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The effect of peak power in a high power impulse magnetron sputtering (HiPIMS) reactive deposition of TiO(2) films has been studied with respect to the deposition rate and coating properties. With increasing peak power not only the ionization of the sputtered material increases but also their energy. In order to correlate the variation in the ion energy distributions with the film properties, the phase composition, density and optical properties of the films grown with different HiPIMS-parameters have been investigated and compared to a film grown using direct current magnetron sputtering (DCMS). All experiments were performed for constant average power and pulse on time (100W and 35 mu s, respectively), different peak powers were achieved by varying the frequency of pulsing. Ion energy distributions for Ti and O and its dependence on the process conditions have been studied. It was found that films with the highest density and highest refractive index were grown under moderate HiPIMS conditions (moderate peak powers) resulting in only a small loss in mass-deposition rate compared to DCMS. It was further found that TiO2 films with anatase and rutile phases can be grown at room temperature without substrate heating and without post-deposition annealing.

Ca-Si-O-N thin films were deposited on commercial soda-lime silicate float glass, silica wafers and sapphire substrates by RF magnetron co-sputtering from Ca and Si targets in an Ar/N-2/O-2 gas mixture. Chemical composition, surface morphology, hardness, reduced elastic modulus and optical properties of the films were investigated using X-ray photoelectron spectroscopy, scanning electron microscopy, nanoindentation, and spectroscopic ellipsometry. It was found that the composition of the films can be controlled by the Ca target power, predominantly, and by the reactive gas flow. Thin films in the Ca-Si-O-N system are composed of N and Ca contents up to 31 eq. % and 60 eq. %, respectively. The films thickness ranges from 600 to 3000 nm and increases with increasing Ca target power. The films surface roughness varied between 2 and 12 nm, and approximately decreases with increasing power of Ca target. The hardness (4-12 GPa) and reduced elastic modulus (65-145 GPa) of the films increase and decrease with the N and Ca contents respectively. The refractive index (1.56-1.82) is primarily dictated by the N content. The properties are compared with findings for bulk glasses in the Ca-Si-(Al)-O-N systems, and it is concluded that Ca-Si-O-N thin films have higher values of hardness, elastic modulus and refractive index than bulk glasses of similar composition. (C) 2017 Elsevier B.V. All rights reserved.

In this work, amorphous thin films in Mg-Si-O-N system typically containing amp;gt; 15 at.% Mg and 35 at.% N were prepared in order to investigate especially the dependence of optical and mechanical properties on Mg composition. Reactive RF magnetron co-sputtering from magnesium and silicon targets were used for the deposition of Mg-Si-O-N thin films. Films were deposited on float glass, silica wafers and sapphire substrates in an Ar, N-2 and O-2 gas mixture. X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and nanoindentation were employed to characterize the composition, surface morphology, and properties of the films. The films consist of N and Mg contents up to 40 at.% and 28 at.%, respectively and have good adhesion to substrates and are chemically inert. The thickness and roughness of the films increased with increasing content of Mg. Both hardness (16-21 GPa) and reduced elastic modulus (120-176 GPa) are strongly correlated with the amount of Mg content. The refractive index up to 2.01 and extinction coefficient up to 0.18 were found to increase with Mg content. The optical band gap (3.1-4.3) decreases with increasing the Mg content. Thin film deposited at substrate temperature of 100 degrees C shows a lower value of hardness (10 GPa), refractive index (1.75), and higher values of reduced elastic modulus (124 GPa) as compared to the thin film deposited at 310 degrees C and 510 degrees C respectively, under identical synthesis parameters.

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We recently showed that Zr1−xTaxBy thin films have columnar nanostructure in which column boundaries are B-rich for x < 0.2, while Ta-rich for x ≥ 0.2. Layers with x ≥ 0.2 exhibit higher hardness and, simultaneously, enhanced toughness. Here, we determine the atomic-scale nanostructure of sputter-deposited columnar Zr0.7Ta0.3B1.5 thin films. The columns, 95 ± 17 Å, are core/shell nanostructures in which 80 ± 15-Å cores are crystalline hexagonal-AlB2-structure Zr-rich stoichiometric Zr1−xTaxB2. The shell structure is a narrow dense, disordered region that is Ta-rich and highly B-deficient. The cores are formed under intense ion mixing via preferential Ta segregation, due to the lower formation enthalpy of TaB2 than ZrB2, in response to the chemical driving force to form a stoichiometric compound. The films with unique combination of nanosized crystalline cores and dense metallic-glass-like shells provide excellent mechanical properties.

We investigate the effect of low-temperature metal pretreatments in order to improve the adhesion of CNx coatings on steel substrates, which is crucial for tribological applications. The substrate pretreatments were conducted using five different metal targets: Ti, Zr, Al, Cr, and W, operated in high power impulse magnetron sputtering mode, known to produce significant ionization of the sputtered material flux. The CNx adhesion, as assessed by Rockwell C tests, did not improve upon Ti and Zr pretreatments. This is primarily ascribed to the fact that no interlayer was formed owing to severe re-sputtering due to high fluxes of doubly-ionized metal species in the plasma. A slight improvement in adhesion was observed in the case an Al pretreatment was carried out, while the best results were obtained using Cr and W. Here, 30-s-long pretreatments were sufficient to clean the steel surface and form a metallic interlayer between substrate and coating. Transmission electron microscopy in combination with energy dispersive X-ray spectroscopy revealed that Al, Cr, and W created intermixing zones at the interlayer/substrate and the interlayer/CNx interfaces. The steel surfaces, pretreated using Cr or W, showed the highest work of adhesion with W-adh(Cr) = 1.77 J/m(2) and W-adh(W) = 1.66 J/m(2), respectively. (C) 2016 Elsevier B.V. All rights reserved.

The catalytic effect of H₂S on the AlCl₃/H₂/CO₂/HCl chemical vapor deposition (CVD) process has been investigatedon an atomistic scale. We apply a combined approach with thermodynamic modeling and densityfunctional theory and show that H₂S acts as mediator for the oxygenation of the Al-surface which will inturn increase the growth rate of Al₂O₃. Furthermore we suggest surface terminations for the three investigatedsurfaces. The oxygen surface is found to be hydrogenated, in agreement with a number of previous works.The aluminum surfaces are Cl-terminated in the studied CVD-process. Furthermore, we find that the AlClOmolecule is a reactive transition state molecule which interacts strongly with the aluminum and oxygensurfaces.

High-power impulse magnetron sputtering (HiPIMS) is a thin film deposition technique that combines the advantages of energetic deposition methods with magnetron sputtering. HiPIMS has so far mostly been utilized for the growth of crystalline coatings. Here we offer a study devoted to metallic glasses, in which we compare Zr60Cu25Al10Ni5 (target composition) thin films deposited by conventional direct current magnetron sputtering (DC) and HiPIMS. Film microstructure is strongly dependent on the choice of the sputtering method. The DC layers show a columnar structure with intra-columnar porosity, which provides a pathway for oxygen diffusion into the film. In contrast, HiPIMS films are column-free and possess about 4% higher density, as revealed by X-ray reflectivity. Electron diffraction reveals a decrease in average atomic spacing for the latter film of about 12%. These differences in film properties and morphology can be attributed to an increase in ad-atom mobility during HiPIMS caused by an increase in ion energy and flux of the film-forming species enabling a more efficient energy and momentum transfer to the growing film surface. The relative contribution of metallic and hence film forming ions to the overall ion flux of the DC plasma compared to the HiPIMS plasma is 13% and 96%, respectively. Additionally, a substrate bias causes the ionized film forming species during HiPIMS to arrive close to the substrate normal reducing shadowing effects. Different microstructures have a direct effect on the average roughness values, which for DC and HiPIMS films are 1.4 nm and 0.2 nm, respectively. The indentation hardness H and Youngs modulus E are higher for the HiPIMS sample, at 9.2 +/- 0.3 GPa and 131.6 +/- 3.6 GPa, respectively. The increase in hardness for the HiPIMS sample as compared to the DC sample (similar to 35%) can be attributed to higher film density, compressive (HiPIMS) as opposed to tensile (DC) stress and the lack of a columnar structure.

The influence of isothermal oxidation on room-temperature mechanical and fracture behaviour of an air plasma-sprayed Ni-23Co-17Cr-12Al-0.5Y bondcoat was investigated by the miniaturised disc bending test (MDBT) technique. Disc specimens were extracted from the bondcoat region of both as-received and oxidised thermal barrier coating (1000 °C, 1000 h). Microstructure analysis revealed that the non-oxidised bondcoat consisted mainly of γ-phase (Ni-structure) and β-NiAl. After 500 h of oxidation no NiAl remained in the bondcoat, an effect due to internal as well as external oxidation of Al. The former resulted in the formation of an extensive oxide network and the latter in the formation of an oxide scale between the topcoat and the bondcoat. The crack propagation behaviour of the bondcoat, both in non-oxidised and oxidised condition can be characterised as intergranular with stable growth. The crack propagation resistance is substantial due to the lamellar grain (splat) orientation and the extensive intergranular oxide network, acting as crack deflection and crack branching mechanisms. As an effect of oxidation, crack propagation resistance of the bondcoat increases but the strain to crack initiation decreases.

Amorphous phosphorous-carbide films have been considered as a new tribological coating material with unique electrical properties. However, such CPx films have not found practical use until now because they tend to oxidize/hydrolyze rapidly when in contact with air. Recently, we demonstrated that CPx thin films with a fullerene-like structure can be deposited by magnetron sputtering, whereby the structural incorporation of P atoms induces the formation of strongly bent and inter-linked graphene planes. Here, we compare the uptake of water in fullerene-like phosphorous-carbide (FL-CPx) thin films with that in amorphous phosphorous-carbide (a-CPx), and amorphous carbon (a-C) thin films. Films of each material were deposited on quartz crystal substrates by reactive DC magnetron sputtering to a thickness in the range 100-300 nm. The film microstructure was characterized by X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. A quartz crystal microbalance placed in a vacuum chamber was used to measure their water adsorption. Measurements indicate that FL-CPx films adsorbed less water than the a-CPx and a-C ones. To provide additional insight into the atomic structure of defects in the FL-CPx and a-CPx compounds, we performed first-principles calculations within the framework of density functional theory. Cohesive energy comparison reveals that the energy cost formation for dangling bonds in different configurations is considerably higher in FL-CPx than for the amorphous films. Thus, the modeling confirms the experimental results that dangling bonds are less likely in FL-CPx than in a-CPx and a-C films.

The microstructural, morphological, optical and water-adsorption properties of nanocrystalline ZnO thin films and ZnO nanowires were studied and compared. The ZnO thin films were obtained by a sol–gel process, while the ZnO nanowires were electrochemically grown onto a ZnO sol–gel spin-coated seed layer. Thin films and nanowire samples were deposited onto crystalline quartz substrates covered by an Au electrode, able to be used in a quartz crystal microbalance. X-ray diffraction measurements reveal in both cases a typical diffraction pattern of ZnO wurtzite structure. Scanning electron microscopic images of nanowire samples show the presence of nanowires with hexagonal sections, with diameters ranging from 30 to 90 nm. Optical characterization reveals a bandgap energy of 3.29 eV for the nanowires and 3.35 eV for the thin films. A quartz crystal microbalance placed in a vacuum chamber was used to quantify the amount and kinetics of water adsorption onto the samples. Nanowire samples, which have higher surface areas than the thin films, adsorb significantly more water.

Highly adherent carbon nitride (CNx) films were deposited using a novel pretreatment with two high power impulse magnetron sputtering (HIPIMS) power supplies in a master-slave configuration: one to establish the discharge and one to produce a pulsed substrate bias. During the pretreatment, SKF3 (AISI 52100) steel substrates were pulse-biased in the environment of a HIPIMS Cr plasma in order to sputter clean the surface and to implant Cr metal ions. Subsequently. CNx films were prepared at room temperature by DC unbalanced magnetron sputtering from a high purity graphite target in a N-2/Ar discharge at 3 mTorr. All processing was done in an industrial CemeCon CC800 system. A series of depositions were obtained with samples at different bias voltages (DC and pulsed) in the range of 0-800 V. Scanning transmission microscopy (STEM) and high resolution transmission electron microscopy (HRTEM) show the formation of an interface comprising a polycrystalline Cr layer of 100 nm and an amorphous transition layer of 5 nm. The adhesion of CNx films evaluated by the Daimler-Benz Rockwell-C reach strength quality HF1, and the scratch tests gives critical loads of 84 N. Adhesion results are correlated to the formation of an optimal interfacial mixing layer of Cr and steel.

Nitrogen deficient c-(Ti0.52Al0.48)Ny, y = 0.92, y = 0.87, and y = 0.75 coatings were prepared in different N-2/Ar discharges on WC-Co inserts by reactive cathodic arc deposition. The microstructure of the y = 0.92 coating show that spinodal decomposition has occurred resulting in the formation of coherent c-TiN- and c-AIN rich domains during cutting. The y = 0.87 and y = 0.75 coatings have exhibited a delay in decomposition due to the presence of nitrogen vacancies that lowers the free energy of the system. In the decomposed structure, grain boundaries and misfit dislocations enhance the diffusion of elements from the workpiece and the substrate (e.g. Fe, Cr, and Co) into the coatings and it becomes more susceptible to crater wear. The y = 0.87 sample displays the highest crater wear resistance because of its dense grain boundaries that prevent chemical wear. The y = 0.92 sample has the best flank wear resistance because the decomposition results in age hardening. The y = 0.75 sample contains the MAX-phase Ti(2)AIN after cutting. The chemical alteration within the y = 0.75 sample and its high amount of macroparticles cause its low wear resistance. The different microstructure evolution caused by different amount of N-vacancies result in distinctive interactions between chip and coating, which also causes difference in the initial wear mechanism of the (Ti,Al)/N-y coatings.

Tritantalum pentanitride (Ta₃N₅) semiconductor is a promising material for photoelectrolysis of water with high efficiency. Ta₃N₅ is a metastable phase in the complex system of TaN binary compounds. Growing stabilized single-crystal Ta₃N₅ films is correspondingly challenging. Here, we demonstrate the growth of a nearly single-crystal Ta₃N₅ film with epitaxial domains on c-plane sapphire substrate, Al₂O₃(0001), by magnetron sputter epitaxy. Introduction of a small amount ~2% of O₂ into the reactive sputtering gas mixed with N₂ and Ar facilitates the formation of a Ta₃N₅ phase in the film dominated by metallic TaN. In addition, we indicate that a single-phase polycrystalline Ta₃N₅ film can be obtained with the assistance of a Ta₂O₅ seed layer. With controlling thickness of the seed layer smaller than 10 nm and annealing at 1000 °C, a crystalline β phase Ta₂O₅ was formed, which promotes the domain epitaxial growth of Ta₃N₅ films on Al₂O₃(0001). The mechanism behind the stabilization of the orthorhombic Ta₃N₅ structure resides in its stacking with the ultrathin seed layer of orthorhombic β-Ta₂O₅, which is energetically beneficial and reduces the lattice mismatch with the substrate.

Direct growth of orthorhombic Ta3N5-type Ta-O-N compound thin films, specifically Ta3-xN5-yOy, on Si and sapphire substrates with various atomic fractions is realized by unbalanced magnetron sputtering. Low-degree fiber-textural Ta3-xN5-yOy films were grown through reactive sputtering of Ta in a gas mixture of N-2, Ar, and O-2 with keeping a partial pressure ratio of 3:2:0.1 in a total working pressure range of 5-30 mTorr. With increasing total pressure from 5 to 30 mTorr, the atomic fraction of O in the as-grown Ta3-xN5-yOy films was found to increase from 0.02 to 0.15 while that of N and Ta decrease from 0.66 to 0.54 and 0.33 to 0.31, respectively, leading to a decrease in b lattice constant up to around 1.3%. Metallic TaNx phases were formed without oxygen. For a working pressure of 40 mTorr, an amorphous, O-rich Ta-N-O compound film with a high O fraction of similar to 0.48, was formed, mixed with non-stoichiometric TaON and Ta2O5. By analyzing the plasma discharge, the increasing O incorporation is associated with oxide formation on top of the Ta target due to a higher reactivity of Ta with O than with N. The increase of O incorporation in the films also leads to a optical bandgap widening from similar to 2.22 to similar to 2.96 eV, which is in agreement with the compositional and structural changes from a crystalline Ta3-xN5-yOy to an amorphous O-rich Ta-O-N compound.

The effect of metal alloying on mechanical properties including hardness and fracture toughness were investigated in three alloys, Ti 0.33Al0.50(Me) 0.17N (Me = Cr, Nb and V), and compared to Ti0.50Al0.50N, in the as-deposited state and after annealing. All studied alloys display similar as-deposited hardness while the hardness evolution during annealing is found to be connected to phase transformations, related to the alloy’s thermal stability. The most pronounced hardening was observed in Ti0.50Al0.50N, while all the coatings with additional metal elements sustain their hardness better and they are harder than Ti0.50Al0.50N after annealing at 1100 °C. Fracture toughness properties were extracted from scratch tests. In all tested conditions, as-deposited and annealed at 900 and 1100 °C, Ti0.33Al0.50Nb0.17N show the least surface and sub-surface damage when scratched despite the differences in decomposition behavior and h-AlN formation. Theoretically estimated ductility of phases existing in the coatings correlates well with their crack resistance. In summary, Ti0.33Al0.50Nb0.17N is the toughest alloy in both as-deposited and post-annealed states.

The phase stability and mechanical properties of wurtzite (w)-Zr(0.25)A1(0.75)N/cubic (c)-TiN and w-Zr(0.25)A1(0.75)N/c-ZrN multilayers grown by arc evaporation are studied. Coherent interfaces with an orientation relation of c-TiN (111)[1-10]IIw-ZrAlN (0001)[11-20] form between ZrA1N and TiN sublayers during growth of the w-ZrAIN/c-TiN multilayer. During annealing at 1100 degrees C a c-Ti(Zr)N phase forms at interfaces between ZrA1N and TiN, which reduces the lattice mismatch so that the coherency and the compressive strain are partially retained, resulting in an increased hardness (32 GPa) after annealing. For the w-ZrAIN/c-ZrN multilayer, there is no coherency between sublayers leading to strain relaxation during annealing causing the hardness to drop. The retained coherency between layers and the compressive strain in the w-ZrAIN/c-TiN multilayer results in superior fracture toughness compared to the w-ZrAIN/c-ZrN multilayer as revealed by cross-sectional investigations of damage events under scratch and indentation tests. (C) 2017 Elsevier B.V. All rights reserved.

Coatings based on CoCrMo cobalt alloy have been designed to increase corrosion resistance of AISI 316L austenitic steel in body fluids. The CoCrMo-C coatings, with different carbon content (from 0 to 65 at.%), were synthesised by reactive magnetron sputtering of the medical CoCrMo (ISO 5832-12) alloy in the argon -acetylene atmosphere. Evolution of their structure, crystalline phase and chemical composition with increasing carbon fraction were investigated by X-ray diffractometry and X-ray photoelectron spectroscopy. Evaluation of corrosion resistance of CoCrMo-C films on 316L steel substrates was performed in Hanks Balanced Salt Solution (HBSS) by means of electrochemical impedance spectroscopy and potentiodynamic polarisation tests. The studies have revealed high chemical inertness of all coatings. Passive/blocking layers formed on their surfaces exhibit a capacitive character, while their resistivity is nearly two orders of magnitude higher compared to the corresponding values obtained for the CoCrMo and 316L alloys tested under similar conditions. The CoCrMo-C coatings provide pitting corrosion protection for 316L austenitic steel. This is expected to extend the residence time of stainless steel in the tissue environment. The 316L/CoCrMo-C systems were also subjected to tribocorrosion tests in HBSS at three electrochemical potentials, i.e. at open circuit, cathodic, and anodic potential. A model was developed to relate the electrical values recorded during tribocorrosion experiments with the phenomena that characterize the coating wear process. It was found that the friction coefficient systematically decreased from 0.7 to 0.1 with increasing the carbon content under all potentials applied. The wear rate observed for majority of the coatings was lower than that for CoCrMo and 316L alloys. For the samples with the highest carbon content, the wear rate under oxidative conditions became even lower than for the cathodic potential.

An amorphous nano-thick oxide layer was produced by plasma oxidation on a AISI 316L stainless steel substrate to increase the adhesion and stability of a fluorocarbon plasma-deposited coating for biomedical applications. This oxide layer decreased the corrosion rate &gt; 10-fold compared with a previous plasma-etched interface. The high corrosion resistance of the oxide layer as a new interface for fluorocarbon plasma-deposited coatings showed significant adhesion improvement by decreasing blisters formation, which are formed due to substrate corrosion. After aging in an aqueous saline solution, defluorination of the coating was less which evidenced that the fluorocarbon coating was more stable on the new interface compared with the plasma-etched interface. The coating on the new interface decreased the corrosion rate &gt; 20-fold in deformed samples compared with uncoated deformed samples. Moreover, the fluorocarbon coatings withstood a 25% plastic deformation and also a two-week aging in an aqueous saline solution. The results revealed remarkable properties of the amorphous oxide layer as a new interface on the adhesion and stability enhancement of the fluorocarbon coating to the SS316L substrate in an aqueous saline solution.

Sputter-deposited titanium diborides are promising candidates for protective coatings in harsh and extreme conditions. However, growing these layers from TiB₂ diboride targets by DC magnetron sputtering usually leads to over-stoichiometric layers with low crystal qualities. Moreover, superlattices with TiB₂ as one of the constituents have been becoming popular, owing to their superior mechanical properties compared to single layer constituents in addition to their use in other applications such as neutron optics. Here, we propose the use of a TiB (Ti:B = 1:1) sputtering target in an on-axis deposition geometry and demonstrate the growth of epitaxial sub-stoichiometric TiB_1.8 thin films. Furthermore, we present the growth of CrB_1.7/TiB_1.8 superlattices, from TiB (Ti:B = 1:1) and stoichiometric CrB₂ targets, with abrupt interfaces as promising materials system for neutron interference mirrors. The high crystal quality structure with well-defined interfaces is the common feature of superlattices which, regardless of application, should be addressed during the growth process.

Utilizing TiB target, all films crystallize in the hexagonal AlB₂ structure. The sub-stoichiometry of the TiB_1.8 films was accompanied by the presence of planar defects embedded in the films. CrB_1.7/TiB_1.8 superlattices exhibited a homogeneous boron distribution within the layers with no sign of B-rich tissue phases through the layers. This study demonstrates the feasibility for TiB as sputter target material, that offers a solution for deposition of TiB₂-based superlattices without the need to adjust the deposition parameters. Such adjustments would otherwise be unavoidable for tuning the TiB2 composition and could affect the growth of the other constituent materials.

Growth temperature (Ts) and ion irradiation energy (Ei) are important factors that influence film growth as well as their properties. In this study, we investigate the evolution of crystal structure and residual stress of TiNb-CrAlHfN films under various Ts and Ei conditions, where the latter is mainly controlled by tuning the flux of sputtered Hf ions using bipolar high-power impulse magnetron (BP-HiPIMS). The results show that TiNbCrAlHfN films exhibit the typical FCC NaCl-type structure. By increasing Ts from room temperature to 600 degrees C, the film texture changes from high-surface-energy (111) to low-surface-energy (100) accompanied by a higher crystal-linity in the out-of-plane direction and a more disordered growth tilt angle to the surface plane. In addition, compressive stress decreases with increasing Ts, which is ascribed to changes in the film growth both in the early and post-coalescence stages and more tensile thermal stress at elevated Ts. In contrast, a clear texture transition window is seen under various Ei of Hf+ ions, i.e., high-surface-energy planes change to low-surface-energy planes as Ei exceeds-110 eV, while low-surface-energy planes gradually transform back to high-surface-energy planes when Ei increases from 210 to 260 eV, indicating renucleation events for Ei &gt; 210 eV. Compressive stress in-creases with increasing Ei but is still lower than that of a reference series with DC substrate bias UDC =-100 V. The study shows that it is possible to tailor properties of FCC-structured high-entropy nitrides by varying Ts and Ei in a similar fashion to conventional transition metal nitrides using the approach of unipolar and bipolar HiPIMS co-sputtering.

Bipolar high-power impulse magnetron sputtering (HiPIMS) is used to achieve ion acceleration for ion bombardment of dielectric thin films. This is realized by increasing the plasma potential (U-p), during the interval in-between the HiPIMS-pulses, using a positive reversed voltage (U-rev). As long as the film surface potential (U-s) is maintained low, close to ground potential, this increase in U-p results in ion-acceleration as ions approach the film surface. The effect of U-rev on the ion bombardment is demonstrated by the growth of dielectric (Al,Cr)(2)O-3 films on two sets of substrates, Si (001) and sapphire (0001) utilizing a U-rev ranging from 0 to 300 V. A clear ion bombardment effect is detected in films grown on the conductive Si substrate, while no, or a very small, effect is observed in films grown on the dielectric sapphire substrate. This is ascribed to the changes in U-s when the substrate is subjected to the bombardment of positive ions. For a film surface that has a high capacitance to ground, U-s remains close to ground potential for an extended time in-between the HiPIMS pulses, while if the capacitance is low, U-s quickly attains floating potential (U-float) close to U-p. The simulated temporal evolutions of U-s for the films by using capacitors show that for a 1 mu m thick (Al,Cr)(2)O-3 film on a conductive substrate, U-s is maintained close to ground potential during the entire 20 mu s that U-rev is applied after the HiPIMS pulse. On the other hand, when a capacitance corresponding to the 0.5 mm thick sapphire substrate is used, U-s rapidly attains a potential close to U-rev.

Selective ion acceleration using a synchronized substrate bias is a common way to tailor the microstructure and intrinsic stress of films grown by high-power impulse magnetron sputtering (HiPIMS), owing to the high degree of sputtered metal ionization and the inherent time separation between different ionic species in the ion fluxes at the substrate position. Here we show that it is possible to achieve selective acceleration of ionic species with different ion masses by employing a synchronized positive reversed pulse (Urev) on the sputtering target itself, after the end of the main HiPIMS pulse, i.e., bipolar HiPIMS (BP-HiPIMS), if the substrate is grounded. The evidence is provided by growing (Al,Cr)2O3 films using BP-HiPIMS where the time delay (Delta tau acc) between the HiPIMS-pulse and the positive reversed pulse as well as the length of the positive reversed pulse (tau acc) are varied. In this way, both film stresses and film crystal structures are altered. The obvious drawback of BP-HiPIMS, that the ion-accelerating potential cannot be applied during the HiPIMS-pulse itself, has been minimized by using short HiPIMS pulses of 20 mu s during which the peak of the substrate ion current density (Js) occurs well after the end of the HiPIMS-pulse indicating that the main portion of the ion fluxes can be accelerated by Urev. An important observation is that the temporal evolution of Js did not change as the different reversed pulse pa-rameters (Urev, Delta tau acc, and tau acc) were altered. This is evidence, that in these experiments, the dominating ion-acceleration occurs in the plasma sheath at the substrate, i.e., similar to the case when synchronized substrate bias is utilized.

Microstructure and macroscopic properties of droplet free CrN films deposited by the recently developed high power pulsed magnetron sputtering (HIPIMS) technique are presented. Magnetron glow discharges with peak power densities reaching 3000 W cm-2 were used to sputter Cr targets in both inert and reactive gas atmospheres. The flux arriving at the substrates consisted of neutrals and ions (approx. 70/30) of the sputtered metal and working gas atoms (Ar) with significantly elevated degree of ionization compared to conventional magnetron sputtering. The high-speed steel and stainless steel substrates were metal ion etched using a bias voltage of -1200 V prior to the deposition of CrN films. The film-to-substrate interfaces, observed by scanning transmission electron microscope cross-sections, were clean and contained no phases besides the film and substrate ones or recrystallized regions. CrN films were grown by reactive HIPIMS at floating potential reaching -160 V. Initial nucleation grains were large compared to conventional magnetron sputtered films, indicating a high adatom mobility in the present case. The films exhibited polycrystalline columnar growth morphology with evidence of renucleation. No intercolumnar voids were observed and the corrosion behavior of the film was superior to arc deposited CrNx. A high density of lattice defects was observed throughout the films due to the high floating potential. A residual compressive stress of 3 GPa and a hardness value of HK0.025=2600 were measured. A low friction coefficient of 0.4 and low wear rates against Al2O3 in these films are explained by the absence of droplets and voids known to contribute to extensive debris generation.

Chromium oxide-based multilayers were deposited by reactive magnetron sputtering in an industrial setup by employing one-fold substrate rotation and cyclic variation of the O₂ flow. This simple method allows deposition of multilayers comprising alternating layers of ~ 1 μm thickness of columnar α-Cr₂O₃ and mixed layers consisting of ~ 50 nm-thick sublayers of amorphous CrO_x and nanocrystalline Cr₂O₃.

Ti–Si–C–N thin films with composition of 1–11 at.% Si and 1–20 at.% C have been deposited onto cemented carbide substrates by arcing Ti–Si cathodes in a CH₄ + N₂ gas mixture and, alternatively, through arcing Ti–Si–C cathodes in N₂. Films of comparable compositions from the two types of cathodes have similar structure and properties. Hence, C can be supplied as either plasma ions generated from the cathode or atoms from the gas phase with small influence on the structural evolution. Over the compositional range obtained, the films were dense and cubic-phase nanocrystalline, as characterized by X-ray diffraction, ion beam analysis, and scanning and transmission electron microscopy. The films have high hardness (30–40 GPa by nanoindentation) due to hardening from low-angle grain boundaries on the nanometer scale and lattice defects such as growth-induced vacancies and alloying element interstitials.

Thin films consisting of TiN nanocrystallites encapsulated in a fully percolated SiNy tissue phase are archetypes for hard and superhard nanocomposites. Here, we investigate metastable SiNy solid solubility in TiN and probe the effects of surface segregation during the growth of TiSiN films onto substrates that are either flat TiN(001)/MgO(001) epitaxial buffer layers or TiN(001) facets of length 1-5 nm terminating epitaxial TiN(111) nanocolumns, separated by voids, deposited on epitaxial TiN(111)/MgO(111) buffer layers. Using reactive magnetron sputter deposition, the TiSiN layers were grown at 550 degrees C and the TiN buffer layers at 900 degrees C On TiN(001), the films are NaCl-structure single-phase metastable Ti1-xSixN(001) with N/(Ti + Si) = 1 and 0 less than= x less than= 0.19. These alloys remain single-crystalline to critical thicknesses h(c) ranging from 100 +/- 30 nm with x = 0.13 to 40 +/- 10 nm with x = 0.19. At thicknesses h greater than h(c), the epitaxial growth front breaks down locally to form V-shaped polycrystalline columns with an underdense feather-like nanostructure. In contrast, the voided epitaxial TiN(111) columnar surfaces, as well as the TiN(001) facets, act as sinks for SiNy. For Ti1-xSixN layers with global average composition values less than x greater than = 0.16, the local x value in the middle of Ti1-xSixN columns increases from 0.08 for columns with radius r similar or equal to 2 nm to x = 0.14 with r similar or equal to 4 nm. The average out-of-plane lattice parameter of epitaxial nanocolumns encapsulated in SiNy decreases monotonically with increasing Si fraction less than x greater than, indicating the formation of metastable (Ti,Si)N solid solutions under growth conditions similar to those of superhard nanocomposites for which the faceted surfaces of nanograins also provide sinks for SiNy.

This paper presents the physical mechanism behind the phenomenon of self-layering in thin films made by industrial scale cathodic arc deposition systems using compound cathodes and rotating substrate fixture. For Ti-Si-C films, electron microscopy and energy dispersive x-ray spectrometry reveals a trapezoid modulation in Si content in the substrate normal direction, with a period of 4 to 23 nm dependent on cathode configuration. This is caused by preferential resputtering of Si by the energetic deposition flux incident at high incidence angles when the substrates are facing away from the cathodes. The Ti-rich sub-layers exhibit TiC grains with size up to 5 nm, while layers with high Si-content are less crystalline. The nanoindentation hardness of the films increases with decreasing layer thickness.

The fracture surfaces from adhesion tested thermal barrier coatings (TBC) have been studied by scanning electron microscopy. The adhesion test have been made using the standard method described in ASTM 633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrates of Hastelloy X. The bond coat (BC) is of NiCoCrAlY type and the top coat (TC) consists of yttria–stabilised–zirconia. Before the adhesion test, the specimens were subjected to three different heat treatments: 1) isothermal oxidation 2) thermal cycling fatigue (TCF) and 3) burner rig test (BRT). The fracture surfaces of the adhesion tested specimens where characterised. A difference in fracture mechanism were found for the different heat treatments. Isothermal oxidation gave fracture mainly in the top coat while the two cyclic heat treatments gave increasing amount of BC/TC interface fracture with number of cycles. Some differences could also be seen between the specimens subjected to burner rig test and furnace cycling.

The adhesion of thermal barrier coatings (TBC) has been studied using the standard method described in ASTM C633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrate coupons of Ni-base alloy Hastelloy X. The bond coat (BC) is of a NiCoCrAlY type and the top coat (TC) consists of yttria–stabilised–zirconia. Before the adhesion test, the specimens were subjected to three different heat treatments: 1) isothermal oxidation at 1100 °C up to 290 h, 2) thermal cycling fatigue (TCF) at 1100 °C up to 300 cycles and 3) thermal shock at ~ 1140 °C BC/TC interface temperature up to 1150 cycles. The adhesion of the specimens is reported and accompanied by a microstructural study of the BC and the thermally grown oxides (TGO), as well as a discussion on the influence of BC/TC interfacial damage on adhesion properties of TBC. The adhesion was found to vary with heat treatment, as well as with heat treatment length.

Thermal barrier coatings (TBCs) are used in gas turbines to prolong the life of the underlying substrates and to increase the efficiency of the turbines by enabling higher combustion temperatures. TBCs may fail during service due to thermal fatigue or through the formation of non-protective thermally grown oxides (TGOs). This study compares two atmospheric plasma sprayed (APS) TBC systems comprising of two identical TBCs deposited on two different substrates (Haynes 230 and Hastelloy X). The thermal fatigue life was found to differ between the two TBC systems. The interdiffusion of substrate elements into the coating was more pronounced in the TBC system with shorter life, however, very few of the substrate elements (only Mn and to some extent Fe) formed oxides in the bond coat/top coat interface. Fractography revealed no differences in the fracture behaviour of the TBCs; the fracture occurred, in both cases, to about 60% in the top coat close to the interface and the remainder in the interface. Nanoindentation revealed only small differences in mechanical properties between the TBC systems and a finite element crack growth analysis showed that such small differences did not cause any significant change in the crack driving force. The oxidation kinetics was found to be similar for both TBC systems for the formation of Al2O3 but differed for the kinetics of non-Al2O3 TGOs where the TBC system with shortest life had a faster formation of non-Al2O3 TGOs caused by a faster Al depletion. The difference in non-Al2O3 TGO growth kinetics was considered to be the main reason for the difference in life.

Thermal barrier coatings (TBCs), when used in gas turbines, may fail through thermal fatigue, causing the ceramic top coat to spall off the metallic bond coat. The life prediction of TBCs often involves finite element modelling of the stress field close to the bond coat/top coat interface and thus relies on accurate modelling of the interface. The present research studies the influence of bond coat/top coat interface roughness on the thermal fatigue life of plasma sprayed TBCs. By using different spraying parameters, specimens with varying interface roughness were obtained. During thermal cycling it was found that higher interface roughness promoted longer thermal fatigue life. The interfaces were characterised by roughness parameters, such as Ra, Rq and Rq, as well as by autocorrelation, material ratio curves, probability plots and slope distribution. The variation of spray parameters was found to affect amplitude parameters, such as Ra, but not spacing parameters, such as RSm. Three different interface geometries were tried for finite element crack growth simulation: cosine, ellipse and triangular shape. The cosine model was found to be an appropriate interface model and a procedure for obtaining the necessary parameters, amplitude and wavelength, was suggested. The positive effect of high roughness on life was suggested to be due to a shift from predominantly interface failure, for low roughness, to predominantly top coat failure, for high roughness.

Coatings from MCrAlY-type alloys are commonly used for oxidation and corrosion protection in gas turbines. As coated components are exposed to high temperature, the coating provides oxidation protection by the formation of an alumina scale, thus depleting the coating of Al which, eventually, will cause the coating to fail. The present study deals with MCrAlY alloy design from a lifing perspective. A previously developed coupled oxidation-diffusion model was used to study the influence of coating composition, substrate composition and oxidation temperature on the expected life of MCrAlY coatings. Eight model coatings, covering the wide range of MCrAlY compositions used industrially, and two model substrates, corresponding to a blade material and a combustor material, were evaluated by the oxidation-diffusion model. Three life criteria were tried: 1) beta-phase-depletion, 2) critical Al content at the coating surface, and 3) a critical TGO thickness. It was shown that the critical TGO thickness was the most conservative life criterion for high-Al coatings on high-Al substrates. For low-Cr and low-Co coatings, the beta-depletion criterion was usually the most conservative. For cases where beta-stability was high (such as at low temperatures and for coatings high in Cr, Co and Al) the critical-Al criterion was often the most conservative.

Ti_(1−x−y)Al_xSi_yN_z (0.02≤x≤0.46, 0.02≤y≤0.28, and 1.08≤z≤1.29) thin films were grown on cemented carbide substrates in an industrial scale cathodic arc evaporation system using Ti-Al-Si compound cathodes in a N₂ atmosphere. The microstructure of the as-deposited films changes from nanocrystalline to amorphous by addition of Al and Si to TiN. Upon incorporation of 12 at% Si and 18 at% Al, the films assume an x-ray amorphous state. Post-deposition anneals show that the films are thermally stable up to 900 ◦C. The films exhibit age hardening up to 1000 ◦C with an increase in hardness from 21.9 GPa for as-deposited films to 31.6 GPa at 1000 ◦C. At 1100 ◦C severe out-diffusion of Co and W from the substrate occur, and the films recrystallize into c-TiN and w-AlN.

Amorphous nitrides are explored for their homogenous structure and potential use as wear-resistant coatings, beyond their much studied nano-and microcrystalline counterparts. (TiB₂)_1−xSi_xN_y thin films were deposited on Si(001) substrates by a hybrid technique of high power impulse magnetron sputtering (HIPIMS) combined with dc magnetron sputtering (DCMS) using TiB₂ and Si targets in a N₂/Ar atmosphere. By varying the sputtering dc power to the Si target from 200 to 2000 W while keeping the average power to the TiB₂-target, operated in HIPIMS mode, constant at 4000 W, the Si content in the films increased gradually from x=0.01 to x=0.43. The influence of the Si content on the microstructure, phase constituents, and mechanical properties were systematically investigated. The results show that the microstructure of as-deposited (TiB₂)_1−xSi_xN_y films changes from nanocrystalline with 2-4 nm TiN grains for x=0.01 to fully electron diffraction amorphous for x=0.22. With increasing Si content, the hardness of the films increases from 8.5 GPa with x=0.01 to 17.2 GPa with x=0.43.

Using a combinatorial approach, Cr, Al and C have been deposited onto sapphire wafer substrates by High Power Impulse Magnetron Sputtering (HiPIMS) and DC magnetron sputtering. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and X-ray diffraction were employed to determine the composition and microstructure of the coatings and confirm the presence of the Cr2AlC MAX phase within both coatings. One location in both the DCMS and HiPIMS coatings contained only MAX phase Cr2AlC. The electrical resistivity was also found to be nearly identical at this location and close to that reported from the bulk, indicating that the additional energy in the HiPIMS plasma was not required to form high quality MAX phase Cr2AlC.

Cr–C/Ag thin films with 0–14 at.% Ag have been deposited by magnetron sputtering from elemental targets. The samples were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to study their structure and chemical bonding. A complex nanocomposite structure consisting of three phases; nanocrystalline Ag, amorphous CrCx and amorphous carbon is reported. The carbon content in the amorphous carbide phase was determined to be 32–33 at.% C, independent of Ag content. Furthermore, SEM and XPS results showed higher amounts of Ag on the surface compared to the bulk. The hardness and Young's modulus were reduced from 12 to 8 GPa and from 270 to 170 GPa, respectively, with increasing Ag content. The contact resistance was found to decrease with Ag addition, with the most Ag rich sample approaching the values of an Ag reference sample. Initial tribological tests gave friction coefficients in the range of 0.3 to 0.5, with no clear trends. Annealing tests show that the material is stable after annealing at 500 °C for 1 h, but not after annealing at 800 °C for 1 h. In combination, these results suggest that sputtered Cr–C/Ag films could be potentially applicable for electric contact applications.

Cr–C/Ag thin films with 0–14 at.% Ag have been deposited by magnetron sputtering from elemental targets. The samples were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to study their structure and chemical bonding. A complex nanocomposite structure consisting of three phases; nanocrystalline Ag, amorphous CrC_x and amorphous carbon is reported. The carbon content in the amorphous carbide phase was determined to be 32–33 at.% C, independent of Ag content. Furthermore, SEM and XPS results showed higher amounts of Ag on the surface compared to the bulk. The hardness and Young's modulus were reduced from 12 to 8 GPa and from 270 to 170 GPa, respectively, with increasing Ag content. The contact resistance was found to decrease with Ag addition, with the most Ag rich sample approaching the values of an Ag reference sample. Initial tribological tests gave friction coefficients in the range of 0.3 to 0.5, with no clear trends. Annealing tests show that the material is stable after annealing at 500 °C for 1 h, but not after annealing at 800 °C for 1 h. In combination, these results suggest that sputtered Cr–C/Ag films could be potentially applicable for electric contact applications.

The Cantor alloy (CoCrFeMnNi) and its variants, in bulk as well as thin films, have been extensively studied. They are known to exhibit cubic crystal structures and thermodynamic stability regardless of their complex chemical composition. Therefore, they may find use as hard, wear-resistant, corrosion and oxidation-resistant coatings. The addition of light elements, such as nitrogen, is known to help improve these properties further through processes such as amorphization and nitride compound formation. Here, we investigate the ternary CrFeCo system to study the effects of nitrogen addition. (CrFeCo)N_y multicomponent thin films are grown on silicon substrates by DC magnetron sputtering. Changes in crystal structure, morphology, mechanical and electrical properties with gradual increases of nitrogen in the film are described and discussed. Increased addition of nitrogen from 14 at.% to 28 at.% in the film leads to a transformation from an fcc to a bcc crystal structure, affects both the mechanical and electrical properties. XPS analysis shows the tendency of nitrogen to bond with Cr over other metals. The films display hardness values between 7 and 11 GPa with resistivities values ranging between 28 and 165 μΩ cm.

The high-temperature oxidation resistance of Ti1-xSixN films with Si content varying in wide range, 0.13 &lt;= x &lt;= 0.91, is evaluated. Films are grown in Ar/N-2 atmospheres using a hybrid high-power impulse and dc magnetron sputtering (HiPIMS/DCMS) configuration with Si target powered by HiPIMS and Ti target operated in DCMS mode. The substrate bias is synchronized to the Si+-rich portions of the HiPIMS pulses in order to promote solid solution formation. A combination of X-ray photoelectron spectroscopy, elastic recoil detection analysis, and cross-sectional scanning electron microscopy reveals a sharp increase in the oxidation resistance for layers with x &gt; 0.50. The thickness of the oxide layer, following 1 h anneal at 800 degrees C in air, is in the range 150-200 nm for 0.13 &lt;= x &lt;= 0.50 and decreases to only 4 nm with x = 0.91, which is similar to 30 times lower than for the best performing Ti1-xAlxN film (x = 0.64) tested under the same conditions. The oxide forming on top of Ti1-xSixN films with x = 0.41 consists of a SiO2-TiO2 two-phase mixture with a molar ratio given by Si/Ti ratio. In Ti1-xSixN layers with x &lt;= 0.31, the presence of grain boundaries, which act as diffusion paths facilitates Si diffusion towards the bulk of the film resulting in that TiO2, the thermodynamically more stable oxide, terminates the surface. Ti0.09Si0.91N films, are essentially unaffected by the anneal and exhibit a hardness of 23 GPa, which is similar to 30% higher than for the reference SiNz film. Moreover, we demonstrate that 25 nm thick Ti0.09Si0.91N capping layers successfully prevent Ti(0.36A)l(0.64)N oxidation at 800 degrees C. Such approach provides superior oxidation protection compared to alloying TiAlN with Si. Our results suggest that multilayers including nm thin layers of high Si-content TiSiN is a most effective approach to improve high-temperature oxidation resistance of functional ceramic thin films.

The resistance to high-temperature oxidation of Ti1-xAlxN films determines performance in numerous applications including coated cutting tools. Here, we present a comprehensive study covering Ti1-xAlxN films with 0 amp;lt;= x amp;lt;= 0.83 annealed in air for 1 h at temperatures T-a ranging from 500 to 800 degrees C. Layers are grown by the combination of high-power impulse and dc magnetron sputtering (HiPIMS/DCMS) in Ar/N-2 atmospheres. We use X-ray photoelectron spectroscopy to study the evolution of surface chemistry and to reconstruct elemental distribution profiles. No dependence of oxidation process on the phase content, average grain size, or preferred orientation could be confirmed, to the accuracy offered by the employed X-ray diffraction techniques. Instead, our results show that, under the applied test conditions, the Ti1-xAlxN oxidation scenario depends on both x and T-a. The common notion of double-layer Al2O3/TiO2 oxide formation is valid only in a limited region of the x-T-a parameter space (Type-1 oxidation). Outside this range, a mixed and non-conformal Al2O3-TiO2 layer forms, characterized by larger oxide thickness (Type-2 oxidation). The clear distinction between different Ti1-xAlxN oxidation scenarios revealed here is essential for numerous applications that can benefit from optimizing the Al content, while targeting a given operational temperature range.

We review results on the growth of metastable Ti1-xAlxN alloy films by hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) using the time domain to apply substrate bias either in synchronous with the entire HIPIMS pulse or just the metal-rich portion of the pulse in mixed Ar/N-2 discharges. Depending upon which elemental target, Ti or Al, is powered by HIPIMS, distinctly different film-growth kinetic pathways are observed due to charge and mass differences in the metal-ion fluxes incident at the growth surface. Al+ ion irradiation during Al-HIPIMS/Ti-DCMS at 500 degrees C, with a negative substrate bias V-s = 60 V synchronized to the HIPIMS pulse (thus suppressing Ar+ ion irradiation due to DCMS), leads to single-phase NaCl-structure Ti1-xAlxN films (x less than= 0.60) with high hardness (greater than30 GPa with x greater than 0.55) and low stress (0.2-0.8 GPa compressive). Ar+ ion bombardment can be further suppressed in favor of predominantly Al+ ion irradiation by synchronizing the substrate bias to only the metal-ion-rich portion of the Al-HIPIMS pulse. In distinct contrast Ti-HIPIMS/Al-DCMSTi1-xAlxN layers grown with Ti+/Ti2+ metal ion irradiation and the same HIPIMS-synchronized V-s value, are two-phase mixtures, NaCl-structure Ti1-xAlxN plus wurtzite AlN, exhibiting low hardness (similar or equal to 18 GPa) with high compressive stresses, up to -3.5 GPa. In both cases, film properties are controlled by the average metal-ion momentum per deposited atom less thanp(d)greater than transferred to the film surface. During Ti-HIPIMS, the growing film is subjected to an intense flux of doubly-ionized Ti2+, while Al2+ irradiation is insignificant during Al-HIPIMS. This asymmetry is decisive since the critical less thanp(d)greater than limit for precipitation of w-AlN, 135 [eV-amu](1/2), is easily exceeded during Ti-HIPIMS, even with no intentional bias. The high Ti2+ ion flux is primarily due to the second ionization potential (IP2) of Ti being lower than the first IP (IP1) of Ar. New results involving the HIPIMS growth of metastable Ti1-xAlxN alloy films from segmented TiAl targets are consistent with the above conclusions.

Metastable Ti1-xAlxN (0.4 less than= x less than= 0.76) films are grown using a hybrid approach in which high-power pulsed magnetron sputtering (HIPIMS) is combined with dc magnetron sputtering (DCMS). Elemental Al and Ti metal targets are co-sputtered with one operated in HIPIMS mode and the other target in DCMS; the positions of the targets are then switched for the next set of experiments. In both cases, the AlN concentration in the co-sputtered films, deposited at T-s = 500 degrees C with R = 1.5-5.3 angstrom/s, is controlled by adjusting the average DCMS target power. Resulting films are analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, elastic recoil detection analysis, and nanoindentation. Mass spectroscopy is used to determine ion energy distribution functions at the substrate. The distinctly different flux distributions obtained from targets driven in HIPIMS vs. DCMS modes allow the effects of Aln+ and Tin+ (n = 1, 2) ion irradiation on film growth kinetics, and resulting properties, to be investigated separately. Bombardment with Aln+ ions (primarily Al+ in the Al-HIPIMS/Ti-DCMS configuration) during film growth leads to NaCl-structure Ti1-xAlxN (0.53 less than= x less than= 0.60) films which exhibit high hardness (greater than30 GPa) with low stress (0.2-0.7 GPa tensile). In contrast, films with corresponding AlN concentrations grown under Tin+ metal ion irradiation (with a significant Ti2+ component) in the Ti-HIPIMS/Al-DCMS mode have much lower hardness, 18-19 GPa, and high compressive stress ranging up to 2.7 GPa. The surprisingly large variation in mechanical properties results from the fact that the kinetic AlN solubility limit x(max) in Ti1-xAlxN depends strongly on, in addition to T-s and R, the target power configuration during growth and hence the composition of the ion flux. AlN with x(max)similar to 64 mol% can be accommodated in the NaCl structure under Aln+ ion flux, compared with similar to 40 mol% for growth with Tin+ flux. The strong asymmetry in film growth reaction paths is due primarily to the fact that the doubly-ionized metal ion flux is approximately two orders of magnitude higher from the Ti target, than from Al, powered with HIPIMS. This asymmetry becomes decisive upon application of a moderate substrate bias voltage, -60 V, applied synchronously with HIPIMS pulses, during growth.

Ti1-xSixN (0 less than= x less than= 0.26) thin films are grown in mixed Ar/N-2 discharges using hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS). In the first set of experiments, the Si target is powered in HIPIMS mode and the Ti target in DCMS; the positions of the targets are then switched for the second set. In both cases, the Si concentration in co-sputtered films, deposited at T-s = 500 degrees C, is controlled by adjusting the average DCMS target power. A pulsed substrate bias of -60 V is applied in synchronous with the HIPIMS pulse. Depending on the type of pulsed metal-ion irradiation incident at the growing film, Ti+/Ti2+ vs. Si+/Si2+, completely different nanostructures are obtained. Ti+/Ti2+ irradiation during Ti-HIPIMS/Si-DCMS deposition leads to a phase-segregated nanocolumnar structure with TiN-rich grains encapsulated in a SiNz tissue phase, while Si+/Si2+ ion irradiation in the Si-HIPIMS/Ti-DCMS mode results in the formation of Ti1-xSixN solid solutions with x less than= 024. Film properties, including hardness, modulus of elasticity, and residual stress exhibit a dramatic dependence on the choice of target powered by HIPIMS. Ti-HIPIMS/Si-DCMS TiSiN nanocomposite films are superhard over a composition range of 0.04 less than= x less than= 0.26, which is significantly wider than previously reported. The hardness H of films with 0.13 less than= x less than= 0.26 is similar to 42 GPa; however, the compressive stress is also high, ranging from -6.7 to -8.5 GPa. Si-HIPIMS/Ti-DCMS films are softer at H similar to 14 GPa with 0.03 less than= x less than= 0.24, and essentially stress-free (sigma similar to 0.5 GPa). Mass spectroscopy analyses at the substrate position reveal that the doubly-to-singly ionized metal-ion flux ratio during HIPIMS pulses is 0.05 for Si and 029 for Ti due to the difference between the second ionization potentials of Si and Ti vs. the first ionization potential of the sputtering gas. The average momentum transfer to the film growth surface per deposited atom per pulse less than p(d)greater than is similar to 20 x higher during Ti-HIPIMS/Si-DCMS, which results in significantly higher adatom mean-free paths (mfps) leading, in turn, to a phase-segregated nanocolumnar structure. In contrast, relatively low less than p(d)greater than values during Si-HIPIMS/Ti-DCMS provide near-surface mixing with lower adatom mfps to form Ti1-xSixN solid solutions over a very wide composition range with x up to 0.24. Relaxed lattice constants decrease linearly, in agreement with ab-initio calculations for random Ti1-xSixN alloys, with increasing x. (C) 2015 Elsevier B.V. All rights reserved.

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.

Sputtered Ni and Ti layers were investigated as substitutes for electroplated Ni as adiffusion barrier between Ti-Si-C and Ti-Si-C-Ag nanocomposite coatings and Cu orCuSn substrates. Samples were subjected to thermal annealing studies by exposure to400 ºC during 11 h. Dense diffusion barrier and coating hindered Cu from diffusing tothe surface. This condition was achieved for electroplated Ni in combination withmagnetron-sputtered Ti-Si-C and Ti-Si-C-Ag layers deposited at 230 ºC and 300 ºC,and sputtered Ti or Ni layers in combination with Ti-Si-C-Ag deposited at 300 ºC.

The development of thermo-mechanical stresses during thermal cycling can lead to the formation of detrimental cracks in Atmospheric Plasma Sprayed (APS) Thermal Barrier Coatings systems (TBCs). These stresses are significantly increased by the formation of a Thermally Grown Oxide (TGO) layer that forms through the oxidation of mainly aluminium in the bondcoat layer of the TBC. As shown in previous work done by the authors, the topcoat–bondcoat interface roughness plays a major role in the development of the stress profile in the topcoat and significantly affects the lifetime of TBCs. This roughness profile varies as the TGO layer grows and changes the stress profile in the topcoat leading to crack propagation and thus failure.

In this work, a two-dimensional TGO growth model is presented, based on oxygen and aluminium diffusion–reaction equations, using real interface profiles extracted from cross-section micrographs. The model was first validated by comparing the TGO profiles artificially created by the model to thermally cycled specimens with varying interface roughness. Thereafter, stress profiles in the TBC system, before and after the TGO layer growth, were estimated using a finite element modelling model described in previous work done by the authors. Three experimental specimens consisting of the same chemistry but with different topcoat–bondcoat interface roughness were studied by the models and the stress state was compared to the lifetimes measured experimentally. The combination of the two models described in this work was shown to be an effective approach to assess the stress behaviour and lifetime of TBCs in a comparative way.

Thermal barrier coatings (TBCs) are extensively used in gas turbine engines in power generation and aerospace applications. Improvements in TBC performance and lifetime are continuously pursued by the gas turbine industry. Suspension plasma spraying (SPS) has shown promising results in recent years as it could produce a porous columnar TBC microstructure exhibiting low thermal conductivity and high durability. Further improvements in lifetime and fundamental understanding of failure mechanisms would lead to their wider application. Lifetime of a TBC system is dependent not only on the topcoat microstructure and chemistry, but also on topcoat-bondcoat interface and bondcoat characteristics as they influence the growth rate of thermally grown oxide (TGO) layer as well as the mismatch stresses generated in the topcoat during operation. Moreover, in SPS TBCs, the column density and porosity in the topcoat are also affected by the bondcoat surface roughness which in turn affects TBC lifetime. In previous work, it was shown that bondcoat surface treatment by shot peening followed by light grit blasting can significantly enhance the cyclic lifetime of SPS TBCs. The objective of this work was to gain further insight into the lifetime improvements due to surface treatment of bondcoat. Commercial NiCoCrAlY powder was deposited by high velocity air fuel (HVAF) and high velocity oxy fuel (HVOF) spraying while SPS was used to deposit yttria stabilised zirconia topcoat. Before spraying the topcoat, the bondcoat samples were subjected to vacuum heat treatment, shot peening, and/or grit blasting. Residual stress measurements were performed by X-ray diffraction on samples with different variants of bondcoat treatments and compared with Almen strip tests. The lifetime was examined by thermal cyclic fatigue testing. The relationships between changes in bondcoat surface roughness, residual stress state and microstructure due to surface treatments, and resultant topcoat microstructure and lifetime were studied and discussed.