Closed-field Magnetron Sputtering Research Articles

Tribocorrosion properties of CrMoN/Ag coatings with various Ag contents in seawater

CrMoN/Ag coatings with various Ag contents were deposited on Ti6Al4V alloys using closed-field magnetron sputtering technique, and their mechanical and tribocorrosion properties were investigated using nanoindentation and tribocorrosion testers, respectively. Additionally, the wear tracks of the coatings were observed and analyzed using scan probe microscope (SPM), scanning electron microscope (SEM) and Raman spectroscopy. The results indicate that the hardness of the coating initially rises and subsequently declines with the increase of Ag content, and reaches the maximum value of 25.4 ± 1.4 GPa at an Ag content of 1.87 at.%. The CrMoN/Ag coating with Ag content of 1.87 at.% has a denser cross-section and lower surface roughness, showing relatively excellent tribocorrosion performance. In addition, CrMoN/Ag coatings with different Ag contents exhibited varying tribocorrosion mechanisms in seawater.

Microstructure and electrochemical characteristics of CrMoN/Ag nanocomposite coatings in seawater

CrMoN/Ag nanocomposite coatings with various Ag contents are deposited on Ti6Al4V alloys using closed-field magnetron sputtering, and their microstructures are detected by XRD, XPS and TEM. The electrochemical characteristics of CrMoN/Ag nanocomposite coatings are investigated using a three-electrode electrochemical workstation. The results show that the phase structure of coating contains (Cr, Mo)N solid solution and Ag crystallites. As the Ag content rises from 0.21 at.% to 4.86 at.%, the amount and size of Ag nanoparticle increase on the coating surface, and the cross-section feature of coating first becomes dense and then sparse. The corrosion resistance of coating in seawater is mainly dominated by its cross-section compactness and the amount of electrochemical active Ag. When the Ag content is 0.59 at.%, the dense cross-section and low surface roughness of coating contribute to its maximum open circuit potential of 0.173 V and charge transfer resistance Rct of 6.497 × 107 Ω∙cm2. But as the Ag content rises beyond 1.87 at.%, the potential drift range and power spectral density of coating gradually increase. Due to the occurrences of nanogalvanic corrosion and pitting corrosion, the corrosion resistance of coating is deteriorated, and then the corrosion current density icorr of coating continuously raises.

Structure and Characterization of TiC/GLC Multilayered Films with Various Bilayers Periods

The spontaneously self-organizing multilayered graphite-like carbon (denoted as GLC) /TiC films with various bilayer periods in the range of 13.3–17.5 nm were deposited on silicon and 1Cr18Mn8Ni5N stainless steel substrates using closed field magnetron sputtering deposition facility. The microstructures and chemical compositions of the prepared multilayered films were characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy respectively. The self-organizing multilayered structures in all of the films consisted of titanium carbide layers and sp2-rich carbon layers periodically alternate arrangement. The TiC contents and bilayer periods of the multilayered films can be controlled by means of adjusting of sputtering current of graphite target. Furthermore, the mechanical and tribological performances of the prepared films were appraised by nano-indentor, scratch measures, and ball-on-plate tribometer respectively. The results indicated that multilayer structure endowed the as-deposited TiC/GLC films outstanding mechanical and tribological properties, especially the multilayer film with 15.9 nm bilayer period deposited at 10 A sputtering current showed the excellent adhesion strength and hardness; Simultaneously it also exhibited the lowest average friction coefficient in the humid environment owing to its high content of sp2 hybrid carbon.

Influence of Ag target current on the structure and tribological properties of CrMoSiCN/Ag coatings in air and water

CrMoSiCN/Ag coatings with various Ag contents were deposited using unbalanced closed-field magnetron sputtering by adjusting Ag target current. There were (Cr, Mo)N solid solution, Ag nano-crystals and amorphous Si-C-N in coatings. As Ag target current increased, the morphological characteristics were changed from refined grains to agglomerate Ag particles on surfaces, and then the surface roughness of coatings increased, while the coating hardness first raised and then declined, while the contact angles of water on coatings decreased. When Ag target current was 0.4 A, the coating presented the lowest friction coefficient and lowest wear rate. The friction-reduced mechanism of CrMoSiCN/Ag coatings with high Ag content was due to the tribo-layer of Ag, MoO3 and Ag2MoO4 in air and hydroxide in water.

Conversion of amorphous TiO2 coatings into their crystalline form using a novel microwave plasma treatment

Crystalline titanium dioxide (TiO2) coatings have been widely used in photo-electrochemical solar cell applications. In this study, TiO2 and carbon-doped TiO2 coatings were deposited onto unheated titanium and silicon wafer substrates using a DC closed-field magnetron sputtering system. The resultant coatings had an amorphous structure and a post-deposition heat treatment is required to convert this amorphous structure into the photoactive crystalline phase(s) of TiO2. This study investigates the use of a microwave plasma heat treatment as a means of achieving this crystalline conversion. The treatment involved placing the sputtered coatings into a 2.45GHz microwave-induced nitrogen plasma where they were heated to approximately 550°C. It was observed that for treatment times as short as 1min, the 0.25-μm thick coatings were converted into the anatase crystalline phase of TiO2. The coatings were further transformed into the rutile crystalline phase after treatments at higher temperatures. The doping of TiO2 with carbon was found to result in a reduction in this phase transformation temperature, with higher level of doping (up to 5.8% in this study) leading to lower anatase-to-rutile transition temperature. The photoactivity performance of both doped and un-doped coatings heat-treated using both furnace and microwave plasma was compared. The carbon-doped TiO2 exhibited a 29% increase in photocurrent density compared to that observed for the un-doped coating. Comparing carbon-doped coatings heat-treated using the furnace and microwave plasma, it was observed that the latter yielded a 19% increase in photocurrent density. This enhanced performance may be correlated to the differences in the coatings' surface morphology and band gap energy, both of which influence the coatings' photoabsorption efficiency.

Microstructure and mechanical properties of multi-constituent superlattice coatings

Superlattice nitride coatings with four different layer constituents, i.e., ZrN, MoN, NbN and AlN, were synthesized using an unbalanced closed-field magnetron sputtering coater. At small superlattice modulation periods, both MoN and AlN layers adapted to the cubic B1 structure due to a template effect, and the coatings exhibited a strong (2 0 0) preferred orientation. Increasing the modulation period above a critical value led to the formation of hexagonal MoN and AlN layers with diminishing (2 0 0) preferred orientation. These microstructure changes were reflected in the coating mechanical properties. Relatively high hardness and Young's modulus values were obtained at small modulation periods, which decreased dramatically above the critical modulation period. The effects of substrate bias on the layer crystallographic structure, coating preferred orientation and mechanical properties were similar to those of the modulation period.

Effect of ferromagnetic substrates on the film growth in magnetized plasma systems

We found substantial differences in TiN films on austenite (non-ferromagnetic) and martensite (ferromagnetic) steel substrates. The films were grown by the reactive PVD in a magnetized M–M (Magnets-in-Motion) linear hollow cathode plasma as well as in a hybrid M–M hollow cathode and microwave ECR plasma system. The martensite steel substrates can, depending on their position and shape, deform the magnetic field of the plasma PVD source and create a certain kind of “bypass” channel for magnetic field lines causing acceleration of charged particles towards the substrate surface. This leads to a considerable enhancement of the particle bombardment of the surface of the martensite steel substrates as compared to non-ferromagnetic substrates already at ground potential. The ion bombardment affects texture and morphology of the growing TiN film. It was found that the substrate bias can control the particle bombardment and compensate the effect of substrate in the film growth at considerable extent. We have also found that, although the observed effect is of particular importance for very high-density plasmas generated by the magnetized hollow cathodes, it also affects the film growth even in conventional closed-field magnetron sputtering systems.

Microstructure, mechanical and tribological properties of novel multi-component nanolayered nitride coatings

Novel multi-component nanolayered nitride coatings composed of four alternating layer constituents in a modulation period ( Λ), i.e., TiN, Mo 2N, ZrN and AlN, were synthesized using the unbalanced closed-field magnetron sputtering technique. The microstructural evolution and mechanical properties of the coatings were investigated over a wide range of the modulation period. X-ray diffraction analysis indicated that at the smallest Λ of 1.8 nm, all the layer constituents formed a single cubic structure, with a lattice constant near the average of the individual constituents. In addition, a moderate (200) preferred orientation was observed in this condition. With increasing modulation period, the preferred orientation diminished and the cubic structure evolved to form hexagonal AlN layers, followed by the formation of crystallographic equilibrium structures of the individual constituents at Λ larger than 20 nm. These microstructural changes had a direct influence on the hardness ( H) and Young's modulus ( E) of the coatings. The maximum hardness of 34.0 GPa, which was considerably higher than the rule-of-mixture hardness of the constituent layers, was obtained at Λ = 31.1 nm. The coatings exhibited lower Young's modulus and significantly higher H 3/ E 2 ratios than the monolayered TiN coating. Dry sliding tests demonstrated that these coatings had a lower coefficient of friction and higher dry sliding wear resistance than TiN coating.

Deposition and characterization of hard-solid lubricant coating by closed-field magnetron sputtering

Thin hard coatings (i.e., TiN, CrN, TiAlN etc.) have been widely accepted particularly in the cutting and forming tool industries. But many of these coatings have higher co-efficient of friction, which does not protect the opposing surface and sometimes in a closed system, the eroded hard coating particles act like grits which propagate the failure of the coatings before the expected time. Recently, hard-solid lubricating coating has been investigated to lower the wear rate and coefficient of friction by the combined effect of soft and hard phases. In the present investigation, TiN+MoSx hard-solid lubricant coating was deposited by closed-field magnetron sputtering from separate Ti and MoS2 target in a N2 gas environment. EDX analysis showed different weight percentages of Mo+S in the TiN+MoSx coatings deposited with different MoSx target currents. In the XRD study, peaks shifting to lower angles compared to pure TiN indicated the incorporation of Mo and S atoms in the TiN matrix. Adhesion was also improved in the TiN+MoSx coatings. Pin-on-disk measurements at normal atmospheric condition against WC ball showed much lower wear and coefficient of friction compared to pure TiN coating.

The influence of ball size on tribological behaviour of MoS 2 coating tested on a ball-on-disk wear rig

The effect of ball diameter on wear and friction of a molybdenum disulphide (MoS 2) coating deposited using the closed-field magnetron sputtering technique has been investigated on a ball-on-disk wear rig sliding against uncoated steel ball-bearing balls. It was observed that the wear rate of the coating decreased significantly with increase in ball diameter. Correspondingly, the average friction coefficient in the steady state of sliding increased with increase in ball diameter. Under the present experimental conditions, the effect of ball size on wear and friction of the coating vanished when the diameter of the ball exceeded 6.35 mm. This phenomenon is thought to be a result of wear mode transition as a function of contact pressure at the apparent area of contact from a low-rate ‘mild’ wear regime to a high-rate ‘severe’ wear regime when the contact pressure exceeds some critical value. Simulation results using a previously presented model based on the above assumption showed a good agreement with the experimental observations.

The tribological properties of MoS 2/metal composite coatings deposited by closed field magnetron sputtering

MoS 2 coatings deposited by closed field magnetron sputtering are dense and adherent and have certain superior tribological properties compared to coatings deposited by other techniques. The properties can be further improved by the co-deposition of small amounts of metal with the MoS 2. The results of scratch adhesion, pin-on-disc and reciprocating wear tests are reported and compared to those from earlier coatings. A number of practical applications are given and, in particular, large improvements in the performance of cutting tools are reported.