J. J. Nainaparampil

Microstructure and vacuum tribology of TiC-Ag composite coatings deposited by magnetron sputtering-pulsed laser deposition

Abstract Composite titanium carbide–silver films have been co-deposited by magnetron sputtering-pulsed laser deposition (MSPLD) to study their friction and wear properties in vacuum. The films deposited were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The silver content in the films ranged from 6 to 46 at.%. Structural characterization of the films revealed that Ag had a nano-crystalline structure when dispersed in the film, but larger crystallites of Ag (∼50–200 nm) also formed on the surface. Films with higher Ag contents showed evidence of higher diffusion rates, leading to a coarser structure and greater surface coverage. Pin-on-disk friction tests were performed under vacuum to observe the friction and wear behavior of these films. Friction was lower with higher Ag content, but wear was higher; the optimal Ag concentration was found to be 15%. SEM images from the surface of the films and wear tracks were obtained to understand the morphology of this type of composite ceramic coating, and revealed Ag layers in the wear track elongated in the direction of wear. Based on these results, the significance of silver as a friction-reducing agent in vacuum environments was demonstrated.

Structural and mechanical properties of TiC and Ti-Si-C films deposited by pulsed laser deposition

TiC and Ti–Si–C films have been deposited by pulsed laser deposition at substrate temperatures ranging from room temperature to 600 °C onto (111) silicon wafers and 440C stainless steel substrates. X-ray diffraction, x-ray photoelectron spectroscopy, and electron microscopy were employed for structural and compositional evaluation of the films, and nano-indentation hardness testing and pin-on-disk wear tests were used to evaluate the mechanical and tribological properties. All the TiC films were highly crystalline except the one deposited at room temperature, whereas for the Ti–Si–C films the degree of crystallinity increased with temperature, ranging from amorphous for the room temperature deposit to about 50% crystalline at 600 °C. The hardness of the TiC films was relatively constant with deposition temperature at about 25 GPa, whereas the hardness of the Ti–Si–C films increased with deposition temperature from 11 to 33 GPa. The temperature dependence of the hardness is attributed to the degree of crys...

Magnetron sputter deposition of WC-Ag and TiC-Ag coatings and their frictional properties in vacuum environments

Abstract Thin films of WC–Ag and TiC–Ag were deposited by magnetron sputtering for the purpose of analyzing their tribological properties in vacuum. X-ray diffraction was used to determine structural properties, and energy dispersive X-ray analysis was used to determine the relative atomic content of silver in the films. Pin on disk friction tests were performed to obtain the coefficient of friction in vacuum. The deposited films showed a structure containing separate carbide/silver phases, as was desired for providing both high wear resistance and low friction. The tribological test results show a significant decrease in the friction coefficient for both TiC–Ag and WC–Ag, to a minimum value of 0.2, with increasing silver content.

Composite coatings incorporating solid lubricant phases

The concept of incorporating a solid lubricant, silver (Ag), within a hard carbide film for vacuum tribology applications is investigated in this paper. SiC/Ag and HfC/Ag films were deposited by magnetron cosputtering at 200 °C onto Si and 440C steel substrates. The composition, phase structure, and morphology in these films was examined using x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The microstructural analysis showed that Ag was incorporated both within and on the surface of the films. There was a strong tendency for Ag to segregate to the film surface. Vacuum tribology tests were conducted using a ball-on-disk test in a vacuum of 1.33 µPa with a 1 N load for 10 000 cycles. For both the SiC/Ag and HfC/Ag films, the average friction coefficients were reduced when sufficient Ag was present. These tests show that carbide-Ag composite films hold promise for vacuum tribology applications.

Mechanical and tribological properties of sub- and superstoichiometric Ti-C and Ti-Si-C films deposited by magnetron sputtering-pulsed laser deposition

The magnetron sputtering–pulsed laser deposition (MSPLD) method has been used to deposit Ti–C and Ti–Si–C films with both sub- and superstoichiometric levels of carbon. The structure and composition of the films were analyzed by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. The mechanical properties were determined by nanoindentation and the tribological properties by pin-on-disk testing. Films deposited with sub- and near stoichiometric levels of carbon had good crystallinity and strong (111) texture. However, films deposited under similar conditions but with a substrate bias resulted in superstoichiometric carbon levels and nanocrystalline or near-amorphous structures. The hardness of these superstoichiometric films was generally lower than the substoichiometric films, but they also exhibited significantly better wear life. The laser power used in the MSPLD process was also found to influence hardness, where increased laser power led to higher hardness levels...

Microstructure Development and the Mechanisms of Lubrication in Magnetron Sputtered HfC-Ag and SiC-Ag Composite Thin Films

A soft thin coating on top of a hard substrate is a highly effective way to reduce friction of sliding mechanical components. However, soft coatings often have high wear and short lifetimes, and the restoring of solid lubricants can be remarkably uneconomical. In our recent work, composite TiC-Ag films were successfully deposited by the magnetron-sputtering pulsed laser deposition technique (MSPLD). Secondary electron (SE) images from the wear tracks revealed that silver migrates to the surface and smears along the sliding direction providing low friction, while the carbide phase provides adequate support and storage for the solid lubricant phase, all resulting in lower wear and longer lifetime. One proposed mechanism for lubrication is the friction-induced thermally activated migration of silver to the surface due to the insolubility of the carbide and silver phases which was corroborated by X-ray diffraction (XRD) analysis. The formation of incoherent interfaces between the two phases, observed by transmission electron microscopy (TEM), may influence the adhesive friction behavior of the soft metal. In this study, we investigate the structural properties and vacuum tribological behavior of SiC-Ag and HfC-Ag films.

Structural and Tribological Properties of TiC/C/Ag Coatings in Vacuum and Ambient Environments

TiC/C/Ag coatings were deposited by magnetron sputtering pulsed laser deposition (MSPLD) combining sputtering from a custom made Ti-Ag (60:40) target with the ablation of carbon. Energy disperse spectroscopy (EDS) was used to determine the elemental composition, and x-ray diffraction (XRD) and cross-sectional scanning electron microscopy (XSEM) to examine the structure of the films. Hardness and reduced modulus measurements were acquired using a nanoindentation technique. The pin-on-disk friction test was used to study the friction behavior of the deposited samples in high vacuum and ambient conditions. Variations in the laser energy and the power of the sputtering gun yielded a set of samples with carbon content that ranged from 15.0 to 95.6 percent. The hardest samples with the highest reduced modulus were those with a moderate carbon content and that were shown to form a titanium carbide phase. Tribological results indicated that there is an optimum composition of a TiC/C/Ag coating (~25 at.% carbon) for which it can be reversible and provide lubrication in both ambient and vacuum.

Structural Properties of Carbon Nitride Films Deposited by Reactive - Pulsed Laser Deposition Technique

Carbon nitride films have been deposited by the reactive pulsed laser deposition technique by ablating carbon in a nitrogen atmosphere at different substrate temperatures and different background pressures of nitrogen. Si(111) and 440C steel substrates were used in the present investigation. Deposited films are uniform and show good adhesion to the substrates. The deposition rates depend on laser fluence, background pressure, and target-substrate distance. The nitrogen concentration in the deposited films increases with increasing background nitrogen gas pressure and laser fluence. Fourier transform infrared spectroscopy has been employed to evaluated CN bonds. X-ray photoelectron spectroscopy has been used to study the composition of the deposited films. X-ray diffraction and atomic force microscopy techniques revealed that the deposited films have an oriented microcrystalline structure after annealing at 900°C with smooth surface. Electronic, mechanical and tribological properties of these films have also been discussed.