A magnetron sputtering technique to prepare a-C:H films: Effect of substrate bias

Amorphous hydrogenated carbon (a-C:H) films were deposited by magnetron sputtering with a mixture gas of Ar and CH₄. The a-C:H films deposited by this method have relatively low internal stress (<1 GPa) compared to some films deposited by conventional deposition process. The effects of substrate bias voltage on microstructure, surface morphology and mechanical properties of the films were investigated by various techniques. It has been found that the polymer-like structure is dominated at low bias voltage (−100 V), while the diamond-like structure with the highest hardness and internal stress is the main feature of the a-C:H films deposited under high bias voltage (−300 V). With increasing the bias voltage further, the feature of diamond-like structure decreases associating with the increase of graphitization. The frictional test shows that the friction coefficient and wear rate of the a-C:H films are depended strongly on structure and mechanical properties, which were ultimately influenced by the deposition method and bias voltage.     

The electrochemical and mechanical properties of Ti incorporated amorphous carbon films in Hanks’ solution

Ti incorporated amorphous carbon (a-C) films with variant Ti contents were prepared by the unbalanced magnetron sputtering process. Scanning electron microscopy, ultraviolet Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy were used to characterize the microstructure of a-C films. The hardness and lubricated tribological properties were assessed using nanoindentation and ball-on-disk tribometer. As the Ti content in a-C films increases from 0 to 15.2 at.%, the sp³ volume fraction, the internal stress and the hardness of the films decreases gradually, while the disorder of sp² bond increases. The electrochemical tests reveal that the a-C films with lower than 1.5 at.% Ti possess good corrosion resistance in Hanks’ solution, while the a-C film with 15.2 at.% Ti is susceptible to crevice corrosion. The reduced friction of the a-C films is due to the sp² bonded film surface and boundary lubrication of the Hanks’ solution. The a-C film with 3.1 at.% Ti exhibits the best wear resistance in Hanks’ solution among the studied films.     

(Ti,Al,Si,C)N nanocomposite coatings synthesized by plasma-enhanced magnetron sputtering

Materials’ surface service property could be enhanced by transition metal nitride hard coatings due to their high hardness, wear and high temperature oxidation resistance, but the higher friction coefficient (0.4-0.9) of which aroused terrible abrasion. In this work, quinternary (Ti,Al,Si,C)N hard coating 3-4 μm was synthesized at 300 °C using plasma enhanced magnetron sputtering system. It was found that the coating's columnar crystals structure was restrained obviously with the increase of C content and a non-columnar crystals growth mode was indicated at the C content of 33.5 at.%. Both the XRD and TEM showed that the (Ti,Al,Si,C)N hard coatings had unique nanocomposite structures composed of nanocrystalline and amorphous nc-(Ti,Al)(C,N)/nc-AlN/a-Si₃N₄/a-Si/a-C. However, the coatings were still super hard with the highest hardness of 41 GPa in spite of the carbon incorporation. That a-C could facilitate the graphitization process during the friction process which could improve the coating's tribological performance. Therefore, that nanocomposite (Ti,Al,Si,C)N coatings with higher hardness (>36 GPa) and a lower friction coefficient (<0.2) could be synthesized and enhance the tribological performance and surface properties profoundly.     

Effect of Chromium on Structure and Tribological Properties of Hydrogenated Cr/a-C:H Films Prepared via a Reactive Magnetron Sputtering System

Hydrogenated Cr-incorporated carbon films(Cr/a-C:H) are deposited successfully by using a dc reactive magnetron sputtering system.The structure and mechanical properties of the as-deposited Cr/a-C:H films are characterized systematically by field-emission scanning electron microscope,x-ray diffraction,Raman spectra,nanoindentation and scratch.It is shown that optimal Cr metal forms nanocrystalline carbide to improve the hardness,toughness and adhesion strength in the amorphous carbon matrix,which possesses relatively higher nano-hardness of 15.7GPa,elastic modulus of 126.8 GPa and best adhesion strength with critical load(L_c) of36 N for the Cr/a-C:H film deposited at CH_4 flow rate of 20 sccm.The friction and wear behaviors of as-deposited Cr/a-C:H films are evaluated under both the ambient air and deionized water conditions.The results reveal that it can achieve superior low friction and anti-wear performance for the Cr/a-C:H film deposited at CH_4 flow rate of 20 sccm under the ambient air condition,and the friction coefficient and wear rate tested in deionized water condition are relatively lower compared with those tested under the ambient air condition for each film.Superior combination of mechanical and tribological properties for the Cr/a-C:H film should be a good candidate for engineering applications.     

Field electron emission from amorphous carbon thin films grown by RF magnetron sputtering

Using a RF magnetron sputtering, amorphous carbon (a-C) and N-doped a-C (a-C:N) thin films were fabricated as field electron emitter. These thin films were deposited on Si(0 0 1) substrate at several temperatures. The field emission property was improved for a-C thin films grown at higher substrate temperatures. Furthermore, a-C:N film exhibits field emission property better than that of undoped a-C film. These results are explained in terms of the change in surface morphology and structural properties of a-C film.     

The microstructure, mechanical and friction properties of protective diamond like carbon films on magnesium alloy

Protective hard coatings deposited on magnesium alloys are believed to be effective for overcoming their poor wear properties. In this work, diamond-like carbon (DLC) films as hard protective films were deposited on AZ91 magnesium alloy by arc ion plating under negative pulse bias voltages ranging from 0 to −200 V. The microstructure, composition and mechanical properties of the DLC films were analyzed by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and nanoindentation. The tribological behavior of uncoated and coated AZ91 magnesium alloy was investigated using a ball-on-disk tribotester. The results show that the negative pulse bias voltage used for film deposition has a significant effect on the sp³ carbon content and mechanical properties of the deposited DLC films. A maximum sp³ content of 33.3% was obtained at −100 V, resulting in a high hardness of 28.6 GPa and elastic modulus of 300.0 GPa. The DLC films showed very good adhesion to the AZ91 magnesium alloy with no observable cracks and delamination even during friction testing. Compared with the uncoated AZ91 magnesium alloy, the magnesium alloy coated with DLC films exhibits a low friction coefficient and a narrow, shallow wear track. The wear resistance and surface hardness of AZ91 magnesium alloy can be significantly improved by coating a layer of DLC protective film due to its high hardness and low friction coefficient.     

Rare earth Ce-modified (Ti,Ce)/a-C:H carbon-based film on WC cemented carbide substrate

WC cemented carbide suffers severe wear in water environments. A novel carbon-based film could be a feasible way to overcome this drawback. In this study, a rare earth Ce-modified(Ti,Ce)/a-C:H carbon-based film is successfully prepared on WC cemented carbide using a DC reactive magnetron sputtering process. The microstructure, mechanical properties,and tribological behavior of the as-prepared carbon-based film are systematically investigated. The results show that the doping Ti forms Ti C nanocrystallites that are uniformly dispersed in the amorphous carbon matrix, whereas the doping Ce forms CeO_2 that exists with the amorphous phase in the co-doped(Ti,Ce)/a-C:H carbon-based film. The mechanical properties of this(Ti,Ce)/a-C:H film exhibit remarkable improvements, which could suggest higher hardness and elastic modulus as well as better adhesive strength compared to solitary Ti-doped Ti/a-C:H film. In particular, the as-prepared(Ti,Ce)/a-C:H film presents a relatively low friction coefficient and wear rate in both ambient air and deionized water,indicating that(Ti,Ce)/a-C:H film could feasibly improve the tribological performance of WC cemented carbide in a water environment.     

Influence of substrate bias voltage on structure and properties of the CrAlN films deposited by unbalanced magnetron sputtering

The CrAlN films were deposited on silicon and stainless steel substrates by unbalanced magnetron sputtering system. The influence of substrate bias on deposition rate, composition, structure, morphology and properties of the CrAlN films was investigated. The results showed that, with the increase of the substrate bias voltage, the deposition rate decreased accompanied by a change of the preferred orientation of the CrAlN film from (2 2 0) to (2 0 0). The grain size and the average surface roughness of the CrAlN films declined as the bias voltage increases above −100 V. The morphology of the films changed from obviously columnar to dense glass-like structure with the increase of the bias voltage from −50 to −250 V. Meanwhile, the films deposited at moderate bias voltage had better mechanical and tribological properties, while the films deposited at higher bias voltage showed better corrosion resistance. It was found that the corrosion resistance improvement was not only attributed to the low pinhole density of the film, but also to chemical composition of films.     

X-ray photoelectron spectroscopic study of nitrogen incorporated amorphous carbon films embedded with nanoparticles

The effect of substrate bias on X-ray photoelectron spectroscopy (XPS) study of nitrogen incorporated amorphous carbon (a-C:N) films embedded with nanoparticles deposited by filtered cathodic jet carbon arc technique is discussed. High resolution transmission electron microscope exhibited initially the amorphous structure but on closer examination the film was constituted of amorphous phase with the nanoparticle embedded in the amorphous matrix. X-ray diffraction study reveals dominantly an amorphous nature of the film. A straight forward method of deconvolution of XPS spectra has been used to evaluate the sp³ and sp² contents present in these a-C:N films. The carbon (C 1s) peaks have been deconvoluted into four different peaks and nitrogen (N 1s) peaks have been deconvoluted into three different peaks which attribute to different bonding state between C, N and O. The full width at half maxima (FWHM) of C 1s peak, sp³ content and sp³/sp² ratio of a-C:N films increase up to −150 V substrate bias and beyond −150 V substrate bias these parameters are found to decrease. Thus, the parameters evaluated are found to be dependent on the substrate bias which peaks at −150 V substrate bias.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

Composition, microstructure, and properties of CrNx films deposited using medium frequency magnetron sputtering

CrN_x films were deposited on stainless steel and Si (1 1 1) substrates via medium frequency magnetron sputtering in a N₂ + Ar mixed atmosphere. The influence of N₂ content on the deposition rate, composition, microstructure, mechanical and tribological properties of the as-deposited films was investigated by means of the X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), nanoindentation and tribometer testing. It was found that the N atomic concentration increased and the phase transformed from a mixture of Cr₂N + Cr(N) to single-phase Cr₂N, and then Cr₂N + CrN to pure CrN phase with the increase of N₂ content. The Cr 2p_3/2 and N 1s of XPS spectra also confirmed the evolution of phase. Accordingly, all films exhibited a typical columnar structure which lies in the zone T of Thornton Model. The mixed Cr₂N and Cr(N) phases showed low hardness and high friction coefficient. Cr₂N possessed higher hardness than CrN while CrN exhibited lower friction coefficient.     

Structure and elastic recovery of Cr-C:H films deposited by a reactive magnetron sputtering technique

Cr-containing hydrogenated amorphous carbon (Cr-C:H) films were deposited on silicon substrates using a DC reactive magnetron sputtering with Cr target in an Ar and C₂H₂ gas mixture. The composition, bond structure, mechanical hardness and elastic recovery of the films were characterized using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and nano-indentation. The film tribological behavior was also studied by a ball-on-disc tribo-tester. The results showed that the films deposited at low C₂H₂ flow rate (<10 sccm) presented a feature of composite Cr-C:H structure, which consisted of hard brittle chromium carbide phases and amorphous hydrocarbon phase, and thus led to the observed low elastic recovery and poor wear resistance of the films. However, the film deposited at high C₂H₂ flow rate (40 sccm) was found to present a typical feature of polymer-like a-C:H structure containing a large amount of sp³ C-H bonds. As a result, the film revealed a high elastic recovery, and thus exhibited an excellent wear resistance.     

Effect of deposition and annealing temperature on mechanical properties of TaN film

Tantalum nitride films (TaN) were synthesized by microwave ECR-DC sputtering. The effects of deposition and annealing temperature on mechanical properties of TaN films were investigated. Cross-section pattern, microstructure and binding energy of the films were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Mechanical properties were evaluated using nano-indentation and scratch tester. The results showed that the maximal hardness value of approximately 40 GPa was deposited in the TaN sample at 573 K. While the preparation temperature decreased, the hardness, modulus and adhesion of TaN film also decreased. Hardness and modulus also decreased with the increase in annealing temperature. Meanwhile the adhesion strength was also sensitive to the annealing temperature, with a maximum adhesion strength of 40 N measured in the TaN film annealed at 448 K. The results demonstrated that a desirable mechanical property of TaN films deposited by DC reactive magnetron sputtering can be obtained by controlling the deposition and annealing temperature.     

Bias voltage effect on the structure and property of chromium copper-diamond-like carbon multilayer films fabricated by cathodic arc plasma

Chromium copper-diamond-like carbon (Cr:Cu)-DLC films were deposited onto silicon and by cathodic arc evaporation process using chromium (Cr) and copper (Cu) target arc sources to provide Cr and Cu in the Me-DLC. Acetylene reactive gases were the carbon source and activated at 180 °C at 13 mTorr, and a substrate bias voltage was varied from −50 V to −200 V to provide the (Cr:Cu)-DLC structure. The structure, interface, and chemical bonding state of the produced film were analyzed by transmission electron microscope (TEM), IR Fourier transform (FTIR) spectra, and X-ray photoelectron spectroscopy (XPS). The results showed that the Cr-containing a-C:H/Cu coatings exhibited an amorphous layer of DLC:Cr layer and a crystalline layer of Cu multilayer structure. The profiles of sp³/sp² (XPS) ratios corresponded to the change of microhardness profile by varying the pressure of the negative DC bias voltage. These (Cr:Cu)-DLC coatings are promising materials for soft substrate protective coatings.     

High-temperature oxidation resistant (Cr, Al)N films synthesized using pulsed bias arc ion plating

(Cr, Al)N films were deposited by pulsed bias arc ion plating on HSS and 316L stainless steel substrates. With pulsed substrate bias ranging from −100 V to −500 V, the effect of pulsed bias on film composition, phase structure, deposition rate and mechanical properties was investigated by EDX, XRD, SEM, nanoindentation and scratch measurements. The high-temperature (up to 900 °C) oxidation resistance of the films was also evaluated. The results show that Al contents and deposition rates decrease with increasing pulsed bias and the ratio of (Cr + Al)/N is almost constant at 0.95. The as-deposited (Cr, Al)N films crystallize in the pseudo-binary (Cr, Al)N and Al phases. The film hardness increases with increasing bias and reaches the maximum 21.5 GPa at −500 V. The films deposited at −500 V exhibit a high adhesion force, about 70 N, and more interestingly good oxidation resistance when annealed in air at 900 °C for 10 h.     

Ti-Cu-N hard nanocomposite films prepared by pulse biased arc ion plating

In this work, Ti-Cu-N hard nanocomposite films were deposited on high-speed-steel (HSS) substrates using a TiCu (88:12 at.%) single multi-component target by pulse biased arc ion plating. The influence of pulse bias voltages was examined with regard to elemental composition, structure, morphology and mechanical properties of the films. The Cu atomic content of Ti-Cu-N films was determined by Electron Probe Micro-Analyzer (EPMA). The structure and morphology were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Hardness and film/substrate adhesion were determined by nanoindenter and scratch test, respectively. The results showed that the content of Cu appeared to be in the range of 1.75-4.5 at.%, depending on pulse bias voltages. The films exhibit a preferred orientation TiN (1 1 1) texture when the substrate bias voltages were −100 V and −300 V, while the preferred orientation change to be a preferred orientation TiN (2 2 0) one when the substrate bias voltages increase to −600 V and −900 V. And no obvious sign of metal copper phase was observed. The SEM morphologies showed some macroparticles (MPs) on the surface of the films and the relative content of the MPs decreased significantly when the substrate bias voltages increased from −100 to −900 V. The maximum value (74 N) of the film/substrate adhesion of the films was obtained when the substrate bias voltage was −600 V with Cu content of 1.75 at.%. Hardness enhancement was observed, the value of the hardness increased firstly and reached a maximum value of 31.5 GPa, corresponding to Cu content of 1.75 at.%, and then it decreased when the substrate bias voltage changed from −100 to −900 V. The hardness enhancement was discussed related to the concept for the design of hard materials.     

Effect of substrate bias and temperature on magnetron sputtered CrSiN films

The combine influence of substrate temperature and bias on microstructure and mechanical properties of CrSiN film was examined. The silicon content and phase constitutions of the films are independent on substrate temperature and bias. The crystal preferred orientation is controlled by substrate bias but unrelated to substrate temperature. The influence of bias (0 V to −300 V) on hardness is more obvious than that of the substrate temperature (100-500 °C).     

Deposition of TiSiN coatings by arc ion plating process

Titanium silicon nitride (TiSiN) thin films were deposited on tungsten cemented carbide tools by cathode arc ion plating (AIP) process using alloy TiSi targets. The effects of silicon addition and negative substrate bias on the development of the textures of films were studied systematically by varying the bias voltage from −20 to −200 V. The structural features of the films were investigated in detail using X-ray diffraction. The effect of the texture on such mechanical properties as hardness and adhesion of the films was also studied. A maximum hardness of 42 GPa was obtained at a DC substrate bias of −150 V. The characteristics of TiSiN thin films exhibited excellent adhesion of over 150 N. The cutting performance of end-mills and drillers was evaluated by milling and drilling of highly hardened material under high-speed cutting conditions. The results reveal that cutting tools with TiSiN coatings markedly outperformed those with TiN coatings, and the uncoated cutting tools. TiSiN coating increased the cutting lifetime to seven times that of the uncoated one.     

Effects of deposition parameters on the structure and mechanical properties of high-entropy alloy nitride films

High-entropy alloy (AlCrNbSiTiV)N nitride films are prepared using direct current (dc) reactive magnetron sputtering, with an equiatomic AlCrNbSiTiV alloy target. Experiments using the grey-Taguchi method are conducted to determine the effect of deposition parameters (dc power, substrate temperature, N₂/(N₂+Ar) flow rate and substrate bias) on the microstructure, mechanical and tribological properties. Orthogonal array (L₉ 3⁴), signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. The coated films are examined using scanning electron microscopy, an atomic force microscope, transmission electron microscopy (TEM), a tribometer and a nanoindenter. The TEM patterns confirm that the (AlCrNbSiTiV)N nitride films have a simple face-center-cubic structure. The experimental results show that a (AlCrNbSiTiV)N film coating significantly improves the mechanical properties. In the confirmation runs, using grey relational analysis, the improvement in friction coefficient is 32.5%, in corrosion current is 28.6%, in hardness H is 29.4%, in elastic modulus E is −18.3%, in H/E is 57.1 and in H³/E² is 225.0%. The samples with (AlCrNbSiTiV)N film coating are classified as HF1 and exhibit good adhesive strength.     

The structure, surface topography and mechanical properties of Si-C-N films fabricated by RF and DC magnetron sputtering

Silicon carbon nitride thin films were deposited on Co-Cr alloy under varying deposition conditions such as sputtering power and the partial pressure ratio of N₂ to Ar by radio frequency and direct current magnetron sputtering techniques. The chemical bonding configurations, surface topography and hardness were characterized by means of X-ray photoelectron spectroscopy, atomic force microscopy and nano-indentation technique. The sputtering power exhibited important influence on the film composition, chemical bonding configurations and surface topography, the electro-negativity had primary effects on chemical bonding configurations at low sputtering power. A progressive densification of the film microstructure occurring with the carbon fraction was increased. The films prepared by RF magnetron sputtering, the relative content of the Si-N bond in the films increased with the sputtering power increased, and Si-C and Si-Si were easily detachable, and C-O, N-N and N-O on the film volatile by ion bombardment which takes place very frequently during the film formation process. With the increase of sputtering power, the films became smoother and with finer particle growth. The hardness varied between 6 GPa and 11.23 GPa depending on the partial pressure ratio of N₂ to Ar. The tribological characterization of Co-Cr alloy with Si-C-N coating sliding against UHMWPE counter-surface in fetal bovine serum, shows that the wear resistance of the Si-C-N coated Co-Cr alloy/UHMWPE sliding pair show much favourable improvement over that of uncoated Co-Cr alloy/UHMWPE sliding pair. This study is important for the development of advanced coatings with tailored mechanical and tribological properties.