Ti–6Al–4V alloys fabricated by inside-beam powder feeding (IBPF) generally exhibit coarse columnar α-lath resulting in slightly poorer mechanical properties than forged parts. In this study, a laser ...remelting strategy with an annular beam was used to improve the microstructure and refine grain size, thus improving the mechanical properties of IBPF components. This is realized by the formation of ultrafine secondary precipitation αs and more recrystallized nuclei. The formation mechanism of compression twins {10 1‾ 1} and dislocation pinning effect in remelted layer were investigated in detail through TEM analysis. Furthermore, texture evolution and slip systems of the remelted layers were analyzed to determine the deformation patterns. Fine grain strengthening and dislocation strengthening was significant, and the tensile strength of Ti–6Al–4V components after laser remelting is higher than those fabricated by inside-beam powder feeding by about 12.7% and 9.3% in transverse and longitudinal directions, respectively.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Ni-30wt%Sn alloy powder beds were remelted using a laser beam to examine regular eutectic and anomalous eutectic growth behavior. The remelted microstructure mainly consisted of primary α-Ni ...dendrites and refined regular lamellar eutectic in the interdendrite space. At the top of the molten pool, the competition between primary α-Ni dendrites and the regular lamellar eutectic can be explained by the maximum interface temperature criterion. Anomalous eutectic was observed at the bottom of the molten pool. The remelting of primary α-Ni dendritic arms formed in the first laser remelting scan had an important effect on the formation of the anomalous eutectic in the second laser remelting scan. This effect led to the formation of globular α-Ni particles with similar Euler's angles in the anomalous eutectic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In the current study, a CoCrFeNiAl0.5Nb0.5 high entropy alloy was manufactured via arc melting and exposed to laser surface remelting. The presence of Nb and Al was limited to the formation of single ...simple cubic phase formations. Both alloys are composed of four phases. Laser remelting did not change current phases, but it affected the microstructure. Hardness increased from 475 HV to 785 HV thanks to the change in phase ratios and grain refinement resulting from laser remelting. Wear resistance improved due to the increase in hardness, and volume losses decreased by 28 %. In short-term high-temperature oxidation, laser remelting enabled better oxidation resistance in alloy since it provided more paths for the diffusion of aluminum, which forms an alumina oxide scale. Interestingly, such a trend was not observed in the increased oxidation period. In the final oxidation stage, the depletion of B2 phases and the formation of inner oxides significantly worsened the oxidation resistance of LR alloy. Although Icorr, which expresses the corrosion resistance of the laser-melted alloy, was higher than before the laser-remelting process, the changes in the alloy's microstructure with rapid cooling caused a decrease in the passivation resistance of laser-remelted CoCrFeNiAl0.5Nb0.5 HEA.
•The produced HEA composed of BCC/B2, FCC and Laves phases.•Laser remelting (LR) homogenized microstructure and enhanced the hardness of HEA.•LR alloy improved the hardness, wear resistance and friction coefficient of HEA.•LR process negatively affected the corrosion of HEA due to decreasing of passivation resistance.•LR-HEA exhibited slightly better oxidation in short term but longer time exposure led to worse oxidation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The effect of tempering temperature on surface hardened AISI H13 tool steel by laser remelting process using an Yb-fiber laser has been investigated. Single remelting tracks were produced in argon ...environment at different laser power and scan speed in the range of 400–600 W and 200–1600 mm/min respectively, maintaining the laser spot diameter fixed at 3 mm. Their effects on geometrical aspects, microstructure and microhardness were analyzed considering the thermal history of molten pool recorded using an IR pyrometer. Microstructure was found to be associated with cooling rate and melt pool lifetime, estimated from the temperature signal. Thereafter, remelted surface with 30% overlapping tracks was generated and subjected to 1 h tempering cycle at different temperatures in 500–900 °C range followed by hardness and wear tests. Hardness was retained fully up to 500 °C and significant softening occurred at 600 °C and 700 °C. At 800 °C and higher temperatures, effects of laser remelting were impaired completely, but substrate got hardened through martensite formation in a conventional manner. Wear resistance followed the trend of hardness. Changes in microstructure and formation of various phases were found to be the reasons behind the modifications in hardness.
•Laser remelting of H13 and its hardness retention after subjecting to tempering is reported•Safe operating temperature for laser remelted H13 tool steel is reported.•Changes in microstructure and mechanical properties with tempering temperature are reported.•Process parameters, molten pool thermal history, geometrical aspects and microstructural evolution are correlated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Surface polishing by laser remelting (SP-LRM) is a novel, versatile, high-speed, and low-cost advanced manufacturing technology for producing high-quality surface finishes. The process utilizes a ...high-power laser that delivers a large amount of instantaneous energy melting a superficial thin layer of material to a molten state. This allows the melt pool to flow driven by thermocapillary and surface tension forces. The target of the process is to melt, reallocate, and resolidify surface peaks into valleys in order to yield a low surface roughness (Sa). SP-LRM, complexity arises from instabilities occurring during laser-material interactions, resulting from non-linear thermodynamics, initial surface topography, overheating, abrupt changes in laser path trajectories involving acceleration and deceleration, and various other factors. These process instabilities significantly affect the attainment of a desired smooth final surface. Presently, the identification of anomalies resulting from a specific set of laser parameters in laser remelting (LRM) is performed offline by assessing the surface topography of LRM using optical profilometer and correlating it with surface non-uniformities that are indicative of process instabilities. This study streamlines the anomaly detection process and identifies the presence of irregularities using an unsupervised clustering machine learning (ML) technique, specifically K-means clustering. During the laser remelting (LRM) process, a high-speed near-infrared (NIR) camera captures relative thermal emission images, which are then classified into a minimum of three clusters using the K-means algorithm. These clusters correspond to positive and negative axial laser beam positions, indicating shifts in the laser spot on the image, and the stability states of laser-material interactions. Preliminary findings show promising results in the employment of artificial intelligence (AI) to enhance LRM as a conventional industrial technology for polishing and structuring tooling surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Laser remelting (LR) treatment was used to regulate the microstructure of AlCoCrFeNiTax high-entropy alloys prepared by vacuum arc melting, and the microstructure and properties of the alloys before ...and after LR treatment were analyzed. The original AlCoCrFeNiTax alloys have typical dendritic morphology and the addition of Ta element promoted the formation of a Laves phase, gradually changing the alloys from two phase (BCC + B2) to three phase (BCC + B2 + Laves phase). After LR treatment, the grains were significantly refined, elemental segregation was alleviated, and a dense remelting layer with a thickness of 1200–1600 µm was formed on the surface of the alloy. In addition, the hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment, mainly caused by the combined effects of solution strengthening, second phase strengthening and fine grain strengthening. At the same time, the corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution is significantly improved by a stable Ta2O5 and TaO2 passivation films and the formation of a dense uniform remelting layer.
•Refractory element was added and LR treatment was conducted on the surface of AlCoCrFeNiTax high entropy alloy.•After LR treatment, elemental segregation on the alloy surface is alleviated and the alloy grains are refined.•A remelted layer of about 1200–1600 µm thickness was formed on the alloy surface after LR treatment.•The hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment.•The corrosion resistance of the alloys in 3.5 wt% NaCl solution is improved by passivation film and remelted layer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The forming quality of thermally sprayed coatings is often severely impacted by inherent defects, including porosity, microcracks, and mechanical bonding. The poor adhesive strength hinders the ...utilization of thermal spray technology when fabricating ceramic-reinforced metal matrix composite coatings (MMCCs). Thus, in this study, a negative defocus laser remelting and injection method (LRI) is introduced to modify a thermally sprayed coating with WC ceramics. The microstructure and mechanical property (microhardness, elastic modulus, and wear resistance) evolution of a LRI-modified WC reinforced composite coating is systematically characterized and compared with that for an as-sprayed coating. The LRI method is proven to improve the inherent defects of the initial coating and avoid severe reactions and dissolution of reinforced particles at high temperatures, and can be used to form a high-quality composite coating with a maximum strengthening effect of the ceramic particles. Compared with the initial coating, the elastic modulus and microhardness of the LRI coating are increased by 57.22% and 111.06%, respectively, whereas the abrasion rate is decreased by 54.33%.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•A new FEM model for laser remelting and surface structure formation was introduced.•Surface structure formation results from deformation of the melt pool ...surface.•Marangoni-convection has virtually no effect on surface structure formation.•Density discontinuity, thermal expansion, and melt pool dynamics are key factors.•Structure height scales linearly for continuous and discontinuous remelting process.
Conventional surface structuring processes often share two crucial disadvantages. Firstly, an additional surface finishing is usually required. Secondly, excess material is wasted. In contrast, during laser remelting, a redistribution of material can be achieved that results in a structured surface with a low micro-roughness. Therefore, this investigation focuses on the mechanism of surface structure formation during laser remelting on the hot work steel H11. A newly developed FEM-model is introduced and surface structure formation is investigated specifically for a sinusoidal modulation of laser power. A fiber coupled Nd:YAG laser was used to emit laser radiation with a focal beam diameter of 250 µm and laser power between 15 W and 215 W. At a scanning speed of 50 mm/s, the structuring of wavelengths from 0.25 mm to 4 mm was investigated. After one process step, structure heights of up to 12 µm were achieved for single tracks. In addition, the theoretical model revealed that melt pool changes lead to a deformation of the melt pool surface, which results in the formation of surface structures. Furthermore, the agreement between simulations and experiments indicates that the Marangoni-convection has only a minor impact on surface structure formation during laser remelting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
