Microstructural Analysis of TiAl x N y O z Coatings Fabricated by DC Reactive Sputtering

TiAl _x N _y O _z coatings were prepared by DC reactive sputtering on AISI D2 tool steel substrates, using a target of Ti-Al-O fabricated from a mixture of powders of Ti (22.60 wt.%), Al (24.77 wt.%), and O (52.63 wt.%). The coatings were deposited on substrates at room temperature in a reactive atmosphere of nitrogen and argon under a pressure of 8.5 × 10⁻³ mbar. X-ray diffraction, electron dispersive spectroscopy, Raman scattering, and nanoindentation techniques were employed to investigate the coatings. The results show that the increment in the nitrogen flow affects the structure and the mechanical properties of the coatings. The sample with the lowest nitrogen flow presented the highest hardness (10.5 GPa) and the Young’s modulus (179.5 GPa). The hardness of the coatings TiAl _x N _y O _z as a function of crystalline grain size shows a behavior consistent with the Hall–Petch relation.     

Effect of N2 flow on low carbon TiAlNC coatings

TiAlNC coatings were prepared under various N₂ flows by reactive dc magnetron sputtering. The composition, microstructure and hardness of TiAlNC coatings were investigated by energy dispersive spectroscopy, X-ray diffraction, scanning electron microscopy and micro Vicker tester. By increasing the N₂ flow, the Al/Ti ratio and the nitrogen content of the coatings increased. It was found that hexagonal AlN phase precipitated under relatively high N₂ flow (e.g. 8 sccm). The increase in the N₂ flow also changed the preferred orientation of fcc Ti(Al)N(C) phase from random to [111], and then to [200]. The coating deposited at low N₂ flow (e.g. 2 sccm) exhibited [111] preferred orientation with porous structure and relatively low hardness. However, when the N₂ flow was relatively high (e.g. 8 sccm), the hcp AlN phase precipitation and N₂-induced grain refinement resulted in a denser multiphase structure, which improved the hardness and toughness of the TiAlNC coating.     

Deposition of thick TiAlN coatings on 2024 Al/SiCp substrate by Arc ion plating

Aluminum-matrix composites with particulate SiC ceramic reinforcements (Al/SiC_p) have received much attention for space and aircraft propulsion applications. It is imperative to deposit thick hard coatings on these composites for protection. TiAlN coatings with a Ti interlayer were deposited by arc ion plating (AIP) on 2024 Al/SiC_p substrates at various nitrogen flow rates. It was found that when the nitrogen flow rate is increased from 100 sccm to 250 sccm, the deposition rate decreases, the coating hardness increases and the adhesion strength decreases. Based on the above results and the principle of gradient materials, the thick gradient TiAlN coatings with a Ti interlayer were successfully deposited on a 2024 Al/SiC_p substrate to a thickness of 60 μm by continuously increasing the nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of elements, hardness, and stresses across the coating thickness.     

Structure-property relations in ZrCN coatings for tribological applications

ZrCN coatings were deposited by dc reactive magnetron sputtering with N₂ flows ranging from 2 to 10 sccm in order to investigate the influence of the nitrogen incorporation on structure and properties. Information about the chemical composition was obtained by glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The evolution of the crystal structure studied by X-ray diffraction revealed the formation of a face-centred cubic ZrCN phase for N₂ flows greater than 4 sccm. Additionally, the presence of an amorphous phase in the coatings deposited with the highest N₂ flows could be evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. This phase can act as a lubricant resulting in a low coefficient of friction as shown in the conducted ball-on-disc tests. Nanoindentation measurements showed that coatings deposited with a 6 sccm N₂ flow had the maximum hardness which also revealed the best performance in the conducted dry cutting tests.     

Influence of air oxidation on the properties of decorative NbOxNy coatings prepared by reactive gas pulsing

In this work the oxidation resistance of DC reactive sputtered niobium oxynitrides and its influence on the properties of the films are studied. The depositions have been carried out by DC magnetron sputtering with a reactive gas pulsing process. The nitrogen flow was kept constant and the oxygen flow was pulsed. Pulse durations of 10 s produced multilayer coatings with a period of λ = 10 nm. Three sets of films with increasing duty cycle (= on-time of high oxygen flow / pulse duration) have been deposited. The films were subsequently annealed in air at 400, 500 and 600 °C, respectively.X-ray diffraction measurements showed a clear and progressive change from a roughly amorphous nature of the films to a crystalline oxide-type compound for those annealed at 600 °C, which was consistent with the composition analysis. For annealing temperatures of 500 and 600 °C, the coatings presented a significant reduction in hardness, approaching the values characteristic of Nb₂O₅-type films. Moreover, the residual stress measurements performed by using the deflection method revealed low values in all the coatings nearly independent on the annealing temperature.Color variation in the CIE − L^?a^?b^? color space and the reflectance in the UV-visible spectrum range of these niobium oxynitrides were investigated and correlated to their chemical composition and structural features. For both properties, the variation tendencies are quite similar, showing the transition from a nitride-type alloy to an oxide-type one with increasing annealing temperature.     

Internal stress in TiAlBN at high temperatures

Hard TiAl(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 ∼ 10 GPa to ∼ 25 GPa. The hardness increase of the coatings after annealing is related to a self-hardening effect.     

AC powered reactive magnetron deposition of indium tin oxide (ITO) films from a metallic target

Transparent highly conductive indium tin oxide (ITO) films for low cost applications were deposited by a reactive dual magnetron sputter process using metallic targets. The magnetrons were equipped with rectangular (130 × 400 mm²) In:Sn targets (90 wt.% In/10 wt.% Sn). A sine wave power supply was used at a frequency of about 70 kHz. All experiments were done in the transition mode at a constant argon flow of 40 sccm and an oxygen flow varied between 35 and 70 sccm. The total pressure was kept constant at 0.4 Pa.The films were deposited onto silicon and float glass substrates which were either moved in an oscillatory manner (dynamic deposition) or fixed in front of the targets (static mode) during deposition. A dynamic deposition rate of about 100 nm × m/min was obtained at an average power of 2 kW/cathode. The film thickness was adjusted to 500 nm. At an optimised Ar/O₂ gas flow ratio of 0.6 we found an electrical resistivity as low as 1.2 × 10^− 3 Ω cm. The refractive index of these films was about 2.05 indicating a dense film structure, while the optical absorption of k = 10^− 2 qualifies these ITO films for many low cost applications. Moreover, the film structure and texture were investigated by XRD methods.Applying a static deposition we have achieved a lower electrical resistivity with a minimum value of 6 × 10^− 4 Ω cm. In this case, the resistivity and the transparency, respectively, were not constant over the substrate but depend on the lateral position in front of the target. To explain this inhomogeneity we have performed spatially resolved deposition rate and Langmuir probe measurements and related their results to film structure and properties. In order to improve the film properties at dynamic deposition the growth conditions have to be homogenised at all substrate positions.     

Structure and properties of cathodic vacuum arc deposited NbN and NbN-based multi-component and multi-layer coatings

Binary Nb-N coatings, ternary Ti-Nb-N and Zr-Nb-N, and multi-layer TiN/NbN coatings consisting of up to 100 alternating TiN and NbN layers, were deposited onto WC-Co substrates, using two different vacuum arc deposition (VAD) systems: with and without magnetic guiding of the metal plasma flow. Binary Nb-N coatings were fabricated by deposition of metal plasma produced by a Nb cathode in a background of reactive nitrogen gas at different pressures, P. Ternary coatings were fabricated at co-deposition of plasmas originating from two different cathode materials. Multilayer coatings were fabricated by alternatively depositing plasmas of Ti and Nb in reactive nitrogen gas. The crystalline coating structure, phase composition, hardness and critical load for coating failure were studied.For binary Nb-N coatings fabricated using both deposition systems, the phase composition, the Vickers hardness, HV, and the critical load strongly depended on the deposition pressure. Using VAD with magnetic plasma guiding, the highest HV of ∼ 42 GPa was measured for coatings deposited at low nitrogen pressure. These coatings contained a hexagonal β-Nb₂N phase and had a relatively low critical load. The highest critical load and HV ∼ 38 GPa were obtained for coatings consisted of a single phase NaCl-type cubic δ-NbN structure, deposited at a higher nitrogen pressure. The structure and properties of Nb-N coatings deposited using VAD without magnetic plasma guiding had a similar correlation with the deposition pressure, however, their hardness values were lower.Ternary Ti-Nb-N and Zr-Nb-N coatings fabricated by both deposition processes had a single phase cubic NaCl-type structure and the hardness higher than that of the binary nitrides TiN, ZrN and NbN. The hardest coatings, HV ∼ 51.5 Pa, deposited with magnetic plasma guiding had a single-phase cubic δ-(Ti,Nb)N structure and a Ti:Nb ratio of ∼ 50:50 (at.%).Multilayer coatings TiN/NbN consisting of 20-40 alternating TiN and NbN layers with total thickness of 4-5 μm increased the life time of cemented carbide cutting inserts at turning tough Ni-base alloys by 2-7 times relative to uncoated cutting tools, while conventional vacuum arc deposited TiN coatings were not effective in machining of these alloys.     

Thermal plasma chemical vapor deposition of wear-resistant, hard Si-C-N coatings

Wear-resistant, hard Si-C-N coatings were synthesized in a triple torch plasma reactor using a thermal plasma chemical vapor deposition process. In this reactor, three dc plasma torches were angled so that their jets converge to form a highly chemically reactive region at the substrate. Vaporized hexamethyldisilazane (HMDSN) was injected through a central injection probe, while nitrogen or hydrogen gases were added through the torches to the argon plasma.Various dissociation, recombination and intermediate reactions were considered to determine what major species exist in the gas phase during the deposition of Si-C-N films. Reactant flow rates were varied to evaluate the thermodynamic equilibrium compositions across a linear temperature profile above the substrate and to identify the species that lead to the production of wear-resistant, hard Si-C-N films.A series of experiments were conducted at low HMDSN flows (∼ 1 sccm) and varying hydrogen and nitrogen flows. Films were characterized by micro X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Indentation tests were conducted on the polished film cross-sections, while wear tests were carried out on the film surfaces. At substrate temperatures below 1000 °C, amorphous Si-C-N films were deposited, while higher temperatures produced crystalline composite films of α- and β-Si₃N₄ and α- and β-SiC. Films produced with hydrogen at low HMDSN flows displayed non-columnar morphology and therefore had higher wear-resistance, indicating the benefit of low reactant-to-plasma gas flow concentrations on film growth. At low HMDSN flows, low nitrogen-to-hydrogen ratios had also shown an increase in film linear density. Small variations in mechanical properties and wear were observed between films grown under low N:H flow ratio conditions (smooth film surfaces). Wear-resistance of films with columnar structures from high N:H conditions was significantly lower, while the hardness was unobtainable. This result indicates the importance of film morphology on mechanical performance.     

Precise control of multilayered structures of Nb-O-N thin films by the use of reactive gas pulsing process in DC magnetron sputtering

Multilayered niobium oxynitride films were deposited onto (100) Si using DC magnetron sputtering with a reactive gas pulsing process. The argon and nitrogen flows were kept constant during sputtering of a pure niobium target and the oxygen flow was pulsed during deposition. Pulse durations of T = 10, 40 and 100 s and duty cycles α = t_ON / T of 0.3, 0.6 and 0.9 were chosen (t_ON = injection time of high oxygen flow). A mounting triangle was used as the pulse shape for the oxygen injection.During thin film deposition the cathode voltage, U_cath, the O₂ and N₂ partial pressures, p(O₂) and p(N₂), were recorded. A delay of both parameters (U_cath, p(O₂)) was observed after each pulse, for the return to the values during t_OFF = T − t_ON (off-time of oxygen injection with high flow).High resolution scanning electron microscopy revealed a multilayered structure for coatings deposited with T = 40 and 100 s. Transmission electron microscopy was used to verify that also the coatings with T = 10 s possess a multilayered structure with a period of λ = 10 nm. Despite this low period small crystallites (< 7 nm) were present in these layers. The indentation hardness and the Youngs modulus were in the range of 8.3-16.5 GPa and 154-180 GPa, respectively.     

Thermal stability of Ta-Si-N nanocomposite thin films at different nitrogen flow ratios

Ta-Si-N thin films were applied as diffusion barriers for Cu interconnections or hard coatings in mechanical application. The resistivity, hardness and thermal stability were the important issues in the interconnections and hard coatings, respectively. In this paper, we investigated the relationship between the microstructures, resistivity, nanohardness and thermal stability of the Ta-Si-N thin films at different nitrogen flow ratios of 0-30% (N₂% = N₂ / (Ar + N₂) × 100%) by magnetron reactive co-sputtering. The Ta-Si-N films were annealed at 600, 750 and 900 °C at about 6 × 10⁻³ Pa for 1 h, respectively, to examine their thermal stability. The microstructures of Ta-Si-N films at low N₂% of 2-10% still retained the amorphous-like phase with nanocrystalline grains in an amorphous matrix at annealing of 600-900 °C. The nanohardness of amorphous-like Ta-Si-N film at N₂% of 3% was measured to be 15.2 GPa much higher than that of polycrystalline film of 10.1 GPa at N₂% of 20%. The average nanohardness of both films is stable up to 900 °C and varied in the range of 0.43-0.83 GPa. The resistivity of the as-deposited Ta-Si-N films increase with increasing N₂ flow rate. It is small around 220-540 μΩ cm for low N₂% of 2-10% while it increases abruptly to about 7700-43,000 μΩ cm at high N₂% of 20-30%. The best thermal stability of resistivity of Ta-Si-N film occurs at the N₂% of 2% in the range of 220 to 250 μΩ cm from RT to 900 °C.     

Density, stress, hardness and reduced Young's modulus of W-C:H coatings

Density, hardness and compressive stress of tungsten contained in an amorphous-hydrogenated-carbon matrix (W-C:H) have been studied as a function of composition and bias voltage. W-C:H coatings were deposited by reactive sputter deposition from a tungsten-carbide (WC) target on silicon substrate in an argon-acetylene plasma. W-C:H coatings obtained at different acetylene flow rates and substrate bias voltages, were characterized by scanning electron microscopy, X-ray diffraction, nanoindentation and substrate curvature method. It has been observed that compressive stress, hardness and reduced Young's modulus decrease when the acetylene flow is increased from 0 to 10 sccm. Also, compressive stress and hardness increases with the substrate bias voltage. In particular, for W-C:H coatings obtained at 5 sccm of acetylene flow, the compressive stress and hardness increase from − 1.6 GPa to − 3.2 GPa and from 19 GPa to 24 GPa, respectively, when increasing the substrate bias from 0 to 200 V. The variation of the internal stress, hardness and density of the coatings is discussed in terms of composition and structure of the W-C:H coatings.     

Comparative study on mechanical properties of MoSiN multilayer films deposited on Si(100) and Ti-covered Si(100) substrates

We deposited MoSiN multilayer films using a MoSi₂ target via pulsed-DC and radio-frequency (RF) magnetron sputtering methods. For the fabrication of the Ti-covered Si(100) substrate, we also grew Ti layers via the RF magnetron sputtering method. To improve the mechanical properties of the as-grown MoSiN thin films, argon and nitrogen plasmas ignited by RF and pulse DC under vacuum conditions were also used with a total pressure of 0.7 Pa, a substrate bias of −100 V, and a substrate ion current density of 1.5 mA/cm². The as-grown MoSiN films were investigated for hardness (Gpa) and macro-stress(s) properties, and the relationship between film composition and micro-structures was analyzed using x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS). The maximum hardness and stress values of the MoSiN films were 32 GPa and −2.5 GPa, respectively, depending on variations of substrates and reactive gas.     

Composition and mechanical properties of AlC, AlN and AlCN thin films obtained by r.f. magnetron sputtering

Aluminum carbide (Al-C), aluminum nitride (Al-N), and aluminum carbonitride (Al-C-N) thin films were grown onto Si [100] substrates by r.f. reactive magnetron sputtering at 400 °C. The Al-N coatings were obtained by sputtering of Al (99.9%) target in Ar/N₂ atmosphere and the Al-C and Al-C-N by co-sputtering of a binary (50% Al, 50% C) target in argon and in Ar/N₂ mixture, respectively. The d.c. bias voltage was varied between 0 and − 150 V. The films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR) and the mechanical properties by nanoindentation. The structure of the films has been determined by XRD, which shows that amorphous films are formed in all cases. The variation of polarization bias voltage produced chemical differences in the films. As the bias voltage is increased, the Al content is reduced in all three materials. The nitrogen content also varied between 10 and 14 at.% for Al-N coatings, remaining practically constant (21 at.%) for the Al-C-N films. The Berkovich hardness results were 7.0, 17.2 and 9.2 GPa for Al-C, Al-N, and Al-C-N films, respectively.     

Synthesis and characterization of hardness-enhanced multilayer oxide films for high-temperature applications

Multilayer oxide coatings consisting of amorphous Al₂O₃ and crystalline TiO₂ nanolayers have been deposited using reactive pulsed d.c. magnetron sputtering at different partial pressures of oxygen. Hardness enhancement has been observed in oxide multilayer coatings with amorphous Al₂O₃ as the majority component. These coatings had greater hardness-to-modulus ratios and showed greater resistance to wear over monolithic Al₂O₃ and TiO₂ majority phase multilayers. Multilayer films retain their high hardness up to ~ 800 °C in air; some hardness enhancement in the Al₂O₃ majority phase multilayer coating remains even after 1 h of air annealing at 1000 °C. The hardness decrease at elevated temperatures is due to the roughening of interfaces between nanolayers, which can be attributed to the annealing-driven change of crystallographic texture of TiO₂ layers.     

Effect of C2H2 gas flow rate on synthesis and characteristics of Ti–Si–C–N coating by cathodic arc plasma evaporation

The influences of C₂H₂ gas flow rate on the synthesis, microstructure, and mechanical properties of the Ti–Si–C–N films were investigated. Quaternary Ti–Si–C–N coatings were deposited on WC-Co substrates using Ti and TiSi (80:20 at.%) alloy target on a dual cathodic arc plasma evaporation system. The Ti–Si–C–N coatings were designed with Ti/TiN/TiSiN as an interlayer to enhance the adhesion strength between the top coating and substrate. The Ti–Si–C–N coatings were deposited under the mixture flow of N₂ and C₂H₂. Composition analysis showed that as the C₂H₂ gas flow increased, the Ti, Si and N contents decreased and the carbon content increased in the coatings. The results showed the maximum nanohardness of approximately 40 GPa with a friction coefficient of 0.7 was obtained at the carbon content of 28 at.% (C₂H₂ = 15 sccm). However, as the C₂H₂ gas flow rate increased from 15 to 40 sccm (carbon content from 25.2 to 56.3 at.%), both the hardness and friction coefficient reduced to 20 GPa and 0.3, respectively. Raman analysis indicated the microstructure of the deposited coating transformed from Ti–Si–C–N film to TiSi-containing diamond-like carbon films structure, which was strongly influenced by the C₂H₂ flow rate and is demarcated at a C₂H₂ flow of 20 sccm. The TiSi-containing diamond-like carbon films reveal low-friction and wear-resistant nature with an average friction coefficient between 0.3 and 0.4, lower than both TiSiN and Ti–Si–C–N films.     

Effect of nitrogen-incorporation on structure, properties and performance of magnetron sputtered CrB2

Transition metal (TM) boron nitrides are promising candidates for protective coatings with self-lubricating abilities as they can combine properties of TM diborides with the lubricity of hexagonal boron nitride (h-BN). Here, we report on Cr-B-N coatings prepared by unbalanced DC magnetron sputtering of a CrB₂ target in argon/nitrogen atmosphere at 450 °C. By varying the nitrogen partial pressure (p_N2) between 0 and 64% of the total pressure (p_Ar + p_N2), the N-content in our coatings could be increased from 0 to 47 at.%. The results obtained from X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show that for p_N2 ≤ 11% a CrB₂-based structure type develops, whereas with increasing p_N2 the microstructure becomes then X-ray amorphous and finally CrN is detected as the sole crystalline constituent. With increasing p_N2 from 0 to 11%, the hardness and indentation modulus rapidly decrease from 40.6 and 397 GPa for CrB₂ to 13.4 and 108 GPa for CrB_2.0N_0.5. All coatings investigated yield only a moderate friction coefficients between 0.5 and 0.7. Based on detailed high-resolution TEM studies, we can conclude that the missing h-BN based lubricity is due to a lack of a significant long-range order.     

Effect of Nano-Sized TiN Additions on the Electrical Properties of Vacuum Cold Sprayed SiC Coatings

Three different contents of nano-sized TiN powers of 20 nm in size were added to nano-sized SiC powders of 40 nm. Vacuum cold spray (VCS) process was used to deposit SiC-TiN composite coatings on Al₂O₃ substrates. Microstructure and phase structure analysis of the samples was performed by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Sheet resistance of the VCS coatings was measured using a four-point probe method. The influences of TiN additions on the electrical resistivity of SiC-TiN composite coatings and the conductive mechanisms were investigated. The electrical resistivity of SiC-TiN coatings decreases with increasing TiN contents, reaching a minimum of 1.82 Ω m with 50 mol% TiN.     

Growth, stress and hardness of reactively sputtered tungsten nitride thin films

Tungsten nitride (WN_x) thin films were deposited on Si(100) substrates using direct current reactive magnetron sputtering in discharging a mixture of N₂ and Ar gas. The effects of nitrogen flow rate (F_N2) and substrate bias voltage (V_b) on the composition, phase structure, and mechanical properties for the obtained films were evaluated by means of X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation. The evolution of phase structure is found closely correlated to N concentration in the films. When V_b = −40 V, with increasing F_N2, the N/W atomic ratio gradually increases in the film, accompanied by a phase transition from cubic β-W to hexagonal WN through face centered-cubic (fcc)-W₂N. At F_N2 = 15 sccm, the N/W atomic ratio gradually decreases with increasing the absolute value of V_b, resulting in a transition from fcc-W₂N to cubic β-W(N) through a mixture of fcc-W₂N + β-W(N). In addition, the increase in implanted nitrogen causes the increase in the compressive stress with increasing F_N2. In contrast, although with increasing the absolute value of V_b from 80 to 160 V the N/W atomic ratio decreases, the increase of the defects caused by increasing ion bombarding energy, dominates the increase of the compressive stress. Furthermore, the maximum hardness value for the films arrives at 38.9 GPa, which is obtained at V_b = −120 V when fcc-W₂N + β-W(N) mixed structure is formed.     

Optical properties and corrosion behaviour of sputtered Zr-B and Zr-B-N coatings

In this paper, we present results on the structure, optical properties and corrosion behaviour of Zr-B and Zr-B-N coatings employing non-reactive and reactive d.c. magnetron sputter deposition. The addition of nitrogen reduced the grain size—coatings deposited at nitrogen flow rates f(N₂) of less than approximately 14 sccm (standard cm³ min^-1) were extremely fine grained, while nitrogen flow rates of more than 14sccm led to fracture-amorphous coatings with a very smooth surface. The hardness and abrasion resistance decreased with the increase in nitrogen content. Pure Zr-B coatings are silver-greyish with metallic brilliance but nitrogen changes the colour from dark grey or black at low contents to interference colours in the amorphous state. Ellipsometric measurements of the refractive index n and adsorption coefficient k supported the results derived from electron microscopy, colour measurements and mechanical testing. The transition point between the fine-grained and fracture-amorphous structure lies in the range of f(N₂) around 10 sccm. The black coatings deposited with such nitrogen levels showed good corrosion and abrasion resistance combined with a satisfying hardness. In some cases, increasing the nitrogencontent improved the corrosion resistance. In potentio- dynamic experiments, more positive free corrosion and pitting potentials were demonstrated. However, in salt spray testing and immersion testing using an artificial sweat solution, no beneficial effect of high nitrogen additions was noticed. Zr-B-N coatings deposited with nitrogen flow values in the range 10–20 sccm offer an excellent choice for decorative purposes, owing to their dark grey or intense black colour and good corrosion resistance.