•Surface modification strategy was successfully applied to improve the performance of the AlCoCrFeNi2.1 EHEA .•The surface microhardness and wear resistance of the modified EHEA enhanced by 59% and ...68%, respectively.•A semi-empirical model was built to estimate the contribution of lamellar spacing in microhardness for the EHEAs.
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Eutectic high-entropy alloys (EHEAs) are a class of prospective structural material in advanced engineering applications due to their excellent mechanical properties and castability. However, few researchers focused on the surface modification of these EHEAs. This study aimed to propose an effective method combining laser remelting and heat treatment to modify the surface of classical AlCoCrFeNi2.1 EHEA. After surface modification, the surface microhardness of the EHEA increased by 59%, and the average friction coefficient and wear rate decreased by 26% and 68%, respectively. The improved performance was mainly attributed to the decrease in lamellar spacing between face-centered cubic (FCC)/body-centered cubic (BCC) (B2) and coherent precipitation of nanoparticles in both FCC and B2 phases. A semi-empirical model was built to estimate the contribution of lamellar spacing to microhardness. The method and model might be applied to modify the surface properties of other EHEAs with lamellar structures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
One of the remaining challenges faced by Directed Energy Deposition is the poor surface finish induced by unmolten particles and the inherent superposition of layers during the process. The DED ...roughness levels are known to be significantly higher than for conventional parts and can become critical for the fatigue life and corrosion of the component. This is why the production of a DED part always requires a post-processing surface finishing step, which is known to be costly and to have a significant impact on the production time. This paper therefore presents an evaluation of single-track roughness induced by the DED process through transversal cross-sections, top-view micrographs, in situ process monitored images, laser triangulation, and contact-type measurements. The main DED process parameters defining the roughness are identified as being the particle diameter, laser beam diameter, and laser power. Finally, laser remelting during the production of cubic samples is proposed as a solution to further mitigate the roughness. Roughness levels on the top surface are reduced up to 86% with sufficiently high laser power settings. Laser remelting is therefore recommended to minimize the roughness, in combination with an optimal process parameter selection.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To further strengthen the AlCoCrFeNi high-entropy alloy (HEA) coating prepared by high-speed laser cladding (HLC), laser remelting (LR) was chosen to reprocess it. The effects of LR on the ...topography, microstructure, growth orientation, phase distribution, and properties were investigated. It was revealed that there were a large number of liquid phase separation (LPS) zones in the HLC coating because of an ultrafast cooling rate. After LR, the LPS zones were eliminated. Compared to HLC coating, the microhardness increased from 622 HV to 762 HV, and the friction coefficient and the wear weight loss were reduced by 0.1 and 0.5 mg, respectively. In electrochemical testing, the self-corrosion potential increased by 45.9 mV and the self-corrosion current density decreased by one order of magnitude. Meanwhile, EBSD analysis indicated that the LPS zones were prone to recrystallization. The LPS zones were nickel-poor, low hardness, also BCC phase, and had a clearer (101) orientation. With the elimination of the LPS zones, the kernel average misorientation values were reduced, Taylor factor values and high angle grain boundaries were increased, and the average grain size was reduced from 2.43 μm to 2.12 μm. Eventually, for LR coatings, the combination of fine grain strengthening, solid solution strengthening, spalling reduction, and Cr element segregation resulted in better wear and corrosion resistances. The overall results show that a reasonable LR application can induce the microstructure of the HLC coating and improve its service properties.
● The AlCoCrFeNi high-entropy alloy coatings were prepared by high-speed laser cladding (HLC) and reprocessed by laser remelting (LR).● There were a large number of liquid phase separation (LPS) zones in the HLC coating. After LR, the LPS zones were replaced by fine equiaxed crystals.● The LPS zones were nickel-poor and low hardness, had a clearer (101) orientation, and tended to spall off in the wear test, causing a decrease in the overall wear resistance of the coating.● As a result of the elimination of the LPS zones, the microhardness and wear resistance of the LR coating were improved by solid solution strengthening and fine grain strengthening.● Appropriate undercooling and more high angle grain boundaries caused by LR provided a larger driving force for grain boundary segregation. The elemental content of Cr at the grain boundaries became higher, and the corrosion resistance of the LR coatings increased significantly. Display omitted
•HLC led to a large number of the LPS zones in the AlCoCrFeNi HEA coating.•LR could successfully eliminate the LPS zones.•Recrystallization made the grains of the LPS zones coarse and soft.•The microhardness and wear resistance of the coating were improved by LR.•Higher Cr content at grain boundaries boosted corrosion resistance of LR coating.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Effect of laser remelting on mechanical properties under cyclic loading was studied.•Effect of laser remelting on wear volume and friction coefficient was studied.•Effect of laser remelting and heat ...treatment on Charpy impact energy was studied.•Anisotropy in hardness, residual stress, Charpy impact energy and wear was studied.•Reciprocating sliding tests with ball above and below configuration were conducted.
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The reliability and quality of additively manufactured parts are questionable. The present study aimed to improve the surface quality and mechanical and tribological properties of a Ti6Al4V alloy manufactured using selective laser melting (SLM). The effects of the laser remelting on its surface topology, mechanical properties, and sliding wear in a ball-on-plate configuration with a ball either above or below the plate were investigated systematically. The influence of the laser remelting approach on the anisotropy of the mechanical and tribological properties was compared with that of the heat treatment approach. The surface quality and high cycle fatigue strength improved with an increase in the number of melting steps. The compressive and impact strengths also increased with an increase in the number of melting steps. The wear resistance in both configurations was higher in the remelted samples than in the samples after SLM. The results confirmed that laser remelting, as an affordable approach, could significantly improve the reliability of parts fabricated by the SLM process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A new method of surface structuring by laser remelting with the help of surface tension (mainly thermocapillary force and solutocapillary force) and volume expansion was proposed. A multiphysics ...coupled numerical model was proposed for this surface structuring method, in which the calculation of surface tension and solutocapillary force is improved. Using the established numerical model, the formation mechanism of the surface structure was explored from the aspects of surface tension, fluid flow, volume expansion, and surface profile evolution. The reason why the surface structure changes from a “W” shape to an “A” shape was explained, and the contributions of thermocapillary force, solutocapillary force, and volume expansion to the surface structure were investigated. The effects of laser power, scanning speed, and beam diameter on the surface profile of the surface structure were studied by experiments, which indicates that the desired surface structure can be obtained by adjusting the process parameters. All the experimental results were simulated by the established numerical model, and the simulation results are in good agreement with the experimental results, indicating that the numerical model is effective and available.
•A new surface structuring by laser remelting was proposed.•The function between main chemical elements and the surface tension was established.•A multiphysics coupled model for the surface structuring was established and verified.•The contributions of thermocapillary force, solutocapillary, and volume expansion was investigated.•The formation mechanism of the surface structure was revealed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High-entropy alloy coating has huge potential application values in improving the service life of the friction parts. The effects of the B-Si ratio and laser remelting on the microstructure, phases, ...mechanical and wear properties of the laser cladding Fe10Co10Ni10Cr4Mo6BxSi10-x coatings were investigated. When x equals 10, the coating crystalizes in a FCC structure together with lots of MxB phases. Si element adding promotes the formation of BCC phase of Fe10Co10Ni10Cr4Mo6BxSi10-x coatings with the appearance of new MxSi and MxBSiy phases, but prevents the formation of MxB and MxBSiy with the decrease of B-Si ratio. When x drops to zero, the microstructure of the coating transforms into a BCC with tiny amounts of FCC and MxSi phase. With the increase of Si element content, Mx(B, Si) standing for any combination of MxB, MxSi and MxBSiy phases decrease. The lowest friction coefficient (0.3786) and wear volume loss (2.46 × 106 μm3) show that Fe10Co10Ni10Cr4Mo6B5Si5 coating has the best wear resistance because of a higher toughness and values of H/E and H3/E2. Laser remelting once reduces the component segregation of the coating, and promotes the formation of BCC and Mx(B, Si) phases. The wear resistance of the coating increases with the improvement of its wear characteristics (H/E, H3/E2 and η). However, when the coating is remelted twice, the wear resistance decreases due to the drop of the hardness and wear characteristics attributed to the dominant position of FCC structure. Fine and uniform microstructure, and proper proportion of hard phases (BCC and Mx(B, Si)) and soft phase (FCC) can increase the mechanical properties and wear resistance of Fe10Co10Ni10Cr4Mo6BxSi10-x coatings.
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•The ratio of BSi affects the phase composition of the coating structure.•Laser remelting times can change the main phase of the coating structure.•The proportion of FCC, BCC, and Mx(B, Si) phases affect the hardness of coating.•The properties depend on the microstructure and proportion of the phases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
