Cr1−xAlxN coatings deposited by lateral rotating cathode arc for high speed machining applications

In this work, a series of Cr_1−xAl_xN (0 ≤ x ≤ 0.7) coatings were deposited on high speed steel substrates by a vacuum arc reactive deposition process from two lateral rotating elemental chromium and aluminum cathodes in a flowing pure nitrogen atmosphere. The composition, structural, mechanical, and tribological properties of the as-deposited coatings were systematically characterized by energy dispersive analysis of X-rays, X-ray diffraction, nanoindentation, and ball-on-disc tribometer experiments. All of the as-deposited CrAlN coatings exhibited a higher hardness than CrN, showing a maximum hardness of about 40 GPa (at around X = 0.63) which is twice higher than that of the CrN. The wear performance under ambient conditions of the CrAlN coatings was found much better, with both lower friction coefficient and wear rate, than TiAlN coatings deposited by the same technique. The wear rate of the CrAlN coatings against alumina counterpart was about 2-3 orders in magnitude lower than that of the TiAlN coatings. Selected CrAlN coatings with the highest hardness were also deposited on some WC-based end-mills. An evident better performance of the CrAlN-coated end-mills was observed than the TiAlN-coated ones for cutting a hardened tool steel material under high speed machining conditions.     

Deposition of nano-scaled CrTiAlN multilayer coatings with different negative bias voltage on Mg alloy by unbalanced magnetron sputtering

In a magnetron sputtering system, the negative substrate bias voltage has been used as a basic process parameter to modify the deposition structure and properties of coatings. In this paper we report the effect of bias voltage ranging from −40 V to −90 V on nano-scaled CrN/TiN/CrN/AlN (CrTiAlN) multilayer coatings synthesized on a Mg alloy by a closed-field unbalanced magnetron sputtering ion plating system in a gas mixture of Ar + N₂. The technological temperature and atomic concentration in the multilayer coatings were controlled by adjusting the current density of different metal magnetron targets and the plasma optical emission monitor. The composition, crystallographic structure, deposition model and friction coefficient of multilayer coatings were characterized by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ball-on-disc testing. The experimental results show that the deposition model and friction coefficient of nano-scaled CrTiAlN multilayer coatings were significantly affected by the negative bias voltage (V_b). The nitride species in multilayer coatings mainly involve CrN, AlN and TiN, and XRD analysis shows that the crystallographic structure was face-centered cubic. Under different bias voltage conditions, the multilayer coating composition shows a fluctuation, and the Al and Cr concentrations respond in the opposite sense to the bias voltage, attaining their greatest values at V_b = −70 V. The surface and cross-sectional morphology shows deposition model change from a columnar model into non-columnar model with the increase in negative bias voltage. The friction coefficient of the nano-scaled multilayer coatings at V_b = −55 V stabilize after 10 000 cycles.     

Correlation between thermal properties and aluminum fractions in CrAlN layers deposited by PVD technique

The CrAlN coatings are a good alternative to conventional CrN coatings especially for high temperature oxidation-resistance applications. Different CrAlN coatings were deposited on silicon (100) by PVD (Physical vapor deposition) technique from two targets (chromium and aluminum) in a reactive nitrogen atmosphere at aluminum applied negative voltage (−300, −500, −700 and −900 V). The composition, structural, mechanical and thermal properties of the as-deposited coatings were systematically characterized by energy dispersive analysis of X-rays, X-ray diffraction, nanoindentation, and the “Mirage effect” experiments.The X-ray diffraction (XRD) data show that in general CrAlN coatings were crystallized in the cubic NaCl B1 structure, with the (1 1 1) and (2 0 0) diffraction peaks observed. Two-dimensional surface morphologies of CrAlN coatings were investigated by atomic force microscope (AFM). The results show that with increasing aluminum proportion the coatings became more compact and denser and their increased correspondingly, showing a maximum hardness of about 36 GPa (30 at% of Al) which is higher than that of CrN. Moreover, the results in this work demonstrate that the variation of aluminum fraction alter the resulting columnar grain morphology and porosity of the coatings. However, the thermal properties are greatly affected by these morphological alterations. The correlation between aluminum fraction in CrAlN coatings and its thermal properties revealed that the conductivity and the diffusivity are influenced primarily by size and shape distribution of the pores and secondarily by a decrease of the stitch parameter dimension.     

Comparison of microstructure and mechanical properties of chromium nitride-based coatings deposited by high power impulse magnetron sputtering and by the combined steered cathodic arc/unbalanced magnetron technique

Sliding, abrasive, and impact wear tests were performed on chromium nitride (CrN)-based coatings deposited on mirror-polished M2 high speed steel substrates by the novel high power impulse magnetron sputtering (HIPIMS) utilising high peak cathode powers densities of 3000 W cm⁻². The coatings were compared to single layer CrN and multilayer superlattice CrN/NbN coatings deposited by the arc bond sputtering (ABS) technique designed to improve the coating substrate adhesion by a combined steered cathodic arc/unbalanced magnetron (UBM) sputtering process. The substrates were metal ion etched using non-reactive HIPIMS or steered cathodic arc at a substrate bias voltage of −1200 V. Subsequently a 2- to 3-μm thick CrN or CrN/NbN coating was deposited by reactive HIPIMS or UBM. No bias was used during the HIPIMS deposition, while the bias during UBM growth was in the range 75-100 V. The ion saturation current measured by a flat electrostatic probe reached values of 50 mA cm⁻² peak for HIPIMS and 1 mA cm⁻² continuous during UBM deposition. The microstructure of the HIPIMS coatings observed by transmission electron microscopy was fully dense in contrast to the voided columnar structure observed in conventional UBM sputtered CrN and CrN/NbN. The sliding wear coefficients of the HIPIMS CrN films of 2.3×10⁻¹⁶ m³ N⁻¹ m⁻¹ were lower by a factor of 4 and the roughness of the wear track was significantly reduced compared to the UBM-deposited CrN. The abrasive wear coefficient of the HIPIMS coating was 2.2×10⁻¹³ m³ N⁻¹ m⁻¹ representing an improvement by a factor of 3 over UBM deposited CrN and a wear resistance comparable to that of the superlattice CrN/NbN. The adhesion of the HIPIMS deposited CrN was comparable to state-of-the-art ABS technology.     

CrN/AlN superlattice coatings synthesized by pulsed closed field unbalanced magnetron sputtering with different CrN layer thicknesses

CrN/AlN superlattice coatings with different CrN layer thicknesses were prepared using a pulsed closed field unbalanced magnetron sputtering system. A decrease in the bilayer period from 12.4 to 3.0 nm and simultaneously an increase in the Al/(Cr + Al) ratio from 19.1 to 68.7 at.% were obtained in the CrN/AlN coatings when the Cr target power was decreased from 1200 to 200 W. The bilayer period and the structure of the coatings were characterized by means of low angle and high angle X-ray diffraction and transmission electron microscopy. The mechanical and tribological properties of the coatings were studied using the nanoindentation and ball-on-disc wear tests. It was found that CrN/AlN superlattice coatings synthesized in the current study exhibited a single phase face-centered cubic structure with well defined interfaces between CrN and AlN nanolayers. Decreases in the residual stress and the lattice parameter were identified with a decrease in the CrN layer thickness. The hardness of the coatings increased with a decrease in the bilayer period and the CrN layer thickness, and reached the highest value of 42 GPa at a bilayer period of 4.1 nm (CrN layer thickness of 1.5 nm, AlN layer thickness of 2.5 nm) and an Al/(Cr + Al) ratio of 59.3 at.% in the coatings. A low coefficient of friction of 0.35 and correspondingly low wear rate of 7 × 10^− 7 mm³N^− 1m^− 1 were also identified in this optimized CrN/AlN coating when sliding against a WC-6%Co ball.     

Effect of layer thickness on thermal properties of multilayer thin films produced by PVD

Cr/CrN/CrAlN, CrN/CrAlN and Cr/CrN thin layers were deposited by PVD (Physical Vapor Deposition). The multilayers were obtained from the combined deposition of different layers Cr, CrN and CrAlN thick films on on AISI4140 steel and silicon substrates at 200 °C, and evaluated with respect to fundamental properties such as structure and thermal properties. Cr, CrN and CrAlN single layers were also prepared for comparison purposes. The structural and morphological properties of PVD layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with EDS + WDS microanalyses, stresses were determined by the Newton’s rings methods using the Stoney’s equation and surface hardening and hardness profiles were evaluated by micro hardness measurements. The XRD data and HRTEM showed that both the Cr/CrN, CrN/CrAlN and Cr/CrN/CrAlN multilayer coatings exhibited B1NaCl structure with a prominent reflection along (200) plane, and CrAlN sub-layer microstructures composed of nanocrystallites uniformly embedded in an amorphous matrix. The innovation of this work was to use the thickness of three different coating types to determine the thermal properties. Furthermore, an empirical equation was developed for the thermal properties variations with temperature of AISI4140 steel coated with different multilayer coatings. The thermal conductivity of CrAlN single layered was lower than the multilayer and the bulk material AISI4140. Moreover, the influences of structure and composition of the multilayer coatings on the thermal properties are discussed.The thermal conductivity of nanoscale thin film is remarkably lower than that of bulk materials because of its various size effects.     

Friction and wear properties of TiCN coatings sliding against SiC and steel balls in air and water

The TiCN coatings were deposited on WC cemented carbides using enhanced cathodic arc magnetron sputtering. The topography of TiCN coatings were observed using scanning electron microscopy (SEM), the composition and structure of TiCN coatings were analyzed by energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The friction and wear properties of TiCN coatings sliding against SiC and steel balls in air and water were investigated using ball-on-disk tribometer. The results showed that the TiCN coatings had a strong (111) preferred orientation. The friction coefficient and the specific wear rates of the TiCN/SiC tribopairs in air were higher than those in water. When the TiCN coatings slid against SiC balls in water, the friction coefficient and the specific wear rates first decreased, and then increased with the normal load, but decreased linearly with the sliding velocity. The lowest friction coefficient of 0.171 was obtained at 3 N and 0.4 m/s, while the lowest specific wear rate of the TiCN coatings was 2.3 × 10^− 6mm³/Nm at 6 N and 0.1 m/s. The TiCN coatings were worn out when the normal loads were higher than 6 N. When the TiCN coatings slid against the SUJ2 and SUS440C balls in water, the friction coefficient increased to 0.271 and 1.026 respectively. The EDS analysis showed that Fe and O elements existed on the wear track. This indicated that the tribochemical reaction occurred at the friction contact area.     

An investigation into the tribological performance of Physical Vapour Deposition (PVD) coatings on high thermal conductivity Cu-alloy substrates and the effect of an intermediate electroless Ni-P layer prior to PVD treatment

The use of high thermal conductivity copper alloys in plastic injection moulds provides the benefit of rapid moulding cycles through effective heat transfer. However, copper alloys are relatively soft and wear rapidly so manufacturers are now developing copper alloys with increased hardness and wear resistance. Their wear resistance can be further improved by the deposition of hard coatings such as electroplated chromium, electroless nickel and Physical Vapour Deposition (PVD) coatings. In this paper, the tribological performance of three proprietary high-strength Cu alloys (Ampcoloy® 940, Ampcoloy® 944 and Ampcoloy® 83) coated with PVD CrN and CrAlN coatings has been evaluated. A medium phosphorous content electroless Ni-P (ENi-P) plated layer was also deposited as a pre-treatment to PVD CrN and CrAlN coatings to increase the load support. The effect of this intermediate ENi-P layer was also evaluated. Surface roughness and instrumented hardness measurements were used to characterise all coated systems in both plated (i.e. with the intermediate ENi-P coating) and standard (i.e. unplated) conditions. Scratch tests were also performed to evaluate the effect of the ENi-P on PVD coating adhesion to Cu alloy substrates. The tribological behaviour of PVD-coated Cu alloy systems was evaluated by pin-on-disc wear tests and ball-on-plate impact tests. Results demonstrate that the ENi-P layer improves the load support for PVD coatings on Cu alloys, thereby improving their tribological performance. However, for PVD-coated Cu alloys in the standard condition, the Cu alloy substrate type plays an important role in the tribological performance of PVD coatings. For instance, PVD CrN coatings were more suited to a certain Cu alloy type whilst CrAlN to the other two types.     

An analysis of macroparticle-related defects on CrCN and CrN coatings in dependence of the substrate bias voltage

Chromium nitride coatings with and without a carbon content being assigned as CrCN and CrN were prepared by cathodic arc evaporation. The effect of negative substrate bias voltages (10-300 V) on the microstructure, phase composition and morphology of the coating surface was studied. X-ray diffraction data show that almost all coatings crystallized in the cubic structure with (111) and (200) diffraction lines appearing only for low negative bias voltage and a (220) diffraction line being present for the coatings deposited at higher negative bias voltages. For CrN coatings obtained at −300 V a hexagonal structure was also observed. In case of CrCN coatings the (220) diffraction line shows much higher intensity than in case of CrN coatings and was significantly broadened. On the surface of the coatings a large number of macroparticles of different size was observed. An increase of bias voltage causes a reduction of the areal density of macroparticles and a decrease of the mean surface roughness Ra.     

Effect of bias voltage on microstructure, mechanical and wear properties of Al-Si-N coatings deposited by cathodic arc evaporation

Al-Si-N coatings were deposited on tungsten carbide (WC-Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al-Si-N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(Cr_xAl_ySi_z)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Si-N films were investigated. Experimental results reveal that the Al-Si-N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si₃N₄ and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from − 30 to − 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of −90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al-Si-N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.     

Influence of substrate bias voltage on the microstructure and residual stress of CrN films deposited by medium frequency magnetron sputtering

In this study, CrN films were deposited on stainless steel and Si (1 1 1) substrates via medium frequency magnetron sputtering under a systematic variation of the substrate bias voltage. The influence of the substrate bias voltage on the structural and the mechanical properties of the films were investigated. It is observed that there are two clear regions: (1) below −300 V, and (2) above −300 V. For the former region, the (1 1 1) texture is dominated as the substrate bias voltage is increased to −200 V. The lattice parameter is smaller than that of CrN reported in the ICSD standard (4.140 Å) and the as-deposited films exhibit tensile stress. Meanwhile, the surface roughness decreases and the N concentration show a slow increase. For the latter region, the (2 0 0)-oriented structure is formed. However, the lattice parameter is larger as compared with the value reported in the ICSD standard, and the surface roughness increases and the N concentration decreases obviously. In this case, the compressive stress is obtained.     

Bias effects on the tribological behavior of cathodic arc evaporated CrTiAlN coatings on AISI 304 stainless steel

In this study, CrTiAlN coatings were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The coating morphology and properties including surface roughness, adhesion, hardness/elastic modulus (H/E) ratio, and friction behavior were analyzed to evaluate the impact of the substrate bias voltage on the coating microstructure and properties. The results suggest that for an optimized value of the substrate bias voltage, i.e. − 150 V, the CrTiAlN coatings showed increased Cr content and improved properties, such as higher adhesion strength, hardness, and elastic modulus in comparison to the coatings deposited by other substrate bias voltage. Moreover, the optimum coatings achieved a remarkable reduction in the steel friction coefficient from 0.65 to 0.45.     

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CN_x) coatings are investigated. CN_x coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400 V 200 W, −400 V 100 W, −800 V 200 W, and −800 V 100 W. The deposition rate, N/C atomic ratio, and hardness of CN_x coatings as well as friction coefficient of CN_x coating sliding against AISI 52100 pin in N₂ gas stream decrease, while the residual stress of CN_x coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0 GPa and lowest residual stress of 3.7 GPa of CN_x coatings are obtained at −400 V 200 W, whereas the lowest friction coefficient of 0.12 of CN_x coatings is achieved at −800 V 100 W. Raman and XPS analysis suggest that sp³ carbon bonding decreases and sp² carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CN_x coatings is controlled by the directly sliding between CN_x coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp³ carbon bonding in the CN_x coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CN_x coatings.     

Effect of substrate bias voltage on structural and mechanical properties of pulsed DC magnetron sputtered TiN-MoSx composite coatings

TiN-MoS_x composite coatings were deposited by pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS) using separate Ti and MoS₂ targets in an Ar and N₂ gas environment. The effect of substrate bias voltage on the structure and mechanical properties of TiN-MoS_x composite coating has been studied. The structure and composition of the coating were evaluated using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) by X-ray and grazing incidence X-ray diffraction (GIXRD). Scratch adhesion tests, Vickers microhardness tests and ball-on-disc tests with a cemented carbide (WC-6%Co) ball were carried out to investigate mechanical properties of the coating. Application of substrate bias was found to transform the structure of TiN-MoS_x composite coating from open columnar to a dense columnar structure. The changes in grain size and texture coefficient appear to be associated with variation in substrate bias voltage. The mechanical properties of the coating such as adhesion and composite microhardness were also observed to be related to the change in bias voltage. A maximum hardness of 22 GPa was obtained for a coating deposited at substrate bias voltage of −40 V. The improved structural and mechanical properties of the coating deposited at −40 V were also reflected in its excellent wear resistance property.     

Depth-resolved residual stress analysis of thin coatings by a new FIB-DIC method

A new methodology for the measurement of depth sensitive residual stress profiles of thin coatings with sub-micrometer resolution is presented. The two step method consists of incremental focused ion beam (FIB) ring-core milling, combined with high-resolution in situ SEM-FEG imaging of the relaxing surface and a full field strain analysis by digital image correlation (DIC). The through-thickness profile of the residual stress can be obtained by comparison of the experimentally measured surface strain with finite element modeling using Schajer's integral method. In this work, a chromium nitride (CrN) CAE-PVD 3.0 μm coating on steel substrate, and a gold MS-PVD 1.5 μm on silicon were selected for the experimental implementation. Incremental FIB milling was conducted using an optimized milling strategy that produces minimum re-deposition over the sample surface. Results showed an average residual stress of σ = −5.15 GPa in the CrN coating and σ = +194 MPa in the Au coating. These values are in reasonable agreement with estimates obtained by other conventional techniques. The depth profiles revealed an increasing residual stress from surface to the coating/surface interface for both coatings. This observation is likely related to stress relaxation during grain growth, which was observed in microstructural cross sections, as predicted by existing models for structure-stress evolution in PVD coatings. A correlation between the observed stress gradients and the in-service mechanical behavior of the coatings is proposed. Finally, critical aspects of the technique and the influence of microstructure and elastic anisotropy on stress analysis are analyzed and discussed.     

A study on the abrasive and erosive wear behavior of arc-deposited Cr-N-O coatings on tool steel

In this study, the cathodic arc evaporation technique, by using the chromium target and controlling the flow rate of nitrogen/oxygen reactive gases, was utilized to deposit three different Cr-N-O coatings (CrN, CrN/Cr(N,O), CrN/Cr₂O₃) on AISI M2 tool steel. Two types of wear tests were applied to evaluate the abrasive and erosive wear behavior of the coated and uncoated specimens. One was the ball-on-disk abrasion test to measure the friction coefficient of these specimens. The other was the erosion test using Al₂O₃ particles (~ 177 µm in size and Mohr 7 scale) of about 5 g, and then the surface morphologies of the eroded specimens were observed. To further understand the coating effects on the two wear behaviors of M2 steel, coating structure, morphology, and adhesion were analyzed using XRD, SEM, and TEM, respectively. The results showed that surface roughness and adhesion of the double-layered coatings (CrN/Cr(N,O) and CrN/Cr₂O₃) were inferior to those of monolithic CrN, but their hardness and elastic modulus were superior to those of CrN. In the abrasive behavior, Cr-N-O coatings reduced the friction coefficient of M2 substrate. In particular, the CrN/Cr₂O₃ has the highest hardness/elastic (H/E) modulus ration, therefore the lowest friction coefficient, among all the coated-specimens tested. In the erosive behavior, the coated specimens exhibited better erosion resistance as compared to the uncoated ones, at the impingement angles of either 30^o or 90^o. Moreover, the erosion resistance of CrN/Cr(N,O) coatings was superior to that of CrN/Cr₂O₃ coatings due to its better adhesion.     

Oxidation resistance of TiN,CrN, TiAlN and CrAlN coatings deposited by lateral rotating cathode arc

In this paper, four kinds of hard coatings, TiN, CrN, TiAlN and CrAlN (with Al/Ti or Al/Cr atomic ratio around 1:1), were deposited on stainless steel substrates by a lateral rotating cathode arc technique. The as-deposited coatings were annealed in ambient atmosphere at different temperatures (500–1000 °C) for 1 h. The evolution of chemical composition, microstructure, and microhardness of these coatings after annealing at different temperatures was systematically analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and nanoindentation experiments. The oxidation behaviour and its influence on overall hardness of these four coatings were compared. It was found that the ternary TiAlN and CrAlN coatings have better oxidation resistance than their binary counterparts, TiN and CrN coatings. The Cr-based coatings (CrN and CrAlN) exhibited evidently better oxidation resistance than the Ti-based coatings (TiN and TiAlN). TiN coating started to oxidize at 500 °C. After annealing at 700 °C no N could be detected by EDX, indicating that the coating was almost fully oxidized. After annealed at 800 °C, the coating completely delaminated from the substrate. TiAlN started to oxidize at 600 °C. It was nearly fully oxidized (with little residual nitrogen detected in the coating by EDX) and partially delaminated at 1000 °C. Both CrN and CrAlN started to oxidize at 700 °C. CrN was almost fully oxidized (with little residual nitrogen detected in the coating by EDX) and partially delaminated at 900 °C. The oxidation rate of the CrAlN coating is quite slow. After annealing at 1000 °C, only about 19 at.% oxygen was detected and the coating showed no delamination. The Ti-based (TiN and TiAlN) coatings were not able to retain their hardness at higher temperatures (≥ 700 °C). On the other hand, the hardness of CrAlN was stable at a high level between 33 and 35 GPa up to an annealing temperature of 800 °C and still kept at a comparative high value of 18.7 GPa even after annealed at 1000 °C, indicating a very promising applicability of this coating for high speed dry machining and other applications under high temperature environments.     

Synthesis and characterization of W reinforced carbon coatings produced by Combined Magnetron Sputtering and Ion Implantation technique

W-containing carbon coatings were deposited on plain carbon steel and titanium substrates by Combined Magnetron Sputtering and Ion Implantation (CMSII) technique. A target made of fine grain graphite with cylindrical tungsten pins mounted in the area of maximum sputtering rate was used. High voltage pulses (− 30 kV, 20 μs, and 25 Hz) were superposed over the DC bias. By adjusting the processing parameters nanocomposite nc-WC_1 − x/a-C coatings with a W content from 20 to 45 at.%, with a hardness of 12-22 GPa and a friction coefficient in the range of 0.12-0.22 were produced. These coatings have a thickness of 10-13 μm, good wear resistance and a good thermal stability up to 673 K.     

Bias effects on microstructure, mechanical properties and corrosion resistance of arc-evaporated CrTiAlN nanocomposite films on AISI 304 stainless steel

CrTiAlN films were deposited on AISI 304 stainless steel by cathodic arc evaporation under a systematic variation of the substrate bias voltage. The effects of substrate bias on the coating morphology and mechanical properties, such as structure, composition, adhesion, hardness and Young's modulus, were studied in details using field emission scanning electron microscopy, X-ray diffraction, electron probe microanalysis and indenter. Polarization test and immersion test were also carried out to evaluate the corrosion behavior of the various films. CrTiAlN films are nanocrystalline that exhibit a CrN/TiAlN multi-layered morphology. At the optimal value of substrate bias voltage (i.e., − 150 V), the CrTiAlN film showed an increased Cr content and improved properties, such as higher adhesion, higher hardness (38 ± 2 GPa), and greater Young's modulus (319 ± 16 GPa) vs. the films deposited at other substrate bias voltages. Moreover, the optimum film has better corrosion resistance in 3.5 wt.% NaCl and 20 vol.% HCl solutions.     

Structure, hardness and thermal stability of nanolayered TiN/CrN multilayer coatings

Nanolayered TiN/CrN multilayer coatings were deposited on silicon substrates using a reactive DC magnetron sputtering process at various modulation wavelengths (Λ), substrate biases (V_B) and substrate temperatures (T_S). X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of the TiN/CrN multilayers was 3800 kg/mm² at Λ=80  Å, V_B=−150 V and T_S=400°C. Thermal stability of TiN, CrN and TiN/CrN multilayer coatings was studied by heating the coatings in air in the temperature range (T_A) of 400-800°C. The XRD data revealed that TiN/CrN multilayers retained superlattice structure even up to 700°C and oxides were detected only after T_A?750°C, whereas for single layer TiN and CrN coatings oxides were detected even at 550°C and 600°C, respectively. Nanoindentation measurements showed that TiN/CrN multilayers retained a hardness of 2800 kg/mm² upon annealing at 700°C, and this decrease in the hardness was attributed to interdiffusion at the interfaces.