查看更多>>摘要：The performance of three WC-based coatings prepared by high velocity oxygen-fuel (HVOF) has been evaluated under both pure mechanical wear and tribocorrosion in 3.5 wt% sodium chloride solution environment. The synergism of corrosion and wear is also calculated. The three coatings were WC cermets with Co, CoCr and Cr3C2-7Ni matrices. The experimental results indicated that the binder phases in the as-sprayed coatings greatly influenced their corrosion and wear performances. In the pure mechanical wear, the WC-12Co coating showed the best wear resistance followed by the WC-10Co4Cr and WC-Cr3C2-7Ni coatings. In tribocorrosion, all three coatings were under corrosion-dominated regime. The WC-12Co coating had the highest corrosion rate result from the selective preferential dissolution of Co phase. The wear process further accelerated the dissolution and removal of Co for the highest material loss rate of WC-12Co coating. The WC-10Co4Cr and WC-Cr3C2-7Ni coatings showed great corrosion resistance due to the CoCr and (W,Cr)(2)C phase, respectively. However, the (W, Cr)(2)C brittle phase was easily broken down mechanically which increased the material loss of WC-Cr3C2-7Ni coating. The formation of CoCr phase reduced the dissolution of the Co and was not easily destroyed under loading, making the WC-10Co4Cr coating have the best tribocorrosion resistance.
查看更多>>摘要：Achieving multifunctional coatings is generally difficult in single layers because the structural features required for each function are hard to consolidate. Here we report a magnetron sputtered 10-mu m-thick coating consisting of a single phase of supersaturated Cr(C) solid solution (~11 at.% C). It is characteristic of a smooth surface, a high compactness, and a fibrous growth structure. The coating displays a combination of high optical reflectance, high hardness, and excellent protection for Zr alloys to high-temperature steam oxidation resistance at 1473 K. These findings open new perspectives for injecting new functions into magnetron sputtered single-layer coatings.
查看更多>>摘要：This study is an effort to investigate the synergic effect of nano-diamond (ND) addition and plasma nitriding (PN) treatment on tribological and structural properties of nickel-boron (NiB) coatings. NiB/ND nanocomposites containing different amounts of NDs (0.0, 0.1, 0.5, and 1.0 g/L) were produced in an electroless bath. Then, plasma nitriding was conducted on the samples for 1 h at 400 ?degrees C in an N-2-H-2 environment. To study phase analysis and examine the surface morphology of the samples, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were utilized. The wear behavior and friction were determined under the normal load of 10 N using the pin-on-disk method. The surface roughness, microstructure, and microhardness were also assessed. The results showed that, as the ND concentration increased, the amorphous structure of as-plated (AP) Ni-B transformed to a semi-crystalline one. Moreover, the amorphous structure of the as-deposited NiB/ND coatings changed to a crystalline one after plasma nitriding, which resulted in a higher hardness value. NiB/0.5ND coating showed the highest hardness value (1523 HV0.1) and the highest wear resistance (0.8x10(-10) Kg/ N.m). The smoothest wear trace with no visible cracks is related to the worn surface of PN NiB/0.5ND sample, suggesting that the NiB/ND nanocomposite can be a promising candidate for surface engineering processes.
查看更多>>摘要：The efficiency of ultra-thin corrosion protection coatings for susceptible to local corrosion AA2024-T3 is demonstrated. For this purpose, with atomic layer deposition (ALD) 50 nm thick TiO2, Al2O3, an Al2O3-TiO2 mixture and Al2O3/TiO2 nanolaminate coatings are grown on AA2024-T3 substrates, receiving different pre treatments prior to ALD coating. One pretreatment involves polishing and cleaning with organic solvents, and the second utilizes an additional low-potential electrochemical treatment in sulfuric acid. The samples are characterized with scanning electron microscopy, scanning transmission electron microscopy, wavelength-dispersive X-ray fluorescence spectroscopy, X-ray diffraction and reflection, and nanoindentation and are tested using linear sweep voltammetry, electrochemical impedance spectroscopy, and immersion in a salt solution. The study shows that ultrathin metal oxide coatings applied via ALD can significantly enhance the corrosion resistance of Al alloys, and the performance depends on the pretreatment of the alloy, as well as on the material/structure of the coating. The best ultrathin coating with less than 100 nm thickness withstood well 1000 h immersion test.
Kuznetsov, G. V.Sivkov, A. A.Ivashutenko, A. S.Nikitin, D. S....
15页
查看更多>>摘要：Controlling the surface wetting of silicon carbide (SiC) ceramics is an urgent problem as its solution will significantly expand the scope of this material. In this work, the submicron SiC ceramics was obtained from the ultradispersed SiC powder fabricated by the plasma dynamic synthesis method. The bulk SiC samples were produced by spark plasma sintering at 1600 degrees C, 1700 degrees C, and 1800 degrees C. The effect of sintering temperature and promising methods of surface modification on wetting, elemental composition and surface roughness of SiC ceramics was studied. The surface modification methods included polishing, laser texturing, low-temperature annealing, magnetron chromium sputtering, and their combination. To predict the type of a texture formed after nanosecond laser radiation, the graphic-analytical method was developed. The best hydrophilic properties of SiC ceramics (the contact angle decreased to 9.3 degrees) were obtained after polishing with subsequent nanosecond laser texturing. The best hydrophobic properties of SiC ceramics (the contact angle increased to 135.3 degrees) were obtained after a combination of polishing, laser texturing, and magnetron chromium sputtering. Controlling the surface wetting of SiC ceramics from hydrophilic to hydrophobic makes it possible to significantly expand the scope of this material, for example, to use it in drop cooling systems of advanced digital devices that emit ultrahigh heat fluxes up to 1000 W/cm(2).
查看更多>>摘要：The following study shows the comparative analysis of the electrochemical properties [beta-TCP/HA]n as a function of the bilayers number (n = 1, 10, 30 and 50), which have been currently implemented on biomedical devices and which do not have detailed studies when these coatings are exposed to a solution that simulates body fluids (Hanks solution). These results determined that by increasing the number of bilayers or interfaces (n = 50 bilayers), the roughness decreased by 46.1% compared to the coating with less bilayers number (n = 1 bilayer). Subsequently, the electrochemical analysis showed an increase of 88.45% in the polarization resistance of the coating with 50 bilayers compared to the coating with 1 bilayer, followed by the comparison of the corrosion rate, which determined a decrease of 95.16% compared to the coating with 50 bilayers with 1 bilayer. Finally, the results obtained evidenced that the [beta-TCP/HA]n coating with n = 50 bilayers presented the best set of properties, demonstrating that this coating is a suitable candidate for use as a protective coating for biocompatible devices.
查看更多>>摘要：Nano-sized copper(II) oxide (CuO) is an interesting material with proficient antibacterial activities but limited due to its toxicity to mammalian cells. In this study, CuO nano-sized needles were coated on the surface of nano silicate platelets (NSP), which were exfoliated from natural montmorillonite clays and with the thickness of about 1 nm, to form nanohybrids. Our findings indicate that NSPs can effectively prevent the aggregation of CuO needles, and significantly enhance antibacterial efficiency without affecting biocompatibility. An optimal antibacterial activity against Staphylococcus aureus exceeding 99% could be obtained, while that for Escherichia coli was about 88%. Electron paramagnetic resonance results suggest that center dot OH radicals, one of the reactive oxygen species generated by CuO/NSP, might damage the cellular components and thus result in the death of bacterial.
查看更多>>摘要：For a coating and substrate system, the ability to jointly resist external force damage determines the tool-life. To enhance such a mutual synergy, one-dimensional ultrafine platelet-grained WC-10Co-0.4TiC-0.6Cr(3)C(2) alloy (PG alloy) was designed and prepared, based on Ti-induced enlargement of the interfacial energy difference. Submicron-grained WC-10Co-0.6Cr(3)C(2) alloy was used as the reference. On the two kinds of substrates, nanomultilayered Al0.55Ti0.45N/TiN coating was deposited. The results show that compared with the reference, PG alloy with a texture coefficient T-CWC(0001) of 3.27 and free of apparent micro-pore defect within the WC grains is characterized by higher hardness (1632 vs. 1567HV30), higher toughness (14.7 vs. 13.4 MPa.m(0.5)), high strength (3737 vs. 4434 MPa), and stronger dislocation-forming ability. By using PG alloy as the substrate, high film adhesion strength (> 100 N) is achieved, and readily formed coherent and semi-coherent interfaces between TiN (film) and WC are revealed by high-resolution transmission electron microscopy observation. As a result of interface strengthening and excellent combination of the substrate and the coating couple, compared with the reference tool, 1.4-1.5 times higher average tool-life under a wet or dry milling condition of 316L stainless steel is achieved.
查看更多>>摘要：Laser modification assisted metallization technology (LAM) is a two-step method to fabricate metallic patterns on ceramic substrates by using laser selective activation and the subsequent electroless plating, which has received widespread attentions in recent years. In this paper, a picosecond laser (ps ~ laser) was first selected as the energy source for LAM to modify the alumina substrates coated with PdCl2 films, the adhesion strength, fracture mechanism and deposition resolution of the subsequent electroless-plated Cu coating, as well as the laser-alumina interaction mechanisms were studied systematically and compared with those obtained by nano -second laser assisted metallization technology (ns ~& nbsp;LAM). The results indicated that the textures with higher surface area and no thermal cracks were fabricated on the ceramic surface treated by ps & nbsp;~ laser, making the adhesion strength of the Cu coating enhanced to as high as 51.1 MPa, in which a mixed failure mode was obtained. Moreover, the minimum width of Cu line fabricated by ps ~ LAM was only about 29 mu m, which was much lower than the 47-53 mu m that obtained by ns & nbsp;~ LAM, and even comparable to the laser spot diameter. Therefore, the ultrafast-laser based LAM technology shows potential in enhancing the performance of circuits on ceramic boards.
查看更多>>摘要：The multilayer ZrC/TaC ablation resistant coatings with different layers were designed and fabricated on the SiC coated carbon/carbon composites by plasma spraying. Based on stress distribution and ablation performance under heat flux of 2.4 MW/m(2), structural parameters of the multilayer ZrC/TaC coatings (total thickness d, number of layers n and thickness ratio R) were discussed and optimized. When R was equal to 1 and d was -300 mu m, the multilayer ZrC/TaC coating with three layers (n = 3) exhibited moderate stress distribution and the best ablation resistance, induced by the ZrC anti-scouring layer with sufficient thickness and effective crack deflection at the interface. The optimized structural parameters for multilayer ZrC/TaC system are considered as follows: (i) the larger d value was beneficial to reducing the residual thermal stress during ablation process; (ii) d/n for the ZrC layer was between 100-150 mu m, while d/n for the TaC layer was between 40-100 mu m.
NSTL
Elsevier