropriate.

Representing Microphysical Uncertainty in Convective‐Scale Data Assimilation Using Additive Noise

AbstractFor convective clouds and precipitation, model uncertainty in cloud microphysics is considered one of the most significant sources of model error. In this study, samples for model microphysical uncertainty are obtained by calculating the differences between simulations equipped with two‐ and one‐moment schemes during a one‐month training period. The samples are then added to convective‐scale ensemble data assimilation as additive noise and combined with large‐scale additive noise based on samples from climatological atmospheric background error covariance. Two experiments, including the combination and large‐scale error only, are conducted for a one‐week convective period. The results reveal that the simulation with a two‐moment scheme triggers more convection and has larger ice‐phase precipitation particles, which produce a stronger signal in the melting layer. During data assimilation cycling, although more water is introduced to the model, it is shown that the combination performs better for both background and analysis and significantly improves short‐term ensemble forecasts of radar reflectivity and hourly precipitation.

Development of high intensity multibeam laser metal deposition system with blue diode lasers for additively manufacturing of copper rod

A 100 W blue diode laser with an optical fiber having a core diameter of 100 μm was developed and installed into a blue diode laser metal deposition system (B-LMD), achieving a laser intensity of 7.58 × 104 W/cm2, four times higher than that of the previous B-LMD system. The increase in laser intensity is expected to enable faster and more efficient 3D processing of pure copper. The authors conducted the rod formation experiment by varying the processing speed. The rod formation process is observed with a high-speed video camera to clarify the mechanism of copper rod formation. As a result of rod formation as a 3D modeling of pure copper, a 30 mm rod was formed in 1.5 s under the following conditions: a laser intensity of 1.27×106W/cm2, a powder feed rate of 220 mg/s, and a processing speed of 20 mm/s. It was found that the mode of rod forming changed depending on the processing speed. When the processing speed is high, the mode becomes molten layer type and the energy efficiency becomes high. In addition, the processing point became closer to the focal point at high speed, and the cross-sectional shape of the formed rod was closer to the circular ones.

Carbon-Based Photothermal Superhydrophobic Materials with Hierarchical Structure Enhances the Anti-Icing and Photothermal Deicing Properties.

Ice formation on the surface of outdoor equipment brings significant inconvenience to human life and production. Superhydrophobic materials with the micro-nanostructure are considered to be effective anti-icing materials. However, repeated icing and deicing processes will destroy the structure and lose anti-icing properties. Herein, low-cost, durable, high-efficiency photothermal superhydrophobic materials were prepared by electrochemical deposition and silanization treatment methods. Combined with the black-body property of carbon materials and the micro-nano hierarchical structure, the as-prepared material has excellent photothermal and superhydrophobic properties. The surface temperature can rise to 90 °C, and the freezing droplets can melt in 100 s under 100 mW/cm2 of sunlight illumination. The superhydrophobic property endows the material with excellent anti-icing performance, and the icing delay time is as long as 3600 s. The melted water droplet can quickly roll off due to the low adhesion of the superhydrophobic surface, which avoids the refreezing of the melted droplet and enhances the photothermal conversion performance. We innovatively use the elemental tracer method to understand the melted water droplet roll off mechanism on inclined surfaces. In addition, the heat transfer model of anti-icing and photothermal deicing processes are established to confirm that the heat required for melting ice during the deicing process is mainly generated by photothermal materials. Finally, the feasibility of practical application of the material was verified by the anti-icing/deicing experiment of a wind turbine blade and ice/frost layer melting experiment. It concludes that the superior anti-icing and deicing properties are realized using the high photothermal conversion and excellent superhydrophobic properties of the prepared photothermal superhydrophobic materials. This study provides a perspective for constructing micro-nano hierarchical structures on the surface and combining them with the abundant solar energy in nature to develop photothermal anti-icing materials for practical application.

SMALL-AMPLITUDE DISCONTINUOUS DISTURBANCES IN PLEISTOCENE DEPOSITS OF THE VOLYN-PODILSKA UPLAND

The paper presents the results of the study of the small-amplitude discon¬tinuous disturbances of the possibly cryogenic (thermokarst) origin. The dislocations were found in the outcrops of Middle and Upper Pleistocene sediments of the Volyn-Podilska Upland, accumulated in periglacial or sub-periglacial conditions. The distur¬bances are represented mostly by the micro-normal faults and also by sheared fractures and are very similar to tectonic (seismogenic) discontinuities. The tectonotypic fractures in the near-surface deposits of the Pleistocene terraces of Western Bug and Styr (five sections within Volhynian Upland, four of them – in the valley of Bug), as well as in the cover of the Late Pleistocene sediments on the slope of the valley of Dniester (Galician Prydnisterya) are subjected to consideration, analysis and interpretation. In the last location the ruptures are represented mostly by the dis¬turbances identified as sheared fractures. In all others there are small-amplitude normal faults. One reverse fault, timed to an ice-wedge cast, was also revealed. Typical micro-normal faults of all sections are steep and have a number of other common features, which testifies to the same or almost identical mechanism of their formation. These features, in particular, are as follows: 1) insignificant (usually up to 2–2.5 m) length in cross-section and small (several centimeters) amplitude of displacement along the rupture plane; 2) gradual attenuation of the fractures up and down the section. All micro-normal faults are confined to sediments (thicknesses) that are partially or completely composed of sand. The formation of the micro-normal faults and other examined ruptures can be ex¬plained by the uneven compaction and the gravitational subsidence of the rocks, and in the section on the slope of the Dniester valley – also by their displacement down along the slope. It is probable that these processes occurred due to: 1) the degradation of the permafrost; 2) the dehydration of the sand deposits during a significant decrease in the groundwater levels; 3) the melting of the buried layers and lenses of snow, which were accumulated during the winter season in the thickness of sandy the niveo-aeolian deposits. In the outcrops of this terrace, they occur no less frequently than the confidently identified ice wedge pseudomorphs. Key words: small-amplitude disturbances; microfaults; thermokarst; Volyn-Podilska Upland.

A lumped parametric analytical model for predicting molten pool temperature and clad geometry in pre-placed powder laser cladding

Pre-placed powder laser cladding is one of the simplest laser-based deposition techniques, having high material usage efficiency and capable to provide sound clad quality. However, the quality along with the geometrical aspects of the deposited layer depends on various energy transfer mechanisms controlled by process parameters. Energy transfer phenomena include the partial absorption of the laser radiation by metal powder layer, melting of the powder layer and transmission of energy to the substrate, along with the losses, like convective heat transfer to the atmosphere and conductive heat transfer to the bulk material. Theses phenomena all together defines the molten pool temperature, which needs to be analyzed to control the geometrical features of the clad and dilution by optimizing the process parameters. Therefore, a lumped parametric analytical model has been formulated and presented in this work for the pre-placed laser cladding process considering energy transfer and loss mechanisms along with the surface tension phenomena of the molten material to predict the molten pool temperature, clad geometry and substrate dilution. The developed model is validated using the experimental results of molten pool temperature of the clad layer, clad width and height as well as the percentage dilution. A continuous mode Yb-Fiber laser system with maximum available laser power of 220 W is used for the deposition of Inconel 625 powder on AISI 304 stainless steel substrate.

Large impact cratering during lunar magma ocean solidification

The lunar cratering record is used to constrain the bombardment history of both the Earth and the Moon. However, it is suggested from different perspectives, including impact crater dating, asteroid dynamics, lunar samples, impact basin-forming simulations, and lunar evolution modelling, that the Moon could be missing evidence of its earliest cratering record. Here we report that impact basins formed during the lunar magma ocean solidification should have produced different crater morphologies in comparison to later epochs. A low viscosity layer, mimicking a melt layer, between the crust and mantle could cause the entire impact basin size range to be susceptible to immediate and extreme crustal relaxation forming almost unidentifiable topographic and crustal thickness signatures. Lunar basins formed while the lunar magma ocean was still solidifying may escape detection, which is agreeing with studies that suggest a higher impact flux than previously thought in the earliest epoch of Earth-Moon evolution.

Conditions for partial and complete crystallization suppression upon quenching from liquid state

For bulk-amorphizing alloys Мg65Сu25Y10 and Zr41,2 Тi13,8Сu12,5Ni10Ве22,5, the thickness and cooling rate of melt layers is calculated, which ensure the formation of X-ray amorphous structures typical for metallic glasses ( lC, vC ), and truly amorphous states without inclusions of «frozen-in crystallization centers» (lc*, vc* ). Correlation of the calculated values lC, vC with the known experimental estimates is C Cachieved. It is shown that both studied alloys demonstrate a predisposition to complete suppression of crystallization processes at physically correct values of the parameters lc* and vc* (10 μm; 1,3·107 K/s and 550 μm; 2,7·103 K/s for alloys based on Mg and Zr, respectively). It is concluded that the most significant factors controlling the tendency of materials to noncrystalline solidification are the decrease in the frequency of non-stationary nucleation with the increase in the rate of QLS, as well as relatively low <1018 m-3 s-1) maximum values of the rate of stationary crystallization centers formation.

Threshold conditions for thermocapillary formation of a deep cavity in the additive process for selective laser melting of a metal powder layer

ABSTRACT The deep penetration mode at selective laser melting of a metal powder layer is determined by a special and intense hydrodynamic process in a thin molten layer at rapid heating of the metal by using a focused beam. This mode is also widely used in laser and electron beam welding. This indicates the similarity of hydrodynamic processes, which differ significantly in the parameters of the applied radiation (power, power density and focusing spot diameter). Threshold conditions of thermocapillary deep penetration (without evaporation) for various metals (Al, Cu, Fe and Ti) in a wide range of changes in beam parameters, including those used for selective laser melting of a powder layer, are investigated. The comparison of calculated and experimental values of the radiation parameters corresponding to the transition to the deep penetration mode for selective laser melting of the powder layer and laser welding is presented. The correlation of these values confirms the thermocapillary mechanism of the deep cavity formation and the similarity of hydrodynamic processes at welding metals by using a laser beam.

Understanding defect structures in nanoscale metal additive manufacturing via molecular dynamics

Additive manufacturing of a single crystalline metallic column at nanoscale is studied using molecular dynamics simulations. In the model, a melt pool is incrementally added and cooled to a target temperature under isobaric conditions to build a metallic column from the bottom up. The polyhedral template matching (PTM) is used to observe the evolution of atomic-scale defects during this process. The solidification is seen to proceed in two directions for an added molten layer. The molten layer in contact with the cooler lattice has a fast solidification front that competes with the slower solidification front that starts from the top of the melt layer. The defect structure formed strongly depends on the speed of the two competing solidification fronts. Up to a critical layer thickness, the defect-free single crystals are obtained as the faster solidification front reaches the top of the melt pool before the initiation of the slower front from the top. A slower cooling rate leads to a reduction in defects, however, the benefits diminish below a critical rate. The defect content can be significantly reduced by raising the temperature of the powder bed to a critical temperature. This temperature is governed by two competing mechanisms: the slower cooling rates at higher temperatures and the increase in amorphousness as one gets closer to the melting point of the metal. Finally, the effect of an added soft inclusion (SiS2) and a hard inclusion (SiC) on the defect structures is explored. The hard inclusion leads to a retained defect structure while soft inclusions reduce defective content compared to the pure metal.

Thermal-hydraulic modelling and analysis of ITER tungsten divertor monoblock

• A mathematical model has been developed to investigate the thermal-hydraulic performance of ITER tungsten divertor monoblock. • The model predicts the thermal response of the divertor structural materials and coolant tube. • The model accounts for the melting, vaporization, and solidification of the upper layer of the divertor facing plasma. • The model is verified against a previous calculation in the literature for DEMO divertor at an incident surface heat flux of 10 MW/m 2 . • The model is used to simulate the divertor materials response subjected to a VDE. The divertor is a fundamental component of fusion power plants, being primarily responsible for power exhaust and impurity removal via guided plasma exhaust. Due to its position and functions, the divertor has to sustain very high heat flux arising from the plasma (up to 20 MW/m 2 ), while experiencing an intense nuclear deposited power, which could jeopardize its structure and limit its lifetime. Therefore, attention has to be paid to the thermal–hydraulic design of its cooling system. In this work a mathematical model has been developed to investigate the steady state and transient thermal–hydraulic performance of ITER tungsten divertor monoblock. The model predicts the thermal response of the divertor structural materials and coolant tube. The coolant tube is divided into specified axial regions and the divertor plate is divided into specified radial zones, and then a two-dimensional heat conduction calculation is performed to predict the temperature distribution for both steady and transient states. A two-dimensional numerical finite difference technique is adapted in Cartesian coordinate system where the implicit scheme is used for transient calculation. The model also accounts for the melting, vaporization, and re-solidification of the upper layer of the divertor facing plasma. The selected heat transfer correlations cover all possible operating conditions of ITER under both normal and off-normal situations. The model is verified against a previous calculation in the literature for DEMO divertor at an incident surface heat flux of 10 MW/m 2 . The model is then used to predict the steady state thermal behaviour of the divertor under incident surface heat fluxes ranges from 2 to 20 MW/m 2 for a bare cooling tube and cooling tube with swirl-tape insertion. It calculates the maximum tube surface heat flux and the minimum critical heat flux ratio for all cases as well. The model is also used to simulate the divertor materials response subjected to high heat flux during a vertical displacement event (VDE) where 60 MJ/m 2 plasma energy is deposited over 500 ms.

An Age Scale for the First Shallow (Sub-)Antarctic Ice Core from Young Island, Northwest Ross Sea

The climate of the sub-Antarctic is important in understanding the environmental conditions of Antarctica and the Southern Ocean. However, regional climate proxy records from this region are scarce. In this study, we present the stable water isotopes, major ion chemistry, and dust records from the first ice core from the (sub-)Antarctic Young Island. We present and discuss various dating approaches based on commonly used ice core proxies, such as stable water isotopes and seasonally deposited ions, together with site-specific characteristics such as melt layers. The dating approaches are compared with estimated precipitation rates from reanalysis data (ERA5) and volcanic cryptotephra shards likely presenting an absolute tie point from a 2001 CE eruption on neighboring Sturge Island. The resulting ice core age scale spans the period 2016 to 1995, with an uncertainty of ±2 years.

Effect of alloying elements on laser surface modification of powder metallurgy to improve surface mechanical properties of beta titanium alloys for biomedical application

Beta-type titanium alloy surfaces (Ti–35Nb–10Ta (TNT) and Ti–30Nb–4Sn (TNS)) were modified by laser using a power of 1000 W and speed of 6.7 mm/s (Condition A) and a power of 1500 W with speed of 10 mm/s (Condition B). Increasing laser conditions, the thickness of the molten layer was also increased. The initial equiaxed grains changes to quite elongated grains shape. The surfaces were structured under α″ martensite, α and matrix β. The β phase content decreased slightly and the α″ phase increased for both alloys increasing the laser conditions. The condition A increased the elastic modulus (E) and decreased the hardness while condition B did not affect the mechanical properties surface for the TNT system compared to base metal (BM). In TNS system the laser condition A decreased the E and increased the hardness while increasing the laser parameters (Condition B) both E and hardness decreased compared to BM. The laser surface treatment was influenced by the levels of alloying elements present promoting most significant changes in the microstructure and mechanical properties in the TNS system.

Role of laser powder bed fusion process parameters in crystallographic texture of additive manufactured Nb–48Ti alloy

Additive manufacturing, known as “3D printing”, is a set of manufacturing technologies that can build parts with complex geometries in a process by adding layers of powder material. The laser powder bed fusion (L-PBF) process is characterized by selectively melting layers of particulate material at a micrometer scale in repetitive patterns. This technology is expected to improve Young's modulus of metallic biomaterials, by controlling the microstructure and crystallographic texture– influenced by the laser power and scanning speed parameters which promote an oriented heat extraction. Implant materials should have low Young's modulus, to avoid a large mismatch with that of the bones. This work investigates the role of the laser power and scanning speed on microstructure and crystallographic texture formation of the Nb–48Ti alloy, fabricated by laser powder bed fusion process, using pre-alloyed plasma atomized powder. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), backscattered electron diffraction technique (EBSD) for crystallographic texture, and Young's modulus was obtained indirectly via EBSD data. The microstructure showed a cellular dendritic solidification morphology formed by epitaxy at the edge of the melt pools. Texture results indicated that higher values of power and scanning speed favored the increasing of a near-cube-on-face texture and a reduction in Young's modulus.

Climatology of Melting Layer Heights Estimated From Cloud Radar Observations at Various Locations

AbstractA melting layer (ML) detection algorithm for cloud radar with polarimetric capability was developed and applied to the cloud radar data collected from five different sites around the world for several years. The retrieved melting layer top height (MLH) showed a very good correspondence with the ECMWF Reanalysis 5 zero degree level data for all five sites. The ML characteristics were distinctively different for different sites, revealing climatological characteristics of ML forming clouds in different regions. Generally, ML tended to occur more frequently in summer than in winter except for a maritime site, where low stratiform clouds formed frequently in summer, the top of which might be lower than the freezing level. In contrast, at two Arctic sites, ML occurred almost exclusively in summer because it was too cold to have an ML in the other seasons. The MLH also varied significantly from site to site but generally was higher during warmer seasons. Based on MLH, two new indices, bulk temperature lapse rate (BLR) and relative depth (RD) of liquid cloud below MLH (RD) were developed, which were useful to explain the environmental characteristics of the five sites. BLR generally increased with the surface temperature at all sites except at the marine site that showed an opposite trend, where a unique synoptic pattern in winter generated high BLR in this cold season. These findings confirm that studies on thermodynamic structures using cloud radars can be broadened, taking advantage of BLR and RD information, as these indices can represent environmental thermodynamic characteristics of the clouds that have ML.

Reducing thermal contact resistance by a novel elastomeric polyethylene glycol/unsaturated polyester resin/graphene thermal interface materials

Reducing thermal contact resistance (TCR) is an important way to enhance heat dissipation of electronic devices. Elastomer is easy to deform, increase the contact area and reduce the TCR, but its wetting condition is not satisfying. In this work, a novel elastomeric thermal interface materials (TIMs) polyethylene glycol/unsaturated polyester resin/graphene (PEG/UPR/G) was designed and prepared. With the increase of temperature, PEG near surface of PEG/UPR/G was released due to phase transformation, and a thin molten layer would be attached to the surface. By this way, the micro bumps on the solid surface were all soaked by the thin layer of molten PEG, which greatly reduced the TCR. In addition, the effect of temperature and pressure on TCR of elastomeric PEG/UPR/G were studied. When the pressure increases from 10 Psi to 50 Psi (65 °C), TCR decreases from 11–14 K ∙ cm2/W to 2–4 K ∙ cm2/W. The TCR will be further reduced to 0.7–0.9 K ∙ cm2/W (75 °C) due to the phase transition of PEG. Moreover, the heat dissipation effect of PEG/UPR/G was evaluated by infrared thermal imager. These results demonstrate that the total thermal resistance is the decisive factor for the final steady-state temperature and the time of unsteady heat transfer.