Deposition and characterization of CrN/Si3N4 and CrAlN/Si3N4 nanocomposite coatings prepared using reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of CrN/Si₃N₄ and CrAlN/Si₃N₄ with varying silicon contents were synthesized using a reactive direct current (DC) unbalanced magnetron sputtering system. The Cr and CrAl targets were sputtered using a DC power supply and the Si target was sputtered using an asymmetric bipolar-pulsed DC power supply, in Ar + N₂ plasma. The coatings were approximately 1.5 μm thick and were characterized using X-ray diffraction (XRD), nanoindentation, X-ray photoelectron spectroscopy and atomic force microscopy. Both the CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings exhibited cubic B1 NaCl structure in the XRD data, at low silicon contents (< 9 at.%). A maximum hardness and elastic modulus of 29 and 305 GPa, respectively were obtained from the nanoindentation data for CrN/Si₃N₄ nanocomposite coatings, at a silicon content of 7.5 at.%. (cf., 24 and 285 GPa, respectively for CrN). The hardness and elastic modulus decreased significantly with further increase in silicon content. CrAlN/Si₃N₄ nanocomposite coatings exhibited a hardness and elastic modulus of 32 and 305 GPa, respectively at a silicon content of 7.5 at.% (cf., 31 and 298 GPa, respectively for CrAlN). The thermal stability of the coatings was studied by heating the coatings in air for 30 min in the temperature range of 400-900 °C. The microstructural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data of the heat-treated coatings in air indicated that CrN/Si₃N₄ and CrAlN/Si₃N₄ nanocomposite coatings, with a silicon content of approximately 7.5 at.% were thermally stable up to 700 and 900 °C, respectively.     

Hard and superhard TiAlBN coatings deposited by twin electron-beam evaporation

Superhard nanostructured coatings, prepared by plasma-assisted chemical vapour deposition (PACVD) and physical vapour deposition (PAPVD) techniques, such as vacuum arc evaporation and magnetron sputtering, are receiving increasing attention due to their potential applications for wear protection. In this study nanocomposite (TiAl)B_xN_y (0.09 ≤ x ≤ 1.35; 1.07 ≤ y ≤ 2.30) coatings, consisting of nanocrystalline (Ti,Al)N and amorphous BN, were deposited onto Si (100), AISI 316 stainless steel and AISI M2 tool steel substrates by co-evaporation of Ti and hot isostatically pressed (HIPped) Ti-Al-B-N material from a thermionically enhanced twin crucible electron-beam (EB) evaporation source in an Ar plasma at 450 °C. The coating stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), in combination with nanoindentation measurements. Aluminium (∼ 10 at.% in coatings) was found to substitute for titanium in the cubic TiN based structure. (Ti,Al)B_0.14N_1.12 and (Ti,Al)B_0.45N_1.37 coatings with average (Ti,Al)N grain sizes of 5-6 nm and either ∼ 70, or ∼ 90, mol% (Ti,Al)N showed hardness and elastic modulus values of ∼ 40 and ∼ 340 GPa, respectively. (Ti,Al)B_0.14N_1.12 coatings retained their ‘as-deposited’ mechanical properties for more than 90 months at room temperature in air, comparing results gathered from eight different nanoindentation systems. During vacuum annealing, all coatings examined exhibited structural stability to temperatures in excess of 900 °C, and revealed a moderate, but significant, increase in hardness. For (Ti,Al)B_0.14N_1.12 coatings the hardness increased from ∼ 40 to ∼ 45 GPa.     

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.     

Mechanical and tribological properties of multi-element (AlCrTaTiZr)N coatings

Multi-element (AlCrTaTiZr)N coatings are deposited onto Si and cemented carbide substrates by reactive RF magnetron sputtering in an Ar + N₂ mixture. The influence of substrate bias voltage, ranging from 0 to − 200 V, on the microstructural, mechanical and tribological properties of these nitride coatings is studied. A reduction in concentration of N and Al is observed with increasing substrate biases. The (AlCrTaTiZr)N coatings show the face-centered-cubic crystal structure (B1-NaCl type). The use of substrate bias changes the microstructure of the (AlCrTaTiZr)N coating from the columns with microvoids in boundaries to the dense and less identified columns. The compressive macrostress increases from − 0.9 GPa to − 3.6 GPa with an increase of substrate bias. The hardness and adhesion increase to peak values of 36.9 GPa and 60.7 N at the bias voltage of − 150 V, respectively. The tribological properties of the (AlCrTaTiZr)N coatings against 100Cr6 steel balls are evaluated by a ball-on-disc tribometer with a 10 N applied load. With an increase of substrate bias, the wear rate reduces while the friction coefficient almost keeps constant at 0.75. The lowest wear rate of 3.65 × 10^− 6 mm³/Nm is obtained for the (AlCrTaTiZr)N coating deposited at the bias voltage of − 150 V.     

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.     

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.     

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.     

Thermal barrier coating systems — analysis of nanoindentation curves

Mechanical properties (Young's modulus E, hardness H, degree of plasticity) of all three components of thermal barrier coatings systems, prepared by electron beam physical vapour deposition (EB PVD), have been investigated by nanoindentation. The power-law exponents n and m, describing the shapes of the loading and unloading nanoindentation curves, increase with peak load for the yttrium-stabilized zirconia top coat (TC), containing 4 mol% Y₂O₃, and the NiCoCrAlY bond coat (BC). The variations of m are correlated to the degree of plasticity. Decrease of the hardness with increasing peak load, generally known as indentation size effect (ISE), is observed only for the TC and the BC. The ISE in the TC is explained using a new empirical equation based on the concept of elastic recovery. The average Young's moduli of the Ni-based superalloy substrate, the BC and the TC are 189 ± 11 GPa, 166 ± 7 GPa, and 126 ± 25 GPa, respectively. The corresponding average hardness values are 3.3 ± 0.3 GPa, 5.5 ± 0.2 GPa, and 6.2 ± 1.7 GPa, respectively. The mechanical properties of the TC show complex behaviour upon annealing at 1000°°C in air, which can be explained by changes in the porosity and the residual stresses.     

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.     

High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputtering

As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr₂N and CrN coatings (up to 55 μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr₂N and CrN coating depositions, respectively, using a 3 kW average target power (16.7 W/cm² average target power density), a 50 mm substrate to target distance and an Ar/N₂ gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr₂N coatings, whereas the Cr₂N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr₂N coatings increased as the coating thickness increased to 30 μm and 20 μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr₂N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55 μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10 μm or higher. The 10-55 μm CrN coating exhibited low wear rates in the range of 3.5-5 × 10⁻⁷ mm³ N⁻¹ m⁻¹. To the contrary, the Cr₂N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹ were observed for different thicknesses.     

Influence of the C content on the mechanical and tribological properties of the TiCN coatings deposited by LAFAD technique

TiCN coatings with different C content were deposited using a large area filtered arc deposition (LAFAD) technique from Ti targets in a mixture of N₂ and CH₄ gases. Scanning electron microscopy (SEM), nano-indentation, and pin-on-disc tribometer were used to characterize the cross-sectional microstructure, hardness, modulus, wear rate, and friction coefficient of the TiCN coatings. The increase in the CH₄ fraction in the gases leads to a continuous increase in the deposition rate of the TiCN coatings as well as an increase in the defect density in the coatings. Nano-indentation results indicate that with an increase of the C content in the coatings, the hardness and elastic modulus increase to a maximum at a C content of 2.8 at.%, then decreases rapidly, which results from the increase in the defect density in the coatings. Tribological test results show that when tested against Al₂O₃ balls, there is no significant change in the friction coefficient (0.78-0.88) of the TiCN coatings with a C content of below 4.6 at.%, but the friction coefficient decreases rapidly to 0.21 with a further increase in the C content to 9.3 at.%. In addition, with increasing C content in the coatings from 0 to 9.3 at.%, the wear rate decreases remarkably from 2.5 × 10⁻⁶ mm³/Nm to 5.3 × 10⁻⁷ mm³/Nm. The low friction coefficient and the formation of a transfer layer correspond to the low wear rate for the TiCN coatings with high C content.     

TiBCN:CNx multilayer coatings deposited by pulsed closed field unbalanced magnetron sputtering

In this study, a combination of nanocomposite and multilayer coating design was investigated in an effort to reduce the coefficient of friction (COF) while maintaining good mechanical properties of the TiBCN coatings. The TiBCN:CN_x coatings consist of TiBCN and CN_x nanolayers which were deposited alternately by reactive sputtering a TiBC composite target (80 mol% TiB₂ + 20 mol% TiC) and a graphite target in an Ar:N₂ mixture using a pulsed closed field unbalanced magnetron sputtering system. Low angle X-ray diffraction and transmission electron microscopy characterizations confirmed that the coatings consist of different bilayer periods in a range of 3.5 to 7.0 nm. The TiBCN layers exhibited a nanocomposite structure, whereas the CN_x layers were in an amorphous state. The mechanical properties and wear resistance of the TiBCN:CN_x multilayer coatings were investigated using nanoindentation and ball-on-disk wear test. The TiBCN:CN_x coatings exhibited high hardness in a range of 20-30 GPa. The highest hardness of 30 GPa was achieved in the coating with a bilayer period of 4.5 nm. A low COF of 0.17 sliding against a WC-Co ball was obtained at a bilayer period of 4.5 nm, which is much lower than those of the single layer TiBCN and TiBC nanocomposite coatings (0.55-0.7).     

Elastic properties of Ni and Ni + Mo coatings electrodeposited on stainless steel substrate

Adhesion coefficient and Young's modulus of Ni and Ni + Mo coatings electrochemically deposited on stainless steel were examined by applying vibrating reed technique. It was shown that adhesion coefficient of the Ni coating slightly decreases (about 8%) with increasing layer thickness (5-40 μm). Young's modulus E_f of these coatings at room temperature was found to be about 130 GPa. The relative adhesion coefficient of the Ni layer decreases with increasing temperature (300-600 K) in relation to the thinnest examined layer (5 μm). Young's modulus of the Ni + Mo coatings decreases with increasing Mo content; for 9 wt.% of Mo E_f = 40 GPa and for 32 wt.% of Mo E_f = 23 GPa.     

CrN/NbN coatings deposited by HIPIMS: A preliminary study of erosion-corrosion performance

Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion-corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion-corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS-HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr²⁺ and 1% Cr³⁺ ions and J_s of 155 mAcm^− 2. For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L_C 80 N, high hardness of 34 GPa and Young's modulus of 381 GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K_C (1.22 × 10^− 15 m³Nm^− 1) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion-corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na₂CO₃ + NaHCO₃ buffer solution with Al₂O₃ particles of size 500-700 µm) at 90° impact angle with a velocity of 4 ms^− 1. Experiments have been carried at − 1000 mV, + 300 mV and + 700 mV representing 3 different corrosion conditions.     

Influence of normal load and sliding speed on the tribological property of amorphous carbon nitride coatings sliding against Si3N4 balls in water

Amorphous carbon nitride (a-CN_x) coatings were deposited on Si₃N₄ disks by an ion beam assisted deposition system. The composition, structure and hardness of the a-CN_x coatings were characterized by Auger electronic spectroscopy, Raman spectroscopy and nano-indentation tester, respectively. The influences of normal load and sliding speed on the friction coefficients and the specific wear rates for the a-CN_x/Si₃N₄ tribo-pairs were investigated and analyzed synthetically by ball-on-disk tribometer. The worn surfaces were observed by optical microscope. The results showed that the a-CN_x coatings contained 12 at.% nitrogen, and their structure was a mixture of sp²and sp³ bonds. The a-CN_x coatings’ nanohardness was 29 GPa. The influence of sliding speed on the friction coefficients and the specific wear rate of the CN_x coatings was more obvious than that of normal load. The friction coefficients and the specific wear rate of the CN_x coatings decreased as the sliding speed increased. At a sliding speed higher than 0.1 m/s, the friction coefficients were less than 0.04. The specific wear rates of the a-CN_x coatings were higher than those of Si₃N₄ balls at a sliding speed below 0.1 m/s, while the specific wear rates of the a-CN_x coatings and the Si₃N₄ balls all fluctuated around a lower level of 10^− 8 mm³/Nm as the sliding speed increased beyond 0.2 m/s. To describe the wear behavior of a-CN_x coatings sliding against Si₃N₄ balls in water with normal loads of 3-15 N and sliding speeds of 0.05-0.5 m/s, the wear-mechanism map for the a-CN_x/Si₃N₄ tribo-pairs in water was developed.     

Microstructure, mechanical and wear properties of laser processed SiC particle reinforced coatings on titanium

Laser processing of Ti-SiC composite coating on titanium was carried out to improve wear resistance using Laser Engineered Net Shaping (LENS™) — a commercial rapid prototyping technology. During the coating process a Nd:YAG laser was used to create small liquid metal pool on the surface of Ti substrate in to which SiC powder was injected to create Ti-SiC metal matrix composite layer. The composite layers were characterized using X-ray diffraction, scanning and transmission electron microscopy equipped with fine probe chemical analysis. Laser parameters were found to have strong influence on the dissolution of SiC, leading to the formation of TiSi₂, Ti₅Si₃ and TiC with a large amount of SiC on the surface. Detailed matrix microstructural analysis showed the formation of non-stoichiometric compounds and TiSi₂ in the matrix due to non-equilibrium rapid solidification during laser processing. The average Young's modulus of the composite coatings was found to be in the range of 602 and 757 GPa. Under dry sliding conditions, a considerable increase in wear resistance was observed, i.e., 5.91 × 10^− 4 mm³/Nm for the SiC reinforced coatings and 1.3 × 10⁻³ mm³/Nm for the Ti substrate at identical test conditions.     

Structural and mechanical stability upon annealing of arc-deposited Ti-Zr-N coatings

Ti-Zr-N coatings were formed by the method of vacuum arc deposition using combined Ti and Zr plasma flows in a N₂ atmosphere at different ratios of arc currents of Ti and Zr cathodes. After deposition, obtained samples were annealed in vacuum at the temperature of 850 °C. The element and phase composition, residual stresses and nanohardness were studied by Auger-Electron Spectroscopy, X-ray diffraction (XRD) and nanoindentation, respectively.XRD analysis reveals the formation of ternary Ti-Zr-N nitride coatings with the structure of solid solutions. It is shown that Ti-Zr-N coatings possess high hardness in comparison with TiN and ZrN binary nitrides. An increase in hardness is observed with increasing Zr content. However, it is established that after annealing coatings keep better stability of hardness with decrease of Zr content. The intrinsic stress in the as-deposited coatings is found to be largely compressive (− 4 GPa) and almost independent of Zr content, but much higher than in ZrN and TiN binary nitrides (− 2 GPa). After annealing, a significant stress relaxation is observed in all coatings due to relief of growth-induced point defects. Stress analysis on as-grown and annealed samples enabled us to determine the stress-free lattice parameter a₀. This latter is expanded by ∼ 0.4-0.7% as compared to Vegard's law.The thermal stability of Ti-Zr-N coatings will be discussed in terms of evolution and interdependence between structure, composition and hardness after annealing.     

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.     

Microstructure, mechanical and tribological properties of Cr1−xAlxN films deposited by pulsed-closed field unbalanced magnetron sputtering (P-CFUBMS)

Nanocrystallized Cr_1−xAl_xN films with various Al contents (0 to 68 at.%) were deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The effects of aluminum content on the microstructure, mechanical and tribological properties of the Cr_1−xAl_xN films have been investigated. It was found that the hardness and elastic modulus of Cr_1−xAl_xN films increased with increasing Al contents in the films and reached the highest value of 36 GPa and 370 GPa, respectively, at an Al content of 58.5 at.%. Addition of Al beyond 64.0 at.% resulted in a change in crystal structure from B1 cubic to B4 hexagonal phase. The wear resistance improved gradually with the increase of Al in the Cr_1−xAl_xN films. A combination of the abrasive and adhesive wear mechanism was proposed based on the SEM and EDS analysis of the wear track. The steady state dry coefficient of friction measured against a WC ball for the Cr_1−xAl_xN films were in the range of 0.36-0.55, and the wear rate was in the 10^− 6 mm³ N^− 1 m^− 1 range.     

Plasma processing for surface modification of trivalent chromium as alternative to hexavalent chromium layer

Plasma source ion implantation (PSII) treatment was undertaken to improve the mechanical properties of electrodeposited trivalent chromium layers. Nitrogen ions were implanted, with energies of − 15 to − 25 keV and doses of 1, 5 and 10 × 10¹⁷ atoms cm^− 2, to modify the surface properties of Cr plating layer. The surface properties of the films were characterized by XRD, SEM, ruby-ball on disk type tribometer and nanoindenter. Polycrystalline CrN films with (200), (220) and (222) orientations were preferentially grown and numbers of surface cracks were increased by N⁺-PSII onto trivalent chromium layers. The surface hardness of the Cr³⁺ plating layer was increased from 16 to 25 GPa by N⁺-PSII. Severe wear and higher friction was observed on N⁺-PSII treated trivalent Cr plating. It seemed that the wear debris from hardened and cracked surface of the N⁺-PSII treated specimen prompted abrasive wear in the wear test. Roughness of the Cr³⁺ plating layers was smoothed with increasing implantation doses.