Surface Melting Process Research Articles

Enhancing Bactericidal Properties of Ti6Al4V Surfaces through Micro and Nano Hierarchical Laser Texturing.

Orthopedic and dental implants made from Ti6Al4V are widely used due to their excellent mechanical properties and biocompatibility. However, the long-term performance of these implants can be compromised by bacterial infections. This study explores the development of hierarchically textured surfaces with enhanced bactericidal properties to address such challenges. Hierarchical surface structures were developed by combining microscale features produced by a microsecond laser and superimposed submicron features produced using a femtosecond laser. Microscale patterns were produced by the pulsed laser surface melting process, whereas submicrometer laser-induced periodic surface structures were created on top of them by femtosecond laser processing. Escherichia coli bacterial cells were cultured on the textured surface. After 24 h, a staining analysis was performed using SYTO9 and PI dyes to investigate the samples with a confocal microscope for live dead assays. Results showed bacterial colony formation onto the microscale surface textures with live bacterial cells, whereas the hierarchical surface textures display segregated and physically damaged bacterial cell attachments on surfaces. The hierarchical surface textures showed ∼98% dead bacterial cells due to the combined effect of its multiscale surface features and oxide formation during the laser processing steps. The efficacy of hierarchical surface textures in enhancing the antibacterial behavior of Ti6Al4V implants is evident from the conducted research. Such laser-based surface treatments can find potential applications in different industrial sectors.

Investigating the effect of laser surface melting process parameters on thermal efficiency by reverse analysis and experimental design

In this paper, the effect of the process parameters such as laser power, shielding gas flow and scanning velocity on the actual laser power reaching the surface and thermal efficiency is investigated. For this purpose, the response surface methodology was used to investigate the effect of the process parameters at three levels. In order to measure the data from a 316L stainless steel, four k-type thermocouples are installed in different positions relative to the motion of the laser beam. The actual power was calculated by reverse analysis using the simulated annealing technique and the temperature history was measured by the thermocouples. The thermal model used is an optimized Rosenthal model, which is considered variable with temperature. The results show that for all thermocouples, the highest values of actual power that reached the surface were obtained at laser power of 200[Formula: see text]W, scanning velocity of 2[Formula: see text]mm/s and shielding gas flow of 30[Formula: see text]Lit/min. In addition, by increasing the laser power from 100 to 200[Formula: see text]W, the thermal efficiency decreases by about 4% to 12%. The thermal efficiency also decreases by about 8%, when the scanning velocity increased from 1 to 3[Formula: see text]mm/s. Moreover, the increase of the shielding gas flow from 25 to 35[Formula: see text]Lit/min initially improved the thermal efficiency and then decreased it. The models obtained from the analysis of variance in the heating cycle are in good agreement with the experimental results, but in the cooling cycle, the accuracy of this model decreases.

Effect of Single-Pass and Overlapping Laser Surface Melting Process on Microstructure and Microhardness of AISI 431 Duplex Steel

Effect of Single-Pass and Overlapping Laser Surface Melting Process on Microstructure and Microhardness of AISI 431 Duplex Steel

Modeling cloud properties over the 79 N Glacier (Nioghalvfjerdsfjorden, NE Greenland) for an intense summer melt period in 2019

AbstractLong believed to be insignificant, melt activity on the Northeast Greenland Ice Stream (NEGIS) has increased in recent years. Summertime Arctic clouds have the potential to strongly affect surface melt processes by regulating the amount of radiation received at the surface. However, the cloud effect over Greenland is spatially and temporally variable and high‐resolution information on the northeast is absent. This study aims at exploring the potential of a high‐resolution configuration of the polar‐optimized Weather Research & Forecasting Model (PWRF) in simulating cloud properties in the area of the Nioghalvfjerdsfjorden Glacier (79 N Glacier). Subsequently, the model simulations are employed to investigate the impact of Arctic clouds on the surface energy budget and on surface melting during the extensive melt event at the end of July 2019. Compared to automatic weather station (AWS) measurements and remote‐sensing data (Sentinel‐2A and the Moderate Resolution Imaging Spectroradiometer, MODIS), PWRF simulates cloud properties with sufficient accuracy. It appears that peak melt was caused by an increase in solar radiation and sensible heat flux (SHF) in response to a blocking anticyclone and foehn winds in the absence of clouds. Cloud warming over high‐albedo surfaces helped to precondition the surface and prolonged the melting as the anticyclone abated. The results are sensitive to the surface albedo and suggest spatiotemporal differences in the cloud effect as snow and ice properties change over the course of the melting season. This demonstrates the importance of including high‐resolution information on clouds in analyses of ice sheet dynamics.

Microstructural characteristics and tribological properties of the localized laser surface treatment of AISI 420 stainless steel

In this study, a localized laser surface treatment (LLST) of AISI 420 including transformation hardening and surface melting processes was utilized using a high-power diode laser (HPDL) under different beam travel speeds in order to obtain transformed hardened and surface melted samples. Microstructural characteristics of the laser processing areas were evaluated using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). Moreover, the tribological properties of the as-received, transformed hardened and surface melted samples were investigated. Obtained tribological results indicated that the surface melted sample has a higher coefficient of friction (COF) and greater sliding wear rate compared with the transformed hardened sample due to the increment of surface roughness and formation of δ-ferrite precipitates respectively.

Investigation of microstructure and residual stress development during laser surface melting of AH36 steel using 3-D fully coupled numerical model

In this study, the microstructure and residual stress development during the laser surface melting process is investigated using a three-dimensional fully coupled numerical model. With a fully coupled model, unlike a sequentially coupled model, the evolution of the temperature, melt flow, microstructure, and stress fields during the entire melting process is computed by directly accounting for their mutual interactions. Therefore, the developed numerical model can reflect the actual laser melting process and predict the solid-state phase transformation and stress development during the process. Laser surface melting experiments are performed on AH36 steel using a 2 kW fiber laser with a rectangular top-hat profile. Residual stresses are measured using the contour method, and the microstructure distributions are examined using an optical microscope. Three process conditions are examined, including a high laser energy condition and an extremely low processing speed, to validate the model. The simulation results agree well with the measurement data.

Laser surface melting and consecutive point-mode forging of DH36 marine steel: Dynamic recrystallization and anisotropism

DH36 marine steel was surface modified by laser surface melting process and further consecutive point-mode forging (LSM-CPF) process. The tensile properties of the coating after LSM-CPF process were significantly improved showing highest yield strength (σ0.2) and tensile strength (σb) for the sample treated with 4000 W laser power and 10% reduction ratio of 721.3 and 884.2 MPa, higher by 49.55% and 41.54% than that of the DH36 matrix, respectively. At the same time, the LSM-CPF process also results in slight anisotropism according to the tensile tests. The electron backscatter diffraction (EBSD) technique was used to investigate the dynamic recrystallization (DRX) mechanism during the CPF process. The appearance of mixed discontinuous-DRX (dDRX) and continuous-DRX (cDRX) behavior is observed under a low reduction ratio. As the deformation proceeds, the DRX mechanism is mainly of the cDRX. The anisotropism of different samples was partially as the result of the DRX behavior resulting in local non-uniformity strain gradient distribution. Additionally, the transmission electron microscope (TEM) method was employed, in order to verify the DRX mechanism. Moreover, the lamellar pearlite structures shown in the CPF zone caused the difference of deformation resistance along with the RD and TD for the 4000 W treatment samples.

A 20‐Year Study of Melt Processes Over Larsen C Ice Shelf Using a High‐Resolution Regional Atmospheric Model: 1. Model Configuration and Validation

AbstractFollowing collapses of the neighboring Larsen A and B ice shelves, Larsen C has become a focus of increased attention. Determining how the prevailing meteorological conditions influence its surface melt regime is of paramount importance for understanding the dominant processes causing melt and ultimately for predicting its future. To this end, a new, high‐resolution (4 km grid spacing) Met Office Unified Model (MetUM) hindcast of atmospheric conditions and surface melt processes over the central Antarctic Peninsula is introduced. The hindcast is capable of simulating observed near‐surface meteorology and surface melt conditions over Larsen C. In contrast with previous model simulations, the MetUM captures the observed east‐west gradient in surface melting associated with foehn winds, as well as the interannual variability in melt shown in previous observational studies. As exemplars, we focus on two case studies—the months preceding the collapse of the Larsen B ice shelf in March 2002 and the high foehn, high melt period of March‐May 2016—to test the hindcast's ability to reproduce the atmospheric effects that contributed to considerable melting during those periods. The results suggest that the MetUM hindcast is a useful tool with which to explore the dominant causes of surface melting on Larsen C.

Laser Surface Melting and Consecutive Point-Mode Forging Hardening of DH36 Marine Steel: Mechanical and Precipitation Behavior

This study investigates the effect of the laser surface melting and consecutive point-mode forging process (LSM-CPF) on the mechanical properties and the microstructure of DH36 marine steel. The microstructual revolution during the LSM-CPF process are revealed by metallographic microscope (OM) and scanning electron microscope (SEM) technique, and the strengthening mechanisms for different samples are also elucidated. The results show that the best yield strength (σ0.2) and tensile strength (σb) for the sample treated with 4000 W laser power and 10% reduction ratio are 721.3 and 884.2 MPa, which are 49.55% and 41.54% higher than that of the DH36 matrix, respectively. The hardness of the coatings decreases along the normal direction with the maximum value of 586.4 HV in the CPF zone for the sample treated with 2000 W laser power and 20% reduction ratio. During the low power LSM-CPF treatment, the nanoscale cementite appear as intragranular due to the inhibited carbon diffusion. The coherent boundary of (110)NbC‖(110)Ferrite, [11¯0]NbC‖[001]Ferrite between NbC and ferrite reduces the nucleation barrier to promote the nucleation of acicular ferrite (AF). The strengthening mechanism for samples treated at 2000 W is found to be dislocation strengthening. During high power laser treatment, pearlite transformation is found to occur with a low cooling rate. In this case, the strengthening mechanism is the boundary strengthening of lamellar pearlite and dislocation strengthening.

The Critical Role of Euro‐Atlantic Blocking in Promoting Snowfall in Central Greenland

AbstractThe Greenland Ice Sheet (GrIS) is losing mass at an increasing rate yet mass gain from snowfall still exceeds the loss attributed to surface melt processes on an annual basis. This work assesses the relationship between persistent atmospheric blocking across the Euro‐Atlantic region and enhanced precipitation processes over the central GrIS during June–August and September–November. Results show that the vast majority of snowfall events in the central GrIS coincide with Euro‐Atlantic blocking. During June–August, snowfall events are produced primarily by mixed‐phase clouds (88%) and are linked to a persistent blocking anticyclone over southern Greenland (84%). The blocking anticyclone slowly advects warm, moist air masses into western and southern Greenland, with positive temperature and water vapor anomalies that intensify over the central GrIS. A zonal integrated water vapor transport pattern south of Greenland indicates a southern shift of the North Atlantic storm track associated with the high‐latitude blocking. In contrast, snowfall events during September–November are largely produced by ice‐phase clouds (85%) and are associated with a blocking anticyclone over the Nordic Seas and blocked flow over northern Europe (78%). The blocking anticyclone deflects the westerly North Atlantic storm track poleward and enables the rapid transport of warm, moist air masses up the steep southeastern edge of the GrIS, with positive temperature and water vapor anomalies to the east and southeast of Greenland. These results emphasize the critical role of Euro‐Atlantic blocking in promoting snowfall processes over the central GrIS and the importance of accurate representation of blocking in climate model projections.

Microstructural Evolution upon 10-wt% Mo Alloying and Laser Surface Melting of M2 High Speed Steels Hardfacings

The article aims to comprehend the microstructural changes, in Plasma Transfer Arc (PTA) deposited M2 high speed steel (HSS) hardfacings upon incorporation of 10 wt% Mo alloying during deposition followed by laser surface melting. PTA deposited hardfacings were produced over 4140 steel. Then Mo alloyed and unalloyed PTA deposits were subjected to laser surface melting (LSM) process. A comprehensive microstructural characterization for all the resultant structures was carried out. Optical metallography using appropriate etching reagents and SEM microscopy in conjunction with XRD techniques were employed to ascertain the matrix structure and carbides morphology. The PTA microstructure was close to equilibrium structure of M2 HSS containing mixture of ferrite/austenite/martensite along with MC, M2C and M6C type carbides. While the LSM of M2 HSS caused higher fraction of martensite and finer grains in the structure resulting in increment in hardness. 10-wt% Mo addition changes the carbides from MC and rod like M2C to fibrous M2C and fishbone like M6C carbides. The LSM of Mo alloyed M2 HSS PTA deposits led to an overall decrease in the fraction of M6C carbides and fibrous M2C carbides accompanied by a decrease in hardness.

Micro-Alloying and Surface Texturing of Ti-6Al-4V Alloy by Embedding Nanoparticles Using Gas Tungsten Arc Welding

Titanium alloy Ti-6Al-4V is known for both its excellent mechanical properties and its low surface hardness. This study explores a two-step process for depositing a hard nanocrystalline coating onto the surface of the Ti-alloy, followed by surface melting, which embeds hard nanoparticles into a thin surface layer of the alloy. The treated surface layer was studied using X-ray diffraction, scanning electron microscopy, and Vicker’s micro-hardness testing. The results of the study show that the surface of the Ti-6Al-4V alloy can be successfully hardened by embedding nanosized Al2O3 particles into the surface using gas tungsten arc welding to melt the surface of the material. Surface melting the Ti-6Al-4V alloy with a 50A welding current produced the maximum microhardness of 701 HV0.2kg. The micro-hardness of the treated surface layer decreased with the increasing size of the nanoparticles, while the roughness of the surface increased with the increasing welding current. The heat input into the surface during the surface melting process resulted in the formation of various intermetallic compounds capable of further increasing the hardness of the Ti-6Al-4V surface.

Experimental and Numerical Analysis of Laser Surface Melting by Using Enthalpy Method

In this study, experimental and numerical applied of heat distribution due to pulsed Nd: YAG laser surface melting. Experimental side was consists of laser parameters are, pulse duration1.3ms, wavelength 1064nm, laser energies 1.5, 2. 6 and 4.3 J, laser beam diameter is 0.6 mm and spot diameter 0.78 mm was applied a low carbon steel type St37 with a dimension 10, 10, 3 mm, length, width and thickness respectively. Numerical analysis side consist of a mathematical model and calculating a thermal cycle by using equation in the enthalpy method applied to determine the cooling rate in fusion zone. The simulation by using the enthalpy method, applied on conduction heat transfer to estimate the cooling rate model in fusion zone and heat affected zones. Cooling rates models are helping to estimate the microstructure and micro hardness distribution in fusion and heat affected zones. The complication of the heat transfer in laser surface melting process, because at in rapid solidification, therefore the enthalpy model is more appropriate for this case. The result shows that increases of laser energy lead to decrease cooling rates and increase width and penetration of fusion zone, also decrease micro hardness in fusion zone and we found an increase in the pool size of fusion and heat affected zones.

Casting and Laser Surface Melting of 316L Stainless Steel from Scrap Resources

316L stainless steel is used in various industrial applications including chemical, biomedical and mechanical industries due to its good mechanical properties and corrosion resistance. Recycling of 316L stainless steel scrap without significantly reducing its value has received recently great attention because of the environmental regulations. In the current work, 316L stainless steel scrap was recycled via casting using Skull induction melting technique. The casted products subsequently subjected to laser surface melting process to improve its surface properties to be used for harsh environment. The results showed defect free surfaces with homogeneous microstructures. Nano size grains were also obtained due to rapid solidification process. Such nano size grains are preferred for extending the usage of the 316L stainless steel in new applications.Corresponding author: E-Mail: elgazzar.ha@gmail.com

Laser-melted surfaces fabricated on MAO films in Al and Si electrolytes

In order to improve the functions of microarc oxidation (MAO) films, the current work investigated the effects of the laser surface melting (LSM) process on MAO films fabricated in different electrolytes. A series of processing experiments was carried out on the composite films. In detail, MAO films using aluminum (Al) and silicon (Si) electrolytes were prepared on a Ti–6Al–4V alloy surface and then treated by using the LSM process. At the same time, the properties of the films, such as phases and morphology, were characterized and analyzed by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that moderate-intensity plasma was more easily obtained on the silicon MAO (Si-MAO) films than on the aluminum MAO (Al-MAO) ones. Similarly, a higher laser power was necessary to liquefy or gasify alumina (Al2O3). Compared with the defective structure of Al-MAO film after LSM, the structure of the Si-MAO film was almost free of defects. The film morphologies showed that an MAO film with low porosity and a smooth surface can be obtained after LSM treatment using proper parameters. In conclusion, the composite silicate system process using the silicon electrolyte had better modification performance.

Evaluation of the Antarctic Boundary Layer Thermodynamic Structure in MERRA2 Using Dropsonde Observations from the Concordiasi Campaign

AbstractRecent high‐resolution dropsonde observations from the 2010 Concordiasi field campaign in austral spring season show that surface‐based inversions (SBIs) over Antarctica are frequently eroded, with well‐mixed boundary layers occurring 33% and 18% of the time in West and East Antarctica, respectively. In this study, using the dropsonde observations, we evaluate the performance of the Modern‐Era Retrospective analysis for Research and Applications, version 2 (MERRA2) in representing the Antarctic boundary layer thermodynamic structure. Results show that MERRA2 has a good overall representation of the Antarctic surface stability and correctly predicts 82% of the SBIs. However, an underprediction of less stable boundary layer occurrence, especially over the elevated East Antarctic plateau, is favored during conditions of increased lower tropospheric stability associated with model dynamics, indicating difficulty in parameterizing turbulence in very stable boundary layers. In addition, a lower tropospheric cool bias (first model level and above) is observed in the MERRA2 reanalysis, especially over West Antarctica, which amplifies in the boundary layer during mixed conditions. The near‐surface cold bias is most pronounced when the model fails to predict mixed layers over West Antarctica and is expected to negatively impact the representation of surface energy budget and melt processes.

Fiber Laser Surface Melting of a NiTi Superelastic Alloy: Influence on Structural and Mechanical Properties

The surface melting of a NiTi superelastic alloy using a high-power laser Yb:Fiber was investigated. The influence of this process on the microstructural and mechanical properties was also examined. The reference material was a 3 mm nitinol strip with a homogeneous austenitic B2 phase. For the laser surface melting process, input fluences were applied from 17.5 to 45 J/mm2. The morphology of the structure and the chemical composition of several regions were determined by optical microscopy, scanning electron microscopy, dispersive energy spectra, and X-ray diffraction techniques. The mechanical properties, such as modulus of elasticity and hardness, were determined using nanoindentation and microindentation techniques. The greatest surface finishing of the fusion zone was observed for the condition 35 J/mm2. Three well-defined regions (fusion zone (FZ), heat-affected zone (HAZ), base metal (BM)) could be observed and dimensions of grain size, width, and depth of the melted pool were directly affected by the laser fluence. The geometry of the molten pool could be controlled by the optimization of the laser parameters. High laser fluence caused preferential volatilization of nickel, dynamic precipitation of intermetallic phases, including Ti2Ni, Ni3Ti, and Ni4Ti3, as well as solubilization of TiC in the matrix, which led to grain refinement. Thus, high laser fluence is a suitable technique to enhance mechanical properties such as hardness and Young’s modulus.

Influence of laser surface melting on the properties of MB26 and AZ80 magnesium alloys

In the present investigation, laser surface melting (LSM) was performed on MB26 and AZ80 magnesium alloys and their surface properties were evaluated. The finite element method (FEM) was used to calculate the resulting temperature during the laser surface melting process. The melted layer average thickness values were about 296 and 190 μm for MB26 and AZ80 alloys, respectively and the variation in the thickness is mainly attributed to the absorption in laser energy. The average grain size of the LSMed MB26 alloy was decreased about 14.5 times and AZ80 had very finer grains than the MB26 along with the fine distribution of second phases. Further, the X-ray diffraction results revealed that the second phase intensities were decreased in both the alloys due to their dispersion. The laser absorption efficiency of MB26 was higher due to the higher plasma attachment during LSM process, thereby has higher melt layer thickness compared to AZ80. The refined microstructure of the melted layer resulted in an increase of micro-hardness up to 110 Hv. Potentiodynamic polarization test results revealed that the corrosion current density (icorr) values of the LSMed MB26 and AZ80 alloys were decreased about 1.8 and 2.5 times, respectively compared to the as-received alloys. A variation in solidification rates of the melt pool due to the alloying elements were attributed to an improvement in the surface and electrochemical properties.

Surface modification of aluminum alloys with carbon nanotubes by laser surface melting

Carbon nanotubes (CNTs) could be an excellent reinforcement for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. Surface modification to improve hardness and other material properties has been performed by laser surface melting (LSM) process, where the laser beam melts the substrate together with alloying elements or reinforcing phase additives. In this work, Multiwalled CNTs (MWCNTs) were mixed by the electrostatic adsorption process with aluminum powder and the resulting mixed powder was laser melted on the surface of a 6061-aluminum alloy substrate. As a result, a modified substrate surface has been obtained from the Al/MWCNT – substrate co-melting, dilution and re-solidification processes. This modified layer was obtained by different LSM parameters and were characterized by Optical (OM) and Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Field Emission Gun Scanning Electron Microscopy (FEG-SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy (RS). The resulting mechanical behavior was evaluated by Vickers microhardness tests. The results showed that the presence of MWCNT in the aluminum powder improves the laser energy absorption, leading to the formation of a deeper modified layer, with segregation of Si particles homogeneously dispersed and improving the hardness. The formation of Al4C3 was not observed, evidencing that the MWCNTs did not react with the molten Al matrix during the LSM process.

Microstructure and mechanical properties of Ni nanoparticle-bonded Inconel 718

Ni nanoparticles were successfully used as a melting point depressant-free filler metal to join Inconel 718 via transient liquid phase (TLP) bonding in a vacuum environment. Ni nanoparticles of 22, 29, and 42 nm in diameters were synthesized by controlling the reducing agent injection rates and the TLP bonding was carried out at up to 1050 °C with heating rates of 2–15 °C/min. Based on the Gibbs-Thomson equation and surface melting models, bonding using Ni nanoparticles occurs due to competing solid-state sintering and surface melting processes. It was found that larger particle size, faster heating rate, and higher maximum temperature resulted in higher bonding strength due to less grain boundary contamination, smaller crystallite size, and more robust metallurgical bonding, respectively. Using a faster heating rate limits the amount of solid-state nanoparticle-nanoparticle sintering that occurs at lower temperatures. The suppression of nanoparticle-nanoparticle sintering as a function of nanoparticle diameter is also discussed. The maximum bonding strength achieved is 243 MPa. According to digital image correlation, the strain is mostly sustained in the Ni-Inconel interfacial region. The fractography of Ni nanoparticle-bonded joints is also discussed in detail.