Direct Current Unbalanced Magnetron Sputtering Research Articles

Plasmonic properties of silver nanoparticles embedded in diamond like carbon films: Influence of structure and composition

In the present study optical properties of hydrogenated diamond like carbon nanocomposite films containing silver nanoparticles (DLC:Ag) deposited by direct current (DC) unbalanced reactive magnetron sputtering were studied in 180–1100nm range. Different substrate bias was used during deposition of the films. Structure of the films was investigated by multiwavelength Raman scattering spectroscopy and X-ray diffractometry (XRD). Chemical composition of the samples was studied by X-ray photoelectron spectroscopy (XPS), surface morphology was investigated by atomic force microscopy (AFM). Red shift of the surface plasmon resonance peak of DLC:Ag films with the increase of Ag atomic concentration was observed. It was found that high atomic concentration of oxygen in DLC:Ag films results in some redshift of the plasmonic peak, too. Such a behavior is explained by increase of the refractive index of the dielectric medium surrounding silver nanoparticle due to possible presence of the silver oxide interlayer at the Ag nanocluster and diamond like carbon matrix interface. It was demonstrated that influence of the increased Ag atomic concentration on position of the surface plasmon resonance peak of DLC:Ag films clearly prevails influence of the increased sp3/sp2 ratio of the diamond like carbon matrix. Correlation between the structure of Ag nanocrystallites studied by XRD and position of the surface plasmon resonance peak position was observed.

Effect of annealing on the mechanical and scratch properties of BCN films obtained by magnetron sputtering deposition

Abstract Boron-carbon-nitride (BCN) films have been fabricated by direct current unbalanced magnetron sputtering. Boron carbide/graphite compound and a mixture of nitrogen and argon are used as target and carrier gas, respectively, during BCN synthesis. The obtained BCN films are annealed at different temperatures under vacuum condition. The effect of annealing temperature on the structure, mechanical properties and scratch behavior of the BCN films has been investigated. The results indicate that no decomposition products are found even the BCN films are annealed at 1000 °C. The hardness and elastic modulus of the films decrease with the increase of annealing temperatures. The BCN film annealed at 600 °C has the strongest scratch resistance. The friction coefficient of all BCN films is in range of 0.05 to 0.15.

Effect of the degree of high power impulse magnetron sputtering utilisation on the structure and properties of TiN films

TiN films were deposited using high power impulse magnetron sputtering (HIPIMS) enabled four cathode industrial size coating system equipped with HIPIMS power supplies. The standard version of this system allows control over the ion bombardment during coating growth by varying the strength of the electromagnetic field of the unbalancing coils and bias voltage applied to the substrate. The coatings were produced in different coating growth conditions achieved in combined HIPIMS — direct current (dc) unbalanced magnetron sputtering (HIPIMS/UBM) processes where HIPIMS was used as an additional tool to manipulate the ionisation degree in the plasma. Four cathode combinations were explored with increasing contribution of HIPIMS namely 4UBM (pure UBM), 1HIPIMS+3UBM, 2HIPIMS+2UBM and 2HIPIMS (pure HIPIMS) to deposit TiN coatings. Optical emission spectroscopy (OES) measurements were carried out to examine the plasma generated by the various combinations of HIPIMS and UBM cathodes. The micro-structural study was done by scanning electron microscopy (SEM). X-ray diffraction (XRD) technique was used to calculate the residual stress and texture parameter. It has been revealed that the residual stress can be controlled in a wide range from −0.22GPa to −11.67GPa by intelligent selection of the degree of HIPIMS utilisation, strength of the electromagnetic field of the unbalancing coils and the bias voltage applied to the substrate while maintaining the stoichiometry of the coatings. The effect of the degree of HIPIMS utilisation on the microstructure, texture and residual stress is discussed. Combining HIPIMS with dc-UBM sputtering is also seen as an effective tool for improving the productivity of the deposition process.

Electrochemical behavior of superhard nanocomposite coatings of TiN/Si3N4 prepared by reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of TiN/Si3N4 are new generation superhard coatings having hardness greater than 40GPa. Apart from high hardness, these coatings exhibit outstanding properties such as improved wear resistance and high oxidation resistance. These coatings also retain their hardness even after heating in air at higher temperatures. The present study reports electrochemical behavior of superhard nanocomposite coatings of TiN/Si3N4 in 3.5% NaCl solution. The nanocomposite coatings with varying silicon contents have been prepared on steel substrates by reactive direct current unbalanced magnetron sputtering. Single-component TiN and Si3N4 coatings have also been included in the investigation. The electrochemical measurements were performed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corroded samples were characterized using scanning electron microscopy and energy dispersive X-ray analysis. The nanocomposite coatings exhibited better corrosion resistance than single-phase TiN coatings. Nyquist and Bode plots obtained from the EIS measurements for bare steel substrate, single-component TiN and nanocomposite coatings were used for evaluating the corrosion behavior. The charge transfer resistance and the double layer capacitance were also calculated using EIS data.

Silicon nitride films for the protective functional coating: Blood compatibility and biomechanical property study

Behaviors of silicon nitride films and their relation to blood compatibility and biomechanical have been interesting subjects to researchers. A systematic blood compatibility and biomechanical property investigation on the deposition of silicon-nitride films under varying N2 and CF4 flows was carried out by direct current unbalanced magnetron sputtering techniques. Significant role of surface property, chemical bonding state of silicon nitride film and blood compatibility, mechanical properties for the films were observed. The chemical bonding configurations, surface topography, contact angle and mechanical properties were characterized by means of X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and nano-indentation technique and CSEM pin-on-disk tribometer. Blood compatibility of the films was evaluated by platelet adhesion investigation. The results of the platelet adhesion tests shown that the effect of fluorine and nitrogen-doped revealed an intimate relationship between the ratio of polar component and dispersion component of the surface energy and its hemocompatibility. Si–N–O coating can be a great candidate for developing antithrombogenic surfaces in blood contacting materials. The chemical bonding state made an adjustment in microstructured surfaces, once in the totally wettable configuration, may improve the initial contact between platelet and biomedical materials, due to the appropriate ratio of dispersion component and polar component. To resist wear, biomedical components require coatings that are tough and hard, have low friction, and are bio-inert. The study suggests that by Si–N coating the metal surfaces could be a choice to prolong the life of the sliding pair Co–Cr–Mo alloy/UHMWPE implants.

Microstructure, mechanical properties and wetting behavior of F: Si–C–N films as bio-mechanical coating grown by DC unbalanced magnetron sputtering

A systematic structure and properties investigation on the deposition of fluorinated silicon–carbon–nitride (Si–C–N) films under varying CF4 flows was carried out by direct current unbalanced magnetron sputtering techniques. Significant role of fluorine and carbon-doped on growth characteristics and mechanical properties in the film was observed. The chemical bonding configurations, surface topography and mechanical properties were characterized by means of X-ray photoelectron spectroscopy (XPS), Raman and infrared spectroscopies, atomic force microscopy (AFM) and nano-indentation technique and CSM pin-on-disk tribometer. It was found that the as-deposited F: Si–C–N films are amphipathic nature, and large variations took place these films’ deposition rate, composition, microstructure and mechanical properties when CF4 flows varied from 0 to 9sccm. At CF4 gas flow rate 9sccm, the F: Si–C–N coatings demonstrated a fluorine content of 5.95at.% and a moderate friction coefficient of 0.03. It is obvious from the hardness results that the F: Si–C–N coating enhances the hardness of the Co–Cr–Mo alloy to approximately 16.3GPa on a smoother surface. The tribological characterization of Co–Cr–Mo alloy with F: Si–C–N coating sliding against ultrahigh molecular weight polyethylene (UHMWPE) counter-surface in fetal bovine serum, shows that the wear resistance of the F: Si–C–N coated Co–Cr–Mo alloy/UHMWPE sliding pair show much obviously improvement over that of uncoated Co–Cr–Mo alloy/UHMWPE sliding pair. The F: Si–C–N and Si–N films have potential properties for joint surface modification applications.

Influence of silver content on the tribomechanical behavior on Ag-TiCN bioactive coatings

Surface modification of bulk materials used in biomedical applications has become an important prerequisite for better biocompatibility. In particular, to overcome the particle generation, low-wear coatings based on carbon (nitrogen) and containing antimicrobial elements such as silver are promising candidates. Thus, the present work explores the potentialities of silver-containing carbonitride-based (Ag-TiCN) thin films prepared by direct current unbalanced reactive magnetron sputtering. The silver content in the coatings was varied from 0 to 26.7 at.% by changing the targets and the fraction of C 2H 2 and N 2 in the gas mixture with Ar. The obtained Ag-TiCN based coatings were characterized in terms of composition and microstructure. Mechanical and tribological properties of the films were studied by nanoindentation and reciprocating pin-on disk testing in a fetal bovine serum solution, respectively. Raman, scanning electron microscope and energy dispersive X-ray analysis was carried out in the contact region after tribological tests to obtain information about the friction mechanism. The cytotoxicity of the coatings was assessed by in vitro tests using fibroblast cells. The coatings comprised a mixture of TiC xN 1 − x , Ag and a-C(N) x phases whose relative proportion varied depending on the Ag/Ti ratio. The mechanical, tribological and cytotoxicity properties were correlated with the chemical and phase composition. When the Ag/Ti ratios were below 0.20 (Ag contents < 6.3 at.%) the films resulted harder (~ 18 GPa) with higher wear resistance (~ 10 −6 mm 3/Nm), showing similar friction coefficient (~ 0.3) and good biocompatibility.

Characterization and properties of quaternary Mo–Si–C–N coatings synthesized by magnetron sputtering technique

In this paper the direct current unbalanced reactive magnetron sputtering and composite target techniques were exploited to deposit quaternary Mo–Si–C–N coatings on Si wafer and stainless steel (1Cr18Ni9) in an Ar/N 2 gaseous mixture. The chemical composition, microstructure, morphology, hardness, and friction coefficient of these films were characterized by means of X-ray diffraction, XPS, field emission scanning electron microscopy, TEM and nanoindentation. With the increase of C content in the range of C/(C + Mo + Si + N) = 0–12 at.%, the crystallite size decreases from 32 nm to 5 nm and the average friction coefficient of Mo–Si–C–N coatings decreases from 0.24 to 0.17, while the hardness increases at first and then decreases after passing a maximum value of about 27 GPa at 9 at.% C. It was suggested that in the Mo–Si–C–N coatings C atoms substitute for the N atoms in the nano-sized crystalline Mo 2N to form Mo 2N(C) solid solution phase and the microstructure of the Mo–Si–C–N coatings may be nano-sized crystalline Mo 2N(C) embedded in the amorphous SiNx and CNx phases.

Assessing Nanotribological Performance and Surface Energies of Inconel-ZrN, Cr-ZrN, Nb-ZrN, and ZrN Thin Films

The nanotribological performance for three groups of metal-ZrN, including Inconel-ZrN, Cr-ZrN, Nb-ZrN, and polycrystalline ZrN thin films has been investigated and results were correlated with surface energy evaluations. Metal-ZrN and ZrN thin films were deposited using direct current (DC) unbalanced magnetron sputtering and their elemental composition was investigated using X-ray photoelectron spectroscopy (XPS). Both nanomechanical and nanotribological properties were evaluated using a triboscope interfaced with an atomic force microscope (AFM) and the surface energies were calculated from the contact angle measurements. The present research reports for the first time on the nanowear behavior, surface roughness, and friction coefficients correlated with surface energies of metal-ZrN and ZrN thin films. All metal-ZrN thin films showed improved nanotribological performance compared to the polycrystalline ZrN. Results indicate that several of the Inconel-ZrN thin film compositions have both superior nanotribological behavior and good wettability and thus have high potential use for wear resistant applications.

Deposition and characterization of TiAlSiN nanocomposite coatings prepared by reactive pulsed direct current unbalanced magnetron sputtering

This work reports the performance of high speed steel drill bits coated with TiAlSiN nanocomposite coating at different Si contents (5.5–8.1 at.%) prepared using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. The surface morphology of the as-deposited coatings was characterized using field emission scanning electron microscopy. The crystallographic structure, chemical composition and bonding structure were evaluated using X-ray diffraction, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, respectively. The corrosion behavior, mechanical properties and thermal stability of TiAlSiN nanocomposite coatings were also studied using potentiodynamic polarization, nanoindentation and Raman spectroscopy, respectively. The TiAlSiN coating thickness was approximately 2.5–2.9 μm. These coatings exhibited a maximum hardness of 38 GPa at a silicon content of approximately 6.9 at.% and were stable in air up to 850 °C. For the performance evaluation, the TiAlSiN coated drills were tested under accelerated machining conditions by drilling a 12 mm thick 304 stainless steel plate. Under dry conditions the uncoated drill bits failed after drilling 50 holes, whereas, TiAlSiN coated drill bits (Si = 5.5 at.%) drilled 714 holes before failure. Results indicated that for TiAlSiN coated drill bits the tool life increased by a factor of more than 14.

Deposition of TiAlN coatings using reactive bipolar-pulsed direct current unbalanced magnetron sputtering

We have deposited TiAlN coatings on high-speed steel (HSS) drill bits, silicon and mild steel substrates using a four-cathode reactive direct current (DC) unbalanced magnetron sputtering system. Asymmetric bipolar-pulsed DC generators have been used to deposit TiAlN coatings from the reactive sputtering of Ti and Al targets in N 2 + Ar plasma. Various treatments have been given to the substrates for improved adhesion of the TiAlN coatings. The process parameters have been optimized to achieve highly adherent good quality TiAlN coatings. These coatings have been characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, nanoindentation, atomic force microscopy, wear tester, potentiodynamic polarization techniques. The performance of the TiAlN coated HSS drill bits is evaluated by drilling a 13-mm thick 304 stainless steel plate, which is considered to be difficult to machine material. The performance evaluation tests have been carried out with and without coolant. The results show significant improvement in the performance of the TiAlN coated HSS drill bits. Furthermore, it has been shown that dry drilling of 304 stainless steel plate is possible with TiAlN coated HSS drill bits. Improvement in the performance of TiAlN coated tools has been attributed to excellent high temperature oxidation resistance and corrosion resistance of TiAlN coatings.

Influence of sulfidation treatment on the structure and tribological properties of nitrogen-doped diamond-like carbon films

The nitrogen-doped diamond-like carbon (DLC) films were deposited on high speed steel (HSS) substrates in the direct current unbalanced magnetron sputtering system. Sulphurized layer was formed on the surface of DLC films by means of liquid sulfidation in the intermixture of urea and thiourea solution in order to improve the tribological properties of DLC films. The influence of sulfidation treatment on the structure and tribological properties of DLC films was investigated in this work. The structure and wear surface morphology of DLC films were analyzed by Raman spectroscopy, XPS and SEM, respectively. It reveals that the treated films are smooth and uniform; and sulfur atoms are bonded chemically. The treated films have broader distribution of Raman spectra in the range of 1000–1800 cm −1 and higher I D/ I G ratio than the untreated films as a result of the appearance of the crystalline graphite structure after the sulfidation treatment. It is showed that the sp 2 relative content increase in the treated films from the XPS measurement. The Raman results are consistent with the XPS results. The tribological properties of DLC films were investigated using a ball-on-disk rotating friction and wear tester under dry friction conditions. It is found that the sulfidation concentration plays an important part in the tribological properties of the treated DLC films. The results showed the treated films with low sulfidation concentration have a lower friction coefficient (0.1) than the treated films with high sulfidation concentration (0.26) and the untreated films (0.27) under the same friction testing conditions, which can be attributed to both the presence of sulfur-containing materials and the forming of the mechanical alloyed layer on the wear surface. Adding the dry nitrogen to the sliding surface in the testing system helps the friction coefficient of the treated films with low sulfidation concentration to decrease to 0.04 further in this work. On the basis of the experimental results, it is indicated that the liquid sulfidation technique, which is low-cost, non-polluting and convenience, would be an appropriate method for the surface treatment of DLC films.

Performance evaluation of reactive direct current unbalanced magnetron sputter deposited nanostructured TiN coated high-speed steel drill bits

The stainless steels, in general, are considered to be difficult-to-machine materials. In order to machine these materials the surface of the tool is generally coated with physical vapour deposition (PVD) hard coatings such as titanium nitride (TiN), titanium aluminum nitride (TiAlN), etc. The adhesion is of vital importance for the performance of tools coated with PVD coatings. Proper surface treatments (in situ and ex situ) are required to achieve highly adherent PVD coatings on tools. We have deposited nanostructured TiN coatings on high-speed steel (HSS) drill bits and mild steel substrates using an indigenously built semi-industrial four-cathode reactive direct current (d.c.) unbalanced magnetron sputtering system. Various treatments have been given to the substrates for improved adhesion of the TiN coatings. The process parameters have been optimized to achieve highly adherent thick good quality TiN coatings. These coatings have been characterized using X-ray diffraction, nanoindentation and atomic force microscopy techniques. The performance of the coated HSS drill bits is evaluated by drilling a 13 mm thick 304 stainless steel plate under wet conditions. The results show significant improvement in the performance of the TiN coated HSS drill bits.

Growth and characterization of aluminum nitride coatings prepared by pulsed-direct current reactive unbalanced magnetron sputtering

Approximately 2.2 μm thick aluminum nitride (AlN) thin films were deposited on silicon and glass substrates using a reactive direct current (DC) unbalanced magnetron sputtering system. Two asymmetric bipolar-pulsed DC generators were used to sputter the aluminum targets in Ar + N 2 plasma. The AlN coatings were deposited at different substrate bias voltages, substrate temperatures and nitrogen flow rates. The coatings were characterized using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy, ellipsometry and nanoindentation techniques. Peaks corresponding to (100), (002), (101) and (102) planes of hexagonal AlN were observed in the XRD data, indicating polycrystalline nature of the AlN coatings. The Raman data showed broad peaks corresponding to E 2 and A 1 (transverse optic) modes of hexagonal AlN. The N 1 s and the Al 2 p 3/2 XPS spectra confirmed the formation of AlN phase. The AlN coating deposited under the optimized process conditions exhibited an average nanoindentation hardness of 12 GPa and an elastic modulus of 225 GPa. The refractive index of the AlN coating was found to be in the range 1.94–2.11 in the wavelength region of 300–1200 nm and the extinction coefficient was almost zero throughout the wavelength range.

Deposition and characterization of CrN/Si 3N 4 and CrAlN/Si 3N 4 nanocomposite coatings prepared using reactive DC unbalanced magnetron sputtering

Nanocomposite coatings of CrN/Si 3N 4 and CrAlN/Si 3N 4 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 + N 2 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/Si 3N 4 and CrAlN/Si 3N 4 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/Si 3N 4 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/Si 3N 4 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/Si 3N 4 and CrAlN/Si 3N 4 nanocomposite coatings, with a silicon content of approximately 7.5 at.% were thermally stable up to 700 and 900 °C, respectively.

The Structure and Mechanical Properties of Ti-Si-B Coatings Deposited by DC and Pulsed-DC Unbalanced Magnetron Sputtering

The structure and mechanical properties of direct current (DC) and pulsed-DC unbalanced magnetron-sputtered Ti-Si-B thin films—hard coatings with the potential for excellent thermal stability and oxidation resistance—are investigated and reported in this paper. The coatings were deposited from composite sputter targets of titanium silicide/boride produced by self-propagating high-temperature synthesis (SHS), a novel and cost-effective technique to produce bulk materials of complex compositions which are difficult to synthesise by other means. Hard (up to 37 GPa) Ti-Si-B coatings possessing amorphous, nanocrystalline and crystalline structures were deposited. The application of pulsed magnetron sputtering (PMS) was found to affect significantly the coating properties such as structure, thickness, hardness (H), reduced elastic modulus (Er) and thus H/Er ratio.

Deposition and characterization of TiAlN/Si 3N 4 superhard nanocomposite coatings prepared by reactive direct current unbalanced magnetron sputtering

Superhard nanocomposite coatings of TiAlN/Si 3N 4 with varying silicon contents were synthesized using reactive direct current (DC) unbalanced magnetron sputtering. The Si and TiAl targets were sputtered using an asymmetric bipolar-pulsed DC power supply and a DC power supply, respectively, in Ar+N 2 plasma. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The elemental composition of the TiAlN/Si 3N 4 nanocomposite coatings was determined using energy-dispersive X-ray analysis and the bonding structure was characterized by X-ray photoelectron spectroscopy. The surface morphology of the coatings was studied using atomic force microscopy. The XRD data showed that the nanocomposite coatings exhibited (1 1 1) and (2 0 0) reflections of cubic TiAlN phase. The broadening of the diffraction peaks with an increase in the silicon content in the nanocomposite coatings, suggested a decrease in the average crystallite size. The TiAlN/Si 3N 4 nanocomposite coatings exhibited a maximum hardness of 43 GPa and an elastic modulus of 350 GPa at a silicon concentration of approximately 11 at%. The hardness and the elastic modulus of the nanocomposite coatings decreased significantly at higher silicon contents. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (400–850 °C) and in vacuum (900 °C). The Raman data of the nanocomposite coatings annealed in air and vacuum showed better thermal stability as compared to that of the TiAlN coatings. Similarly, the nanocomposite coatings deposited on mild steel substrates exhibited improved corrosion resistance.

Investigation of nanostructure evolution and twinning of nanocrystallites in Ti–B x–N y nanocomposite thin films deposited by magnetron sputtering at low temperature by means of HRTEM and Monte Carlo simulations

Nanostructure evolution and deformation of nanocrystallites in Ti–B x –N y thin films with different B contents were investigated using high-resolution transmission electron microscopy, X-ray diffraction and Monte Carlo simulations. The Ti–B x –N y films were deposited on unheated Si (1 0 0) substrates by reactive unbalanced direct current magnetron sputtering in an Ar–N 2 gas mixture. The results indicated that pure TiN films contained well-crystallized nanocrystallites, while incorporation of B into TiN led to the formation of nanocomposite thin films of nanocrystalline (nc) Ti(N,B) grains embedded in amorphous TiB 2–BN matrices. When the B content was relatively low (about 16 at.%), two differently sized nanocrystallites with average grain sizes of about 9 and 3 nm, respectively formed. Addition of more B (27 at.% or more) produced smaller and more uniform nanocrystallites, followed by a decrease in the distribution density of nanocrystallites in the amorphous matrix. With increasing B content, more [0 0 2]-oriented grains were formed, accompanied by a gradual decrease in grain size of the nanocrystallites. Twinning deformations were found to occur in nanocrystallites with incorporation of B, and were further activated with increasing B content, which was attributed to the decrease in grain size with B content and the formation of solid solution nc-Ti(N,B) via incorporation of B into the TiN lattice. Using Monte Carlo simulations, the effects of the mixed amorphous TiB 2–BN phase on microstructure evolution and grain growth in nc-Ti(N,B) were also studied. The results indicated that the formation of such an amorphous phase at the grain boundary could hinder the growth of Ti(N,B) grains and the mean grain size showed an exponential decay with boron concentration, in good agreement with our experimental observations.

Superhard nanocomposite coatings of TiN/Si 3N 4 prepared by reactive direct current unbalanced magnetron sputtering

Approximately 1.5-μm-thick superhard nanocomposite coatings of TiN/Si 3N 4 with varying silicon contents were deposited on silicon and stainless steel (SS 304) substrates by reactive direct current (DC) unbalanced magnetron sputtering. An asymmetric bipolar-pulsed DC power supply and a DC power supply were used to sputter Si and Ti targets, respectively in Ar + N 2 plasma. Structural characterization of the coatings was done using X-ray diffraction (XRD). The bonding structure of the nanocomposite coatings was characterized by X-ray photoelectron spectroscopy (XPS). The elemental composition of the TiN/Si 3N 4 nanocomposite coatings was determined using energy dispersive X-ray analysis. The mechanical properties of the coatings were measured using a nanoindentation hardness tester. The surface morphology of the coatings was studied using atomic force microscopy. The nanocomposite coatings exhibited a broad (200) reflection of cubic TiN phase in the XRD data. There was a significant broadening of the (200) reflection with an increase in the silicon content in the nanocomposite coatings, which suggested a decrease in the average crystallite size. Nanoindentation data showed that about 1.5-μm-thick TiN/Si 3N 4 nanocomposite coatings exhibited a maximum hardness of 5200 kg/mm 2 and an elastic modulus of 340 GPa at a silicon concentration of approximately 12 at.%. The hardness and the elastic modulus of the nanocomposite coatings decreased with further increase in the silicon content. Structural changes as a result of heating (400–850 °C) of the nanocomposite coatings in air were characterized using micro-Raman spectroscopy. The Raman data showed that the nanocomposite coatings started to oxidize at 800 °C as compared to TiN, which have been oxidized even at 500 °C. To isolate the oxidation-induced spectral changes as a result of heating of the coatings in air, the samples were also annealed in vacuum at 850 °C under similar conditions. The Raman data of the vacuum-annealed coatings showed no phase transformation even after annealing up to 850 °C. The corrosion behaviors of single-phase TiN and TiN/Si 3N 4 nanocomposite coatings deposited on stainless steel substrates were investigated using potentiodynamic polarization in 3.5% NaCl solution. The results indicated that the nanocomposite coatings exhibited superior corrosion resistance as compared to the uncoated substrate. The wear data showed that the nanocomposite coatings also exhibited better wear resistance as compared to the uncoated substrate.

Residual stresses in titanium nitride thin films deposited by direct current and pulsed direct current unbalanced magnetron sputtering

This work presents a study on the effect of deposition parameters on the residual stresses developed in titanium nitride (TiN) thin films deposited onto cemented carbide (WC-Co) substrates. Depositions were conducted by reactive unbalanced magnetron sputtering of a single titanium target. Six different conditions were selected, varying parameters such as bias (0, − 50 or − 100 V), power applied to the target (direct current or pulsed direct current) and, in the cases where substrate bias was zero, substrate condition (ground or floating). Pulsed power was applied at a frequency of 50 kHz and with a reverse pulse time of 1 μs. Residual stresses were evaluated through X-ray diffraction, using the sin 2 ψ method. Results confirmed the effect of substrate bias on the residual stresses of thin films. Additionally, it was possible to observe that by pulsing the power to the target, residual stress varies as a consequence of the increased ion energy.