The Processes-Based Attributes of Four Major Surface Melting Events over the Antarctic Ross Ice Shelf

The Ross-Amundsen sector is experiencing an accelerating warming trend and a more intensive advective influx of marine air streams.As a result,massive surface melting events of the ice shelf are occurring more frequently,which puts the West Antarctica Ice Sheet at greater risk of degradation.This study shows the connection between surface melting and the prominent intrusion of warm and humid air flows from lower latitudes.By applying the Climate Feedback-Response Analysis Method(CFRAM),the temporal surge of the downward longwave(LW)fluxes over the surface of the Ross Ice Shelf(RIS)and adjacent regions are identified for four historically massive RIS surface melting events.The melting events are decomposed to identify which physical mechanisms are the main contributors.We found that intrusions of warm and humid airflow from lower latitudes are conducive to warm air temperature and water vapor anomalies,as well as cloud development.These changes exert a combined impact on the abnormal enhancement of the downward LW surface radiative fluxes,significantly contributing to surface warming and the resultant massive melting of ice.

Assessment of Greenland surface melt algorithms based on DMSP and SMOS data

Satellite-borne microwave radiometers provide essential measurements to study the surface melt state of ice sheets. Therefore, selecting suitable microwave radiometer data is critical to characterize the spatial distribution of surface melt. In this study, we investigated the Greenland Ice Sheet and evaluated the usefulness, as climate indicators, of data acquired by microwave radiometers onboard the F17 satellite of the United States of America Defense Meteorological Satellite Program(DMSP) and the Soil Moisture and Ocean Salinity(SMOS) satellite of the European Space Agency. First, surface melt was simulated using the DMSP dataset as input for a brightness temperature threshold algorithm, the Microwave Emission Model of Layered Snowpacks(MEMLS2), and the SMOS dataset as input for the L-band Specific MEMLS(LS-MEMLS). For accuracy evaluation, the simulation results were then compared with surface melt estimates derived from air temperature measurements at Automatic Weather Stations and from ice surface temperature measurements from the Moderate Resolution Imaging Spectroradiometer(MODIS) satellite-borne instrument. Our results show that global(over Greenland) MEMLS2 simulation performance(overall accuracy 83%) was higher than that of LS-MEMLS(overall accuracy 78%). However, in southeastern Greenland, MEMLS2 omission error was markedly higher than that of LS-MEMLS, whereas LS-MEMLS could detect longer-lasting surface melt than MEMLS2. This analysis showed that DMSP-based surface melt simulations are more accurate than SMOS-based simulations, thereby providing a data selection reference for surface melt studies of the Greenland Ice Sheet.

Greenland Ice Sheet surface melt:A review

Surface melt has great impacts on the Greenland Ice Sheet （GrlS） mass balance and thereby has become the focus of significant GrlS research in recent years. The production, transport, and release processes of surface meltwater are the keys to understanding the poten- tial impacts of the GrlS surface melt. These hydrological processes can elucidate the following scientific questions： How much melt- water is produced atop the GrlS？ What are the characteristics of the meltwater-formed supraglacial hydrological system？ How does the meltwater influence the GrlS motion？ The GrlS supraglacial hydrology has a number of key roles and yet continues to be poorly understood or documented. This paper summarizes the current understanding of the GrlS surface melt, emphasizing the three essential supraglacial hydrological processes： （1） meltwater production： surface melt modeling is an important approach to acquire surface melt information, and areas, depths, and volumes of supraglacial lakes extracted from remotely sensed imagery can also provide surface melt information; （2） meltwater transport： the spatial distributions of supraglacial lakes, supraglacial sarams, moulins, and crevasses demonstrate the characteristics of the supraglacial hydrological system, revealing the meltwater transport process; and （3） meltwater release： the release of meltwater into the englacial and the subglacial ice sheet has important but undetermined impacts on the GrlS motion. The correlation between surface runoff and the GrlS motion speed is employed to understand these influences.

Molecular dynamics simulation of surface melting behaviours of the V(110) plane

The modified analytic embedded-atom method and molecular dynamics simulations are applied to the investigation of the surface premelting and melting behaviours of the V（110） plane by calculating the interlayer relaxation, the layer structure factor and atomic snapshots in this paper. The results obtained indicate that the premelting phenomenon occurs on the V（110） surface at about 1800K and then a liquid-like layer, which approximately keeps the same thickness up to 2020K, emerges on it. We discover that the temperature 2020K the V（110） surface starts to melt and is in a completely disordered state at the temperature of 2140K under the melting point for the bulk vanadium.

Effects of TIG Surface Melting and Chromium Surface Alloying on Microstructure, Hardness and Wear Resistance of ADI

Microhardness and wear resistance of different rnicrostructures formed by TIG （tungsten inert gas） surface melting and chromium surface alloying （using ferrochromium） of ADI （austempered ductile iron） were studied. Surface melting resulted in the formation of a ledeburitic structure in the melted zone, and this structure has a hardness up to 896 HV as compared to 360 HV in that of ADI. Moreover, chromium surface alloying resulted in the formation of different structures including： （1） a hypereutectic structure consisting of primary （Fe,Cr）7C3 carbides and a eutectic matrix of transformed austenite （into martensite and retained austenite）, as also （Fe,Cr）7C3 carbides, with a hardness of 1078 HV; （2） a hypoeutectic structure consisting of the same eutectic along with transformed primary austenite, with a hardness of 755 HV; and （3） a ledeburitic structure with an acicular morphology and a hardness of 896 HV. The results also indicated that surface melting reduced the wear rate of the ADI by approximately 37%. Also, chromium surface alloying yielded a superior wear behavior and reduced the wear rate of the treated specimens by about 38% and 70%, depending on the structures formed.

Corrosion and cavitation erosion resistance enhancement of cast Ni–Al bronze by laser surface melting

Laser surface melting (LSM) was applied on a cast Ni–Al bronze (NAB), which was a crucial material for marine ship propellers. A 720 μm-thick LSM layer with fine equiaxed and dendritic microstructures was obtained. After immersion for 30 days, the corrosion rate of cast NAB was reduced by 25% after LSM. Preferential corrosion occurred and deep corrosion pits appeared at α + κIII microstructure for the cast NAB. LSM NAB underwent general corrosion, and a much more protective film formed on the surface because of the homogenized microstructure. The mass loss of the cast NAB was approximately 2.1 times larger than that of LSM NAB after cavitation erosion (CE) in 3.5 wt.% NaCl solution for 5 h. For the two materials, the mechanical impact effect was dominantly responsible for CE damage. Therefore, the improved hardness and homogenized microstructure contributed to the improved CE resistance of LSM NAB. CE destructed the film, shifted the open circuit potential toward a more negative value, and raised the current density by an order of magnitude. Corrosion at the cast eutectoid microstructure and the dendrites of LSM NAB facilitates the degradation under the cavitation attack. CE-corrosion synergy was largely caused by corrosion-enhanced-CE.

Study on microstructure and properties of laser surface melted layer of AZ31B magnesium alloy

An attempt has been made to improve the surface properties of AZ31B magnesium alloy through solid solution hardening and refinement of microstructures using a CO2 laser as a heat generating source. X-ray diffraction （XRD） was used to identify the phases. Microstructure and properties of laser melted layer of AZ31B magnesium alloy were observed or tested by means of optical microscope （OM）, scanning electron microscope （SEM）, micro-hardness equipment and electrochemical corrosion equipment etc. The results show that the microstructure of laser melted layer becomes finer significantly and uniform. Compared with the substrate, the content of β-Mg17 Al12 phase of melted layer decreases comparatively. Microhardness of the laser melted layer is improved to 50 -95 HV0. 05 as compared to 40 -45 HV0.05 of the AZ31B Mg alloy substrate. The results of electrochemical corrosion show that the corrosion resistance of laser surface melted layer has been improved.

Microstructure and surface texture driven improvement in in-vitro response of laser surface processed AZ31B magnesium alloy

The present work explored effects of laser surface melting on microstructure and surface topography evolution in AZ31B magnesium alloy.Thermokinetic effects experienced by the material during laser surface melting were simulated using a multiphysics finite element model.Microstructure and phase evolution were examined using scanning electron microscopy,X-ray diffraction,and electron back scatter diffraction.Surface topography was evaluated using white light interferometry.The interaction of surface melted samples with simulated body fluid was monitored by contact angle measurements and immersion studies up to 7 days.Laser surface melting led to formation of a refined microstructure with predominantly basal crystallographic texture.Concurrently,the amount ofβphase(Mg_(17)Al_(12))increased with an increase in the laser fluence.βphase preferentially decorated the cell boundaries.In terms of topography,the surface became progressively rougher with an increase in laser fluence.As a result,upon immersion in simulated body fluid,the laser surface melted samples showed an improved wettability,corrosion resistance,and precipitation of mineral having composition closer to the hydroxyapatite bone mineral compared to the untreated sample.

Corrosion resistance of pulsed laser modified AZ31 Mg alloy surfaces

The effect of laser surface melting on the corrosion resistance of AZ31 Mg alloy in 0.1 M NaCl solution was investigated using different laser processing conditions(energy densities of 14 and 17 J cm^(-2)).Laser treatment induced rough surfaces primarily composed of oxidized species of Mg.XPS analysis revealed that the surface concentration of Al increased significantly as a consequence of LSM.Electrochemical impedance spectroscopy showed that the laser treatment remarkably increased the polarization resistance of the AZ31 Mg alloy and induced a passive-like region of about 100 mV,as determined by potentiodynamic polarization.Analysis of the results obtained provide solid evidence that within the immersion times used in this study,LSM treatment increased the corrosion resistance of AZ31 Mg alloy under open circuit conditions and anodic polarization.

Laser Surface Modification of Lean-alloyed Austenitic Stainless Steel for Corrosion Resistance

In order to reduce the cost of the austenitic stainless steels(ASSs),the expensive austenite former(nickel) is often substituted by manganese.However,manganese is generally seen to have a detrimental effect on the corrosion resistance.In the present study,the feasibility of laser surface modification of a lean-alloyed ASS(FeCrMn) for enhancing pitting corrosion resistance was investigated.Laser surface modification of FeCrMn was successfully achieved by a 2.3 kW high power diode laser(HPDL).Cyclic polarization tests for FeCrMn after laser surface modification in 3.5% NaCl solution at 25 ℃ were performed by using a potentiostat.The pitting resistance of the laser-modified specimens was found to be significantly improved as reflected by the noble shift in pitting potential.This could be attributed to redistribution of manganese sulphide leading to a more homogenous and refined microstructure.Pitting corrosion resistance of the laser-treated FeCrMn followed by subsequent citric acid passivation was found to be further improved as reflected by the noble shift in pitting potential to 0.18 V.

EBSD Characterization of the Laser Remelted Surface Layers in a Commercially Pure Mg

Laser surface melting has been applied on a commercially pure Mg. The microstructure and texture modifications encountered in the surface layers were carefully investigated by using electron backscattered diffraction （EBSD） technique. Due to the melting followed by rapid solidification and cooling, a layer having graded microstructures and texture formed. At the bottom of the melted layer, the solidified Mg grains have an elongated shape with a 〈0001 〉 basal fibre texture nearly parallel to sample normal direction, while equiaxed grains were observed in the top melted layer having a much weaker basal fibre texture. Solidification twinning and deformation twinning were found in the vicinity of the melt/substrate interface where the Mg grains grow larger due to the heating. In addition, no epitaxial type grain growth was observed at the melt/substrate interface.