查看更多>>摘要：Highly reactive aluminum-fluorine composites with novel structures have attracted much attention in the past decades. However, there is not a specific mechanism to explain the combustion-supporting or inducing effect of F-polymer on aluminum powders. Herein, we present a systematic study of the induced reaction mechanism and propose a new elaboration. Two types of Nano-aluminum/Poly(vinylidene fluoride) (n-Al/PVDF) composites are fabricated via electrospray and mechanical mixing method, respectively. The electrospray sample excites a Pre Ignition Reaction (PIR) between fluorine and the Al2O3 shell at a low temperature, and simultaneously the specific surface area, surface element state and alumina shell structure of aluminum powders change to some extent. However, the surface structure of the physical mixture does not change significantly in the same temperature range. On this basis, we studied the relationship between the change of surface structure and the enhanced combustion performance of aluminum in electrospray sample. The results show that the combustion supporting effect of PVDF on aluminum powder should be attributed to the corrosion of the alumina shell and the loose structure of the PIR product.
查看更多>>摘要：MnFeCoNiCu high entropy alloy (HEA) coatings with and without graphene oxide (GO) incorporation was deposited onto a mild steel substrate by the electrodeposition method. Coating morphology, phase constitution, corrosion properties, and coatings surface chemistry before and after corrosion in a 3.5 wt% NaCl solution was investigated. A predominantly body-centered cubic (BCC) phase with a minor fraction of face-centered cubic (FCC) phase was obtained in the pristine coating. Whereas a nearly equal volume fraction of FCC and BCC phases formed in coatings with increasing GO content. Corrosion characteristics of the MnFeCoNiCu HEA coatings with different GO content were studied. All the GO containing coatings exhibited higher corrosion resistance than the coating without GO in 3.5 wt% NaCl solution. The corrosion resistance of the coatings increased with increasing GO content. The surface chemistry of the coatings before and after exposure was studied by X-ray photoelectron spectroscopy (XPS). These results showed that the GO incorporation into the MnFeCoNiCu matrix enhanced the formation of stable oxides, which can reduce ionic diffusion, thus improving the corrosion resistance of the MnFeCoNiCu HEA-GO coatings when compared to the MnFeCoNiCu HEA coating without GO.
查看更多>>摘要：This paper discusses the development of a reactive sputtering process for the deposition of epitaxially grown AlN films on Si(111) using a technology suitable for 8 '' substrates. X-ray diffraction (XRD) and rocking curves (RC) are used to determine the crystalline orientation. The influence of substrate temperature, target-substrate distance and target voltage on the full width at half maximum (FWHM) of the RC is investigated. The film deposition was performed on Si(111) wafers and on AlN-on-Si(111) templates prepared by metal organic chemical vapor deposition (MOCVD). Based on the sixfold symmetry identifiable in the pole figure of the AlN(302) plane reflections, oriented in-plane film growth on Si(111) was verified for the process. Best oriented films sputtered directly on Si(111) achieved for 500 nm AlN films featured a RC-FWHM of 0.93. of AlN(100) and 0.77. of AlN(002). Root mean square roughness (RMS) of the samples varied between 2.3 nm and 2.8 nm. The deposition rate was between 70 nm/min and 100 nm/min. Films deposited onto the MOCVD templates grew maintaining the crystalline quality of the MOCVD substrate, verified by the FWHM of the RC of in-plane and out-of-plane reflections.
查看更多>>摘要：Mg2SiO4 coatings were formed on cp-Mg by Plasma Electrolytic Oxidation (PEO) using electrical regimes based on sawtooth anodic current pulses with extended ascending or descending segments (ramps). Voltage, current and light emission signals were simultaneously acquired to derive and analyse the evolution of system current and discharge population density during PEO process, while optical emission spectroscopy was employed for identification of plasma species. Coating morphological characterisation was carried out using Scanning Electron Microscopy. Phase composition was identified by X-ray diffraction. The corrosion performance was evaluated with Electrochemical Impedance Spectroscopy at various periods of exposure to corrosive media (0.5 wt% NaCl). It was shown that the application of sawtooth pulses allowed the controlling of microdischarge characteristics and coating morphology in both pulsed unipolar and reversed current regimes. Results further demonstrate that the application of anodic sawtooth pulses with the negative ramp facilitated defect healing during coating formation leading to production of more uniform PEO coatings with lower porosity and a slower degradation rate of magnesium substrate. A steady decay in the coating resistance with immersion time provides a possibility for controlling magnesium degradation and thereby for optimisation of component lifetime in applications where predictable Mg dissolution rate is required, such as sacrificial anodic protection of metallic structures and resorbable biomedical implants.
Gharibi, RezaSafavian, SaraTeimouri, Mohammad Bagher
12页
查看更多>>摘要：The present work has considered designing bioactive and biocidal coatings to address the unsatisfactory performance of implanted medical devices due to microbial contamination. The non-leaching biocidal polyurethanesiloxane coating was fabricated through the sol-gel reaction of monocomponent soybean oil prepolymer containing the reactive alkoxysilane, quaternary ammonium, and urethane moieties (Si-PPU) on a model metallic substrate. The Si-PPU prepolymer was prepared by three-step synthesis, including the carbonation of ESBO with CO2, urethane formation through the non-isocyanate approach, and simultaneous quaternization, and alkoxysilane functionalization. The adhesion strength of about 2.75 MPa to an aluminum plate, high pendulum hardness (254 s(-1)), superior flexibility, and high impact resistance could meet biomedical coating applications' requirements. The superior contact-active biocidal activity towards Gram-negative and Gram-positive bacteria was provided by prepared coating. Meanwhile, no evidence for cytotoxicity was observed, and the coating presented favorable cell adhesion and proliferation. The high cell viability (> 90%) and low hemolysis rate (HR < 1%) confirmed the cytocompatibility of coatings.
查看更多>>摘要：The adhesion strength between the circuit and substrate is a key factor that affects the performance of elec-tronics. Laser modification assisted metallization technology (LAM), which can fabricate high-adhesion metallic pattern on ceramic without masks, is generally considered as a promising selective metallizing method. However, it seems lack of the reports about how the texturing patterns affect the coating adhesion on ceramic up to now. In this paper, three kinds of texturing patterns-parallel groove texture (PGT), parallel wave texture (PWT) and square net texture (SNT) with different laser scanning spacings (D) were fabricated on ceramic substrates by laser modification, and the copper was selectively electroless-plated on the textured surface. Then, the influences of textures on the adhesion strength and fracture mechanism of copper-ceramic were studied systematically. Results indicated that the adhesion were significantly affected by the surface area, microstructures and structural defects of the textures. Compared with PGTs and PWTs, SNTs showed a more significant effect on improving the adhesion, in which a reliable obtuse-angled anchoring bond was generated at D = 60 mu m (sample SN60), making the fracture take place at the copper, ceramic and copper-ceramic interface simultaneously, and the maximum adhesion strength as high as 43.2 MPa was obtained.
查看更多>>摘要：Metal matrix composites are widely used in aircraft and aerospace components due to their low weight and high strength. Since their processing by conventional methods is quite problematic, laser processing techniques have to be used and optimized. In this study, two SiC particle-reinforced Al matrix composites with different volume refractions and average particle sizes, namely SiCp/AA2024 (45%, 30 mu m) and SiCp/AA6061 (60%, 3 mu m) were irradiated by a nanosecond laser with a pulse fluence range of 0.68-6.83 J/cm(2). The ablated surface morphology evolution was studied by SEM, and the elements' distribution was analyzed by EDS. At increased pulse fluence, the molten matrix firstly spilled from spaces between silicon carbide particles and then spread on their surfaces, forming a smooth surface in the first composite with small particle size but failing to cover SiC particles in the second one with large particle size. The SiC particles on the laser-treated surface were seriously oxidized, while distributions of Al and Si elements on the laser-ablated surfaces were independent. The dispersion of Si element increased with the fluence. The ablation threshold and surface roughness of SiCp/AA6061 was lower than those of SiCp/AA2024, in contrast to the ablation depth. The performed thermal simulation confirmed the heat conduction existence between the matrix and reinforcement, as well as the particle's volume refraction and average size effects on the heating behavior of SiCp/Al composites. The results obtained are considered instrumental in substantiating the applicability of various laser processing techniques to SiC particle-reinforced Al matrix composites.
查看更多>>摘要：The combination of laser surface texturing and heat treatment process was barely investigated in the past, particularly for improved surface characteristics of Ti6Al4V. Hereby, the important role of laser scanning and post heat treatment in improving the oxygen diffusion depth and overall surface characteristics was analyzed. Polished Ti6Al4V surface was scanned using Nd:YAG nanosecond laser and analyzed for the oxygen pickup, phase change and hardness variation. The laser textured surface was heat treated to grow oxide coating over textured surface. In comparison with heat treated surface, the synergic effect of laser scanning and heat treatment improved the surface hardness by 15% and raised the TiO2 rutile phase fraction from 0.36 to 0.73. The dual engineered Ti6Al4V surface was found to have superior HF1 quality adhesion strength along with the presence of low magnitude tensile residual stress. The increase in oxygen diffusion depth, diffusion coefficient and TiO(2 )rutile phase fraction due to synergic effect of laser scanning and heat treatment were associated to the Ti2O(3) and C doping assisted anatase to rutile transformation mechanism.
查看更多>>摘要：Thermal shock resistance is highly important to the selection of practical accident tolerance fuel coatings (ATFCs). The performance of three coatings (Cr, CrN and (Cr/CrN)(24)) prepared by radio frequency magnetron sputtering (RFMS) were compared in thermal shock tests at 900- 1200 degrees C. The interface stability, microstructural evolution and oxidation behaviors of the (Cr/CrN)(24) multilayer coatings were systematically investigated. The results indicate that the thinning of the Cr2O3 layer is related to the evaporation of volatile CrO2(OH)(2) during quenching in boiling water. The coatings exhibited severe performance degradation at 1200 degrees C mainly because of significant mutual diffusion of Cr and Zr, which caused oxygen to diffuse into the substrates and form ZrO2. The relationship between the microstructure evolution and element diffusion is analyzed in detail.
查看更多>>摘要：Since decades, protective hard coatings with thicknesses of a few micrometers are grown by physical or chemical vapor deposition (PVD, CVD) on cutting tools to improve their application performance. For the huge variety of cutting applications, different coating materials are used, which typically belong to the material classes of nitrides, carbides, carbonitrides, borides, boronitrides or oxides, frequently in bi-or multilayer stacks. The present work surveys typical hard coatings belonging to the respective material classes, deposited by PVD as well as CVD. Pioneering studies in this field as well as recent findings contributing to the establishment of comprehensive "synthesis - structure - property - application performance" relationships of the respective coatings are discussed and the current state-of-research is reviewed. Condensed summaries and comparisons between PVD and CVD coatings are given at the end of each subsection. In addition, current and future challenges for the hard coatings community are surveyed.
NSTL
Elsevier