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•Equimolar CrMnFeCoNi high entropy alloy coating are prepared by laser cladding.•The cladding layer forms a simple FCC phase solid solution with identical dendritic structure.•The ...cladding layer exhibits a noble corrosion resistance in both 3.5wt.% NaCl and 0.5M sulfuric acid.•Element segregation makes Cr-depleted interdendrites the starting point of corrosion reaction.
Equimolar CrMnFeCoNi high entropy alloy (HEA) is one of the most notable single phase multi-component alloys up-to-date with promising mechanical properties at cryogenic temperatures. However, the study on the corrosion behavior of CrMnFeCoNi HEA coating has still been lacking. In this paper, HEA coating with a nominal composition of CrMnFeCoNi is fabricated by laser surface alloying and studied in detail. Microstructure and chemical composition are determined by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are used to investigate the corrosion behavior. The coating forms a simple FCC phase with an identical dendritic structure composed of Fe/Co/Ni-rich dendrites and Mn/Ni-rich interdendrites. Both in 3.5wt.% NaCl solution and 0.5M sulfuric acid the coating exhibits nobler corrosion resistance than A36 steel substrate and even lower icorr than 304 stainless steel (304SS). EIS plots coupled with fitted parameters reveal that a spontaneous protective film is formed and developed during immersion in 0.5M sulfuric acid. The fitted Rt value reaches its maximum at 24h during a 48h’ immersion test, indicating the passive film starts to break down after that. EDS analysis conducted on a corroded surface immersed in 0.5M H2SO4 reveals that corrosion starts from Cr-depleted interdendrites.
Studies have confirmed the regulatory effects of microRNAs (miRNAs) in osteoarthritis (OA) progression. MiR-4287 has been identified by a previous study as a downregulated miRNA in chondrocytes ...treated with IL-1β and TNF-α. However, the function of the underlying mechanism of miR-4287 in OA is elusive. IL-1β-treated chondrocytes were used as OA cell models. RNA expression was accessed using RT-qPCR. Cell Counting Kit-8 (CCK-8) assay was used to determine the chondrocytes' viability and proliferation. The protein levels of inflammation factors (IL-8, IL-6, and TNF-α), matrix metalloproteinases (MMP 1, MMP3, MMP13), and chondrogenic genes (COL2A1, SOX9, and Aggrecan) were detected using western blot analysis. Luciferase reporter assays were performed for interaction exploration. HE staining and Safranin O/Fast Green staining was used to access the pathological changes in OA mouse tissues and cartilage degeneration in OA mouse. MiR-4287 was downregulated in chondrocytes treated with IL-1β and OA mouse models. MiR-4287 overexpression promoted the viability, and proliferation and attenuated the inflammation response and destruction of cartilage in IL-1β-stimulated chondrocytes. Receptor-interacting protein kinase 1 (RIPK1) was a target gene of miR-4287 in chondrocytes. MiR-4287 negatively regulated RIPK1 expression. RIPK1 overexpression was revealed to reverse the miR-4287-mediated effects on proliferation and inflammatory response in IL-1β-stimulated chondrocytes. Moreover, miR-4287 was demonstrated to inhibit the pathological changes, cartilage degeneration and inflammation response in OA mice models. In conclusion, miR-4287 is a critical molecule in OA development, which attenuates inflammatory response in vivo and in vitro by targeting RIPK1.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Plasma arc additive manufacturing (PAM) is a novel additive manufacturing (AM) technology due to its big potential in improving efficiency, convenience and being cost-savings compared to other AM ...processes of high energy bea\m. In this research, several Ti-6Al-4V thin walls were deposited by optimized weld wire-feed continuous PAM process (CPAM), in which the heat input was gradually decreased layer by layer. The deposited thin wall consisted of various morphologies, which includes epitaxial growth of prior β grains, horizontal layer bands, martensite and basket weave microstructure, that depends on the heat input, multiple thermal cycles and gradual cooling rate in the deposition process. By gradually reducing heat input of each bead and using continuous current in the PAM process, the average yield strength (YS), ultimate tensile strength (UTS) and elongation reach about 877MPa, 968MPa and 1.5%, respectively, which exceed the standard level of forging. The mechanical property was strengthened and toughened due to weakening the aspect ratio of prior β grains and separating nano-dispersoids among α lamellar. Furthermore, this research demonstrates that the CPAM process has a potential to manufacture or remanufacture in AM components of metallic biomaterials without post-processing heat treatment.
Deposited Ti-6Al-4V wall by optimized weld wire-feed continuous plasma arc additive manufacturing process (CPAM) consisted of various morphologies with different microstructure. The evolution of microstructures, including prior β grains, horizontal layer bands, martensite and basket weave microstructure, relate to gradually decrease heat input of layer by layer and multiple thermal cycles. The microstructure of α lamellar with nano-dispersoids significantly improve the mechanical properties without post-processing heat treatments, moreover, the mechanical properties exceed the standard level of forging. Display omitted
•Aspect ratio of prior β grains are affected by gradually reducing heat input.•Horizontal layer bands results from the influence of multiple thermal cycles.•α lamellar with nano-dispersoids significantly improves mechanical properties.•Different <11–20> poles forming three dominating orientations.
Thick-section steel has been widely used in many heavy industries. Traditionally, very thick steel plates could be welded by using submerged arc welding and other welding processes. However, there ...were more or less drawbacks in these welding methods. Laser welding, a high-energy density welding method, is being considered for such structures to improve the production efficiency and reduce the residual stresses of the joints. In this study, butt joints with narrow gap were welded using a high-power CO
2
laser. The effect of welding parameters including the relative position between the laser beam and the filler wire, welding speed, and the distance from the intersection of the beam and wire to root of the groove on the weld bead geometry and welding defects was studied. Additionally, high-speed photography was introduced in the experiment as an efficient method to record the total process of welding, especially the transfer of molten drop. The study found that when the beam was focused on the center of the groove, the filler wire could be melted successfully even though it would tremble slightly during welding process. The optimized distance from the intersection of the beam and wire to groove root was 3 mm. Later, butt weld joints of 70-mm-thick steel plate without lack of fusion can be obtained under optimized welding parameters.
Osteoarthritis (OA) is a degenerative disease characterized by synovial inflammation. MiR-18a-3p was reported to be downregulated in knee anterior cruciate ligament of OA patients. In the present ...study, the specific functions and mechanism of miR-18a-3p in OA were explored. An in vitro model of OA was established using 10 ng/ml IL-1β to treat ATDC5 cells, and medial meniscus instability surgery was performed on Wistar rats to establish in vivo rat model of OA. RT-qPCR revealed that miR-18a-3p was downregulated in IL-1β-stimulated ATDC5 cells. MiR-18a-3p overexpression inhibited secretion of inflammatory cytokines and concentration of matrix metalloproteinases, as shown by ELISA and western blotting. The binding relation between miR-18a-3p and pyruvate dehydrogenase phosphatase catalytic subunit 1 (PDP1) was detected by luciferase reporter assays. MiR-18a-3p targeted PDP1 and negatively regulated PDP1 expression. Results of rescue assays revealed that PDP1 upregulation reserved the suppressive effect of miR-18a-3p overexpression on levels of inflammatory cytokines and matrix metalloproteinases in IL-1β-stimulated ATDC5 cells. H&E staining was used to observe pathological changes of synovial tissues in the knee joint of Wistar rats. Safranin O-fast green/hematoxylin was used to stain cartilage samples of knee joints. MiR-18a-3p overexpression suppressed OA progression in vivo. Overall, miR-18a-3p improves cartilage matrix remodeling and suppresses inflammation in OA by targeting PDP1.
An IN718 alloy coating was prepared by high-power diode laser cladding. 980STA standard heat treatment and direct aging (DA) were employed to improve the properties of this coating. The niobium ...segregation in the as-deposited coating and the heat-treated coating had been investigated using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDAX). The results showed that 980STA standard heat treatment improved the microhardness of the coating significantly, and Laves concentration was reduced from 30.6 vol pct to about 11.4 vol pct after 980STA. The niobium concentration in Laves of the 980STA-treated coating was higher than that of DA-treated coating and as-deposited coating. Only a small portion of niobium in the coating was precipitated in the form of
γ
″ during the 980STA heat treatment. The rest of niobium was the alloying element for solid-solution strengthening and the constituent element of Laves. The niobium segregation facilitated the formation of Laves.
The rapid cooling rate was achieved during laser remelting with high scanning speed. The microstructure and precipitations in the INCONEL 718 remelted layer were investigated by scanning electron ...microscope (SEM), transmission electron microscope (TEM), and solid phase microextraction (SPME). The phase transition temperatures were carried out by differential thermal analysis (DTA). The results showed that columnar-dendritic and equiaxial structures appeared in different regions of the remelted layer. The dendritic spacing of the columnar dendrite and equiaxed grain size decreased with increasing scanning speed. The precipitations in the remelted layer consisted of Laves, granular phase, and a small quantity of quadrangular nitride (Ti, Nb)N. The granular phase Nb(Al, Ti) was precipitated at about 1272 K (999 °C) with the spontaneous decomposition of the supersaturation Laves during the cooling stage, and the small-size granule became coarsened to 0.2 to 0.9
μ
m during the cooling stage. The noncoherent relationship existed between the granular phase and austenite, and the coarsening of granule was related to the cube root of the diffusion coefficient, interfacial energy, and diffusion time. The microhardness of the remelted layer was increased by increasing the cooling rate due to the Nb atomic solid solution strengthening caused by the distorted elastic stress field and the short-range internal stress.
•We investigate the effect of natural attapulgite powders as lubrication additive on the friction and wear performance of a steel tribo-pair.•Attapulgite powders can remarkably decrease the friction ...coefficient and wear rate of carbon steel friction couples.•A tribofilm composed of iron oxides and silicon oxides has formed on the worn surface under the lubrication of oil containing attapulgite powders.•We reveal the friction-reducing and anti-wear mechanism from the standpoint of tribochemistry, mineralogy and materials science.
Tribological properties of the surface-modified attapulgite powders as additive to lubricating oil for mated steel contact were investigated. The results indicated that the attapulgite powders exhibit good performance in reducing wear and friction coefficient. Such effect can be attributed to the formation of a smooth and compact tribo-film composed of multiple oxides on the worn surface.
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