Surface Remelting Research Articles

Surface Modification of Additively Manufactured Ti6Al4V through In-Situ Nitrogen-Assisted Laser Surface Remelting

Abstract Laser surface remelting is a widely used method for surface modification of titanium and related alloys, particularly to enhance its workability in the biomedical industry through surface nitriding. The present work aims to develop the nitride surface over the LPBF-processed Ti6Al4V substrate by introducing the nitrogen environment in the build chamber during the remelting. The effects of different laser power and laser scan speeds were studied over the surface topography and elemental changes of the remelted surface. The result shows an increase in surface roughness with selective laser remelting, which could enhance cell proliferation or osseointegration, which is advantageous for biomedical applications.EDX results show a significant increase in nitrogen content in terms of weight percentage for the in-situ remelted surface. XRD phase analysis shows the presence of titanium(Ti) and aluminium(Al) nitride peaks, and X-ray Photon-electron Spectrometry (XPS) also indicates the formation of nitrogen bonds with Ti and Al, which were initially missing in the substrate. The results reported here confirm the nitride surface formation over the substrate due to the in-situ remelting under the nitrogen environment for the LPBF-processed Ti6Al4V, which could be used for improved biomedical applications.

Texture Analysis of Inconel 718 with Different Modes During Single-Track Laser Surface Re-Melting

Texture Analysis of Inconel 718 with Different Modes During Single-Track Laser Surface Re-Melting

Icosahedral phase formation by laser surface remelting of a decagonal-based Al-Cu-Fe-Cr alloy

Icosahedral phase formation by laser surface remelting of a decagonal-based Al-Cu-Fe-Cr alloy

Laser surface remelting enhances microstructure uniformity and improves corrosion resistance of low-alloy steel weld metals

Laser surface remelting enhances microstructure uniformity and improves corrosion resistance of low-alloy steel weld metals

Surface Enhancement of Titanium Ti-3Al-2.5V Through Laser Remelting Process-A Material Analysis.

This study evaluates the effects of laser parameters on the surface remelting of the Ti-3Al-2.5V alloy. A ms-laser equipped with a coaxial gas-pressure head integrated into a Swiss-type turning machine is used for the laser remelting process of cylindrical parts. The influence of different pulse frequencies, as well as varying intensities, is investigated. The results reveal that surface micro-cracks can be eliminated through laser remelting. Increasing the input laser intensity also increases the size of the melting pool. A similar effect is observed with higher pulse frequencies. The metallurgical microstructure and the size of the heat-affected zone of the remelted surface at different input laser energy levels are also examined. The results indicate that input laser energy influences phase transformation in the metallurgical microstructure, which correspondingly results in variations in micro-hardness within the heat-affected zone. The variations in laser fluence lead to a surface hardness improvement of approximately 15%.

Tuning pores and mechanical properties for the heterogeneous interface of laser directed energy deposited IN718/316L laminate via in-situ laser surface remelting

In the past decades, laser directed energy deposition (L-DED) of multi-material attracts much attention for the integration of structure and performance. However, interfacial pores and limited mechanical properties are still bottlenecks. The present study introduces the in-situ laser surface remelting (LSR) treatment to L-DED of IN718/316 L laminate. During the LSR process, the continuous-wave (CW) near-infrared fiber printing laser rescans the whole surface after completely depositing the bottom material. When the bottom material was selected as 316 L and IN718, the pores around the heterogeneous interface were obviously eliminated and the proportion of high angle grain boundaries (HAGBs) was respectively lifted by 85.1 % and 149.1 % with slightly reduced average grain diameter after LSR treatment. Eventually, 8.5 % and 58.9 % increase in the elongation were respectively achieved. According to the numerical investigation, the “pinch-off” of bubble is observed during LSR process for the first time and the necking is enhanced with increased remelting laser power when the bottom material is IN718. Furthermore, the pore below the molten pool is prone to enlarge with stress concentration. This work can provide a novel guidance for the defect-free AM-built laminate.

Improved wear and corrosion resistance of magnesium AZ80 alloy prepared by laser surface remelting

Laser surface remelting (LSR) is a laser-based surface treatment method. In the LSR process, microstructural defects such as cracks and porosity are suppressed in addition to grain refinement, and the mechanical properties are improved. The present research investigated the effects of LSR parameters on the microstructure, wear, and corrosion behavior of Mg AZ80 alloy. The results showed that in LSR, the coarse-grained (29.8 μm) structure of AZ80 was transformed into a fine-grained structure (3.1 μm) with no microstructural defects. The evaporation of Mg during LSR and the formation of Al-rich and Mg-poor phases are the most important challenges in the surface treatment of AZ80. This limitation was solved by optimizing the LSR parameters, which included a gas flow rate of 2 L min−1, pulse duration of 3 ms, scanning speed of 3 mm s−1, pulse frequency of 8 Hz, and heat input of 64 J mm−1. The prevention of Mg evaporation was associated with the elimination of porosity and cracks, reducing of the solidification range, and uniform distribution of β-Mg17Al12 precipitation phases in α-Mg refined grains. The tribological behavior of the laser-treated region showed that the COF, depth of the wear scar, wear rate, and wear volume loss were reduced by 18%, 48%, 37%, and 66%, respectively, compared to AZ80. This result is attributed to the refinement of α-Mg grains and the uniform distribution of β-Mg17Al12 in the laser-treated region. The results of the polarization curves of the corrosion test in 3.5 wt% NaCl solution showed that the optimal laser-treated region with the lowest corrosion current density (34.68 × 10−6 μA.cm−2) and highest self-corrosion potential (1.425 V) exhibited the highest corrosion resistance. A slight change in the breakdown potential current slope in the laser-treated region indicates the formation of a protective film on the surface after the completion of LSR, which increases corrosion resistance.

Refined Microstructure and Enhanced Anticorrosion Properties of Mg–4Y–3Nd–0.5Zr Alloy Fabricated by Laser Surface Remelting

Refined Microstructure and Enhanced Anticorrosion Properties of Mg–4Y–3Nd–0.5Zr Alloy Fabricated by Laser Surface Remelting

Optimized Laser Surface Remelting of 3D-Printed Ti6Al4V Manufactured Through Electron Beam Melting

Optimized Laser Surface Remelting of 3D-Printed Ti6Al4V Manufactured Through Electron Beam Melting

Enhancing the corrosion properties and microhardness of titanium alloy by laser surface remelting

Laser surface remelting (LSR) was performed on the Ti80 alloy, and the effects of different laser powers with 50 W, 100 W and 200 W on the microstructure, microhardness and corrosion properties were systematically investigated. The results showed that after LSR treatment, the microstructure of the Ti80 alloy was significantly refined because of the rapid cooling effect of laser processing, and the microhardness of the remelted zone gradually increased with the increase of laser power. The electrochemical test results reveal that the corrosion resistance of the Ti80 alloy can be significantly improved after LSR treatment and the corrosion resistance in 3.5 wt% NaCl solution was as follows from high to low: 100 W>50 W>200 W>As-received. It was concluded that the content of Ti2O3 decreased and TiO2 increased after LSR, and the stability of the passive film exhibited a corresponding improvement. The LSR can improve the surface hardness and corrosion resistance of the Ti80 alloy, which can be attributed to the homogenization of the composition of the remelting zone and the reduction of the point defect density of passive film. It is believed that results documented in this study can provide an important reference for deepening understanding of the surface modification mechanisms of LSRed Ti80 alloys.

The Impact of Welding Parameters on the Welding Strength of High Borosilicate Glass and Aluminum Alloy

This study adopts a new surface pretreatment method, Laser Surface Remelting (LSR). This experiment aims to establish a set of laser welding process parameters suitable for aluminum alloy and glass under this specific pretreatment. This experiment explores the impact of laser welding parameters on the welding strength between high borosilicate glass and aluminum alloy. The study specifically investigates the effects of four process parameters: defocus amount, laser power, frequency, and pulse width on the welding outcome. The results indicate that the welding quality between the aluminum alloy and glass reaches its optimum when the defocus amount is zero (i.e., when the laser converges at the interface between the glass and the metal) and the laser welding parameters are set to a power of 250 W, a welding speed of 1 mm/s, a welding frequency of 10 Hz, and a pulse width of 2.5 ms. The experiment also analyzes the fracture morphology under different parameters, summarizing the locations and causes of fractures, and establishing the relationship between the fracture location and the welding strength.

Effect of surface remelting on the characteristics of IN718 components fabricated using laser powder directed energy deposition

Laser Powder Directed Energy Deposition (LP-DED) fabricated components exhibit poor surface finish, necessitating additional post-processing steps prior to their practical application. Enhancing the surface quality of additively manufactured IN718 specimens through conventional post-processing methods is particularly challenging, given the material’s poor machinability and the complexity of the fabricated components. The current study is centered on comprehending the impact of Laser Surface Remelting (LSR) on the surface properties of Laser Powder Directed Energy Deposited (LP-DED) IN718 material. To gain insights into how remelting influences surface characteristics, remelting was carried out using various sets of parameters. The remelted zone exhibited a refined grain structure, leading to increased hardness. Moreover, significant reductions in surface roughness and residual stress were observed in the remelted samples. Regression analysis indicated that laser power played a pivotal role, with positive impact on surface finish and depth of influence but a negative impact on residual stress and hardness. Therefore, considering all the comparison metrics, remelting using laser power of 150 W and a scan speed of 1140 mm min−1 were found to yield optimal surface conditions.

Influence of Mg Content on Microstructure Coarsening, Molten Pool Size, and Hardness of Laser Remelted Al(-x)-Mg-Sc Alloys.

Investigations leading to high-quality surfaces and optimized properties in laser remelted Al-Mg-Sc alloys remain scarce. Laser surface remelting (LSR) has been used for the final treatment of these alloys processed through additive manufacturing. However, the direct microstructure responses of the treated cast surfaces have not yet been investigated. In the present research, Al-3, 5, and 10 wt %-Mg-0.1 wt %-Sc alloys plates were processed using LSR to study the effects of local melting and rapid solidification. The morphology of the α-Al phase, microstructure coarsening, and hardness were mapped from the bottom to the top of the molten pools, varying with local Mg content and laser heat input (2.5 J/mm, 5 J/mm, and 10 J/mm). This study aimed to create a comprehensive map of the microstructures, hardness, and molten pool sizes under various conditions. The findings may help to optimize these alloys through understanding laser processing parameters. Methods used included CALPHAD computations, optical microscopy, SEM, EDS, image analysis, hardness tests, and heat flow models. The results obtained showed α-Al cell growth with bands in all alloys with hardness changes correlating with cell spacing and heat input. Higher Mg content resulted in more refined cells and a higher fraction of bands. Increased Mg content decreased the thermal diffusivity and enthalpy of melting, enlarging the molten pool size. Hardness increased with decreasing heat input and higher Mg content in the tested alloys, especially in the Al-10 wt %-Mg-0.1 wt %-Sc alloy as the heat input was varied.

In-situ laser surface remelting of laser powder bed fused AlSi10Mg alloy at argon and nitrogen protective gases: Multiscale analysis

In the recent decades, laser powder bed fusion (LPBF) of aluminum alloy has been widely used in many fields. However, the poor surface quality, inevitable defects, and limited mechanical performance are obvious obstacles. In-situ laser surface remelting (LSR) is a promising method to give a second opportunity for the defect elimination. In this work, the LSR protective gas (argon and nitrogen) on the surface roughness, porosity, and microstructure of LPBF-fabricated AlSi10Mg alloy are experimentally compared. The nitrogen shows significant superiority in the surface flatness and densification enhancement compared with argon gas. After LSR at nitrogen gas, the average grain size reduces by 8.7 % and the low-angle grain boundaries increases from 70.9 % to 99.7 %. Moreover, a two-dimension mesoscale FEM (Finite Element Method, FEM) model is established to investigate the movement of multi pores inside the molten pool. Attributed to the lower density and dynamic viscosity and larger thermal conductivity, the combination of multi pores is significantly drastic with obvious surface fluctuation during LSR at nitrogen gas. According to the density functional theory (DFT) calculation, the absolute adsorption energies of nitrogen on Al (100) and Al (110) surfaces are generally larger, revealing that the argon gas is easier to be adsorbed on the processing aluminum layer during LSR treatment. Furthermore, the vacancy defects in the aluminum layer play positive roles in the adsorption of gas. This work establishes the importance of the protective gas on the LSR treatment, and provides a multiscale analysis method for the pore evolution.

Secondary electron yield reduction of 316L stainless steel prepared by selective laser melting and surface remelting for electron cloud inhibition

Secondary emission (SE) can influence the performance of microwave devices, particle accelerators, etc. Particularly, secondary emission resulting in the formation of electron cloud effect in accelerators can induce various effects, such as the reduction of beam quality, beam lifetime and detector sensitivity. Reducing the Secondary electron yield (SEY) of material surfaces is very important for the inhibition of electron cloud in accelerators. A novel method based on selective laser melting (SLM) and surface remelting is initially proposed in this paper to process metallic materials with low SEY. As a commonly used material in accelerators vacuum pipes, 316 L stainless steel was manufactured by SLM to form surface morphologies with low SEY. The maximum SEY of as-received SLM fabricated and surface remelted SLM fabricated 316L stainless steel are 1.39 and 1.14 (the lowest one in this paper), respectively. On the other hand, the surface resistivities of as-received SLM fabricated (1.371 μΩ m) and surface remelted SLM fabricated 316L stainless steel (0.893–1.536 μΩ m) are higher than cast 316L stainless steel (0.78 μΩ m), which is mainly attributed to their higher surface roughness.

Modelling grain refinement under additive manufacturing solidification conditions using high performance cellular automata

Despite increasing applications of additively manufactured parts, they still suffer from anisotropic mechanical properties and can experience cracking due to coarse columnar grain structures induced by metal 3D printing. Microstructural control is promising avenue to overcome these challenges, but requires deeper understanding of factors controlling solidification, particularly regarding grain refinement. Addressing this gap, this study explores grain refinement in Al-Cu alloys with a process-microstructure linking cellular automata-finite difference (CAFD) approach supported by single-track laser surface remelting (LSR) experiments. To enhance the understanding of nucleation behaviour in alloys under additive manufacturing solidification conditions, this research analyses the influence of nucleation parameters on the post-LSR microstructures. Additionally, this study explores the computational dimensions of microstructure modelling, testing CA mesh sensitivity effects and benchmarking our CAFD models on two high-performance computing platforms. The CAFD model captures well the key microstructural features observed in LSR Al-Cu alloys with and without grain refiner addition. It is shown that the maximum nucleation density has a significant effect on the final microstructure, resulting in different proportions of coarse columnar grains resulting from epitaxial solidification, newly nucleated thin columnar grains, and equiaxed grains.

The effect of laser surface melting on the microstructure, microsegregation and solidification path of service-aged ECY768 cobalt-based gas turbine nozzle

In this study, the laser surface melting of cobalt-based superalloy ECY768, which has been in service for 40,000 h at a temperature of 1000 °C, has been investigated. Subsequently, laser surface welding and post-welding heat treatment is performed on the samples. This study was conducted in order to restore the microstructure of the damaged service-aged gas turbine nozzle to as-cast state. The results showed that by performing laser surface remelting, the microstructure of as-cast state can be approached. Also, the results of this study have investigated the weldability, microsegregation and solidification path of this superalloy, and it can be used in the repairing this superalloy in the industry. Laser surface melting was performed using a continuous wave fiber laser at various speeds of 10, 12, 14, 20, 50, and 70 mm/s. The microstructure and phase characteristics of the samples were examined using optical and scanning electron microscopes. Upon analyzing the macrostructure of the weld metal, it was observed that the depth of the melt zone at the speed of 12 mm/s is 585 ± 40 μm. In the investigating the microstructure of the solidification modes, namely planar, cellular, columnar dendritic, and equiaxed dendritic, it was observed that microsegregation occurs during laser welding of the samples due to the presence of heavy elements such as tantalum and tungsten. The solidification distribution coefficient for tantalum was calculated to be 0.37, which increased to 0.60 after the solution annealing heat treatment, resulting in an improved segregation behavior. Characterizing the surface hardness profiles of laser-melted samples it was observed that the hardness in the melt zone significantly increased compared to the base metal. The results of the current research indicate that the weldability (resistance to various welding defects, especially hot cracks) of the cobalt-based superalloy ECY768 is acceptable, and this process can be used for rejuvenating service-aged ECY768 cobalt-based gas turbine nozzle.

New insights into enhancing the mechanical properties of 6061-T6 aluminum alloy MIG welded joints by constructing bionic heterostructure

The trade-off between strength and toughness is a long-term challenge for engineering metal structural materials. However, natural materials overcome the inverse relationship between strength and toughness through their unique structures. Inspired by plant leaves and dragonfly wings, a ‘soft-hard’ alternating bionic heterostructure is prepared on 6061-T6 Al alloy MIG welded joints by laser surface remelting (LSR) technology. After LSR, the grain size of the laser treated zone is significantly refined, dislocation density is increased, and the formation of fine and stable GP zone and β′′ phase is promoted, enhancing microhardness and tensile properties of the LSRed sample. By adjusting the laser stripe spacing and distribution angle, stress transfer and redistribution can be optimized, effectively improving the tensile properties of the welded joint can be. Compared to as-welded sample, the tensile strength, yield strength and elongation of LSRed sample can be increased by 30.6 %, 13.6 % and 102 %, respectively. In addition, the bionic heterostructure composed of grain size gradient, dislocation gradient and precipitated phases gradient can effectively develop heterogeneous deformation induced (HDI) stress strengthening and HDI strain hardening, enabling synergistic strengthening of strength and toughness.

In Situ Prediction of Microstructure and Mechanical Properties in Laser-Remelted Al-Si Alloys: Towards Enhanced Additive Manufacturing.

Laser surface remelting of aluminum alloys has emerged as a promising technique to enhance mechanical properties through refined microstructures. This process involves rapid cooling rates ranging from 103 to 108 °C/s, which increase solid solubility within aluminum alloys, shifting their eutectic composition to a larger value of silicon content. Consequently, the resulting microstructure combines a strengthened aluminum matrix with silicon fibers. This study focuses on the laser scanning of Al-Si aluminum alloy to reduce the size of aluminum matrix spacings and transform fibrous silicon particles from micrometer to nanometer dimensions. Analysis revealed that the eutectic structure contained 17.55% silicon by weight, surpassing the equilibrium eutectic composition of 12.6% silicon. Microstructure dimensions within the molten zones, termed 'melt pools', were extensively examined using Scanning Electron Microscopy (SEM) at intervals of approximately 20 μm from the surface. A notable increase in hardness, exceeding 50% compared to the base plate, was observed in the melt pool regions. Thus, it is exemplified that laser surface remelting introduces a novel strengthening mechanism in the alloy. Moreover, this study develops an in situ method for predicting melt pool properties and dimensions. A predictive model is proposed, correlating energy density and spectral signals emitted during laser remelting with mechanical properties and melt pool dimensions. This method significantly reduces characterization time from days to seconds, offering a streamlined approach for future studies in additive manufacturing.

Improving mechanical properties and corrosion behavior of biomedical Ti-3Zr-2Sn-3Mo-25Nb alloy through laser surface remelting

Laser surface remelting offers a promising approach to enhance both the mechanical properties and corrosion resistance of metallic materials by tailoring their surface microstructures. This investigation specifically observed a phase transformation in the Ti-3Zr-2Sn-3Mo-25Nb (TLM) alloy from β to lamellar martensite α“ during the process, resulting in a refined grain structure. Geometrical phase analysis (GPA) revealed heightened internal compressive stress and the accumulation of dislocations along the β/α” interface, contributing to increased strength following laser treatment. Notably, the treated TLM alloy exhibited improved ductility, attributed to the presence of {332} 〈113〉 twinning during dynamic recrystallization. Moreover, the laser-treated surface significantly enhanced corrosion resistance compared to the untreated alloy. This study is anticipated to present an effective approach to prolonging the lifespan of TLM alloy by manipulating its surface microstructure through laser surface remelting.