查看更多>>摘要：The effect of B concentration on phase formation and oxidation resistance of (Ti0.35Al0.65)By coatings with y = 1.7, 2.0, 2.4 was investigated. Elemental B targets in radio frequency mode and a compound Ti0.4Al0.6 target in direct current mode were sputtered. The B concentration was varied systematically by adjusting the applied power to the respective magnetrons, while keeping the power supplied to the magnetron with the Ti0.4Al0.6 target constant. Measured lattice parameters and elastic properties are consistent with ab initio predictions. The oxidation resistance at 700 degrees C in air for up to 8 h was compared to a cathodic arc evaporated (Ti0.37Al0.63)0.49N0.51 coating with an Al/Ti ratio of 1.69 +/- 0.20 which is very similar to 1.84 +/- 0.40 for the boride coatings. Scanning transmission electron microscopy imaging revealed oxide scale thicknesses of 39 +/- 7 and 101 +/- 25 nm for (Ti0.35Al0.65)B2.0 and (Ti0.37Al0.63)0.49N0.51 after 8 h, respectively. Hence, the close to stoichiometric diboride outperforms the nitride coating. This behavior can be understood based on composition and structure analysis of the oxide scales: While the protective layer on the diboride is primarily composed of Al and O, the porous oxide layer on the nitride coating contains Ti, Al and O.
查看更多>>摘要：There are significant challenges in controlling uniformity of crystal inclination angles, growth orientations and film thicknesses to generate dual-mode surface acoustic waves (e.g., Rayleigh ones and shear-horizontal ones) for lab-on-a-chip applications. In this study, we demonstrate large area (up to three inches) and uniformly inclined piezoelectric ZnO films, sputtering-deposited on silicon using a glancing angle deposition method. Characterization using X-ray diffraction showed that the inclined ZnO films have an average crystal inclination angle of 29.0 degrees, apart from the vertical (0002) orientation, at a substrate tilting angle of 30 degrees. Reflection signals of ZnO/Si surface acoustic wave devices clearly show the generations of both shear horizontal surface acoustic waves and Rayleigh waves. The Rayleigh waves enable efficient acoustofluidic functions including streaming and transportation of sessile droplets. Excitation direction of Rayleigh waves on the acoustofluidics versus the inclined angle direction has apparent influences on the acoustofluidic performance due to the anisotropic microstructures of the inclined films. The same device has been used to demonstrate biosensing of biotin/streptavidin interactions in a liquid environment using the shear-horizontal surface acoustic waves, to demonstrate its potential for integration into a complete lab-on-a-chip device.
查看更多>>摘要：The beneficial effect of surface engineering on the wear and corrosion performance of Ti-6Al-4V alloy for biomedical purposes has recently gained a lot of interest. To date, researchers have shown TiN ceramic coatings to be an effective strategy to improve the poor tribocorrosion properties of Ti-based alloys. However, coating degradation and adhesions remains a major hurdle to overcome for successful clinical translation. Recently, a duplex TPON + TiN treatment process on Ti-alloy has been suggested for applications involving with high contact loads. For the first time, this technique was extended to the Additive Layer Manufactured (ALM) Ti-6Al4V alloys in an attempt to enable load bearing patient personalised implants. The bio-tribology and corrosion resistance of the coated ALM materials were compared with that of the coatings on conventional wrought manufactured alloy for orthopaedic applications. XRD analysis showed that the coatings on both substrates are primarily composed of TiN. The Knoop microhardness technique proved a tribologically effective diffusion layer with a case depth of 35-45 mu m. The LC2 and LC3 values were measured above 40 N and 60 N which is an excellent cohesive and adhesive strength for these types of the coatings. Electrochemical measurements in both static and sliding conditions showed a quick recovery capability of the protective layer in 25% Foetal Bovine Serum (FBS) diluted in Phosphate Buffered Saline (PBS) electrolyte. The static electrochemical measurements also showed reduced corrosion current densities when compared to that of the bulk Ti-alloy. Coating on both substrates showed an excellent wear resistance which is correlated to the enhanced load bearing capacity of the coated surfaces. While the coating thickness was 3-6 mu m, the wear depth was only 0.3 mu m after 2 h of reciprocating sliding wear test.
查看更多>>摘要：The present work focuses on the preparation of amorphous Si-B-C-N coatings to protect gamma-TiAl intermetallic alloys against oxidation above 750 ? that otherwise leads to surface degradation and embrittlement. The film fabrication process included the deposition of an amorphous Si interlayer at a temperature of 700 ? to promote adhesion. Subsequently, Si-B-C-N coatings were prepared by pulsed dc and rf magnetron co-sputtering from Si and B4C targets in Ar + N-2 gas mixtures. Specifically, we studied the oxidation behavior of the coatings and the evolution of the microstructure, composition, and mechanical properties upon an isothermal oxidation test performed in laboratory air at 800 ? for 100 h. We found that an optimized Si(4)0B(5)C(2)N(47) (at.%) coating protects the gamma-TiAl alloy substrate against oxidation by a combination of several effects: a) Interdiffusion of Si and Ti results in the formation of Ti(x)Si(y )phases on the film-substrate interface promoting adhesion of the coating, b) Diffusion of Ti to the surface is effectively inhibited and no fast-growing TiO2 is formed at the outer surface, and c) Stable amorphous structure of Si-B-C-N coatings hinders inward oxidation of O. Investigation of the oxidation kinetics at 800 ? up to 1000 h proved that Si-B-C-N coating serves as an efficient oxidation barrier demonstrated by the significantly reduced mass gain and the parabolic oxidation rate constant (1.05 x 10(-13) g(2).cm(-4).s(-1)) compared to the uncoated gamma-TiAl alloy (5.65 x 10(-13) g(2).cm(-4).s(-1)).
查看更多>>摘要：Multicomponent alloy thin films including high entropy alloy (HEA) and medium entropy alloy (MEA) thin films have drawn lots of attention from researchers and industries because of their outstanding properties, such as high hardness, good wear and corrosion resistance. Among several kinds of multicomponent alloy systems, the refractory HEA and MEA are characterized by their high temperature strength and stable thermal properties. In this work, the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films were fabricated by a magnetron co-sputtering system. The structure of W-Nb-Ta-Ti-N coatings changed from BCC to B1 FCC nitride phase when the nitrogen concentration reached 42.6 at.%. The microstructure of BCC structured W-Nb-Ta-Ti-N thin films changed from a coarse columnar to a dense feature as the nitrogen content increased from 0 to 16.2 at.%. A maximum hardness of 24.4 GPa was obtained for the BCC structured W34.3Nb21.7Ta26.4Ti1.4N16.2 thin film. The best adhesion property and the lowest coefficient of friction were found for the FCC W31.1Nb9.6Ta13.1Ti3.6N42.6 nitride thin film. The corrosion resistance of 304SS substrate in 5 wt% NaCl aqueous solution was greatly enhanced by the deposition of the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films. The best corrosion resistance can be seen for the nitrogen-free W37.9Nb25.8Ta28.8Ti7.5 thin film due to its dense microstructure, highest Ta and Nb contents, high configurational entropy and sluggish diffusion effects.
查看更多>>摘要：Discharge phenomena in electrolytes were discovered many decades ago. However, the research and develop-ment of plasma oxidation in electrolytes for surface engineering have only truly been actively performed in recent years, particularly stimulated by a review paper entitled Plasma Electrolysis for Surface Engineering published in 1999. Among plasma electrolysis processes, plasma electrolytic oxidation (PEO) caught the most attention from academic and industrial communities. However, PEO has been largely restricted to valve metals, such as Al, Mg and Ti and their alloys. This research intends to explore the current boundaries of the PEO process and extend it into non-valve metals. The paper therefore first describes the coating growth mechanisms in non -valve metals, which are different from the conventional PEO (conversion) process on valve metals. Particular emphasis is given to revealing details of the coating deposition behavior through direct observations and analysis of non-valve metallic substrates and their coatings formed at different timescales of the PEO process. Copper and ferrous materials are chosen as appropriate non-valve metal substrates and their coating properties in terms of mechanical, corrosion, thermal and electrical aspects are summarized. The results show that high hardness and adhesion strength, high corrosion resistance, good thermal and electrical insulation performances are achievable for PEO-derived coatings on non-valve metals. These properties also open doors for emerging applications, for example in electrical vehicles. Such applications are presented by reporting the coating application on an e -motor bearing and brake disc as two examples. Future research perspectives are discussed with a hope to stir a new wave of PEO research for non-valve metals as realized by the first review paper for the previous wave of plasma electrolysis research.
查看更多>>摘要：Approximately 30 to 40 years ago the group of Stan Vep.rek of the University of Zurich described the fabrication of silicon thin films by formation and decomposition of silicon hydride. In their paper they described how pieces of silicon exposed to a low-pressure hydrogen plasma could promote the formation of a volatile silicon hydride. The hydride was then transported to a hot substrate which caused its thermal decomposition and the formation of the silicon film. Hollow cathodes under appropriate experimental conditions can produce a semi-resonant high-density plasma. In a previous study we used such a high-density hydrogen plasma to etch pieces of quartz but under extreme conditions, we observed that rather than etching there was deposition of a thin film of the metal used for the electrode of the hollow cathode. In this paper we describe the etching of the metal (Mo or Ta) lining of a water-cooled cylindrical hollow cathode by a high-density hydrogen plasma. The metal hydride vapour generate in the plasma by chemical sputtering was directed, by the gas flow, to the quartz substrates which were maintained at various temperatures in excess of 573 K. Here the metal hydride was thermal decomposed, and a thin film of the metal was formed. To improve the experimental reproducibility a special substrate heater was constructed such that four quartz substrates could be simultaneously exposed to the metal hydride vapour, but with each substrate at a different temperature: each approximately 30.3 K greater than the neighbouring one. In this way, depositions under identical plasma conditions could be carried out at the same time, but at four different temperatures. We report the deposition rate as a function of the substrate temperature, the hydrogen gas flow and the RF or P-DC plasma power applied to the hollow cathode.
Gudmundsson, J. T.Fischer, J.Hinriksson, B. P.Rudolph, M....
15页
查看更多>>摘要：The ionization region model (IRM) is applied to model high power impulse magnetron sputtering (HiPIMS) discharges with a Cu target. We apply the model to three discharges that were experimentally explored in the past, or applied to deposit thin copper films, with the aim to quantify internal plasma process parameters and thereby understand how these discharges differ from each other. The temporal variation of the various neutral and ionic species, the electron density and temperature, as well as internal discharge parameters, such as the ionization probability, back attraction probability, and ionized flux fraction of the sputtered species, are determined. We demonstrate that the Cu+ ions dominate the total ion current to the target surface and that all the discharges are dominated by self-sputter recycling to reach high discharge currents. Furthermore, the ion flux into the diffusion region is dominated by Cu+ ions, which represents roughly 80% of the total ion flux onto the substrate, in agreement with experimental findings. For the discharges operated with peak discharge current densities in the range 0.9 - 1.3 A cm-2, the ion back-attraction probability of the Cu+ ion (beta t) is low compared to previously investigated HiPIMS discharges, or in the range 44 - 50%, while the ionization probability (alpha t) is in the range 61 - 69%, and the ionized flux fraction is in the range 32 - 40%. It is, furthermore, found that operating these Cu HiPIMS discharges at lower working gas pressures (in the present case around 0.5 Pa) is beneficial in terms of optimizing ionization of the sputtered species.
Kiryukhantsev-Korneev, Ph. V.Sytchenko, A. D.Sviridova, T. A.Sidorenko, D. A....
13页
查看更多>>摘要：The Mo-Si-B, Mo-Zr-Si-B, and Mo-Hf-Si-B coatings were deposited by magnetron sputtering of the MoSi2-MoB, MoSi2-MoB-ZrB2 and MoSi2-MoB-HfB2 targets. The composition and structure of coatings were investigated by glow discharge optical emission spectroscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron and Raman spectroscopy. Mechanical properties were measured by nanoindentation method. The short-time oxidation resistance of coatings was evaluated at temperatures of 1100, 1300, and 1500 degrees C. The results showed that all coatings deposited onto alumina substrates were characterized by a dense columnar structure. Mo-Si-B coatings contained phases of hexagonal h-MoSi2 and amorphous a-MoB. With the addition of Zr and Hf, an increase in the lattice parameter and a decrease in the grain size of h-MoSi2 by 50 and 25%, respectively, were observed. The base Mo-Si-B coating had a high hardness of 30 GPa. The introduction of Zr and Hf led to a decrease in hardness by 24 and 20%, respectively. The Mo-Si-B coating was characterized by a minimal oxidation depth (<10 nm) at 1100 degrees C and 1300 degrees C, but a network of cracks that penetrated to the substrate was formed. Cracks on the surface of the Mo-Zr-Si-B and Mo-Hf-Si-B coatings were not observed; the formation of oxide layers, 0.3-2.0 mu m thick, was revealed. The oxidation resistance of coatings at temperature of 1500 degrees C increased in direction Mo-Si-B -> Mo-Hf-Si-B -> Mo-Zr-Si-B. The best results for the MoZr-Si-B coating were associated with a smaller grain size, higher thermal stability, and the formation of a protective layer based on SiO2 with the inclusion of ZrO2 crystallites.
查看更多>>摘要：The soft sparking regime of Plasma Electrolytic Oxidation (PEO) of valve metals attracts increasing attention as it enables a better process control with improved energy efficiency and coatings with enhanced performance to be obtained. Here, the discharges softening phenomenon was characterised by evaluation of changes in electrical signal, composition of gaseous products and morphology of the metal-oxide interface in PEO coatings on Al. The coatings were formed using two electrical regimes retarding or promoting soft sparking conditions. Harmonic analysis of PEO process has been performed using independent evaluation of the positive and negative half waves of polarisation signal. The composition of gas evolved during the PEO process was evaluated by a quantitative gas analyser. Coatings were characterised by scanning and transmission electron microscopy with energy dispersive spectroscopy and small area electron diffraction. It was found that discharge softening is accompanied with a decrease in oxygen evolution rate, an increase in equivalent capacitance of anodic process as well as structural and compositional changes near the metal-oxide interface. The experimental findings provide further support to the explanation of discharge softening phenomenon by narrowing the active zone at the metal oxide interface due to intercalation of hydrogen species into anodic alumina under cathodic polarisation. Such mechanistic understanding allows rational regime selection, in-situ process control and optimisation of the coating properties to be performed that paves the way to intellectual manufacturing approach based on careful process monitoring in operando.
NSTL
Elsevier