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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 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: 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]

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]