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•The developments in the field of laser surface remelting have been critically analyzed.•Laser surface remelting tends to enhance the microstructure and mechanical properties of ...materials and coatings.•Tribological properties of materials are improved after laser surface remelting.•Pros of laser surface remelting in the manufacturing and post-treatment processes have been evaluated.
Surface defects like porosity, cracks, coarse grains, surface roughness, etc. have a huge impact on the strength and performance of materials. Due to this, surface treatments have become an important part in the field of materials to attain certain desirable mechanical properties and surface properties. Surface of parts treated with laser surface remelting exhibits excellent surface and mechanical properties. It is a computer-based technique which provides the advantage of treating selective surfaces. Laser surface remelting tends to enhance corrosion resistance, microhardness, wear resistance, fatigue strength, and tensile strength of the materials. To achieve certain mechanical properties with laser surface remelting, an optimized set of laser processing parameters is essential. Laser surface remelting has become a compulsory treatment for parts manufactured by Additive Manufacturing (AM) processes as these processes provide poor surface, porosity, and hot cracking defects which ultimately affect the performance of parts. This paper critically evaluates the advancements which have been made in the field of laser surface remelting to get better surface quality, improved mechanical and tribological properties.
This study explores using high-energy pulsed laser to improve the surface property and corrosion behavior of Ti-6Al-4V, aiming to develop a more eco-friendly and efficient approach. The study ...comprises conventional cast samples, advanced 3D-printed samples, and their respective laser-treated counterparts, all tested in a 3.5 wt% NaCl solution. The findings showed that sample 3 (as-3D-printed) had a more stable passivation film than sample 1 (as-cast). The laser-treated surface of sample 2 (laser-treated cast) greatly enhances film stability and resistance. Moreover, sample 4 (laser-treated 3D-printed) exhibited significantly better corrosion performance compared to sample 3 (as-3D-printed) due to the increased thickness of the passivation film in the laser-treated samples, resulting in higher film corrosion resistance. The results reveal that laser remelting treatment can eliminate macroscopic defects, reduce grain size, increase grain boundary density, and generate denser and more stable passivation films on the surface of Ti-6Al-4V, leading to reduced corrosion currents during dynamic potential polarization. Furthermore, laser remelting treatment has the capability to transform and refine the α phase into a finer lamellar and needle-like structure, thereby increasing the density of passivation nucleation sites during the corrosion process, resulting in the formation of a high-density passivation layer, and ultimately improving the corrosion resistance. By gaining a better understanding of the underlying mechanisms involved in high-energy pulsed treatment, this work provides valuable insights that can be used to optimize the treatment process and improve the overall surface properties of Ti-6Al-4V alloys.
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•The microstructure of cast and 3D-printed Ti-6Al-4V differs, impacting passivation film thickness and resistance.•Laser remelting treatment significantly improves corrosion resistance of cast and 3D-printed parts.•Laser treatment increases the density of grain boundaries on surface, improving passivation layer stability.
A surface layered structure of the Al0.5CoCrFeNiSi0.25 high-entropy alloys was prepared via laser remelting (LR). The microstructures were characterized via optical microscopy, scanning electron ...microscopy, and electron backscatter diffraction techniques. The microhardness and wear properties of the LR alloys were evaluated in comparison with the as-cast alloy. The results showed that the microstructure of the surface layers can be tailored by changing laser scanning speed. With increasing the laser scanning speed from 3 mm/s to 7 mm/s, the thickness of the molten pool gradually decreased. Meanwhile, the microstructure of the layers changed from BCC + FCC dual-phase layers to BCC phase layers (BCC + B2 phase). And the thickness of BCC + FCC dual-phase layers gradually decreased. When the laser scanning speed reached 7 mm/s, the microstructure of the surface layer was only the BCC phase and the hardness of the BCC layer was doubled compared with the as-cast alloy, which also resulted in a sequential increase in scratch resistance. The relatively high hardness of the layered structure also led to its macroscopic wear resistance higher than that of the as-cast alloy, and the wear mechanism was mainly abrasive wear.
•A layered structure with difference microstructure can be tailored by changing laser scanning speed.•The BCC phase layer is achieved with high laser scanning speed of 7 mm/s and its hardness is doubled than the as-cast alloy.•The hardness and wear resistance is enhanced after remelting.
This study focuses on the microstructure, tensile and fatigue properties of laser beam welded butt joints in 4 mm thick sheets of duplex stainless steel 2205. The microstructural characteristics of ...the joints were investigated via optical microscopy and electron backscattered diffraction. A 300 μm wide heat affect zone with increased ferrite content and a nearly fully ferritic 800 μm wide fusion zone were found. No porosity could be found with X-ray radiography. Microhardness measurements revealed increased strength in the fusion and heat affect zones of the weldments. Uniaxial tensile and stress controlled fatigue tests were performed in order to characterize the mechanical properties of specimens containing laser beam welded joints and the base material. The specimens containing weldments were stronger, but less ductile than the base material, due to the weld metal restricting deformation. The as-welded joints exhibited worse fatigue performance than the base material due to the notch at the excess weld metal. The fatigue properties of the specimens containing joints could be elevated to the base material level by a laser surface remelting treatment.
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•Established correlation of microstructure, joint geometry, tensile and fatigue properties•Overmatched joint impinges deformation in its vicinity and changes the failure mode.•Laser surface remelting improves fatigue properties to base-material level.
There is an increasing reckoning that the thermoelectric performance of a material is dependent on its microstructure. However, the microstructure-properties relationship often remains elusive, in ...part due to the complexity of the hierarchy and scales of features that influence transport properties. Here, we focus on the Heusler-Fe2VAl compound, which shows promising thermoelectric properties, is non-toxic, cheap, and consist of earth-abundant elements. We directly correlate microstructure and local properties, using advanced scanning electron microscopy methods including in-situ four-point-probe technique for electron transport measurements. The local thermal conductivity is investigated by scanning thermal microscopy. Finally, atom probe tomography provides near-atomic scale compositional analysis. To locally manipulate the microstructure, we use laser surface remelting. The rapid quenching creates a complex microstructure with a high density of dislocations and small, elongated grains. We hence showcase that laser surface remelting can be employed to manipulate the microstructure to reduce the thermal conductivity and electrical resistivity, leading to a demonstrated enhancement of the thermoelectric performance at room temperature.
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•Pulsed laser remelting was used to generate ripple-like features on Ti6Al4V surfaces.•Laser remelting improved wear, corrosion and tribocorrosion resistance of the ...surfaces.•Viability and differentiation of hAMSCs were dependent upon the ripple topographies.•Topographies of the rippled structures also influenced the orientation of the cells.
Laser-based surface modification methods are employed to augment the surface properties of engineering components. In the presented work, pulsed laser remelting of Ti6Al4V surfaces using a long pulsed laser was used to generate ripple-like micro-features with different feature sizes. The resultant surfaces exhibited improved corrosion and tribocorrosion resistance. Anisotropic wetting characteristics of the laser remelted surfaces led to elongation of water droplets on the surfaces. The osteogenic potential of the surfaces as well as the orientations of human mesenchymal stem cells on the surfaces were dependent on the surface features. On surfaces having 20 μm ripples, differentiation of stem cells towards osteoblastic lineage was higher than that on acid etched surfaces, and the cells were prominently oriented across the ripples, parallel to the laser scanning track. On the other hand, surfaces having 100 μm ripples suppressed the cellular activities on them. While the resistance to corrosion and tribocorrosion of laser remelted surfaces can be attributed to the evolved microstructure and the formation of stable oxide layers, the physical characteristics like topography and wettability dictated cellular behavior on the surfaces. Taken together, the work demonstrates the use of pulsed laser remelting as a simple yet potentially effective route towards manufacturing Ti6Al4V orthopedic implants with improved biofunctionalities.
•After the LSR, two surface modification zones (RZ and HAZ) with distinct microstructures appear in Zr-4 and N36.•Average hardness values of RZs of Zr-4 and N36 are ∼30% higher than their ...substrates.•Wear rates of the LSRed Zr-4 and N36 alloys are ∼30% and 18% lower than their substrates.•Compared with LSRed Zr-4, higher hardness and wear resistance of LSRed N36 is attributed to addition of 1 wt.% Nb.
Two typical Zr alloys (Zr-4 and N36) for nuclear applications were surface-treated by laser surface remelting (LSR). Electron channeling contrast imaging and electron backscatter diffraction were used to characterize their main microstructure characteristics before and after the LSR, which were also correlated with their hardness and wear resistance. The results show that two surface modification zones with distinct microstructure characteristics appear in both the LSRed Zr alloys: (i) remelting zone (RZ) composed of fine α laths with dense internal nano-twins, and (ii) heat affected zone (HAZ) consisting of blocky α, lath α and second phase particles. The average hardness values of the RZs of Zr-4 and N36 alloys are 254.9 ± 8.5 HV and 269.5 ± 7.9 HV, respectively, ∼30% higher than their substrates. The wear rates of the LSRed Zr-4 and N36 alloys are found to be about 30% and 18% lower than their substrates, respectively, indicating significantly improved wear resistance. Comprehensive analyses reveal that refined grains, solid solution and internal nano-twins generated by ultrafast heating and cooling during the laser treatment have jointly led to the enhanced surface hardness of the LSRed Zr alloys, accounting for their improved wear resistance as well. Compared to the Zr-4 alloy, the refinement of the surface microstructure of the N36 alloy after the LSR treatment is more remarkable, contributing to higher hardness and wear resistance, which is mainly related to the addition of 1 wt.% Nb.
The selective laser melting (SLM) of aluminium alloys is of interest to researchers because of these alloys’ potential applications in the aerospace and automotive domains. Post-processing is ...generally required in order to enhance the mechanical properties of devices that involve moving parts, where surface mechanical properties are significant factors. This paper describes a preliminary study that was conducted to investigate the effect of post-processing on the microstructure and mechanical properties of SLM fabricated AlSi10Mg alloy, with an emphasis on the laser surface remelting (LSR) process. The experimental results demonstrate that the heat treatment degraded tensile strength while improving ductility by achieving grain growth and residual stress release. The yield strength obtained in the experiment was reduced from 200 to 100 MPa, whereas the elongation increased from 6 to 22%. The LSR process was found to contribute to an improvement in surface finish. The surface roughness indicator
R
a
was determined to be 0.93 μm in the LSR post-processed sample, compared to a fairly high value of 19.3 μm in the as-fabricated samples. The LSR process also enhanced the microhardness by refining the microstructure; the Si eutectic dendritic structure that formed was found to be finer than that of the as-fabricated samples. Compared to the as-fabricated samples, the LSR process contributed to a 19.5% increase in microhardness. The findings suggest that the microstructure and mechanical properties of SLM-fabricated AlSi10Mg parts could be tailored by suitable post-processing such as heat treatment and LSR. The significance of this research is its proposal of a novel technique to enhance surface hardness using LSR, which is a significant step towards the combination of SLM and LSR processes to manufacture customised aluminium components for the automotive and aerospace sectors.
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•A crystalline-amorphous nanostructured top surface layer is developed on a high-entropy alloy by laser surface processing.•The phase decomposition-mediated mechanisms forming the ...crystalline-amorphous nanostructured surface layer are uncovered.•Localized micro-pillar compression tests on surface layer shows an ultrahigh yield strength and a good compression strain .•The co-deformation cooperative actions include dislocation activities in nanograins but crystallization in amorphous GBs.•The co-deformation cooperative effects subsequently lead to the grain coarsening via GB-mediated plasticity.
Heterogeneous crystalline-amorphous nanostructures have been documented to show superior strength-ductility synergy via the co-deformation cooperative effects of nanograins and amorphous grain boundaries. In this work, a facile laser surface remelting technique with rapid cooling rate was successfully developed to fabricate a ∼ 100 μm-thick gradient nanostructured layer accompanied by phase decomposition on a TiZrHfTaNb0.2 high-entropy alloy, where a ∼ 5 μm-thick crystalline-amorphous nanostructured top surface layer with an average grain size of ∼ 7 nm was obtained. Such crystalline-amorphous nanostructured layer shows an ultrahigh yield strength of ∼ 6.0 GPa and a compression strain of ∼ 25 % during the localized micro-pillar compression tests. The atomic observations reveal that co-deformation cooperative mechanisms include the well-retained dislocation activities in nanograins but crystallization in amorphous grain boundaries, which subsequently lead to the grain coarsening via grain boundary-mediated plasticity. This study sheds light on the development of high-performance high-entropy alloys with novel crystalline-amorphous nanostructures and provides significant insight into their plastic deformation mechanisms.
•Laser surface remelting of Inconel 718 is carried out.•Correlation between scan speed, cooling rate and microstructure is reported.•Process map based on cooling rate to generate preferred ...microstructure is developed.•Higher cooling rates resulted in decreased elemental segregation in Inconel 718.•Higher cooling rates resulted in improved performance of remelted samples.
In the area of laser material processing, laser surface remelting has been found to be an effective method of improving surface properties such as hardness, wear, and corrosion resistance. However, the scale of improvement depends on the evolving microstructure and phases, which depend on the cooling rates. Therefore, in the present study, laser surface remelting of Inconel 718 was carried out and a process-structure–property relationship with respect to the cooling rates has been developed. During the laser surface remelting process, the molten pool thermal history i.e. cooling rate, molten pool lifetime, and solidification shelf time is monitored and estimated using an IR pyrometer. The evolution of microstructure is later correlated with these parameters. With an increase in scan speed, the cooling rate is found to increase resulting in transformation of microstructure from equiaxed grains to columnar epitaxial growth. Based on the results obtained, a process map is proposed to establish a particular type of microstructure with respect to the cooling rate. Further, the effect of cooling rate and microstructure on the surface hardness and specific wear rate has also been investigated. Both surface hardness and specific wear rate got reduced with decreasing cooling rate at a slower scan speed due to grain coarsening and an increase in elemental segregation or Laves phase formation.
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