Search

Abstract: The ablated surface morphology feature of plasma sprayed Cr2O3 coatings on heat-resistant steel irradiated by high-intensity pulsed ion beam (HIPIB) at an ion current density of 300–500A/cm2 with a shot number of 1–10 was investigated by using scanning electron microscopy, X-ray diffractometry, microhardness testers, respectively, in order to explore the modification mechanism of HIPIB onto coatings. HIPIB irradiation caused a melting and ablating of Cr2O3 coating surface and formed a thin remelted Cr2O3 layer with compact structure. At the low ion current density of 300A/cm2, the splat melting and cavity sealing caused a partially compact surface with several microcracks. And a discontinuous remelted Cr2O3 layer on the compact matrix coating was obtained. With increasing the ion current density to 500A/cm2, the reformed splats by serious splat melting and sufficient cavity sealing induced a more compact surface with a continuous and thicker remelted layer, companying with a slight increase of microcracks. The enlarged splats reformed by serious splats remelting and sufficient cavities sealing induced a gradually compact and smooth surface on the irradiated Cr2O3 coatings with increasing the shot number and a more uniform and smooth surface with compact structure was obtained by the agglomeration of the enlarged splats after 10 shots. It is found that the change in microhardness of the compact remelted layer was consistent with the sealing feature on the irradiated surface. [Copyright &y& Elsevier]

Abstract: The 0–1.5 mol% Er3+-doped Al2O3 films have been prepared on the thermally oxidized SiO2/Si(100) substrate in the dip-coating process by the sol–gel method, using the aluminium isopropoxide [Al(OC3H7)3]-derived γ-AlOOH sols with the addition of erbium nitrate [Er(NO3)3·5H2O]. The continuous Er3+-doped Al2O3 films with the thickness of about 1.2 μm were obtained for nine coating cycles at a sintering temperature of 900 °C. The aggregate size for the Er3+-doped Al2O3 films increased with increasing the Er3+ doping concentration from 0 to 1.5 mol%. The root-mean-square roughness of the films was independent on the Er3+ doping, which was about 1.8 nm for the 0–1.5 mol% Er3+-doped Al2O3 films. The γ-Al2O3 phase with a (110) preferred orientation was produced for the Al2O3 film. The photoluminescence (PL) spectra of 0.1–1.5 mol% Er3+-doped Al2O3 films were observed at the measurement temperature of 10 K. There was no significant change for the PL peak intensity with the increase of Er3+ doping concentration from 0.1 to 1.5 mol%, and similar full width at half maximum of about 40 nm was detected for the 0.1–1.5 mol% Er3+-doped Al2O3 thin films. The Er3+-doped Al2O3 films possess the available PL properties for use in planar optical waveguides. [Copyright &y& Elsevier]

Abstract: 1 mol%Er3+–10 mol%Yb3+ codoped Al2O3 thin films have been prepared on thermally oxidized SiO2/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC3H7)3] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er3+–Yb3+ codoped Al2O3 thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er3+–Yb3+ codoped Al2O3 thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC3H7)3. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er3+–Yb3+ codoped Al2O3 thin films, which is unrelated to the addition of DMF. Controllable formation of the Er3+–Yb3+ codoped Al2O3 thin films may be explained by the fact that the DMF assisted the deprotonation process of ;OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films. [Copyright &y& Elsevier]

Surface integrity and interface structure of coating materials play a key role in tribological and corrosion behaviors in harsh working environments in nuclear power plants. In this work, we focus on the investigations of tribological behaviors in air and seawater of CrN/TiN superlattice coatings deposited by the combined deep oscillation magnetron sputtering with pulsed dc magnetron sputtering, which were irradiated by high-intensity pulsed ion beam (HIPIB) with ion energy density of 1–3 J/cm2 and shot number of 1–5. At 1 J/cm2, the increased shot number leads to a broaden (111) peak of face-centered cubic crystal structure, indicating grain size refinement. At 3 J/cm2, the increased shot number results in the coarsening grain, and superlattice structure gradually disappeared at 2 shots, finally the coatings fell off from substrate at 5 shots. The highest hardness (H), H/E* (E*, effective Young's modulus) and H3/E*2 of the coatings irradiated at 1 J/cm2 and 5 shots are achieved at 38.7 GPa, 0.1 and 0.387, respectively. The increased ion energy density and shot number result in the decrease in Rockwell C HF adhesion level from HF1 to HF6. At 1 Jcm−2 and 1 shot, tribological behavior of irradiated coatings in air was dominated by oxidative wear with coefficient of friction (COF) of 0.51 and specific wear rate of 4.2 × 10−7mm3N−1m−1. The irradiated coatings show excellent tribocorrosion properties in seawater with high open circuit potential of 0.32 V, low COF of 0.14 and specific tribocorrosion rate of 6.1 × 10−8mm3N−1m−1 without pitting corrosion under moderate HIPIB irradiation due to high surface integrity and stability of well-defined interfaces and dense microstructure. With an increase of energy density and shot number, wear mechanism in air changes to severe adhesive and oxidative wear, while tribocorrosion mechanism is gradually dominated by plough wear coupled with pitting corrosion. [ABSTRACT FROM AUTHOR]

TiAlSiN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system by reactive sputtering from Ti 0.475 Al 0.475 Si 0.05 targets using modulated pulsed power magnetron sputtering (MPPMS) under a floating substrate bias. The ratio of the nitrogen flow rate to the total gas flow rate ( f N 2 ) was varied from 0 to 40%. The application of MPPMS as sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When f N 2 = 0%, an amorphous-like structure Ti 0.479 Al 0.454 Si 0.066 coating was deposited with a hardness of 10 GPa. When nitrogen was added, an optimized nanocomposite structure of nc -TiAlN/ a -Si 3 N 4 formed in the TiAlSiN coating deposited at f N 2 = 10%, in which 5–10 nm TiAlN nanocrystallites were embedded in a 2–3 nm thick amorphous Si 3 N 4 matrix. As the f N 2 was increased up to 40%, the elementary composition of the coatings remained almost the same, but the grain size of nanocrystallites approached to 10–20 nm and the AlN phase gradually precipitated. A maximum hardness (H) of 33.2 GPa, a hardness to the elastic modulus (E) ratio of 0.081 and an H 3 /E* 2 ratio of 0.19 GPa were found in the coating deposited at f N 2 = 10%. The friction coefficient of the TiAlSiN coatings was around 0.8–0.9 as sliding against a Si 3 N 4 counterpart under a normal load of 0.5 N. A wear rate of 2.0 × 10 − 5 mm 3 N − 1 m − 1 was measured in the TiAlSiN coatings deposited at f N 2 = 20–40%. As only a low residual stress is found in the TiAlSiN coatings, we consider the complete phase separation is responsible for the enhanced mechanical and tribological properties of the nc -TiAlN/ a -Si 3 N 4 nanocomposite coatings. [ABSTRACT FROM AUTHOR]

Deep oscillation magnetron sputtering (DOMS) is an alternative high-power pulsed magnetron sputtering technique, which offers virtually arc-free depositions especially for reactive depositions of some insulating coatings under optimized pulsing conditions. CrN/TiN superlattice coatings with a modulated period (Λ) ranging from 5.7 to 10.2 nm were deposited using a combination of DOMS and pulsed dc magnetron sputtering in a closed field unbalanced magnetron sputtering system. As a Λ was increased from 5.7 to 10.2 nm, CrN/TiN superlattice coatings with the increased Cr/(Cr + Ti) ratio from 0.177 to 0.496 exhibited a single phase face-centered cubic structure with a strong {111} texture. Correspondingly, the hardness, the H/E* and H 3 /E* 2 ratios showed an initial increase, followed by a decrease. The coatings at Λ = 6.3 nm with the Cr/(Cr + Ti) ratio of 0.294 and fine grain size of about 30 nm showed the highest hardness of 36 GPa, H/E* ratio of 0.093 and H 3 /E* 2 ratio of 0.313. It also showed a mild abrasive wear with the lowest friction coefficient and specific wear rate of 0.27 and 0.5 × 10 − 6 mm 3 N − 1 m − 1 , respectively. With increasing Λ, the friction coefficient and specific wear rate decreased and then increased. The dominant wear mechanism changed from oxidative wear to mild abrasive wear, and then to severe oxidative wear. The changes of H, H/E* and H 3 /E* 2 ratios and adhesion of CrN/TiN superlattice coatings resulted in variation of tribological properties and wear mechanism. [ABSTRACT FROM AUTHOR]

Deep oscillation magnetron sputtering (DOMS) is a novel high power impulse magnetron sputtering technique, which offers large voltage oscillation packets to generate a stable high-power discharge plasma with high ionization under virtually arc-free conditions. CrN/TiN superlattice coatings were deposited using a combined DOMS and pulsed dc magnetron sputtering (PDCMS) in a closed field unbalanced magnetron sputtering configuration. The Cr target was powered at 400 W by DOMS and Ti target was powered at 2000 W by PDCMS. The negative substrate bias ( V s ) ranged from 0 V to −100 V. As the V s was increased, CrN/TiN superlattice coatings showed a single phase face-centered cubic structure with a strong (1 1 1) texture. Correspondingly, the coatings exhibited the dense microstructure with well-defined interfaces between CrN and TiN layers. The increase in V s led to a decrease in grain size and an increase in the compressive residual stress. The hardness and Young's modulus of the coatings increased with increasing V s . The H / E * and H 3 / E * 2 ratios and critical loads L C in scratch test showed an initial increase, followed by a decrease. The wear mechanism changed from severe adhesion wear to abrasion wear. The coating deposited at V s = −60 V exhibited mild abrasion wear with the lowest friction coefficient of 0.27 and the lowest specific wear rate of 0.5 × 10 −6 mm 3 N −1 m −1 due to high hardness, H / E * and H 3 / E * 2 ratios, L C1 and L C3 of 36 GPa, 0.094, 0.316, 15.3 N and 24 N, respectively. The coatings also exhibited increasing pitting corrosion resistance with lower current density and higher corrosion potential in 3.5 wt% NaCl aqueous solution. Combined DOMS + PDCMS techniques can provide the engineering surfaces for the industrial applications with the combined improvement in wear and corrosion resistance. [ABSTRACT FROM AUTHOR]

Abstract: Low-pressure oxygen and argon plasmas were used to pre-treat nylon fabrics, and the modified fabrics, together with the raw fabrics, were subsequently coated with single walled carbon nanotubes (SWCNTs) by a dip-drying process. Scanning electron microscopy (SEM) and Raman spectroscopy analyses indicated the attachment of SWCNTs onto nylon fabrics. After the coating with SWCNTs, the plasma modified fabrics exhibited sheet resistance of as low as 2.0kΩ/sq. with respect to 4.9kΩ/sq. of the raw fabrics, presumably owing to the increase of fibre surface roughness incurred by the plasma modification, which is evidenced by SEM analyses. Fourier transform infrared spectroscopy (FTIR) analysis indicates the incorporation of oxygen functionalities on fibre surfaces in the plasma modification. This is responsible for the variation of the electrical conductance of SWCNT-coated fabrics with the type of plasma and the duration of plasma ablation. [Copyright &y& Elsevier]

Abstract: Cr–C–N coatings with different compositions, i.e. (C+N)/Cr atomic ratios (x) of 0.81–2.77, were deposited using pulsed closed field unbalanced magnetron sputtering by varying the chromium and graphite target powers, the pulse configuration and the ratio of the nitrogen flow rate to the total gas flow rate. Three kinds of nanostructures were identified in the Cr–C–N coatings dependent on the x values: a nano-columnar structure of hexagonal closed-packed (hcp) Cr2(C,N) and face-centered cubic (fcc) Cr(C,N) at x =0.81 and 1.03 respectively, a nanocomposite structure consisting of nanocrystalline Cr(C,N) embedded in an amorphous C(N) matrix at x =1.26 and 1.78, and a Cr-containing amorphous C(N) structure at x =2.77. A maximum hardness of 31.0GPa and a high H/E ratio of 1.0 have been achieved in the nc-Cr(C,N)/a-C(N) nanocomposite structure at x =1.26, whereas the coating with a Cr-containing amorphous C(N) structure had a minimum hardness of 10.9GPa and a low H/E ratio of 0.08 at x =2.77. The incorporation of carbon into the Cr–N coatings led to a phase transition from hcp-Cr2(C,N) to fcc-Cr(C,N) by the dissolution into the nanocrystallites, and promoted the amorphization of Cr–C–N coatings with the precipitation of amorphous C(N). It was found that a high x value over 1.0 in the Cr–C–N coatings is the composition threshold to the nanostructure transition. [Copyright &y& Elsevier]

Abstract: A nondestructive method to determine the density of coating has been proposed in this paper based on the ultrasonic reflection coefficient phase spectrum (URCPS). A model was set up first to represent the ultrasonic waves reflected from a coating system at normal incident, and the relation between the extremum of URCPS and the coating density was established to provide the principle of determining the density. The ultrasonic method was validated on a series of ZrO2–7wt.%Y2O3 (YSZ) coatings with various density. The specimens were prepared by electric beam physical vapor deposit (EB-PVD). After deposition, the specimens were irradiated using high-intensity pulsed ion beam (HIPIB) at different ion current density of 100 and 200A/cm2 to change coating density. The coating densities of as-deposited and post irradiation by HIPIB were derived to be 4940–5030, 5200–5320 and 5390–5470kg/m3, respectively. The relative error between the coating density measured by the ultrasonic method and Archimedean principle ranging from 2.53% to 6.11%, indicates that the proposed ultrasonic quantification method provides a reliable nondestructive way to determine coating density. [Copyright &y& Elsevier]

Abstract: ZrO2 ceramic coatings, which often call thermal barrier coatings (TBCs), fabricated by electron beam physical vapor deposition (EB-PVD), are widely used in high-temperature environment of aircraft and industry gas-turbine engines, because of the excellent strain tolerance imparted by the columnar structure. However, channels separating the columnar grains in EB-PVD TBCs provide paths for oxygen or other aggressive species from ambient atmosphere into the bond coat, resulting in the premature spallation-failure during high-temperature service. In our previous study, high-intensity pulsed ion beam (HIPIB) technique has been proposed to modify the EB-PVD TBCs, where a melted, densified top layer can be produced as a result of extremely thermal effect induced by the HIPIB irradiation. In this paper, HIPIB melting process is investigated numerically using a physical model based on experimental data, taking into account the surface morphology of HIPIB-melted TBCs to explore the mechanism of interaction between HIPIB and the coatings. Deposition process of the beam energy in TBCs was simulated by Monte Carlo method, and the non-linear equations describing the thermal conducting process were solved numerically based on the deposited energy to obtain the evolution of the temperature field of TBCs. The calculated melting depth of irradiated EB-PVD TBCs is consistent with results obtained in the HIPIB irradiation experiments. [Copyright &y& Elsevier]

Homostructure NbN nanocomposite coatings with cubic δ-NbN phase and hexagonal δ'-NbN phase were deposited by modulated pulsed power magnetron sputtering (MPPMS) under varied nitrogen flow rate f N2 from 15% to 30%. Low f N2 favored the formation of δ'-NbN phase with (100) preferred orientation and δ-NbN phase with (200) preferred orientation, while high f N2 favored the formation of δ-NbN phase with (200) preferred orientation. The NbN coatings were characterized as the nanocomposite coatings with δ'-NbN nanocrystallites embedded into δ-NbN matrix. The hardness and modulus of NbN coatings went up to 36 GPa from 30 GPa and 460 GPa from 366 GPa as f N2 increased to 20% with residual compressive stress from 0.47 GPa to 1.93 GPa, then decreased to 29 GPa and 389 GPa with residual compressive stress of 1.01 GPa as f N2 further increased. Meanwhile, the toughness of coatings increased with the content of δ'-NbN phase showing an abrupt change of NbN coating toughness under the f N2 of 30%. The homostructure NbN nanocomposite coatings with both enhanced hardness and toughness were achieved by forming nanocomposite structure at low f N2. The results showed that the essential conditions of the design criterion for hard and tough coatings should be arranged in the impact of weight as follows: 1) the designed microstructure, 2) the compressive residual stress, 3) high H/E and H3/E2, 4) high W e. • NbN nanocomposite coatings were deposited by MPPMS under varied nitrogen flow rate. • Hexagonal δ'-NbN phase was observed in coatings under low nitrogen flow rate. • The mechanical properties showed a nonlinear response with discharge peak power. • Homostructure in NbN nanocomposite coatings could alleviate the Friedel oscillations. • The conditions of design criterion for tough and hard coatings were rearranged. [ABSTRACT FROM AUTHOR]

• TiAlSiN nanocomposite coatings were deposited by MPPMS. • Thermal conductivity of coatings was tested by transient thermoreflectance technique. • Thermal conductivity decreased with increase of bias voltage. • Grain size decreased with increase of bias voltage. • The decrease of grain size led to the increase of phonon scattering. Hard Ti-Al-Si-N coatings are widely used in cutting tools, due to their excellent mechanical properties and superior thermal properties. In this study, Ti-Al-Si-N coatings are deposited by modulated pulsed power magnetron sputtering, with various substrate bias voltages from −35 V to −130 V. As the bias voltage goes up, the composition of coatings remained nearly unchanged, maintained as a constant of Ti 0.18 Al 0.26 Si 0.05 N 0.51. However, the Ti-Al-Si-N coatings have a decrease in (200)-preferred orientation; dense columnar structure (Zone I) of Ti-Al-Si-N coatings gradually evolves into featureless and flat cross sections structure (Zone T). As increasing the substrate bias voltage, the hardness increases from 31.2 GPa to 37.5 GPa, the H/E* value increases from 0.079 to 0.090, while the compressive residual stress of coatings raises from -1.22 GPa to -2.15 GPa. The thermal conductivity of coatings is examined by transient thermoreflectance technique, which decreases from 5.4 W/m*K to 2.1 W/m*K with the bias voltage. The values of electric resistivity ρ for all coatings are very large, ranging from 147 kΩ⋅m to 173 kΩ⋅m. The electronic thermal conductivity has no contribution to the thermal conductivity of Ti-Al-Si-N coatings, which is mainly determined by the phonon thermal conductivity. As increasing the substrate bias voltage, the average grain size of Ti-Al-Si-N nanocomposite coatings decreases from 16 nm to 5 nm. The interfacial density per unit volume is therefore increased, and leading to more interface scattering of the phonons in the heat transport progress, which is the key parameter in determining thermal conductivity of Ti-Al-Si-N nanocomposite coatings. [ABSTRACT FROM AUTHOR]