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•Amorphous/crystalline coatings were prepared by laser cladding with rectangular spot.•Laser remelting can decrease cracks, and improve the surface quality of cladding coating.•Laser ...remelting can refine the microstructure and induce the formation of amorphous phases.•Laser remelting can enhance the corrosion resistant and microhardness of cladding coating.
The WC reinforced Fe-based amorphous composite coatings were prepared by laser cladding with rectangular spot. The effect of laser remelting on the microstructure and properties of composite coatings was investigated. The results showed that laser remelting can reduce the cracks and porosities of the cladding coating and improve its surface quality. Large amounts of crystalline phases were precipitated at the top of the cladding and remelting coatings. However, the microstructure at the top of the remelting coating was finer compared to that at the top of the cladding coating. With increasing distance from the surface of substrate, the amorphous phase appeared within the remelting coating and large amounts of carbides rich in Fe and Mo, Fe23B6, γ-Fe and Cr9.1Si0.9 phases were also precipitated in the remelting coating. As a result, the corrosion resistance of the remelting coating was higher than that of the cladding coating. The microhardness of the remelting coating was approximately 1.13 times higher than that of the cladding coating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this paper, the remelting process is applied to Laser Directed Energy Deposition (L-DED) to repair single crystal superalloys. The main formation modes of stray grains in single crystal epitaxial ...growth were analyzed, and the inhibitory effect of remelting process on stray grains in single crystal epitaxial growth using L-DED was studied. Comparative experiments between remelting and non-remelting processes have been conducted. Three process parameters in the remelting process: power, z-axis lift and cladding-remelting interval time were studied. The impact of different remelting process parameters on single crystal epitaxial growth and the formation of stray grains has been studied. Remelting has been shown to effectively prevent the formation of stray grains during the solidification of the melt pool, which are otherwise caused by the presence of unmelted powder during the powder feeding phase of the L-DED process. A cladding layer without stray grains on both sides is obtained. After remelting, the epitaxial growth structure can achieve larger cellular and columnar dendritic zones and smaller primary dendrite arms. A favorable epitaxial growth structure was obtained in this paper, under the optimized remelting process window.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Large columnar grains with epitaxial growth are commonly obtained in the additive manufacturing of alloys, resulting in anisotropic mechanical properties and even hot-tearing cracks. Here, we ...demonstrate a new approach via remelting-introduced columnar-to-equiaxed transformation to promote the formation of fully-equiaxed microstructures in the additive manufacturing of Ni32Co30Cr10Fe10Al18 eutectic high-entropy alloy. Our present work displays promising isotropic mechanical properties with a superior combination of strength and ductility, compared to conventional as-cast and other as-printed eutectic high-entropy alloys. This novel finding could be applicable to the additive manufacturing of other eutectic systems for equiaxed microstructure control and performance optimization.
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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 improved the surface quality of the coating.•Laser surface remelting tends to reduce the pore inside the coating.•After remelting, the microstructure can be refined.•Due to laser ...remelting process, the hardness of the coating was increased.
The work aimed to improve the forming quality of multi-pass coatings synthesized by laser remelting in situ. The influence-relation model of the overlap rate on surface flatness and dilution rate of coatings was constructed by the single-factor method. The functions of laser power, scanning speed, defocusing distance, and scanning mode on the surface flatness and pore area of remelted coatings were studied by mixed horizontal orthogonal test, and the influence law of process parameters on surface flatness and internal pore area was revealed. Flatness increased first and then decreased with the increased overlap rate. Energy acting on the substrate decreased, and the dilution rate decreased. When the dilution rate was satisfied, the overlap rate corresponding to the maximum value of the flatness fitting curve was 26.7%. The scanning speed and laser power of remelting significantly affected coating flatness and the signal-to-noise ratio of the pore area. The signal-to-noise ratio of flatness to the pore area was positively correlated with laser power and negatively correlated with the scanning speed. When the scanning speed of remelting decreased, the duration of the molten pool increased, and its solidification rate decreased. Therefore, bubbles in the molten pool had sufficient time to overflow, which increased coating flatness and decreased the internal pore area.The optimum process parameters under multi-index optimization of integrated flatness and pore area were as follows using grey relational analysis: the laser power of 1,600 W, scanning speed of 3 mm/s, a defocusing distance of 10 mm, and parallel cladding direction. Sticky powders in the coating disappeared under the optimal remelting process parameters, and flatness and the internal pore area were improved. Maximum hardness was increased from 1,281.7HV to 1,454.2 HV, with an increase of 13.46%. The grain size was small and hardness was improved due to the increased tissue density in the remelting area of the coating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•In-situ TiN-Al2O3 and cuboidal B2 phase combined strengthening HEA coatings•A square internally and round externally dual-phase nanoparticle structure formed.•Thermite reaction occurs during laser ...remelting.•The grains in AlCoCrFeNi HEA coatings were refined by additive TiN.
High-entropy alloy (HEA) coatings are of great importance in the fabrication of wear resistance materials. HEA coatings containing ceramic particles as reinforcement phase usually have better wear performance. In this study, AlCoCrFeNi(TiN)x (x: molar ratio; x=0, 0.2, 0.4, 0.6, 0.8, 1.0) HEA coatings were fabricated on Q235 steel by plasma spray first and then subjected to laser remelting. The experimental results confirm that plasma spray together with post laser remelting could result in the in-situ formation of TiN-Al2O3 ceramic particles and cuboidal B2 phase in the AlCoCrFeNi(TiN)x HEA coatings. The in-situ TiN-Al2O3 and nano-cuboidal B2 precipitation phase strengthened the coatings and improved their wear-resistance properties. Due to the dispersion of hard phase and nano-particles resulting from second heating, the microhardness of the AlCoCrFeNi(TiN) coatings significantly increased from 493 to 851 HV after laser remelting. For the same reasons, the wear-resistance performance was also significantly promoted after 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
Laser-induced forward transfer (LIFT) has emerged as a versatile technique for printing high-resolution metal microstructures. However, a common drawback of this method is the inadequate coalescence ...of the deposited metal microdroplets, which results in inferior electrical and mechanical properties. This paper proposes a novel approach for fabricating high-performance metal micropillars using a single-pulsed laser to alternately deposit and remelt metal microdroplets. Specifically, an ultraviolet nanosecond laser was used to induce the deposition of copper microdroplets, forming a patterned powder bed with high resolution. Subsequently, a laser pulse train was applied to fuse the patterned powder bed. The results showed that voids and microdroplet delamination were eliminated in the printed copper micropillars, whose yield strength and elastic modulus increased threefold, approaching 63% of those of the bulk metal. The remelting behavior of the deposited microdroplets was elucidated by modelling and analysing the thermal accumulation effects of a laser pulse train. A remelting map was proposed, including the non-melting, remelting, and vaporizing regimes. According to the depth of melt pool, the evolutions of morphology and microstructure in the depositing and remelting process were elucidated. Hence, this study advances the LIFT process for fabricating high-performance metal microstructures.
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•Alternate deposition and remelting microdroplets was proposed to eliminate voids and delamination suffered by LIFT.•The yield strength and elastic modulus of printed micropillars were measured to augment threefold, approaching 63% of the bulk metal.•Laser remelting regime was elucidated, including the non-melting, remelting, and vaporizing regions.•The morphology and microstructure of printed micropillar were governed by remelting depth.
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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) is often used during selective laser melting (SLM) processes to improve the densification degree and top surface quality of the products. However, researches regarding its ...effects on side surface quality, residual stress, microstructure, and mechanical property are still quite lacking. The influence of the repeated usage of LR on a solidified layer is also not very clear. To address these issues, LR treatments with the cyclic numbers of 1–3 on every solidified layer have been employed during the SLM processes of a Ti-5Al-2.5Sn alloy in this study and their influences on deposition quality, residual stress, microstructure, and mechanical property were researched. The results first indicated that although the improvement in top surface quality and densification degree would be more and more notable with the increase of LR cycles, the side surface quality could not be improved through all the LR treatments. Then, it was shown by the hole-drilling tests on the surface centers of several 15 × 15 × 3 mm3 thin-plate specimens that when 1 cycle of LR was conducted on every solidified layer, the principal residual stress at the hole bottom of the SLM sample could be far beyond that of the non-treated one. In contrast, when 2 or 3 cycles of LR were conducted, the measured principal residual stresses could be reduced to lower than that of the non-treated ones. It was also proved that unlike the non-treated sample which presented a martensite-dominated microstructure with a very weak texture, all the LR-treated samples exhibited two kinds of preferential orientations. Finally, tensile properties of the stress-relieved samples were tested and it was seen that under the combined influence of the densification and the microstructure factors, the elongations of the LR-treated samples became slightly higher than that of the non-treated one whereas the tensile strengths were nearly identical. In summary, this paper demonstrates that there is still limitation in using LR as an auxiliary process of the SLM production of titanium products. The possible increase in residual stress and the formation of strong textures should be particularly considered.
•Laser remelting (LR) led to texture formation within the SLM Ti-5Al-2.5Sn.•Improvement in density and top surface quality is notable at higher LR cycles.•Imposing 1 cycle of LR on each solidified layer led to increase in residual stress.•Elongation increased after LR treatment whereas tensile strength was not affected.•Side surface quality could not be effectively improved through LR treatments.
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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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•Micro-scale Fe82Cr16SiB coating is prepared by single-layer extreme high-speed laser cladding.•The flatness of Fe82Cr16SiB coating and structural refinement could be improved by ...laser remelting.•The corrosion resistance, hardness and wear resistance of Fe82Cr16SiB coating are improved by remelting treatment.
With scanning speeding of 20 ∼ 200 m/min, extreme high-speed laser cladding is a high-efficiency choice to fabricate thin protective coatings with thickness of 0.01 ∼ 0.25 mm on metal parts. Laser remelting is considered as an effective strategy to improve surface characteristics. In the present paper, mirco-scale Fe82Cr16SiB alloy single-layer coatings are successfully prepared on H13 steel substrate by above integrated process with slow scanning speed below 5 m/min. The flatness of the defect-free coatings is substantially improved with the formation of a refined gradient microstructure along the growth direction. The remelted coating exhibits enhanced corrosion resistance, higher hardness, good wear resistance with lower friction coefficient.
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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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