Structural and tribological characterization of amorphous and crystalline titanium-nickel coatings

The interest in titanium-nickel (TiNi) alloys has increased with the discovery of the versatile properties of these alloys. In this study, the structural, mechanical and tribological properties of amorphous and crystalline TiNi coatings were investigated. The TiNi coatings were deposited with magnetron sputtering system. The crystallization process was conducted in a vacuum heat treatment furnace. The structural properties of the coatings were investigated with XRD, SEM and EDS analyses. Micro-hardness and pin-on-disc wear tests were used to obtain the mechanical and tribological properties of the coatings. AISI D2 steel, AISI 52100 steel, Aluminum 2024 alloy and copper were used as substrate materials, hence the effects of different substrates were also investigated. The highest coating hardness was obtained as 8.5?GPa and the lowest coefficient of friction value was obtained as 0.18. The tribological tests showed that the amorphous and crystalline TiNi coatings have different coefficient of friction and wear rate and using different substrate affects these properties.     

Characterization of (Ti1−xAlx)N films prepared by radio frequency reactive magnetron sputtering

(Ti_1−xAl_x)N films were deposited by radio frequency reactive magnetron sputtering on a high speed steel substrate. The structure and composition of the coatings were analysed by various techniques. Hardness and adhesion of the films were investigated using Vickers micro-indentation and scratch test respectively, whereas their tribological properties were studied using a pin-on-disk tribometer. The results show that increasing aluminium content leads to increase hardness of the films and to decrease their wear resistance when sliding against a magnesia-stabilized zirconia ball. On the contrary, no clear dependence of the film adhesion on the aluminium concentration was detected.     

High temperature friction and wear behavior of MoS<Subscript>2</Subscript>/Nb coating in ambient air

MoS₂ coatings are well-known for their solid lubricant properties and used as self-lubricants in vacuum and inert gas environments, and such coatings are not used in atmospheric conditions because of their deteriorating tribology. The tribological performance of MoS₂ solid lubricant coatings in the different atmospheres has been improved by the codeposition of a small amount of another metal. In this study, the tribological behavior of MoS₂/Nb coatings was investigated in ambient air at temperatures up to 500°C by using high-temperature pin-on-disc tribo testers and alumina balls as counterfaces. MoS₂/Nb coatings were deposited on silicon wafers and AISI 52100 steel substrate by closed-field unbalanced magnetron sputtering. The structural analyses of the coatings were performed using X-ray diffraction and scanning electron microscopy techniques. The hardness was measured using a microhardness tester.     

Applicability of DLC and WC/C low friction coatings on Al2O3/TiCN mixed ceramic cutting tools for dry machining of hardened 52100 steel

The present work examines the applicability of DLC and WC/C low friction coatings on Al₂O₃/TiCN based mixed ceramic cutting tools for the dry and hard turning of AISI 52100 steel (62 HRC). The characterization of coated tools reveals that the coatings retain very low values of surface roughness, whereas the DLC coating exhibits much higher microhardness when compared to the WC/C coating. On the other hand, the WC/C coating exhibit a coarse surface morphology virtually due to the tungsten doping. Later, continuous turning tests were executed with the help of coated and uncoated cutting tools under dry cutting conditions, and their performance was investigated in terms of machining forces, cutting temperature and tool wear. Coating delamination by flaking and peeling is quite prominent in the case of both the coatings; however, it is less severe for the WC/C coated tool. The coatings help to reduce machining forces, cutting temperatures and tool wear, but the performance of coated tools converge towards uncoated tool as the cutting speed, and feed rate is increased. Both the coatings prevent the development of cracks near the cutting edge with WC/C coating exhibiting superior wear behavior basically due to its multilayered structure and better thermal stability. Moreover, the tested low friction coatings don't serve as thermal barriers and only the lubrication generated due to graphitization at the chip-tool interface is mostly responsible for the improved machining performance.     

Comparison of structure and tribological properties of MoS2-Ti films deposited by biased-dc and pulsed-dc

A closed field unbalanced magnetron sputter (Teer-CFUBMS/550) system was used for the deposition of MoS₂-Ti composite coatings on steel substrate (AISI D2) using biased-dc and pulsed-dc. The tribological properties of MoS₂-Ti coatings were characterized by pin-on-disc wear tester under atmospheric conditions. Structural analysis was pointed out using X-ray diffraction and SEM-EDS. The microstructure and chemical composition of MoS₂-Ti films are very strongly influenced by the sputtering process conditions. While X-ray diffraction pattern of films deposited using pulsed-dc shows mainly (0 0 2) reflections, the films deposited by dc-bias exhibit random orientation being both (0 0 2) and (1 0 0) reflections. Tribological performance of the films deposited using both techniques were compared in view of both crystallographic orientation and Ti content.     

Nanostructure,mechanical and tribological properties of reactive magnetron sputtered TiCx coatings

This study describes the correlation between microstructure, mechanical and tribological properties of TiC_x coatings (with x being in the range of 0–1.4), deposited by reactive magnetron sputtering from a Ti target in Ar/C₂H₂ mixtures at ~ 200 °C. The mechanical and tribological properties were found to strongly depend on the chemical composition and the microstructure present. Very dense structures and high hardness, combined with low wear rates and friction coefficients, were observed for coatings with chemical composition close to TiC. X-ray diffraction and X-ray photoelectron spectroscopy analysis, used to evaluate coating microstructure, composition and relative phase fraction, showed that low carbon contents in the coatings lead to sub-stoichiometric nanocrystalline TiC_x coatings being deposited, whilst higher carbon contents gave rise to dual phase nanocomposite coatings consisting of stoichiometric TiC nanocrystallites and free amorphous carbon. Optimum performance was observed for nanocomposite TiC_1.1 coatings, comprised of nanocrystalline nc-TiC (with an average grain size of ~ 15 nm) separated by 2–3 monolayers of an amorphous a-DLC matrix phase.     

Influence of WS2 content on high temperature wear performance of magnetron sputtered TiN-WSx thin films

TiN-WS_x thin films with varying WS_x content were co-deposited by reactive magnetron sputtering. GAXRD analyses showed that the addition of 4 at.% WS_x led to loss of crystallinity of TiN phase and a complete amorphous characteristic was manifested upon incorporation of 19 at.% WS_x. Nanohardness results indicated that TiN-WS_x containing 4 and 19 at.% WS_x presented 19.7 GPa and 18.4 GPa, respectively, following the rule of mixtures. Friction coefficient and wear rates measured in reciprocated tribological tests revealed that TiN-WS_x coatings present an improved tribological performance when compared to pure TiN thin film at room temperature, registering friction coefficient of 0.42 ± 0.05 and 0.19 ± 0.03 for samples with 4 and 19 at.% WS_x, respectively. Wear tests at high temperatures evidenced that sample with 4 at.% WS_x did not provide advanced protection to substrate at 343 K and above due to deterioration. On the other hand, coating with 19 at.% WS_x maintained low friction coefficient up to 343 K, registering an optimum wear rate of 0.86 × 10⁻¹⁷ m²/N with no cracking occurrence.     

Hard machining performance of PVD AlCrN coated Al2O3/TiCN ceramic inserts as a function of thin film thickness

In the present work, AlCrN coating was deposited on Al₂O₃/TiCN ceramic inserts with varying thin film thickness using physical vapor deposition (PVD) technique. The thickness, surface morphology, chemical composition, hardness and adhesion strength of the coating to the substrate were characterized by field-emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro-indentations and scratch tests respectively. The machining performance of uncoated and coated tools was investigated in hard turning of AISI 52100 steel (62 HRC) under dry environment. The cutting behavior was analyzed in terms of machining forces, tool temperature, wear, friction and chip morphology. Further, a 3D finite element model with hybrid friction criterion has been adopted to support the experimental findings. The results revealed that coating/substrate adhesion and edge radius were the deciding criteria for the machining performance of coated tools with 3 µm coating thickness tool exhibiting best turning performance on Al₂O₃/TiCN mixed ceramic insert.     

Mechanical and tribological assessment of composite AlCrN or a-C:Ag-based thin films for implant application

The present study focuses on the comparison of cathodic arc deposited AlCrN (ternary coating) and Ag alloyed a-C (amorphous carbon base coating) on chrome nitride (CrN) medical grade 316 LVM stainless steel. The work comprises of morphological, structural, nanomechanical and tribological evaluation in physiological simulated body fluid (SBF) lubrication following conditions pertaining to simulated hip joint. According to the findings, H/E, H³/E² and E_coating/E_substrate significantly effect the nanomechanical and tribological properties of the coatings. While a-C:Ag/CrN exhibited better L_y value compared to AlCrN/CrN due to better surface quality, the later has shown higher L_c2 value during nanoscratch test attributed to lower H³/E² and higher plastic work done. Inspite of lower friction coefficient, a-C:Ag/CrN observed higher wear rate during simulated tribotest attributed to low hardness, separate graphitic structure due to Ag doping and sudden increase of friction coefficient ascribed to severe abrasive delamination of a-C:Ag top layer. The wear mechanism observed under SEM microscopy indicate severe adhesion of Ti6Al4V counterbody on AlCrN/CrN coated surface. The size of wear debris obtained with AlCrN/CrN-Ti6Al4V tribopair was larger in size compared to a-C:Ag/CrN-Ti6Al4V tribopair. Nevertheless, despite inferior surface quality and lower L_y value and larger wear debris size, AlCrN/CrN coating performed better in nanoscratch (at L_c2 value) and demonstrated lower wear in simulated tribotest in physiological SBF condition.     

Micromechanical and microtribological properties of BCN thin films near the B4C composition deposited by r.f. magnetron sputtering

Ternary materials with compositions in the B–C–N system offer properties of great interest. In particular, mechanical and tribological properties are expected to be excellent, as they can combine some of the specific properties of BN, B₄C and C₃N₄. In this paper, BCN thin films deposited by r.f. magnetron sputtering are characterized by their micromechanical and microtribological behavior. BCN coatings with different composition were obtained by varying the N₂/Ar proportion in the sputtering gas. Hardness and elastic modulus of the coatings were measured by nanoindentation. The adhesion and friction coefficient against diamond have been evaluated by microscratch and the coatings have been characterized in their wear behavior at the nanometric scale. These mechanical and tribological properties have been related to film composition and structure, which have been studied in a previous work. It is found that the measured wear resistance at the nanometric scale is directly related to the coating microhardness rather than friction behavior or adhesion of the coating to the substrate, which are the determinant factors in the macroscopic scale wear behavior.     

Wear-resistant Ti–Al–Ni–C–N coatings produced by magnetron sputtering of SHS-targets in the DC and HIPIMS modes

The hard wear-resistant nanocomposite Ti–Al–Ni–C–N coatings were deposited by direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS) in the Ar, Ar+15%N_2, and Ar+25%N₂ atmospheres. The structure of coatings was analyzed using the X-ray diffraction analysis, glow discharge optical emission spectroscopy, and scanning electron microscopy. Mechanical and tribological properties were measured using the nanoindentation and scratch testing as well as by tribological testing using the “pin-on-disc” scheme. Electrochemical corrosion resistance and oxidation resistance of coatings were investigated. The results suggest that the coatings are based on the FCC phases TiCN and Ni₃Al with crystallites size ~3 and ~15 nm, correspondingly. DCMS coatings with optimal composition were characterized by hardness 34 GPa, stable friction coefficient <0.26 and wear rate <5 × 10^-6 mm³N^-1m^-1. Application of HIPIMS mode allowed the increase of adhesion strength, tribological properties and corrosion resistance of coatings.     

Microstructure and tribological properties of multilayered ZrCrW(C)N coatings fabricated by cathodic vacuum-arc deposition

In this study, a series of ZrCrW(C)N multilayer coatings with various transition layers were deposited on AISI304 stainless steel using cathodic vacuum-arc deposition in N₂–C₂H₂ gas mixture. The tribological behaviors of sliding against Al₂O₃ balls under dry friction and lubricant conditions were investigated using a reciprocating tribometer. The results demonstrated that the ZrCrW(C)N coatings comprised (Zr, Cr, W) (C, N) crystallites and an amorphous carbon phase. It possessed a nano-hardness of 35.4 GPa and an elastic modulus of 417.7 GPa. The friction coefficient of the coating was reduced by 14% compared to that of the 304 matrices, and the wear mechanism changed from adhesive wear to slight abrasive wear under the lubrication steady state. Under dry friction conditions, the ZrCrW(C)N coatings with the entire CrWN transition layer exhibited wear rates of 1.27 ± 0.04 × 10^?8 mm³ (N m)^?1, which were one order of magnitude lower than that of the 304 steel. Compared with the untreated AISI304 stainless steel, the ZrCrW(C)N coating exhibits excellent mechanical and tribological properties under lubricated and dry friction conditions, which are crucial for engineering applications.     

Wear behavior of graded Cr-CrN-Cr(1−x)Al(x)N coatings synthesized by closed-field unbalanced magnetron sputtering for advanced machining operations

Graded Cr-CrN-Cr_(1?x)Al_(x)N coatings were synthesized onto M42 HSS substrates used in advanced machining operations by closed-field unbalanced magnetron sputtering (CFUBMS). The tribological behavior of these graded coatings was explored in detail by advanced electron microscopy, confocal laser scanning microscopy, nanoindentation and dry sliding wear tests. The presence and magnitude of residual stresses in these coatings were determined by the XRD – sin²ψ method, which revealed increasing compressive stresses with increasing Al content. The coating surface morphology, mechanical properties were determined prior to dry sliding wear by atomic force microscopy (AFM) and nanoindentation methods, which yielded decreasing surface roughness (R_a) as well as enhancement of hardness and modulus along with increase in H/E and H³/E² ratios with increasing Al content. Tribological investigation was performed with a pin-on-disc arrangement by keeping the sliding velocity (0.2?ms^?1) and normal axial load (10?N) constant and varying the sliding distance. Specific wear rates of the order ~ 10^–17 m³ N^?1 m^?1 were encountered for all coatings with the wear rates increasing as the Al content increased implying a decrease of wear resistance of the coatings. Abrasive wear has been found to be the dominant wear mechanism during dry sliding wear. Increasing modulus mismatch between coating and substrate can be mainly attributed to a decrease in wear resistance of the coatings.     

Tribological behaviour and chemical characterisation of Si-free and Si-containing carbon nitride coatings

In the present paper, we compare the tribological behaviour of Si-free and Si-containing carbon nitride films grown on high speed steel substrates against steel counterfaces. The CN_x coatings have been prepared by magnetron sputtering of a carbon target in a N₂ atmosphere while the SiCN_x films were obtained by the same method, but adding a vapour pressure of Si(CH₃)₃Cl. In the case of pure CN_x, the presence of water molecules in the gas phase produces a negative effect in the tribological response while the Si-containing film is able to maintain a low friction value (0.12) even under humid atmosphere similarly to Si-DLC coatings. To achieve a better understanding of the friction mechanism, both Si-free and Si-containing films were characterised by Energy Filtered Transmission Electron Microscopy (EFTEM), X-Ray Photoelectron Spectroscopy (XPS) and Infrared Spectroscopy (IR). The buffer effect of silicon-doped CN_x, decreasing the moisture sensitivity of the friction coefficient, is attributed to the adsorption of water molecules on SiO₂ domains formed in the Si-containing films. This adsorbed water may lubricate the contact in humid atmosphere allowing the shear strength to diminish.     

Mechanical and high pressure tribological properties of nanocrystalline Ti(N,C) and amorphous C:H nanocomposite coatings

This paper reports on the mechanical and high pressure tribological properties of nanocrystalline (nc-) Ti(N,C)/amorphous (a-) C:H deposited, using low temperature (～ 200 °C) DC reactive magnetron sputtering. The mechanical properties are affected by the nc-Ti(N,C)/a-C:H phase fraction ratio. For increasing C contents (from 31 to 47 at.%) an increase of the a-C:H phase content and a degradation of the nanocrystalline phase occurs leading to a reduction in nanoindentation hardness (H) values (from 15 to 9 GPa) and reduced modulus (Er) values (from 150 to 80 GPa). A strong correlation between H/E ratio and wear performance was exhibited by the coatings. The synthesized coatings survived up to 100 m sliding distance when tested using pin-on-disc sliding configuration at > 4.5 GPa contact pressures and the measured friction coefficient values were similar for all films (μ ～ 0.21–0.25).     

Advanced TiC/a-C:H nanocomposite coatings deposited by magnetron sputtering

TiC/a-C:H nanocomposite coatings have been deposited by magnetron sputtering. They consist of 2–5 nm TiC nanocrystallites embedded in the amorphous hydrocarbon (a-C:H) matrix. A transition from a columnar to a glassy microstructure has been observed in the nanocomposite coatings with increasing substrate bias or carbon content. Micro-cracks induced by nanoindentation or wear tests readily propagate through the column boundaries whereas the coatings without a columnar microstructure exhibit substantial toughness. The nanocomposite coatings exhibit hardness of 5–20 GPa, superior wear resistance and strong self-lubrication effects with a friction coefficient of 0.05 in air and 0.01 in nitrogen, under dry sliding against uncoated bearing steel balls. Especially, reversible transitions from low to ultra-low friction are observed if the atmosphere is cycled between ambient air and nitrogen. The lowest wear rate is obtained at high humidity.     

Corrosion and friction resistance of TiVCrZrWNx high entropy ceramics coatings prepared by magnetron sputtering

High entropy alloy coatings have attracted much attention because of their high hardness, low-level fault energy, and chemical stability. Nevertheless, this type of coating would inevitably suffer from wear, corrosion, aging, and so on. Hence, a novel coating with corrosion and friction resistance would be constructed for broadening its application scenarios. In this work, TiVCrZrWN_x high entropy ceramics coatings were prepared by reactive magnetron sputtering. The microstructure, mechanical properties, friction, and corrosion resistance of the coatings deposited at different nitrogen flow rates have been studied. The microstructure of TiVCrZrWN_x coatings is strongly dependent on the nitrogen flow rate and forms a stable FCC structure when the nitrogen flow rate reaches 24 sccm. The pure TiVCrZrW coating is 15.65 GPa, with the increase of nitrogen flow rate (24 sccm), the coating hardness reaches 21.27 GPa. The corrosion resistance of the coatings also increases continuously. According to the results of the impedance spectrum and polarization curve, the charge transfer resistance value of the coating gradually increases with the content of nitrogen, the current density rapidly decreases to a minimum as the potential increases. In terms of tribological behavior, the formation of V₂O₅ during the sliding in seawater could significantly reduce the coefficient of friction from 0.603 to 0.383. Therefore, TiVCrZrWN_x HECs coatings simultaneously possess high hardness, toughness, and excellent resistance to friction and corrosion, which is expected to provide a new and reliable method for the research field of coatings in the maritime field.     

Tribocorrosion behaviour of TiCxOy thin films in bio-fluids

Decorative coatings require not only an attractive appearance for market applications, but also an ability to protect the surface underneath. Because of this, corrosion, wear and their combined effects (termed tribocorrosion) are particularly important for lifetime prediction. In this paper, the tribocorrosion behaviour of a range of single layered titanium oxycarbide, TiC_xO_y, coatings, produced by DC reactive magnetron sputtering, has been studied and reported as a function of electrode potential and applied load. The study was conducted in a reciprocating sliding tribo-system (Plint TE 67/E) in a bio-fluid (an artificial perspiration solution) at room temperature. During the wear tests, both the open-circuit potential and the corrosion current were monitored. The results showed that electrode potential and load have a significant influence on the total material loss. The variations in R_p (polarization resistance) and C_f (capacitance) before and after sliding, obtained by Electrochemical Impedance Spectroscopy (EIS) were evaluated in order to provide an understanding of the resistance of the film in such conditions. Tribocorrosion maps were generated, based on the results, indicating the change in mechanisms of the tribological and corrosion parameters for such coatings, as a function of load and applied potential.     

Effect of plasma sprayed and laser re-melted Al2O3 coatings on hardness and wear properties of stainless steel

Commercially available austenic stainless steel substrate was coated with commercially available, raw Al₂O₃ powder applied by means of plasma spraying method and then re-melted with CO₂ laser beam of various parameters. Tribological and mechanical properties of the 120 J/mm and 160 J/mm laser re-melted coatings were compared with the tribological and mechanical properties of the “as-sprayed” coating. The influence of the laser beam of various parameters on the microstructure, phase constituents, and mechanical and tribological properties of the ceramic coating was investigated by means of scanning electron microscopy, light microscopy, computer tomography, X-ray diffraction technique and nanoindentation tests. The micro sliding wear performance of the coatings was tested using a nanoindenter. The study showed an improvement of the mechanical and tribological properties caused by the laser treatment. The best results were achieved for coating re-melted with 120 J/mm laser beam.     

Complex study of protective Cr3C2–NiAl coatings deposited by vacuum electro-spark alloying,pulsed cathodic arc evaporation,magnetron sputtering,and hybrid technology

Coatings were obtained by vacuum electro-spark alloying (VESA), pulsed cathodic arc evaporation (PCAE), magnetron sputtering (MS) techniques and VESA-PCAE-MS hybrid technology using Cr₃C₂–NiAl electrodes. The structure of the coatings was analyzed using scanning and transmission electron microscopy, X-ray diffraction and energy-dispersive spectroscopy. Mechanical properties were determined by nanoindentation, while tribological properties were assessed using pin-on-disk tribometer. Corrosion resistance was estimated by voltammetry in 1 N H₂SO₄ and 3.5%NaCl solutions. Oxidation resistance tests were performed at 800°С in air. The VESA coating had the highest thickness, low friction coefficient and high wear resistance. PCAE coating demonstrated the highest hardness (24 GPa) and elastic recovery (59%), oxidation resistance and superior corrosion resistance both in 1 N H₂SO₄ (i_corr = 70 μА/cm²) and 3.5%NaCl (i_corr = 0.74 μА/cm²) solutions. The MS coating had average mechanical properties and low corrosion current density (71 μА/cm²) in 1 N H₂SO₄. Deposition of coatings using VESA-PCAE-MS hybrid technology led to an increase in corrosion and oxidation resistance at least by 1.5 times in comparison with the VESA coating.