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• Generation of hard phases and grain refinement in enhanced bionic units. • Bionic unit samples have good hard-soft alternating bionic structure. • Quantitative relation between distribution spacing and wear resistance is obtained. • Hard-soft bionic structure improves wear resistance by altering the wear pattern. • Adjusting the distribution spacing has a more positive effect on wear resistance. In this study, the biomimetic unit samples (BUSs) of hard-soft structure with different distribution spacings were successfully prepared by laser quenching biomimetic processing technique (LQBPT). Firstly, the microstructure, microhardness, tribological properties and wear surfaces were investigated. The BUSs had randomly oriented martensite and M 7 C 3 , and the grains were refined, resulting in favorable hard-soft structures. Compared to the untreated samples, the BUS at distribution spacing of 3 mm had excellent wear resistance. Its average friction coefficient and weight loss were reduced by 17.95 % and 40.0 %, respectively. Then, it was investigated the quantitative relationship between the distribution spacing and the wear resistance and its wear resistance mechanism. This improved wear resistance was attributed to hard-soft biomimetic structure. [ABSTRACT FROM AUTHOR]

To strengthen face-centered cubic structured high entropy alloys, this paper explores a new method of ceramic reinforced CoCrFeNiMo 0.2 high entropy alloy composite gradient coating. In this study, four sets of gradients were created by first preparing a pristine alloy coating without silicon carbide content on the substrate, followed by preparing composite coatings with varying silicon carbide mass fractions (8 %, 16 %, 24 %) on the pristine coatings. The coatings were then analyzed for their phase composition, microstructure, microstructure evolution process, and friction wear properties. The study reveals that the microstructure of the initial alloy coating consists of a single-phase face-centered cubic solid solution. It is observed that intragranular segregation occurs in the coating, resulting in the boundary enrichment of Mo and Cr elements. As the silicon carbide addition increases, the segregation behavior becomes more pronounced, and the generation of body-centered cubic phase is observed. The second, third, and fourth layers exhibit significantly higher average hardness, measuring at 594 HV, 722 HV, and 788 HV respectively. This can be attributed to the presence of body-centered cubic structure, carbide, and grain boundary strengthening effects. On average, the hardness of these layers is three to four times higher than that of the first layer. With an increase in the number of layers, the wear mechanism changes from adhesive wear to abrasive wear. The wear rates of the second, third, and fourth layers were all reduced by at least 87 % compared to the first layer. However, there were different forms of abrasive wear observed between these layers. The findings of this study have significant engineering implications. • The microstructural evolution of columnar grains to equiaxed dendrites was studied. • The high-density of dislocations enhances the diffusion of Mo and Cr elements. • The tissue shows phase separation act containing the BCC structure. • The shift behavior of the wear mechanism of the gradient structure was studied. [ABSTRACT FROM AUTHOR]

The AlCoCrFeNi high-entropy alloy coatings were prepared by laser cladding (LC) and reprocessed by laser remelting (LR). Laser remelting caused cracks on the coating surface, but the cracks of boronized laser remelting (LR-B) coating were significantly suppressed. Compared to the LR coating, the microhardness of the LR-B coating increased from 643 HV to 1008 HV, the friction coefficient decreased from 0.55 to 0.45, and the self-corrosion potential increased by 134 mV. The crack elimination contributed to the transition of 25% of the BCC phase to the FCC phase. The property enhancement was mainly due to the fine grain strengthening, dislocation strengthening, and Cr 2 B reinforced particles as reinforced phase. [Display omitted] • A trace amount of boron was doped in the protective gas during laser remelting. • The cracks of the boronized laser remelting (LR-B) coating were significantly suppressed. • With the addition of boron, the FCC phase and Cr 2 B were formed. • The Cr 2 B second-phase strengthening increased microhardness and wear resistance. • The Cr 2 B particles in the LR-B coating resulted in excellent corrosion resistance. To avoid cracking of the AlCoCrFeNi high-entropy alloy (HEA) coating during laser remelting (LR), a trace amount of boron (B) was doped in the protective gas. Compared to the LR coating, the cracks of the boronized laser remelting (LR-B) coating were significantly suppressed, the microhardness increased from 643 HV to 1008 HV, the friction coefficient decreased from 0.55 to 0.45, and the self-corrosion potential increased by 134 mV. The crack elimination mainly contributed to the transition of 25 % of the BCC phase to the FCC phase, and the property enhancement was due to the fine grain strengthening, dislocation strengthening, and Cr 2 B reinforced particles generation. This novel finding can be applied to other BCC structure HEA coatings for macroscopic crack control and optimization of wear and corrosion resistances. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]