查看更多>>摘要：To improve the high-temperature oxidation resistance, Al2O3-Nb2O5/NbAl3 composite coating with or without TiO2 particles was prepared on Nb-based alloy through a two-step method of halide activated pack cementation (HAPC) and micro arc oxidation (MAO). NbAl3 layer was firstly formed on the substrate by HAPC treatment. Then, TiO2 was introduced into the Al2O3-Nb2O5 coating on NbAl3 by hydrolysis reaction of K2TiF6 during MAO process. In this paper, the effect of TiO2 on the morphology and formation of the MAO coating was studied. Furthermore, the oxidation resistances of the TiO2-Al2O3-Nb2O5/NbAl3 and Al2O3-Nb2O5/NbAl3 composite coated Nb alloy were investigated. The results showed that the addition of K2TiF6 could promote the growth of MAO coating and increase the density. After oxidation at 1200 degrees C for 100 h, a dense protective oxides scale was found on the TiO2-Al2O3-Nb2O5/NbAl3 coating sample, and the weight gain was only 4.75 mg/cm(2), which was significantly lower than the coated sample without TiO2. The mechanism of oxidation resistance enhancement of coating with TiO2 should be ascribed to the formation of a dense TiO2 + Al2O3 scale, which could effectually prevent the diffusion of O and suppress the formation of Nb2O5.
查看更多>>摘要：Surface-modified Zr alloys by protective coatings are being developed as the most viable near-term accident tolerant fuel (ATF) claddings. Herein, an amorphous FeCrAlMoSiY coating was deposited on Zr alloys by magnetron sputtering. The key performance of specimens in terms of ion irradiation, autoclave corrosion, and high-temperature steam oxidation were studied using X-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). We found that the surface of the irradiated coating became more compact with a lower surface roughness than the as-deposited coating. Meanwhile, the hardness and indentation modulus decreased slightly after irradiation. After 30 days autoclave corrosion, a continuous spinel FeCr2O4 scale was formed on the surface, and the residual coating had the same composition and similar to 76% in thickness of that of the as-deposited coating. During the 1200 ?degrees C steam oxidation of that corroded sample, the protective alpha-Al2O3 scale was formed underneath the FeCr2O4 layer, along with the formation of a diffusion barrier at the coating-substrate interface. These findings highlight the potential of the FeCrAlMoSiY coating considered as a protective coating for ATF claddings.
查看更多>>摘要：The effect and mechanism of ultrasonic vibration on the microstructure and performance of laser cladding 316L coating has been studied, providing a theoretical basis and technical support for the application of the ultrasonic assisted laser cladding process. The results show that ultrasonic vibrations with different amplitudes can effectively improve the macroscopic forming quality of the cladding layer, among which the ultrasonic vibration with 17.5 mu m amplitude is the best. Ultrasonic vibration can also significantly improve the micro-forming quality of the cladding layer, such as homogenizing the structure, refining grains and reducing porosity. The wear mechanism of the cladding layer with an ultrasonic assistance of 17.5 mu m is mainly abrasive wear, so the wear resistance has been significantly improved. The ultrasonic-assisted cladding layer exhibits significant passivation behavior in 3.5 wt% NaCl solution. It may be that the surface roughness reduction and grain refinement caused by ultrasonic assistance can improve the integrity and compactness of the cladding layer, so the dynamic equilibrium process of the dissolution and reformation of the passive film is changed, which can improve the corrosion resistance of the surface. There are some equiaxed grains in the columnar-grains area of the ultrasonic assisted cladding layer, mainly because the inside of some primary columnar grains has gone through a process of lattice distortion -> dislocation multiplication -> substructure rotation -> formation of small-angle grain boundary -> misorientation accumulation -> formation of new grains in the process of ultrasonic-assisted laser cladding of 316L stainless steel.
Chen, XiTiamiyu, Ahmed A.Schuh, Christopher A.LeBeau, James M....
7页
查看更多>>摘要：Successful cold spray processing requires the formation of metallurgical bonds at the interface between particle impact sites and the substrate. While surface contamination on either the particle or substrate can interfere with metallurgical bonding, the details of particle/substrate interface chemistry are usually obscured or lost during the nanoseconds-long particle impact process. To provide a direct, detailed account of particle-substrate interfacial chemistry, we perform post-mortem scanning transmission electron microscopy and spectroscopy of impact sites of single copper microparticles, launched with a laser-induced particle impact tester, on a copper substrate. In addition to native oxides, we find that amorphous carbon and spherical copper oxide dispersoids are also present near/at the interface. Further, these features are found to influence metallurgical bonding. These results offer additional considerations for optimizing the quality of the cold spray deposition process.
查看更多>>摘要：Titanium matrix fiber-reinforced plastic composites had attracted increasing interest in marine and other fields because of their excellent mechanical and corrosion resistance. However, the interfacial bonding strength between the titanium matrix and the plastic is an important factor limiting its wide application. In this paper, the surface of titanium alloy TC4 (Ti-6Al-4V) was anodized to form an oxide layer with a 1-2 mu m crack structure on the surface of titanium alloy. Then the titanium alloy was combined with plastic polyphenylene sulfide (PPS) by direct injection molding. The results show that different oxide layer structures on the surface of titanium alloy, which can be obtained by different anodizing times and anodizing temperatures, can obtain TC4-PPS composites with different bond strengths. The maximum bond strength of TC4-PPS composites was 16.8 MPa when the anodizing temperature was 90 degrees C and the oxidation time was 30 min. We also discussed the effect of titanium alloy oxide layer surface morphology, wettability, roughness, composition, failure mode, and glass fiber on the bonding strength, which is important for expanding the application of titanium alloy and plastic composite.
查看更多>>摘要：In this study, combinatorial magnetron sputtering was used to deposit Nb-B-C coatings in a wide composition range. The phase formation, thermal stability and mechanical properties of these coatings were investigated in relation to their composition and deposition conditions. The studied coatings were amorphous, short range ordered or exhibited crystalline phases such as Nb, NbC and NbB2. Higher energy flux to the coating achieved by the use of bias and heating during deposition resulted in coatings being crystalline over a wider composition range. Annealing of the coatings after deposition resulted in a higher degree of crystallinity as well as an increase in hardness and effective elastic modulus. The hardness of the coatings was up to 22.5 +/- 0.7 GPa before and up to 35.0 +/- 0.6 GPa after annealing. The effective elastic modulus was up to 240 +/- 10 GPa before and up to 310 +/- 7 GPa after annealing. Coatings with a high B content exhibited the highest hardness and elastic modulus in both cases. Coating powder was prepared by sputtering a Nb2BC target and studied using differential scanning calorimetry. The powder exhibited a crystalline NbC phase before and after annealing up to 900 ?. The material was stable in an Ar atmosphere in the studied temperature range. In an Ar + O-2 mixture, the powder was stable up to similar to 580 degrees C. At this temperature, an oxidation reaction started, resulting in the formation of Nb2O5.
Rakoch, Alexander G.Tuan, Tran VanKhabibullina, Zukhra, VBlawert, Carsten...
16页
查看更多>>摘要：Mechanisms of PEO coatings formation on AA2024 aluminum alloy in an aqueous solution, containing 3 g/L NaOH and 5 g/L Na2O..2.9SiO(2).18H(2)O (base electrolyte) and with addition of 1.5 g/L CoOOH.H2O, are studied. This addition results in a formation of black coatings. It is determined that structure, phase and elemental compositions of the coatings correlated with the corrosion properties. For coatings, grown in the base electrolyte, anodic and cathodic current densities and the value of impedance modulus (|Z| (f=0.01Hz)) improves with the increase of the coatings thickness due to the healing of internal pores during extended PEO processing, according to the results of electrochemical measurements in 0.5 wt% NaCl solution. However, the results of electrochemical tests of coatings, synthesized in the electrolyte with CoOOH.H2O differ. For short-term immersion (up to 24 h), thin coating (-17 mu m) demonstrates the lowest current densities and the highest value of impedance modulus (|Z| (f=0.01Hz)) in comparison to the thicker coatings (-48, 82 mu m). However, after longer exposure (up to 168 h) the thickest coating (-82 mu m) has the best long-term stability. This behavior and the most probable mechanism of black coatings formation are suggested and explained as function of coating properties and exposure time in NaCl solution.
查看更多>>摘要：In this article we show the optical, mechanical and surface properties change depending on the Hf-Zr-Ce-Y-O thin film composition. Hf4Zr4CeY2O21 shows up to three times higher hardness compared to binary HfZrO4 oxide and up to 50% higher hardness compared to cubic ZrO2 and HfO2 due to the solid solution hardening effect. Equimolar film exhibit a high transmittance > 85% and high hydrophobicity with the water contact angle asymptotic to 106?degrees. Variation of the elemental composition in Hf-Zr-Ce-Y-O is allows to simultaneously tune mechanical and wetting properties for the optimum configuration depending on the application.
Yuan, ChengqingWood, Robert J. K.Lu, PingChang, Jiangfan...
18页
查看更多>>摘要：Nature-inspired eco-friendly superhydrophobic surfaces have attracted great interests from fundamental research to antifouling application. Nanocomposite coatings are an economical way to fabricate superhydrophobic sur-faces. This paper studies how the coating topography can be controlled by using different nanoparticle sizes and concentrations. Six three-dimensional surface parameters are used to define the resulting topography and explore the correlations with wettability. Three unique scenarios are proposed based on the relationship between the two key parameters core void volume (Vvc) and core material volume (Vmc) to assess the relationship between surface roughness and solid-liquid contact area fraction (f). A water contact angle (WCA) of 152.6 and contact angle hysteresis (CAH) of 2.9?degrees are obtained by employing dual-sized nanoparticles at 45% nanoparticle con-centration (wt./wt.), which is up to 10% less than the superhydrophobic coating fabricated by using single-sized nanoparticles (30 nm). Furthermore, Vvc and peak sharpness dominate f, consequently dominating the wetta-bility in the transitional state and Cassie state, respectively. The antifouling tests using Phaeodactylum tricornutum and Bacillus sp. show a negative correlation between f and antifouling performance, and the minimum adhesion ratios are only 0.41% and 0.53%, respectively. The superhydrophobic surfaces with Vvc/Vmc > 1 are shown to be better for antifouling applications. These findings are important for designing superhydrophobic nano-composite coatings for antifouling performance.
查看更多>>摘要：Titanium boride, TiBx, thin films were grown by direct current magnetron co-sputtering from a compound TiB2 target and a Ti target at an Ar pressure of 2.2 mTorr (0.3 Pa) and substrate temperature of 450 ?degrees C. While keeping the power of the TiB2 target constant at 250 W, and by varying the power on the Ti target, P-Ti, between 0 and 100 W, the B/Ti ratio in the film could be continuously and controllably varied from 1.2 to 2.8, with close-tostoichiometric diboride films achieved for P-Ti = 50 W. This was done without altering the deposition pressure, which is otherwise the main modulator for the composition of magnetron sputtered TiBx diboride thin films. The film structure and properties of the as-deposited films were compared to those after vacuum-annealing for 2 h at 1100 ?degrees C. As-deposited films consisted of small (?50 nm) randomly oriented TiB2 crystallites, interspersed in an amorphous, sometimes porous tissue phase. Upon annealing, some of the tissue phase crystallized, but the diboride average grain size did not change noticeably. The near-stoichiometric film had the lowest resistivity, 122 mu omega cm, after annealing. Although this film had growth-induced porosity, an interconnected network of elongated crystallites provides a path for conduction. All films exhibited high hardness, in the 25-30 GPa range, where the highest value of similar to 32 GPa was obtained for the most Ti-rich film after annealing. This film had the highest density and was nano-crystalline, where dislocation propagation is interrupted by the off-stoichiometric grain boundaries.
NSTL
Elsevier