Preventing hydrogen damage is an important issue in materials design. To prevent such damage, CrN coating is investigated as a very promising candidate for hydrogen damage protection. In this study, the theoretical analysis of hydrogen adsorption on CrN surfaces was studied. It was found that most CrN surfaces are inert to hydrogen and do not adsorb it. This finding is suggested to explain the hydrogen protection caused by these coatings. To demonstrate these abilities of CrN coatings, we used the Pulsed-DC magnetron sputtering method to produce CrN layers on gadolinium substrates. The coated samples were exposed to hydrogen, characterized by SEM, XRD, and GD-OES, and show no hydrogen damage, were the uncoated ones exhibited a massive hydrogen attack.

ZrO2-Al2O3 coatings were deposited on a floating substrate at a temperature of 370°C. Various coating compositions, ranging from pure zirconia to 50at.% alumina content, were deposited by reactive pulsed-DC magnetron sputtering using 51mm diameter Zr and Al targets. The coating had a Zr-Al-O solid solution structure that was composed of nano-size cubic-ZrO2 grains (20±5nm) with aluminum cations distributed inside them. The deposited coatings were annealed up to 1350°C and their structural changes were studied using Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Vickers hardness measurement. Two exothermic annealing events were observed. The first event appeared at 700–750°C and was contributed to aluminum segregation to the grain boundaries, and the formation of a nanocomposite-ZrO2/amorphous-Al2O3 structure. The second event appeared at 1000–1200°C and was related to coarsening (“Ostwald ripening”) of the ZrO2 grains. The coating hardness after the first event was stabilized to 19.5±1.1GPa because of the segregation, which hindered grain growth. However, after a second DSC cycle of the coating, only one sharp endothermic transformation peak was observed at onset temperature of 1060±5°C. This was associated with grain growth accompanied with zirconia transformation from the cubic to the monoclinic phase.

The influence of deposition parameters (substrate temperature and bias voltage) on the properties of ZrO2– Al2O3 coatings (composition, microstructure, hardness, adhesion, and wear coefficient) was studied. The properties of the coatings that were produced by Pulsed-DC Magnetron Sputtering (PMS) were compared to those prepared by Filtered Vacuum Arc Deposition (FVAD). The coatings were deposited on Si and WC substrates at temperatures, Td of 25–500 °C and biases, Vb, floating and down to –200 V. The PMS deposition rate was 0.15±0.01 nm/s, while that of FVAD was 10±2 nm/s. X-ray diffraction indicated that PMS coatings had a stabilized cubic-ZrO2 structure at all Td when Vb ≤ -50 V or a tetragonal-ZrO2 structure at Vb ≥ -100 V. FVAD coatings had a stabilized tetragonal-ZrO2 structure at all Td and Vb. Coatings deposited on unheated substrates by both PMS and FVAD at floating potential had low hardness, <10 GPa. However, increasing Td to 370 °C increased the hardness of both PMS and FVAD coatings to 16±1 GPa. In the FVAD coatings, a further increase of Td to 500°C raised the hardness to 22±1 GPa. The maximum hardness, 25.9±2.6 GPa, was achieved at Vb=– 150 V (PMS coatings, unheated substrate) and was partly due to an increase in compressive stress (1066 MPa). The coating adhesion increased with Td, reaching more than 100 N at Td = 500°C (FVAD coatings, Vb=-50 V). aNRC-Negev, P.O.Box 9001, Beer-Sheva 84190, Israel bAdvanced Coatings Center, Rotem Industries Ltd., Mishor Yamin, D.N. Arava 86800, Israel cElectrical Discharge and Plasma Laboratory, Faculty of Engineering, Tel-Aviv University, Tel-Aviv, Israel *Corresponding author

Ternary zirconia-alumina coatings with different compositional ratios, ranging from pure zirconia to 50% alumina content, were deposited by reactive sputtering from two targets, Zr and Al, in argon-oxygen mixtures. The coating composition was controlled by the Zr/Al target power ratio provided by two pulsed-DC power supplies. The coatings were ~1 µm thick and they were deposited on floating potential substrates at a temperature of 650±3K. XRD indicated that the pure zirconia coatings possessed a monoclinic structure with a grain size of 35-40 nm. Adding alumina to the zirconia coating stabilized the cubic zirconia phase and decreased the grain size to 10-15 nm. The alumina phase in the coatings remained amorphous. The hardness of the nanocomposite structure increased from 11.6±0.5 GPa to 16.1±0.5 GPa for an alumina content of 17%. At higher alumina concentrations, the zirconia phase became amorphous and the hardness decreased to 10-11 GPa. Structure stability of the zirconia-alumina coatings was studied by measuring the coating structure and hardness after annealing at temperatures up to 1173 K. Pure zirconia (m-ZrO2) coatings had low structure stability; the hardness reached a maximum value of 18±1 GPa after annealing at a temperature of 773-873K; however, at higher annealing temperatures the hardness decreased, reaching a minimum value of 12.3±0.6 GPa after annealing at 1173K. The hardness of the nanocomposite ZrO2/Al2O3 coating with various compositions increased with annealing temperature. The hardness of a coating with an alumina content of 17% reached a high value of 19.2±0.5 GPa after annealing at 1073-1173 K. Measurements of post annealing XRD analyses indicated that the stabilization of the coating structure with c-ZrO2/a-Al2O3 phases is the reason for the higher structure stability. From the analyses of phase stability and hardness before and after annealing, we conclude that adding alumina to the zirconia phase promotes the formation of nanocomposite c-ZrO2/a-Al2O3 coatings with a markedly higher stability than single-phase m-ZrO2. Highlights: 1. ZrO2/Al2O3 nanocomposite coatings were deposited by co-sputtering from Zr and Al targets. 2. Adding alumina to the zirconia coating stabilized the cubic zirconia phase. 3. ZrO2-17% Al2O3 coatings had a grain size of 10-15 nm and a hardness of 16.1±0.5 GPa. 4. ZrO2/Al2O3 coatings maintained a high hardness after annealing at 1173K with a high value of 19 GPa for alumina content of 17%. 5. The ZrO2/Al2O3 nanocomposite coatings were crack-free after annealing at 1173K.

Al2O3-ZrO2 coatings were deposited using a vacuum arc deposition system equipped with two co-planar cathodes. The plasma was injected into a cylindrical magnetic duct through annular anode apertures toward a substrate or an electrostatic ion current probe positioned on the duct axis, in vacuum and in a low-pressure oxygen or argon + oxygen background. Ion current and arc voltage measurements and visual observation of the cathode spots were used to find stable arcing conditions, using a straight plasma duct configuration. The cathode spot operation and transport of the plasma beam in the duct were studied as a function of arc current (I (arc) = 25-200 A) and oxygen or oxygen + argon pressures (P = 0.1-1.5 Pa). Coatings were fabricated by exposing Si or WC-Co substrates simultaneously to Al and Zr plasmas using a 1/8 torus filter configuration in O-2 + Ar pressures. The coating composition, structure, microhardness, adhesion, and wear behavior were studied as functions of the deposition parameters. Favorable conditions for stable arcing were obtained with I (arc) = 75 and 100 A for Al and Zr plasmas, respectively. The ion current decreased, and the arc voltage increased with the oxygen pressure. Behavior of the ion current and arc voltage suggested that cathode poisoning started at P = 0.5 Pa. Deposition rates were 0.3-0.6 mu m/min, depending on the substrate position. All coatings were "Zr rich", i.e., the Zr:Al ratio was in the range of 1.2-5.6 depending on the substrate position and deposition conditions. The coatings with higher ZrO2 concentration were harder and had better resistance to wear. The coating's hardness reached a maximum of similar to 22-24 GPa at a deposition temperature of 500 A degrees C or a negative bias voltage of 75-100 V.

Al 2 O 3 –ZrO 2 coatings were deposited using a vacuum arc deposition system equipped with two co-planar cathodes. The plasma was injected into a cylindrical magnetic duct through annular anode apertures toward a substrate or an electrostatic ion current probe positioned on the duct axis, in vacuum and in a low-pressure oxygen or argon + oxygen background. Ion current and arc voltage measurements and visual observation of the cathode spots were used to find stable arcing conditions, using a straight plasma duct configuration. The cathode spot operation and transport of the plasma beam in the duct were studied as a function of arc current ( I arc = 25–200 A) and oxygen or oxygen + argon pressures ( P = 0.1–1.5 Pa). Coatings were fabricated by exposing Si or WC–Co substrates simultaneously to Al and Zr plasmas using a 1/8 torus filter configuration in O 2 + Ar pressures. The coating composition, structure, microhardness, adhesion, and wear behavior were studied as functions of the deposition parameters. Favorable conditions for stable arcing were obtained with I arc = 75 and 100 A for Al and Zr plasmas, respectively. The ion current decreased, and the arc voltage increased with the oxygen pressure. Behavior of the ion current and arc voltage suggested that cathode poisoning started at P = 0.5 Pa. Deposition rates were 0.3-0.6 μm/min, depending on the substrate position. All coatings were “Zr rich”, i.e., the Zr:Al ratio was in the range of 1.2–5.6 depending on the substrate position and deposition conditions. The coatings with higher ZrO 2 concentration were harder and had better resistance to wear. The coating’s hardness reached a maximum of ~22–24 GPa at a deposition temperature of 500 °C or a negative bias voltage of 75–100 V.

In a PACVD system, titanium alloys were exposed to inductive radio-frequency (RF) plasmas of H-2+N-2 and Ar+BCl3+H-2+N-2 gas mixtures for their nitriding and boron nitride respectively. Hard nanocomposite thin films of RAIN and TiAlBN were formed on Ti-6Al-4V alloys in an inductive RE plasma of Ar+H-2+N-2 and Ar+3.5 vol.% of BCl3+H-2+N-2, respectively. The substrates were grounded, i.e., self-biased, during plasma thin film formation for 30 min each. TiAlBN was deposited by sputtering in a reactive PVD system. A quadrupole mass spectrometer (QMS) sampled the plasma at a constant distance of 0.5 cm from the sample surface in real time. The mass species (m/e) at 0.5 cm were recorded during the deposition process. To separate the particles reaching the substrate surface from those leaving it, the narrocomposite thin films coated samples of Ti alloys were introduced in an RF plasma of Ar+H-2 mixture without the presence of N-2 and BCl3 and negatively biased up to V-b = -350 V The QMS at 0.5 cm measures the etched and sputtered species from the surface of the coated samples. Comparing the QMS results between the grounded samples with the monomers in the RF plasma and the negatively biased voltage samples without monomers in the Ar+H-2 plasma the net plasma surface interactions (PSI) were evaluated. The behavior of the coating process of nanocomposite thin films of TiAlN and TiAlBN on the Ti alloy samples is strongly dependent on the plasma surface phenomena. (C) 2007 Elsevier B.V. All rights reserved.

In the present work, we performed a case study of the wear resistance of 3μm thick film systems consisting of TiCN single-layer and TiN/TiCN double-layer structures deposited by electron beam evaporation onto plasma-nitrided PH15-5 steel. We particularly focused on the wear resistance of the duplex-treated (nitriding+deposition) coatings before and after annealing at 1123±3K using a ball-on-disk tribometer. We found that the plasma-nitrided layer prepared in a dual-mode microwave-radiofrequency discharge improved the wear resistance by nearly one order of magnitude compared to untreated steel (wear volume of 0.9±0.2×10−6mm3 compared to 8.7±0.2×10−6mm3). In addition, the experiments showed that the nitrided-layer between the steel and the hard coating acts as a diffusion barrier which maintains the wear resistance of the duplex-treated coatings composed of TiCN or TiN/TiCN layers.

Hard TiAI(B)N coatings were deposited by radio-frequency magnetron sputtering in reactive mode in an argon and nitrogen environment using a TiAlB target with 12 at.% of boron. The deposition was carried out under ion bombardment at various negative bias voltages in the range of 0 to 170 V, and at substrate temperatures between 453 and 523 K. The internal stress in the coatings was studied at room temperature as a function of annealing temperatures in ambient air up to 1123 K. The heating duration was 2 h followed by annealing for 1 h. The microstructure, phase composition and hardness were also studied prior to and after annealing.We found that the TiAlBN coatings consist of TiAl3 and TiN phases. With increasing ion bombardment, the structure of the coatings changes from columnar to nano-scale features. Prior to annealing we also observed a correlation between the residual stress and hardness. After annealing, the compressive stresses of the TiAl(B)N coatings decreased from 1.0 GPa to less than 0.2 GPa, while the hardness remained constant or increased from similar to 10 GPa to similar to 25 GPa. The hardness increase of the coatings after annealing is related to a self-hardening effect. (c) 2006 Elsevier B.V. All rights reserved.

Nitriding was carried out in low pressure plasma excited by single- or dual-frequency discharge modes, at a substrate temperature of 523 K, followed by the deposition of 3 gm thick TiCN or TiN/TiCN coatings at a PH15-5 substrate temperature of 723 K. The nitrided layer was comprised of two distinct sublayers, namely a compound layer and a diffusion layer, with a total thickness of similar to 60 mu m. The compound layer was gamma'-Fe4N and the diffusion layer was a solid solution of nitrogen in iron. The thickness of the compound layer fabricated by a single mode plasma is similar to 5 mu m, while that fabricated by dual-frequency mode plasma is similar to 35 mu m.It was found, using a ball-on-disk test, that the plasma nitrided layer fabricated by dual-frequency mode improved wear resistance by nearly one order of magnitude and improved the erosion resistance by a factor of two, compared with untreated steel. This improvement was common to the two nitriding treatments and both types of hard coatings. In particular, a thicker compound layer did not impair the wear resistance or the erosion resistance of the duplex treatment. The erosion resistance shows a linear dependence on the hardness of the uppermost nitrided or deposited layer. (c) 2006 Elsevier B.V. All rights reserved.

Thermal stability of TiAlBN and TiN/TiCN hard coatings was studied by evaluating the stress-temperature curves and the wear resistance after annealing up to 1123 K The microstructure, phase composition and hardness were studied prior and after annealing.Prior to annealing, a correlation between the residual stress and hardness was observed. After annealing, the compressive stresses of the TiAlBN coatings decreased from 1.0 GPa to less than 0.2 GPa, while the hardness remained constant or increased from similar to 10 GPa to similar to 25 GPa. The hardness increase of the coatings after annealing is related to the self-hardening effect.The effect of the plasma nitriding mode prior to the deposition of 3 gm thick TiCN or TiN/TiCN coatings on the wear resistance of the duplex-treated coating (nitriding and deposition) was studied. The stability of the wear resistance of the duplex treated-coating was also examined after one hour of annealing at 1123 K It was found that the plasma-nitrided layer in the duplex treatment maintains the wear resistance stability of the annealed duplex-treated hard coatings.