Search

This article presents the results of a study on composite coatings based on high-entropy FeCoNiCrCuNb alloys with varying niobium content obtained through high-speed laser cladding. The primary objective of the research is to investigate the influence of composition on the structure, mechanical characteristics, and behaviour of the coatings. Microstructure analyses were performed using scanning electron microscopy and energy-dispersive spectroscopy analysis. The microhardness, shear strength, and coefficient of friction of the composite coatings were examined. It was demonstrated that the microstructure of the coatings is characterized by fine grains and the presence of columnar crystals. An increase in copper content leads to a transition to the face-centred cubic phase with elevated niobium content, influencing the mechanical characteristics. It was revealed that niobium-containing composite coatings exhibit improved mechanical properties and wear resistance. The incorporation of niobium synergistically affects the mechanical characteristics of the alloys. The obtained results hold practical applicability in the field of engineering, particularly where wear resistance and strength are of paramount importance.

The aluminum alloy performance gradient plate was prepared by friction stir joining. Analysis results of the macro morphology, microstructure, and hardness of the aluminum alloy performance gradient plate prepared under various parameters show that when the feed speed of the stirring tool is 250 mm/min, the downward pressure of the stirring tool is 6.6 mm, and the rotation speed of the stirring tool changes from 200 rpm to 800 rpm. The macroscopic morphology of the aluminum alloy gradient plates prepared by the method first changed from burr to smooth, and vice versa. There is a different cross-section morphology of the prepared aluminum alloy gradient plates, however, the aluminum alloy plates are stirred and involved with each other, and the grains of the prepared plates are refined. The hardness of the upper and lower surfaces of the aluminum alloy gradient sheet decreases, whereas that of the upper surface of the side increases, and that of the middle and bottom sides also decreases. However, the hardness of the middle side of the sheet prepared with the rotation speed of the stirring tool at 800 rpm increases, but that of the bottom side still decreases. Obtained through analysis that the performance of the aluminum alloy gradient sheet prepared at the stirring tool rotation speed of 500 rpm increases in equal proportion to achieve a good performance gradient change.

This study investigates the preparation of a high-performance Cr3C2/Ni60A coating on 45# steel through laser cladding technology. The microstructure, residual stress, phase composition, hardness, and wear resistance of the coating are analyzed. The results reveal that the solidification structure of the molten pool exhibits a progression from coarse columnar crystals and dendrites near the interface with the substrate to equiaxial crystals at the coating surface. The coating primarily consists of Fe-Ni solid solution, Cr7C3, and Cr23C6 phases. As the Cr3C2 mass percentage in the Cr3C2/Ni60A composite powder increases, the formation of the Cr7C3 and Cr23C6 phases is suppressed. A pronounced stress concentration occurs at the interface between the coating and the substrate, leading to an increased dislocation density and localized grain deformation. When the Cr3C2 mass percentage reaches 45% and 55%, the coating surface exhibits a higher density of induced cracks due to the combined effects of microstructural changes and thermal influences. The maximum microhardness of the coating ranges from 520 HV1 to 556 HV1, approximately three times that of the substrate. The wear resistance of the coating initially increases and then decreases with increasing Cr3C2 content. The wear resistance is optimal at a 35% Cr3C2 mass ratio, with a wear loss of 0.15 mg—five times lower than that of the substrate. The primary wear mechanism is abrasive wear, although localized fatigue and adhesive wear are also observed. [ABSTRACT FROM AUTHOR]

Aluminum-based composite layers with different TiB2 contents were prepared by implanting TiB2 reinforcement powders with mass fractions of 1%, 3%, 5%, and 7% into 7075 aluminum alloy sheets using Friction Stir Processing (FSP) technique. The influence of TiB2 content on the friction and wear performance of the modified aluminum-based composite layers was investigated. The results showed that the incorporation of TiB2 reinforcement powders can reduce the friction coefficient and wear volume of the materials, thereby improving the friction and wear performance. Moreover, as the mass fraction of TiB2 reinforcement powder increases, the overall friction coefficient and wear volume of the composite materials exhibit a gradual decrease trend, with adhesive wear being the predominant wear mechanism. [ABSTRACT FROM AUTHOR]

Welding of 10 mm thick AZ31B magnesium alloy by stir friction welding technique. The effects of process parameters on the microstructure, tensile strength and impact resistance of the joints were analyzed. The results showed that the joints were formed with good quality and no obvious defects, and the joints were fine-grained and accompanied by grain dislocations. The grain dislocation in the hot machine influence zone is more obvious there is a dense grain dislocation zone, and the distribution is not uniform. When the spindle speed is 800 and 1000 rpm, respectively, the best impact resistance of the welded joint impact work is 8.02 J, which is about 94.2% of the impact resistance of AZ31B magnesium alloy base material. When the spindle speed is 1000r/min and the welding speed is 150 mm/min, the tensile strength of the welded joint is the largest, reaching 85.8% of the base material and the post-break elongation is 1.9 times that of the base material. Thick plate magnesium alloy plate welded joints overall performance is not uniform, welded plate bottom mechanical properties of the worst, weld core area doped magnesium alloy oxide, joint tensile fracture crack source from the bottom of the plate to the weld surface expansion. [ABSTRACT FROM AUTHOR]

The 10 mm thick 7075-T6 aluminum alloy plate is welded by friction stir welding with the inclination of the main shaft of 0.5°. There is no obvious thinning on the weld surface, and the welded joint is well formed. The microstructure of the joint as a whole is "funnel" shaped, and there are multi gradient flat "onion rings". The grains in the weld nugget zone are equiaxed and the grains are significantly refined, and the grains in the heat-mechanical affected zone appear mixed crystal phenomenon and have obvious deformation. During the welding process, the hardness of the welded joint is reduced due to high temperature annealing. When the spindle speed is 500 rpm and the welding speed is 120 mm/min, the maximum surface hardness of the welded joint is 178.77HV. Compared with the base metal after annealing, the hardness of the weld nugget area is increased by about 25% due to the grain refinement strengthening and the precipitation of the reinforcing phase. The wear resistance of welded joints is inversely proportional to the hardness. When the spindle speed is 300 rpm and the feed speed is 120 mm/min, the wear resistance is the best. The friction type is mainly adhesive wear, supplemented by particle wear and fatigue wear. [ABSTRACT FROM AUTHOR]

We report the mitogenomes of the pouched lamprey (Geotria australis) and least brook lamprey (Lampetra aepyptera) in the families Geotriidae and Petromyzontidae, respectively. Both of the mitogenomes contain the 37 typical vertebrate genes. Their gene order and contents are identical to those of previously described lamprey mitogenomes. The mitogenome ofG. australis(17 080 bp) is the largest among the 10 reported lamprey mitogenomes, owed to two long noncoding regions. The mitogenome ofL. aepypterais 77 bp longer (16 236 bp) than that of the congeneric European river lampreyL. fluviatilis, a size difference mostly due to different copy numbers of tandem repeats in the noncoding regions. The phylogenetic analysis supports that the pouched lamprey (Geotriidae) diverged earlier from the common ancestor of lampreys than the Petromyzonids, and the placement of the least brook lamprey in the genusLampetra. [ABSTRACT FROM AUTHOR]

The complete mitogenomes of two lampreys with complex taxonomic histories, the Korean lamprey (Lethenteron morii) and the American brook lamprey (L. appendix) were determined. Three-nt length difference between two genomes occurred ontRNA-Ser2and control region 2. Except for 3 indel sites, there are 58 variable sites between two genomes which occurred on 11 of the 13 protein-coding genes (aside fromCOX3andND3) and 2 ofrRNAs, tRNAs, control regions and intergenic regions. Among these sites, 15 sites are non-synonymous substitution sites occurred on 8 protein-coding genes includingCOX1-COX2, ND1-ND2, ND4-ND6andATPase6. Control region 1 contains 4 consecutive 39-nt repetitive strings and a 26-nt repetitive string in control region 2 is repeated 3.8 times in both lampreys. The observed level of similarity between nucleotide sequences (99.62%) implies the Korean lamprey and American brook lamprey are very close relatives and should be assigned into the same taxonomic genus. [ABSTRACT FROM PUBLISHER]

The complete mitogenomes of paired species northern brook lamprey (Ichthyomyzon fossor) and silver lamprey (I. unicuspis) is reported. The two mitogenomes show a 13 bp length difference on thetRNA-Glyand two control regions. The gene order and contents are conserved in the two lampreys and identical to the lamprey mitogenomes published. Except for three indel polymorphic sites, there are 27 SNP sites which are all synonymous substitution sites and occurred on 9 protein-coding genes, tworRNAsand onetRNA. The control region1 contains six consecutive 39-nt repetitive strings in both lampreys. A 7-nt repetitive string in the control region2 is repeated 3 and 5 times in northern brook lamprey and silver lamprey, respectively. The observed level of similarity between nucleotide sequences (99.74%) is consistent with the hypothesis that northern brook lamprey and silver lamprey represent two ecotypes of one species. [ABSTRACT FROM PUBLISHER]