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.     

Mechanical properties, deformation behaviors and interface adhesion of (AlCrTaTiZr)Nx multi-component coatings

In this study, (AlCrTaTiZr)N_x multi-component coatings with quinary metallic elements were developed as protective hard coatings for tribological application. The mechanical properties, creep behaviors, deformation mechanisms and interface adhesion of the (AlCrTaTiZr)N_x coatings with different N contents were characterized. With increasing the N₂-to-total (N₂ + Ar) flow ratio, R_N, during sputtering deposition, the (AlCrTaTiZr)N_x coatings transformed from an amorphous metallic phase to a nanocomposite and finally a crystalline nitride structure. The hardness of the coatings accordingly increased from 13 GPa to a high value of about 30 GPa, but the creep strain rate also increased from 1.3 × 10^− 4 to 7.3 × 10^− 4 1/s. The plastic deformation of the amorphous metallic coating deposited with R_N = 0% proceeded through the formation and extension of shear bands, whereas dislocation activities dominated the deformation behavior of the crystalline nitride coatings deposited with R_N = 10% and 30%. With increasing R_N, the interface adhesion energy between the coatings and the substrates was also enhanced from 6.1 to 22.9 J/m².     

Magnetron reactively sputtered Ti-DLC coatings on HNBR rubber: The influence of substrate bias

In this study, Ti-containing diamond-like carbon (Ti-DLC) coatings have been deposited on HNBR (hydrogenated nitrile butadiene) rubber and also on Si wafer as reference via unbalanced magnetron reactive sputtering from a Ti target in C₂H₂/Ar plasma. The deposition rates of coatings on rubber and Si wafer were about the same. Columnar structures resulting from a rough interface were often observed in the coatings deposited on rubbers. Only at a high bias voltage of − 300 V the coating on HNBR rubber became column-free whereas a bias voltage of − 100 V could already restrain the columnar structure and thus produced dense and smooth coatings on Si wafer. A segmented morphology of the coatings on HNBR rubber is formed as a result of the large difference in thermal expansion between the coating and HNBR rubber. The crack network that separates the patches plays an important role in maintaining the coating flexibility. The size of the patches reduces with increasing bias voltage and thus the variation of deposition temperature. A high bias voltage enhances the hardness of Ti-coating and the rubber-coating adhesion, and guarantees a good tribological performance. When sliding against ø6 mm 100Cr6 steel ball counterpart, very low coefficients of friction were achieved (< 0.25 for the coated rubber versus > 1.3 for the uncoated). The Ti-DLC coating can be considered as a promising material for the enhancement of tribological performance of rubbers.     

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.     

Influence of the N2 partial pressure on the mechanical properties and tribological behavior of zirconium nitride deposited by reactive magnetron sputtering

Zirconium nitride was deposited by reactive unbalanced magnetron sputtering at different N₂ partial pressures, on an AISI 316L stainless steel substrate. The mechanical properties of the coatings were evaluated by means of nanoindentation tests employing a Berkovich indenter and loads which varied between 120-9000 µN. The sliding wear behavior of the substrate-coating systems was studied under a normal load of 2 N using a ball-on-disc tribometer, with an AISI 52100 ball (6 mm diameter) as counterpart. It has been found that N₂ partial pressure has a significant effect both on the hardness and corresponding Young's modulus of the coatings. As the N₂ partial pressure increases from 1 × 10^− 4 Torr to 10 × 10^− 4 Torr, the hardness and Young's modulus of the coatings decrease from 26 to 20 GPa and 360 to 280 GPa, respectively. The nanoindentation tests revealed the presence of a third oxide layer (10 nm thick, approximately) on the surface of the coating. Scanning electron microscopy (SEM) analysis performed on the worn triboelements indicated that both abrasive and adhesive wear mechanisms could take place in addition to the substrate plastic deformation. The deposition conditions and coating mechanical integrity determine the predominant wear mechanism.     

Tribological properties of duplex Cr-Si-N coatings on SS410 steel

Hardness and other mechanical properties of CrN can be enhanced by adding small amounts of Si, an effect that can possibly be attributed to solid solution hardening. In the present work, tribological properties of the Cr-Si-N coatings on SS410 steel substrates were studied. These samples were prepared by a duplex treatment consisting of surface nitriding and deposition of a Cr bond-coat, which also provides the highest adhesion. The influence of silicon concentration on the tribological properties was determined by ball-on-disc and ball-on-flat tests, while the wear mechanism against an alumina ball was assessed by analyzing the wear track and the wear debris using SEM, EDX and Raman spectroscopy. It was found that the coating containing 2.3 at.% of Si, corresponding to the solubility limit, exhibits the best mechanical and tribological performance: the wear rate of the SS410 substrate has been reduced by a factor of 500, corresponding to a hardness and wear coefficient of 25 GPa and 2-4 × 10^− 7 mm³/N m, respectively.     

Influence of substrate bias, deposition temperature and post-deposition annealing on the structure and properties of multi-principal-component (AlCrMoSiTi)N coatings

Nitride films are deposited from a single equiatomic AlCrMoSiTi target by reactive DC magnetron sputtering. The influence of the substrate bias and deposition temperature on the coating structure and properties are investigated. The bias is varied from 0 to − 200 V while maintaining a substrate temperature of 573 K. And the temperature is changed from 300 to 773 K whilst maintaining a substrate bias of − 100 V. From X-ray diffraction analysis, it is found that all the as-deposited coatings are of a single phase with NaCl-type FCC structure. This is attributed to the high mixing entropy of AlN, CrN, MoN, SiN, and TiN, and the limited diffusion kinetics during coating growth. Specific aspects of the coating, namely the grain size, lattice constant and compressive stress, are seen to be influenced more by substrate bias than deposition temperature. In fact, it is possible to classify the deposited films as large grained (~ 15 nm) with a reduced lattice constant (~ 4.15 Å) and low compressive residual stresses for lower applied substrate biases, and as small grained (~ 4 nm) with an increased lattice constant (~ 4.25 Å) and high compressive residual stresses for applied biases of − 100 V or more. A good correlation between the residual stress and lattice constant under various deposition conditions is found. For the coatings deposited at − 100 V, and at temperatures above 573 K, the hardness could attain to the range of 32 to 35 GPa.Even after annealing in vacuum at 1173 K for 5 h, there is no notable change in the as-deposited phase, grain size or lattice constant of the coatings but an increase in hardness. The thermal stability of microstructure is considered to be a result of the high mixing entropy and sluggish diffusion of these multi-component coatings. For the anneal hardening it is proposed that the overall bonding between target elements and nitrogen is enhanced by thermal energy during annealing.     

Effect of bias voltage on microstructure and properties of Ti-doped graphite-like carbon films synthesized by magnetron sputtering

Ti-doped graphite-like carbon (GLC) films with different microstructures and compositions were fabricated using magnetron sputtering technique. The influence of bias voltages on microstructure, hardness, internal stress, adhesion strength and tribological properties of the as-deposited GLC films were systemically investigated. The results showed that with increasing bias voltage, the graphite-like structure component (sp² bond) in the GLC films increased, and the films gradually became much smoother and denser. The nanohardness and compressive internal stress increased significantly with the increase of bias voltage up to −300 V and were constant after −400 V. GLC films deposited with bias voltages in the range of -300--400 V exhibited optimum adhesion strength with the substrates. Both the friction coefficients and the wear rates of GLC films in ambient air and water decreased with increasing voltages in the lower bias range (0--300 V), however, they were constant for higher bias values (beyond −300 V) . In addition, the wear rate of GLC films under water-lubricated condition was significantly higher for voltages below −300 V but lower at high voltage than that under dry friction condition. The excellent tribological performance of Ti-doped GLC films prepared at higher bias voltages of −300--400 V are attributed to their high hardness, tribo-induced lubricating top-layers and planar (2D) graphite-like structure.     

Mechanical performance and nanoindenting deformation of (AlCrTaTiZr)NCy multi-component coatings co-sputtered with bias

This work develops (AlCrTaTiZr)NC_y multi-component coatings by co-sputtering of AlCrTaTiZr alloy and graphite in an Ar/N₂ mixed atmosphere with the application of different substrate biases. All the (AlCrTaTiZr)NC_y coatings deposited in different conditions exhibited a simple face-centered cubic structure. As the applied substrate bias and graphite-target power increased, the (AlCrTaTiZr)NC_y coatings transformed from a large columnar structure with a [111] preferred orientation to a dense, ultrafine nanocomposite structure. With increasing substrate bias and graphite-target power, the hardness, H/E ratio and H³/E² ratio of the coatings increased from 20 to 35 GPa, from 0.07 to 0.12 and from 0.10 to 0.43 GPa, respectively, attributed to the densification of the coatings, the refinement of grains, the introduction of covalent-like carbide bonds, the formation of nanocomposite structure and the existence of large lattice distortions. Because of the severe distortions in the multi-component coatings caused by the addition of differently-sized atoms, the deformation mechanism was dominated by the activity of low-angle dislocations and/or stacking faults.     

Hexagonal diamond formation on steel substrates by negative bias microwave plasma enhanced chemical vapor deposition

This paper reports for the first time the synthesis of hexagonal diamond thin films on high-speed steel substrates by multi-mode microwave plasma enhanced chemical vapor deposition. Before deposition of the films, the substrate surface was treated by scratching with diamond powder. The deposited films were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy. The XRD patterns of (100) and (101) planes and the Raman peaks at ~ 1317-1322 cm^− 1 were observed, confirming the formation of hexagonal diamond phase in the prepared films. The effects of voltage bias on the phase formation, microstructure and hardness of the films were also studied by setting the voltage to 0, − 70, − 150 and − 190 V. The highest hardness of 23.8 GPa was found in the film having clusters of size about 550 nm deposited under a bias voltage of − 150 V. These clusters were built up of grains of size about 14 nm.     

Laser engineered surfaces from glass forming alloy powder precursors: Microstructure and wear

Fe-based metallic glass forming powders have been deposited on mild steel substrates using high power laser cladding. Coatings microstructures have been analysed by scanning- and transmission-electron microscopy and at varying substrate dilutions, have been found to comprise a 100 to 500 nm interdendritic austenitic phase and a dendritic dual-phase of ferrite/martensite. The application of double layer coatings has shown microstructural refinement. This leads to a needle-like microstructure resulting in a nanoindentation tested hardness increase from ~ 11 GPa up to almost 15 GPa. The layers have been subjected to both dry sliding wear and 3-body microscale abrasive wear testing. The dry sliding results show the layers to exhibit excellent wear resistance - particularly at high speed (50 cm s^− 1) with wear rate values of ~ 1 × 10^− 8 mm³/Nm being recorded for the double layer coatings. The single layer coatings reveal a micro-wear mechanism connected with the slip between the ferrite and martensite in the dendritic dual-phase. Microscale abrasive wear testing also reveals that the layers have a good wear resistance, with wear scars exhibiting characteristic material removal by micro-chipping. There is no preferential abrasion of any one phase, nor are track over-lap areas, cracks or pores found to result in varying wear scar dimensions.     

偏压对MPP制备AlTiSiN纳米复合涂层结构及性能的影响

目的实现对AlTiSiN纳米复合涂层微观组织结构的调控及力学性能优化。方法利用可调控脉冲磁控溅射技术,通过调控基体偏压(-50～-250 V)制备了不同偏压条件下的AlTiSiN纳米复合涂层。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能量色散谱仪(EDS)、原子力显微镜(AFM)、薄膜综合性能测试仪及球盘摩擦试验仪,测试了涂层的微观组织结构、组成成分、表面形貌、力学性能及摩擦学性能。结果偏压对涂层元素组成影响不大。微观组织结构方面,不同偏压条件下制备AlTiSiN纳米复合涂层的晶面衍射峰宽化现象明显,呈现纳米晶组织结构。-200V条件下制备的涂层的晶面衍射峰呈"馒头峰"形态,表明涂层结晶性能出现明显下降,呈类非晶组织结构;偏压升至-250V时,高能离子对涂层生长表面的持续轰击作用,使得涂层生长表面升温明显,导致结晶性能出现明显改善。涂层表面光滑致密,表面粗糙度最低可达1.753nm。力学性能方面,随基体偏压的升高,涂层硬度在取得最大值后逐渐下降,最高硬度可达25.9 GPa,H/E*系数可达0.13。摩擦学性能方面,偏压为-200 V时,涂层磨损率取得最小值4.7×10~(-15) m~3/(N×m)。结论改变基体偏压,成功实现了涂层微观组织结构的调控生长,进而达到了优化涂层组织结构、力学性能及摩擦学性能的目的。     

Mechanical and tribological properties of duplex treated TiN, nc-TiN/a-SiNx and nc-TiCN/a-SiCN coatings deposited on 410 low alloy stainless steel

The use of hard and superhard nanocomposite (nc) coatings with tailored functional properties is limited when applied to low alloy steel substrates due to their low load carrying capacity. Specifically in this work, in order to enhance the performance of martensitic SS410 substrates, we applied a duplex process which consisted of surface nitriding by radio-frequency plasma followed by the deposition of single layer (TiN, nc-TiN/a-SiN_x or nc-TiCN/a-SiCN) or multilayer (TiN/nc-TiN/a-SiN_x, TiN/nc-TiCN/a-SiCN) coating systems prepared by plasma enhanced chemical vapor deposition (PECVD). We show that plasma nitriding gives rise to a diffusion layer at the surface due to diffusion of nitrogen and formation of the α-Fe and ε-Fe₂N phases, respectively, leading to a surface hardness, H, of 11.7 GPa, compared to H = 5 GPa for the untreated steel. Among the TiN, nc-TiN/a-SiN_x and nc-TiCN/a-SiCN coatings, the latter one possesses the highest H value of 42 GPa and the highest H³/E_r² ratio of 0.83 GPa. Particularly, the TiN/nc-TiCN/a-SiCN multilayer coating system exhibits superior tribological properties compared to single layer TiN and multilayer TiN/nc-TiN/a-SiN_x coatings: this includes excellent adhesion, low friction (C_f = 0.17) and low wear rate (K = 1.6 × 10^− 7 mm³/N m). The latter one represents an improvement by a factor of 600 compared to the bare SS410 substrate. The significance of the relationship between the H/E and H³/E_r² ratios and the tribological performance of the nano-composite coatings is discussed.     

Pulsed laser deposition of antifriction thin-film MoSex coatings at the different vacuum conditions

MoSe_x coatings were obtained by pulsed laser deposition in vacuum at the pressure of background Ar gas up to 10 Pa. The deposition temperature was 200 °С. The films were studied by means of X-ray diffraction, scanning and transmission electron spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy of helium ions. The tribological properties of thin-film coatings were investigated by pin-on-disk testing in air with 50% relative humidity. In addition, wear tracks were studied by micro-Raman spectroscopy. Chemical composition, structure, and tribological properties of the coatings were found to be sensitive to the presence of the inert gas. Thus, increasing the gas pressure from 10^− 4 to 10 Pa changes the chemical composition, so that the ratio of the atomic concentrations of Se and Mo (x = Se/Mo) increases from 1.5 to 2.4 in the principal deposition zone. The changing of the structure concerns the accumulation of distortions in the lattice of MoSe_x nano-crystals as increasing the distance between the basal planes and intensive formation of nano-sized inclusions of the amorphous phase and Mo nano-crystals in the volume of the coatings. At the optimal gas pressure (∼ 2 Pa), the composition of the coating was close to the stoichiometric one, and the layer adjacent to the substrate consisted of MoSe_x nano-crystals with the basal planes parallel to the substrate surface or oriented at small angles to the surface. The thickness of the oriented layer in such coatings was greater than the thickness of the similar layer in the coatings deposited in vacuum (10^− 4 Pa). The tribological properties of MoSe_x coatings deposited on substrates of stainless steel type 95 × 18 (18 at.% Cr) depend on the gas pressure. The friction coefficient in air decreases from 0.08 for deposition at the background pressure of 10^− 4 Pa to 0.04 for deposition at the optimal pressure. This change in the deposition conditions has only a marginal effect on the coating durability. Means to increase the durability are also considered.     

Performance of W-TI-(N) coated pins in lubricated pin-on-disk tests

W-Ti-(N) thin films were deposited on polished bearing steel balls by dc magnetron sputtering varying the partial pressure ratio, pN₂/pAr. The tribological behaviour was accessed by pin-on-disk testing with contact geometry of uncoated and coated 100Cr6 balls sliding against uncoated different disk materials used as stamping sheet. Different types and amounts of lubricants were used in the tests.In non-lubricated tests, friction coefficients (μ) as high as 0.8 were achieved. For the more ductile sheet materials (Al alloy and Zn-coated steel) strong adhesion was observed. The best compromise between low wear rate and low friction coefficient was achieved for N-containing coatings deposited without ion gun assistance.In lubricated conditions, a significant decrease of the friction coefficient down to 0.05 and a reduction of the wear coefficient in more than one order of magnitude down to < 10^− 16 m²N^− 1 were reached in relation to non-lubricated tests. Very good tribological results were achieved using the corrosion protection oil as lubricant, with amounts usually applied for protection of sheet materials (2 g/m²). It was found that the wear coefficient of the coated ball decreased linearly with increasing hardness of the coating, being the best that deposited with N contents in the range from 35 at.% to 40 at.%. The tribological performance of the coated samples was approximately constant even when the amount of used lubricant was reduced to only 25% of the initial value (0.5 g/m²).     

偏压对TiAlN涂层微观结构、力学和摩擦学性能的影响（英文）

采用磁过滤真空阴极弧在ZL109合金表面沉积由TiAl和TiAlN组成的TiAlN多层涂层,并系统研究偏压对涂层微观结构和性能的影响。结果表明,涂层具有以TiAlN相为主的多相结构。随着偏压的增大,由于原子迁移率和晶格畸变的增加,TiAlN择优取向由(200)晶面向(111)晶面转变。同时,涂层的硬度、弹性模量和附着力表现出相同的变化趋势,即先增大后减小。当偏压为75 V时,TiAlN涂层具有最高的硬度(～30.3 GPa)、弹性模量(～229.1 GPa)、附着力(HF 2)和最低的磨损率(～4.44×10^-5 mm³/(N·m))。与未涂覆ZL109合金相比,TiAlN涂层合金表面的力学和摩擦学性能得到有效提高。     

Characteristics and tribological performance of DLC and Si-DLC films deposited on nitrile rubber

The characteristics and tribological performance of DLC and Si-DLC films with and without Si–C interlayers were studied in this paper. The films were deposited on nitrile rubber using a closed field unbalanced magnetron sputtering ion plating system. The film properties and characteristics were determined by scanning electron microscopy (SEM), hydrophobicity studies, Raman spectroscopy and tribological investigations. Tribological performance of these films was investigated using a pin-on-disc tribometer under applied loads of 1 N and 5 N under conditions of dry and wet sliding. The effect of immersing the films in water on tribological performance was also examined. The results show that the morphology of the films had a crack-like network. At a substrate bias of − 30 V, the coatings were characterised by a very dense non-columnar microstructure. The highest value of the ratio of intensities of the D and G peaks (I_D/I_G) was 1.2 for Si-DLC film with Si–C interlayer. The lowest value of 0.7 was observed for DLC film. The contact angle (CA) of water droplets showed that the films were hydrophobic. These results are interpreted in terms of hybridisation of carbon in these coatings. The tribological investigation showed a dependence on both the tribological condition under investigation and the atomic percentage of Si in the films. At 5 N normal load the lowest wear depth was observed for DLC films.     

Mechanical and tribological properties of multilayered TiSiN/CrN coatings synthesized by a cathodic arc deposition process

The monolayered TiSiN and multilayered TiSiN/CrN were synthesized by cathodic arc evaporation. The Ti/Si (80/20 at.%) and chromium targets were used as the cathodic materials. With the different I_[TiSi]/I_[Cr] cathode current ratios of 1.8, 1.0, and 0.55, the multilayered TiSiN/CrN coatings possessed different multilayer periods (Λ) of 8.3 nm, 6.2 nm, and 4.2 nm. From XRD and TEM analyses, both the monolayered TiSiN and multilayered TiSiN/CrN revealed a typical columnar structure and B1-NaCl crystalline, no peaks of crystalline Si₃N₄ were detected. Among the multilayered TiSiN/CrN coatings, the multilayered coating with Λ = 8.3 nm possessed higher hardness of 37 ± 2 GPa, higher elastic modulus of 396 ± 20 GPa and the lower residual stress of − 1.60 GPa than the monolayered (Ti_0.39Si_0.07)N_0.54 coating(− 7.25 GPa). Due to the higher Cr/(Ti +Cr + Si) atomic ratio, the multilayered TiSiN/CrN with Λ = 5.5 nm possessed the lowest friction coefficient. But the lowest of wear rate was obtained by the multilayered TiSiN/CrN with Λ = 8.3 nm, because of higher H³/E^?2 ratio of 0.323 GPa. The monolayered TiSiN possessed the highest wear rate of 2.87 μm²/min. Therefore, the mechanical and tribological property can be improved by the design of multilayered coating.     

直流基体偏压对Al-Cr-Si-N涂层结构和力学性能的影响

采用电弧离子镀技术在不同直流偏压下沉积Al-Cr-Si-N涂层,研究基体偏压对涂层成分、微观结构和性能的影响。结果表明:Al-Cr-Si-N涂层以密排六方结构和面心立方结构的AlN相为主,随着基体负偏压增加,涂层的衍射峰整体向小角度方向偏移:涂层内残余压应力逐渐增加,最大值为-0.77 GPa;涂层硬度和摩擦系数变化不明显。当基体负偏压为-40V时,Al-Cr-Si-N涂层的特征参数H/E和H~3/E~(*2)均达最大值,分别为0.15和0.37GPa,此时涂层具有最佳的耐磨性能,摩擦系数亦最低。     

Control of lubricant transport by a CrN diffusion barrier layer during high-temperature sliding of a CrN-Ag composite coating

CrN-Ag composite coatings, 2 and 5 μm thick and containing 22 at.% Ag solid lubricant, were grown on Si(001) and 440C stainless steel substrates by reactive co-sputtering at T_s = 500 °C, and were covered with 200 nm thick pure CrN diffusion barrier cap layers. Annealing experiments at T_a = 625 °C, followed by quantitative scanning electron microscopy, energy dispersive x-ray spectroscopy, and Auger depth profile analyses indicate considerable Ag transport to the top surface for a barrier layer deposited at a substrate floating potential of −30 V, but negligible Ag diffusion when deposited with a substrate bias potential of −150 V. This is attributed to ion-irradiation induced densification which makes the cap layer an effective diffusion barrier. High temperature tribological sliding tests of this coating system against alumina balls at T_t = 550 °C indicate an initial friction coefficient μ = 0.43 ± 0.04 which decreases monotonically to 0.23 ± 0.03. This is attributed to the development of wear mediated openings in the barrier layer which allow Ag lubricant to diffuse to the sliding top surface. In contrast, pure CrN exhibits a constant μ = 0.41 ± 0.02 while CrN-Ag composite coatings without cap layer show a low transient μ = 0.16 ± 0.03, attributed to Ag transport to the surface, that however increases to μ = 0.39 ± 0.04 after ~ 6000 cycles as the Ag reservoir in the coating is depleted. That is, the dense CrN cap layer reduces the Ag lubricant flow rate and therefore prolongs the time when the coating provides effective lubrication. This results in a cumulative wear rate over 10,000 cycles of 3.1 × 10⁻⁶ mm³/Nm, which is 3.3 × lower than without diffusion barrier layer.