Erosion wear of CrN,TiN, CrAlN,and TiAlN PVD nitride coatings

Four nitride coatings (CrN, ZrN, CrAlN, and TiAlN) were deposited on YT15 cemented carbide by cathode arc-evaporation technique. Microstructural and fundamental properties of these nitride coatings were examined. Erosion wear tests were carried out, the erosion wear of these nitride coatings caused by abrasive particle impact was compared by determining the wear depth and the erosion rates of the coatings. The wear surface features were examined by scanning electron microscopy. Results showed that the coatings with Al (CrAlN and TiAlN) exhibited higher erosion wear resistance over those without Al (CrN and TiN). The H³/E² of the coating seemed to play an important role with respect to its erosion wear in erosion tests. AlTiN and CrAlN coatings being with high H³/E² exhibited lower erosion rates, while CrN coating with low H³/E² showed higher erosion rates under the same test conditions. Analysis of eroded surface of the coatings demonstrated that the TiN and CrN coatings exhibited a typical brittle fracture induced removal process, while AlTiN and CrAlN coatings showed mainly micro cutting and cycle fatigue fracture of material removal mode.     

Mechanical properties and oxidation resistance of CrAlN/BN nanocomposite coatings prepared by reactive dc and rf cosputtering

CrAlN/BN nanocomposite coatings were deposited through reactive cosputtering, i.e., pulsed dc and rf sputtering, of CrAl and h-BN targets, respectively. X-ray diffraction (XRD) and selected area electron-diffraction (SAED) analysis indicated that the CrAlN/BN coating consists of very fine grains of B1 structured CrAlN phase. With an increasing BN volume fraction of over 8 vol.%, the nanocrystalline nature of the grains is revealed through a dispersion of fine grains in the CrAlN/BN coating. A cross-sectional observation using a transmission electron microscope (TEM) clarified that the coating demonstrating the highest level of hardness has a fiber-like structure consisting of grains that are ~ 20 nm in width and ~ 50 nm in length. X-ray photoelectron spectroscopy (XPS) analysis revealed that the coating consists mainly of CrAlN and h-BN phase. The indentation hardness (H_IT) and effective Young's modulus (E*) of the coatings increased with the BN phase ratio, reaching a maximum value of ~ 46 and ~ 440 GPa at ~ 7 vol.% of BN phase; it then decreased moderately to ~ 40 and ~ 350 GPa at 18 vol.% of BN, respectively. Furthermore, CrAlN/BN coatings showed superior oxidation resistance compared with CrAlN coatings. After annealing at 800 °C in air for 1 h, the indentation hardness of CrAlN coatings decreased to 50% of the as-deposited hardness; in contrast, the hardness of CrAlN/BN nanocomposite coatings either stayed the same or increased, attaining a value of about 46 GPa. After annealing at 900 °C for 1 h, the hardness of all the coatings decreased to about 40%.     

Friction and wear properties of TiN,TiAlN, AlTiN and CrAlN PVD nitride coatings

Four nitride coatings, TiN, TiAlN, AlTiN and CrAlN were deposited on YG6 (WC + 6 wt.% Co) cemented carbide by cathodic arc-evaporation technique. The friction and wear properties were investigated and compared using ball-on-disc method at high speed with SiC ball as a counter material. The tests were evaluated by scanning electron microscopy, X-ray diffractometer, energy dispersive X-ray, micro hardness tester and an optical profilometer. The results showed that TiN and TiAlN coatings presented lower friction coefficient and lower wear rate, and that high Al content AlTiN and CrAlN coatings didn't present better anti-wear properties in this test. Oxidation and abrasive wear were the main wear mechanism of TiN coating. In spite of the observation of micro-grooves and partial fractures, TiAlN possessed perfect tribological properties compared with the other coatings. High Al content increased the chemical reactivity and aroused severe adhesive wear of AlTiN coating. CrAlN coating presented better properties of anti-spalling and anti-adhesion, but abundant accumulated debris accelerated wear of the coating under this enclosed wear environment.     

Sintering behavior and non-linear properties of ZnO varistors processed in microwave electric and magnetic fields at 2.45 GHz

A study of the densification behavior and grain growth mechanisms of ZnO-based varistors composed of 98 mol.% ZnO–2 mol.% (Bi₂O₃, Sb₂O₃, Co₃O₄, MnO₂) has been carried out. The pressed samples were sintered in microwave electric (E) and magnetic (H) fields using a single-mode cavity of 2.45 GHz. The effect of the sintering temperature (900–1200 °C), holding time (5–120 min) and sintering mode (E, H) on the microstructure and electrical properties of the sintered varistor samples were investigated. The grain growth kinetics was studied using the simplified phenomenological equation Gⁿ = kte^(?Q/RT). The grain growth exponent (n) and apparent activation energy (Q) values were estimated for both electric and magnetic heating modes and were found to be n = 3.06–3.27, Q = 206–214 kJ mol^?1, respectively. The lower value of n estimated in the E field was attributed to a volume diffusion mechanism, whereas the higher n value in the H field sintering was correlated mainly to a combined effect of volume and surface diffusion processes. Samples sintered in the H and E fields showed high final densities. Moreover, the ones sintered in the H field presented slightly higher density values and bigger grains for all sintering temperatures than E field heated ones. The optimal sintering conditions were achieved at 1100 °C for a 5 min soaking time for both H and E field processed samples, where respectively densities of 99.2 ± 0.5% theoretical density (TD) and 98.3 ± 0.5% TD along with grain size values of G = 7.2 ± 0.36 μm and G = 6.6 ± 0.33 μm were obtained. Regarding the electrical properties, breakdown voltage values as high as 500–570 V mm^?1 were obtained, together with high non-linear coefficients α = 29–39 and low leakage currents (J_l ≈ 5 × 10^?3 mA cm^?2), respectively, for E and H field sintered varistor samples. Moreover, samples sintered in an H field systematically exhibited higher breakdown voltage values compared to the ones sintered in the E field. This was attributed to an improved coupling between the H field and the present dopants within the ZnO matrix, this latter being mostly semiconductive, thus leading to an enhanced reactivity and improved properties of the electrostatic barrier.     

Effect of Annealing Temperature on Tribological Properties and Material Transfer Phenomena of CrN and CrAlN Coatings

This study evaluates the effects of annealing temperature and of the oxides produced during annealing processes on the tribological properties and material transfer behavior between the PVD CrN and CrAlN coatings and various counterface materials, i.e., ceramic alumina, steel, and aluminum. CrAlN coating has better thermal stability than CrN coating in terms of hardness degradation and oxidation resistance. When sliding against ceramic Al₂O₃ counterface, both CrN and CrAlN coatings present excellent wear resistance, even after annealing at 800 °C. The Cr-O compounds on the coating surface could serve as a lubricious layer and decrease the coefficient of friction of annealed coatings. When sliding against steel balls, severe material transfer and adhesive wear occurred on the CrN and CrAlN coatings annealed at 500 and 700 °C. However, for the CrAlN coating annealed at 800 °C, much less material sticking and only small amount of adhesive wear occurred, which is possibly due to the formation of a continuous Al-O layer on the coating outer layer. The sliding tests against aluminum balls indicate that both coatings are not suitable as the tool coatings for dry machining of aluminum alloys.     

Effect of hydrogen on internal friction and elastic modulus in titanium alloys

The effect of hydrogen on the variation with temperature of internal friction (Q^?I) and elastic modulus (E) of a number of Ti-based alloys has been studied in the Hz and kHz frequency ranges. A relaxation peak of internal friction with a high degree of relaxation (Q^?I_max ～ 10^?1) and with a ΔE effect is observed in all hydrogen-doped samples at T ～ 600 K at ～1 kHz, and at T ～ 500 K at ～1 Hz. Such a peak is not present in samples without hydrogen. The activation energy W and the frequency factor v₀ of the observed relaxation are determined to be W ～ 1.55 eV, v₀ ～ 10¹⁷ s^?1. It is shown that the observed effects are connected with the mechanism of grain boundary relaxation, as the introduction of hydrogen into titanium alloys leads to the formation of fine-grained structures.     

Structural and mechanical properties of AlTiN/CrN coatings synthesized by a cathodic-arc deposition process

Monolayered AlTiN and Multilayered AlTiN/CrN coatings were synthesized by a cathodic-arc deposition process, using TiAl (with 50/50 and 33/67 at.%) and Cr elemental cathodes. The atomic ratio of Al/(Ti + Al) in the AlTiN coatings was reduced to 0.44 and 0.61, respectively, compared with the corresponding Ti₅₀Al₅₀ and Ti₃₃Al₆₇ cathode materials. The multilayered AlTiN/CrN films showed smaller crystallite size, larger lattice strain, higher hardness, higher residual stress, and better adhesion strength as well than the monolayered AlTi films. The multilayered Al_0.35Ti_0.22N_0.43/CrN coating exhibited the highest hardness of about 38 GPa and the highest H³/E*² ratio value of 0.188 GPa, indicating the best resistance to plastic deformation, among all the coatings studied.     

Microstructural evolution and grain boundary sliding in a superplastic magnesium AZ31 alloy

Tensile experiments on a fine-grained single-phase Mg–Zn–Al alloy (AZ31) at 673 K revealed superplastic behavior with an elongation to failure of 475% at 1 × 10^?4 s^?1 and non-superplastic behavior with an elongation to failure of 160% at 1 × 10^?2 s^?1; the corresponding strain rate sensitivities under these conditions were ～0.5 and ～0.2, respectively. Measurements indicated that the grain boundary sliding (GBS) contribution to strain ξ was ～30% under non-superplastic conditions; there was also a significant sharpening in texture during such deformation. Under superplastic conditions, ξ was ～50% at both low and high elongations of ～20% and 120%; the initial texture became more random under such conditions. In non-superplastic conditions, deformation occurred under steady-state conditions without grain growth before significant flow localization whereas, under superplastic conditions, there was grain growth during the early stages of deformation, leading to strain hardening. The grains retained equiaxed shapes under all experimental conditions. Superplastic deformation is attributed to GBS, while non-superplastic deformation is attributed to intragranular dislocation creep with some contribution from GBS. The retention of equiaxed grain shapes during dislocation creep is consistent with a model based on local recovery related to the disturbance of triple junctions.     

Structural and mechanical properties of corundum and cubic (AlxCr1−x)2+yO3−y coatings grown by reactive cathodic arc evaporation in as-deposited and annealed states

Coatings of (Al_xCr_1?x)_2+yO_3?y with 0.51 ? x ? 0.84 and 0.1 ? y ? 0.5 were deposited on hard cemented carbide substrates in an industrial cathodic arc evaporation system from powder-metallurgy-prepared Cr/Al targets in pure O₂ and O₂ + N₂ atmospheres. The substrate temperature and bias in all the deposition runs were 575 °C and ?120 V, respectively. The composition of the coatings measured by energy dispersive X-ray spectroscopy and elastic recoil detection analysis differed from that of the facing targets by up to 11%. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed, depending on the Cr/Al ratio of the coatings and O₂ flow per active target during deposition. The corundum phase was promoted by high Cr content and high O₂ flow per target, while the cubic phase was observed mostly for high Al content and low O₂ flow per active target. In-situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum, completed in the temperature range of 900–1100 °C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio <0.4 was 26–28 GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28–30 GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al–Cr–O have improved resistance to crater wear at the cost of flank wear compared with TiAlN coatings.     

Characterization of titanium aluminide alloy components fabricated by additive manufacturing using electron beam melting

Intermetallic, γ-TiAl, equiaxed, small-grain (～2 μm) structures with lamellar γ/α₂-Ti₃Al colonies with average spacing of 0.6 μm have been fabricated by additive manufacturing using electron beam melting (EBM) of precursor, atomized powder. The residual microindentation (Vickers) hardness (HV) averaged 4.1 GPa, corresponding to a nominal yield strength of ～1.4 GPa (～HV/3), and a specific yield strength of 0.37 GPa cm³ g^?1 (for a density of 3.76 g cm^?3), in contrast to 0.27 GPa cm³ g^?1 for EBM-fabricated Ti–6Al–4V components. These results demonstrate the potential to fabricate near net shape and complex titanium aluminide products directly using EBM technology in important aerospace and automotive applications.     

Structural and mechanical properties of Cr–Al–O–N thin films grown by cathodic arc deposition

Coatings of (Cr_xAl_1?x)_δ(O_1?yN_y)_ξ with 0.33 ? x ? 0.96, 0 ? y ? 1 and 0.63 ? δ/ξ ? 1.30 were deposited using cathodic arc evaporation in N₂/O₂ reactive gas mixtures on 50 V negatively biased WC–10 wt.% Co substrates from different Cr and Al alloys with three different Cr/Al compositional ratios. For N₂ < 63% of the total gas, ternary (Cr,Al)₂O₃ films containing <1 at.% of N forms; as determined by elastic recoil detection analysis. Increasing the N₂ fraction to 75% and above results in formation of quaternary oxynitride films. Phase analyses of the films by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy show the predominance of cubic Cr–Al–N and cubic-(Cr,Al)₂O₃ solid solutions and secondary hexagonal α-(Cr,Al)₂O₃ solid solution. High Cr and Al contents result in films with higher roughness, while high N and O contents result in smoother surfaces. Nanoindentation hardness measurements showed that Al-rich oxide or nitride films have hardness values of 24–28 GPa, whereas the oxynitride films have a hardness of ～30 GPa, regardless of the Cr and Al contents. Metal cutting performance tests showed that the good wear properties are mainly correlated to the oxygen-rich coatings, regardless of the cubic or corundum fractions.     

Surface modification of NiTi/PZT heterostructure thin films using various protective layers for potential MEMS applications

The present study explored the in-situ deposition of hard and adherent nanocrystalline protective coatings on NiTi/PZT/TiO_x thin film heterostructure prepared by dc/rf magnetron sputtering. Protective layers (AlN, CrN and TiCrN) of approximate thickness (~ 200 nm) were used to improve the surface, mechanical and corrosion properties of NiTi/PZT/TiO_x heterostructure without sacrificing the shape memory effect and ferroelectricity of the NiTi and PZT layers, respectively. The influence of the protective layer on structural, electrical and mechanical properties of NiTi/PZT/TiO_x heterostructure was systematically investigated and the results were compared. Nanoindentation studies were performed at room temperature to determine the hardness and reduced modulus. The surface modified NiTi/PZT/TiO_x heterostructures were found to exhibit high hardness, high elastic modulus and thereby better wear resistance as compared to pure NiTi/PZT/TiO_x films. From the results of potentiodynamic polarization test conducted in 1 M NaCl solution, the CrTiN coated NiTi/PZT/TiO_x heterostructure showed the best corrosion resistance with the lowest corrosion current density (1.52 × 10^? 8 A cm^? 2) and the highest protective efficiency (96.8%). The results presented here prove the potential of a surface modified NiTi/PZT/TiO_x heterostructure to be used in various microelectromechanical (MEMS) applications.     

Microstructure and grain boundary relaxation in ultrafine-grained Al/Al oxide composites

The microstructure and grain boundary relaxation in ultrafine-grained Al/Al oxide composites were studied by electron microscopy observation and internal friction measurement, respectively. Both the microstructure and the internal friction behavior of the composites were strongly influenced by the thermomechanical treatment parameters. All the Al particles were still covered by the native amorphous oxide shells in those composites sintered at T < 823 K, and no indication of Al grain boundary relaxation was detected. Some Al oxide shells were cracked, resulting in the formation of a few Al–Al grain boundaries between adjacent particles in the sample sintered at 823 K, and one internal friction peak centered at ～440 K was detected. All the oxide shells were broken into small fragments in those samples sintered at T ? 843 K, and two internal friction peaks were detected, one prominent peak at ～440 K and one weak peak at ～540 K. A microstructure with a bimodal grain size distribution of Al was formed via partial recrystallization after thermomechanical treatment of the sample sintered at 893 K, and two internal friction peaks with comparable intensity were detected. The internal friction peaks were associated with the relaxation of Al grain boundary in the composites.     

同步脉冲偏压对Hi PIMS技术低温沉积CrN涂层结构及性能影响

针对高性能CrN涂层无法实现低温可控制备的技术瓶颈,利用具备高溅射材料离化率的高功率脉冲磁控溅射技术,调控同步脉冲偏压,改善涂层生长动力学条件,实现CrN涂层的低温可控沉积。开展同步脉冲偏压与涂层化学组成、组织结构、力学、摩擦学及耐腐蚀性能间关联关系研究。同步脉冲偏压在提升沉积离子束流迁移能的同时可显著降低荷能Ar+对成膜表面的持续轰击作用,达到改善涂层致密性及膜基结合力的目的。此外,沉积CrN涂层晶粒细化显著,硬度及弹性模量明显升高,最高可达13.8 GPa、236.7 GPa。涂层力学性能优化及致密性提升显著改善了摩擦学与耐腐蚀性能,涂层磨损率最低可达2.49×10^-15m³/(N·m),同时涂层可耐受120h中性盐雾腐蚀环境考核。为实现高性能CrN涂层的低温可控制备,扩展其在温度敏感基体领域的适用范围提供了新的设计思路与技术支撑。     

A comparative study of reactive direct current magnetron sputtered CrAlN and CrN coatings

Approximately 1.5 μm thick CrN and CrAlN coatings were deposited on silicon and mild steel substrates by reactive direct current (DC) magnetron sputtering. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the coatings was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD data showed that the CrN and CrAlN coatings exhibited B1 NaCl structure. Nanoindentation measurements showed that as-deposited CrN and CrAlN coatings exhibited a hardness of 18 and 33 GPa, respectively. Results of the surface analysis of the as-deposited coatings using SEM and AFM showed a more compact and dense microstructure for CrAlN coatings. The thermal stability of the coatings was studied by heating the coatings in air from 400 to 900 °C. The structural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data revealed that CrN coatings got oxidized at 600 °C, whereas in the case of CrAlN coatings, no detectable oxides were formed even at 800 °C. After annealing up to 700 °C, the CrN coatings displayed a hardness of only about 7.5 GPa as compared to CrAlN coatings, which exhibited hardness as high as 22.5 GPa. The potentiodynamic polarization measurements in 3.5% NaCl solution indicated that the CrAlN coatings exhibited superior corrosion resistance as compared to CrN coatings.     

Structural evolution and grain growth kinetics of the Fe–28Al elemental powder during mechanical alloying and annealing

The structural evolution and grain growth kinetics of the Fe–28Al (28 at.%) elemental powder during mechanical alloying and annealing were studied. Moreover, the alloying mechanism during milling the powder was also discussed. During mechanical alloying the Fe–28Al elemental powder, the solid state solution named Fe(Al) was formed. The lattice parameter of Fe(Al) increases and the grain size of Fe(Al) decreases with increasing milling time. The Fe and Al particles were first deformed, and then, the composite particles of the concentric circle-like layers were generated. Finally, the composite particles were substituted by the homogeneous Fe(Al) particles. The continuous diffusion mixing mechanism is followed, mainly by the diffusion of Al atoms into Fe. During annealing the milled Fe–28Al powder, the order transformation from Fe(Al) to DO₃-Fe₃Al and the grain growth of DO₃-Fe₃Al occurred. The grain growth kinetic constant, K = 1.58 × 10⁻⁹ exp(−540.48 × 10³/RT) m²/s.     

Erosion performance and characterization of nanolayer (Ti,Cr)N hard coatings for gas turbine engine compressor blade applications

(Ti,Cr)N nanolayer coatings were deposited on Ti–6Al–4V, 17-4PH and Inconel 718 substrates using cathodic arc physical vapor deposition for improved erosion and corrosion resistance. Coating corrosion performance was highly dependent on the coating thickness and packing factors and correlated with increased chromium content within the (Ti,Cr)N nanolayer coatings. The change in cathode current predominantly affected coating thickness and the bias affected the packing factor. Erosion tests of the coated and uncoated substrates at both 30° and 90° erodent impingement angles were conducted using angular aluminum oxide media at particle velocities up to 145 m/s. Chromium evaporator current and substrate bias were varied to change film stoichiometry and microstructure for erosion performance evaluation. When chromium evaporator current was varied, the increase in chromium content led to an increase in binary CrN phase volume and a decrease in TiN phase volume. The increase in CrN phase volume decreased both hardness and erosion performance at both impingement angles. Lower bias values resulted in better erosion performance. At 30° erodent impingement, all coated samples outperformed the uncoated substrate; whereas, for 90° impingement, only coatings deposited at low bias values (? 25 V, ? 50 V, and ? 100 V) and high Ti:Cr ratios (> 2.4) outperformed the uncoated substrate. The primary coating failure mechanism was microchipping.     

Oxidation behavior,microstructure evolution and thermal stability in nanostructured CrN/AlN multilayer hard coatings

CrN/AlN multilayer coatings with modulation period of 4 and 12.3 nm were manufactured by RF magnetron sputtering. The films were annealed at temperatures 800–950 °C for 1 h in air environment. The microstructure evolution and chemical composition of the formed oxides after heat treatment were identified by transmission electron microscope (TEM) and energy dispersive spectrometer (EDS). After heat treatment at 800 °C for 1 h, three regions which formed on the surface of CrN/AlN coatings with 12.3 nm modulation was observed, including the Al-rich layer covered at the topmost surface, the mixed nano-crystalline Al₂O₃ and Cr₂O₃ film and the spherical nano-voids embedded in between. On the contrary, for CrN/AlN coating with a modulation period of 4 nm, the dense oxide layer around 37 nm formed on the top of the un-reacted film was much thinner than that of CrN/AlN coating with 12.3 nm. Besides, no nano-voids was detected which implied that the outward diffusion of atom species was suppressed as compared to that in the film with 12.3 nm. The presence of the topmost Al-rich layer protected the multilayer coating from the outward diffusion of Cr and Al, as well as the inward diffusion of oxygen. After 950 °C for 1 h and 800 °C for 16 h, the grain growth of surface oxides occurred and non-uniform interface between oxide and coating was also determined by TEM in the CrN/AlN multilayer coating with 12.3 nm. However, no substantial oxidations were detected in the coating with modulation period of 4 nm. It was evident that the CrN/AlN multilayer with smaller modulation period exhibited better oxidation resistance.     

Influence of Pb segregation on the deformation of nanocrystalline Al: Insights from molecular simulations

Molecular dynamics straining simulations using a two-dimensional columnar model were run for pure Al with grain sizes from 5 to 30 nm, and for 10 nm grain size Al–Pb alloys containing 1, 2 and 3 at.% Pb. Monte Carlo simulations showed that all the Pb atoms segregate to the grain boundaries. Pb segregation suppresses the nucleation of partial dislocations and twins during straining. At 3 at.% Pb, no dislocations or twins are observed throughout the straining history. It also appeared that Pb tends to segregate to the same locations in grain boundaries that were favorable for partial dislocation emission. Grain boundaries with Pb segregates were very robust against dissociation during straining compared to pure Al. The yield stress determined from stress–strain curves showed a decrease with increasing Pb content, supporting a similar observation for the hardness change measured on nanocrystalline Al–Pb alloys.     

Structure and properties of selected (Cr–Al–N,TiC–C,Cr–B–N) nanostructured tribological coatings

The paper will present the state-of-art in the process, structure and properties of nanostructured multifunctional tribological coatings used in different industrial applications that require high hardness, toughness, wear resistance and thermal stability. The optimization of these coating systems by means of tailoring the structure (graded, superlattice and nanocomposite systems), composition optimization, and energetic ion bombardment from substrate bias voltage control to provide improved mechanical and tribological properties will be assessed for a range of coating systems, including nanocrystalline graded Cr_1−xAl_xN coatings, superlattice CrN/AlN coatings and nanocomposite Cr–B–N and TiC/a-C coatings. The results showed that the superlattice CrN/AlN coating exhibited a super hardness of 45 GPa when the bilayer period Λ was about 3.0 nm. Improved toughness and wear resistance have been achieved in the CrN/AlN multilayer and graded CrAlN coatings as compared to the homogeneous CrAlN coating. For the TiC/a-C coatings, increasing the substrate bias increased the hardness of TiC/a-C coatings up to 34 GPa (at −150 V) but also led to a decrease in the coating toughness and wear resistance. The TiC/a-C coating deposited at a −50 V bias voltage exhibited an optimized high hardness of 28 GPa, a low coefficient of friction of 0.19 and a wear rate of 2.37 × 10⁻⁷ mm³ N⁻¹ m⁻¹. The Cr–B–N coating system consists of nanocrystalline CrB₂ embedded in an amorphous BN phase when the N content is low. With an increase in the N content, a decrease in the CrB₂ phase and an increase in the amorphous BN phase were identified. The resulting structure changes led to both decreases in the hardness and wear resistance of Cr–B–N coatings.