Bussell, B. C.Gibson, P. N.Lawton, J.Couture, P....
19页
查看更多>>摘要：Aluminium-doped ZnO (AZO) thin films were deposited by remote plasma sputtering of a ZnO:Al2O3 98:2 wt% ceramic target in a pulsed DC configuration. The target power was kept constant at 445 W and the RF plasma power was varied between 0.5 and 2.5 kW. The as-deposited AZO thin films exhibited an optimum resistivity of 6.35 x 10(-4) omega.cm and optical transmittance of 92% at a RF plasma power of 1.5 kW. The thin film microstructure, chemical composition, and residual stress were investigated using SEM, RBS, XPS and XRD. Accurate determination of the chemical composition and correct interpretation of GIXRD data for AZO thin films are a particular focus of this work. The AZO layer thickness was 500-700 nm and Al content in the range of 2.3-3.0 at.%, determined by RBS. The AZO thin films exhibited a strong (002) preferential orientation and grain sizes between 70 and 110 nm. The (103) peak intensity enhancement in GIXRD is proven to be a result of the strong (002) preferential orientation and GIXRD geometrical configuration rather than a change in the crystallite orientation at the surface. XPS depth profiles show preferential sputtering of O and Al using a 500 eV Ar+ beam, which can be reduced, but not eradicated using an 8 keV Ar-150(+) beam. The preferential sputtering can be successfully modelled using the simulation software TRIDYN. A plasma power of 1.5 kW corresponds to a highly ionised plasma and various microstructural and compositional factors have all contributed to the optimum low resistivity occurring at this plasma power. The grain size exhibits a maximum in the 1.25-1.5 kW range and there is improved (002) orientation, minimising grain boundary scattering. The highest carrier concentration and mobility was observed at the plasma power of 1.5 kW which may be associated with the maximum in the aluminium doping concentration (3.0 at.%). The lowest residual stress is also observed at 1.5 kW.
查看更多>>摘要：Advanced materials with superior properties are always desired to extend the applicabilities and functionalities in practical applications. However, with the rising complexity of materials composition and processing, especially after the proposal of the novel materials design concept "High Entropy Materials (HEMs)", the materials development becomes even more complicated. To accelerate the materials development continuum, numerous approaches have been proposed.In this work, we exploit an experimental combinatorial approach to investigate phase formation and microstructure evolution of reactively co-sputtered multiple principle elemental nitride thin films in a wide compositional space in the Hf-Nb-Ti-V-Zr-N system. The correlation among elemental composition, structure and mechanical properties of the deposited thin films has been addressed. Among all compositions, a Hf3.5Nb2.6Ti22.9V4.9Zr17.7N thin film shows an optimum hardness of 39.3GPa. The presence of a single-phase crystal structure of (HfNbTiVZr)N thin films within wide compositional space is probed and has been demonstrated. Furthermore, high-throughput scratch test examination of the high entropy nitride (HfNbTiVZr)N thin films show that coatings with a ratio of hardness to reduced modulus (H/Er) around 0.1 would have favorable scratch resistance.
查看更多>>摘要：A carburizing treatment of AISI 304L austenitic stainless steel was performed at a low temperature of 450 ? using the low-pressure hollow cathode plasma source technique. The hollow cathode plasma was produced in a cathodic cage made of stainless steel screen inlaid with a stainless steel tubes array. A pulsed high voltage power, with a peak voltage of 800 V and a pulse frequency of 30 kHz, was applied at a low gas pressure of 50 Pa. The austenitic stainless steel samples were carburized with a direct current bias of-200 V under the CH4/H-2 ratio changing in a range from 0.11 to 9, for a carburizing time of 4 h. Under the lower CH4/H-2 ratio of 0.11, a diamond-like carbon film of approximately 260 nm thick formed on the stainless steel surface. As the CH4/H-2 ratio increased to 0.67 and 1, both carburizing cases possessed a similar thickness of about 11 mu m, with the surface carbon concentration being 6 to 6.5 at.%. A layer of carbon supersaturated face-centered-cubic (gamma C) phase formed, together with carbon-rich (Fe,Cr)5C(2) carbide precipitation. Under the highest CH4/H(2 )ratio of 9, a single gamma C phase layer was obtained in a carburizing case of similar thickness, with a high surface carbon concentration of 7.5 at.%. The maximum surface hardness value of HV0.25 N 7.1 GPa occurred on the single gamma C phase layer. No pitting corrosion occurred on the single gamma C phase in the polarization curve. The higher passive film resistance and the lower donor and acceptor concentrations and flat band potential indicated that a more compact passive film is grown on the gamma C phase layer. The (Fe,Cr)5C(2 )carbide precipitates in the gamma C phase matrix degraded the passivity of the gamma C phase layer due to the reduced compactness of the passive film. A carbon transport competition mechanism between carbon adsorption onto the surface and carbon inward diffusion that was mainly dependent on the heavier CHn+ ion bombardment, was proposed to explain the transition with increasing CH4/H-2 ratio from carbon film deposition, to a carburizing case composed of ae single gamma C phase, with both increased hardness and higher corrosion resistance.
查看更多>>摘要：Alternating TiB2-DCMS and Cr-HiPIMS layers are used to fabricate TiB2/Cr multilayer films with varying the Cr interlayer thickness, 2 and 5 nm, and the substrate bias during growth of Cr interlayers from floating, to -60 V and -200 V. The effects of multilayer structure on mechanical properties, static oxidation, and tribological behavior of the TiB2/Cr multilayers are investigated. The results reveal that TiB2 nanocolumns renucleate at each Cr interface maintaining smooth film surface and film density. Interlaying with Cr with thicknesses of 2-5 nm improves the resistance to oxidation at 500-600 degrees C as compared to TiB2 monolayer. The increase of the thickness of the Cr interlayers from 2 to 5 nm decreases the hardness of the multilayer slightly but deteriorates the wear rate significantly. The friction coefficients at 500 degrees C are lower than those at RT due to boric acid liquid lubrication induced by surface oxidation. The TiB2/Cr multilayer films show higher wear resistance than TiB2 monolayer. The multilayer films with 2 nm-thick Cr deposited at -60 V have the lowest recorded wear rates. Irradiation with 200 eV Cr+ leads to interface mixing, resulting in the formation of B-deficient TiBx phase (x < 2) and higher wear rates compared to multilayers grown at -60 V.
Carvalho, IsabelLima, M. JoseNobre, DavidMarques, S. Mariana...
13页
查看更多>>摘要：Diabetic foot is one of the most serious complications of diabetes, the appearance of foot ulcers is highly susceptible to the prevalence of infections. In this sense, thin films of silver (Ag) and silver oxide (AgOx) were deposited by the dc reactive magnetron sputtering technique on different leather substrates for application in insoles and/or footwear inside in order to functionalize them, thus promoting antibacterial properties. A detailed characterization is described to the uncoated and coated leathers. Cytotoxicity and antimicrobial activity were evaluated and, a silver antimicrobial mechanism was suggested. Among the uncoated and coated leathers, AgOx modified samples have higher CoF indicating that this coating can permit higher immobilization of the foot in relation to the skin. The AgOx coating has also impressive antibacterial and antifungal activity without causing any cytotoxic effect, suggesting the potential application of AgOx modified leathers to diabetic specialized footwear.
Delgado, A.Garcia-Zarco, O.Restrepo, J.Rodil, S. E....
10页
查看更多>>摘要：AlCrN coatings have long been used to endure the lifetime of cutting tools due to their high hardness and good mechanical qualities. Vanadium (V) additions to AlCrN coatings were studied for their mechanical and tribological properties against Al2O3 counterparts using the linear reciprocating sliding test. The AlCrN and AlCrVN coatings were deposited using cathodic multi-arc evaporation to steel substrates. We evaluated the effect of a high fraction of V into equimolar Al and Cr coatings, which is different from those reported in previous works. X-ray diffraction patterns and Raman spectroscopy demonstrated that the structure remained as the metastable face center cubic. Microidentation tests demonstrated that AlCrVN coating has a higher hardness than AlCrN coating, probably due to an improved microstructure and larger nitrogen incorporation. The wear resistance of the hard steel substrate was significantly increased using both hard coatings. However, no significant changes were observed in the coefficient of friction and wear rate. The results show that V addition significantly improved the mechanical and adhesive capabilities of the AlCrN coating without compromising the oxidation resistance at moderate temperatures (< 500 C).
Hans, MarcusCzigany, ZsoltNeuss, DeborahSaelker, Janis A....
12页
查看更多>>摘要：Single-phase metastable cubic (V,Al)N thin films with columnar microstructure were grown by high power pulsed magnetron sputtering at 440 ? and the thermal decomposition mechanisms were systematically investigated by post-deposition vacuum annealing from 600 to 900 ?. The onset of spinodal decomposition into isostructural V-and Al-rich cubic nitride phases is demonstrated after cyclic vacuum annealing at 700 ?. Moreover, at this temperature, evidence for aluminum diffusion to grain boundaries and triple junctions is provided by correlation of transmission electron microscopy and atom probe tomography data. The formation of Al-rich regions can be understood by the more than 25% lower activation energy for bulk diffusion of aluminum compared to vanadium as obtained from ab initio calculations. It is reasonable to assume that these Al-rich regions are precursors for the formation of wurtzite AlN, which is unambiguously identified after annealing at 800 ? by microscopy and tomography. The significantly larger equilibrium volume of wurtzite AlN compared to the cubic phase explains its initial formation exclusively at triple junctions and grain boundaries. In contrast, twin boundaries are enriched in vanadium. Interestingly, the formation of the wurtzite phase at grain boundaries and triple junctions can be tracked by resistivity measurements, while X-ray diffraction and nanoindentation data do not support an unambiguous wurtzite phase formation claim for annealing temperatures < 900 ?. Hence, it is evident that previously reported formation temperatures of wurtzite AlN in transition metal aluminum nitrides, determined by other characterization techniques than chemical and structural characterization at the nanometer scale and/or resistivity measurements, are overestimated.
NSTL
Elsevier