No abstract

Nanostructured TiCrN films were grown on Si (100) wafers by reactive DC unbalanced magnetron cosputtering technique without external heating and voltage biasing to the substrates. The effects of Ti sputtering current on the chemical composition, chemical state, electronic structure, crystal structure, and morphology of the TiCrN films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FE-SEM), respectively. The results showed that all prepared films were formed as an understoichiometric (Ti, Cr)N solid solution with the fcc B1 type phase. The films exhibited a nanostructure with a crystallite size of less than 14 nm. The deconvolution of XPS spectra revealed the chemical bonding between Ti, Cr, N, and O elements. The addition of Ti contents led to the decrease of valence electrons filled in the d conduction bands which result in the change of binding energy of electrons in core levels. The roughness of the films was found to increase with increasingITi. The cross-sectional morphology of the films showed columnar structure with dome tops.

Silver tantalate (AgTaO 3 ) coatings have been found to exhibit outstanding tribological properties at elevated temperatures. To understand the mechanisms involved in the tribological behavior of the Ag-Ta-O system, tantalum oxide coatings with a small content of silver were produced to investigate the metastable nature of this self-lubricating material. The coatings were produced by unbalanced magnetron sputtering, ball-on-disk wear tested at 750 C, and subsequently characterized by X-ray diffraction, Scanning Auger Nanoprobe, cross-sectional Scanning Electron Microscopy, and Transmission Electron Microscopy. Complementary molecular dynamic simulations were carried out to investigate changes in the chemical and structural properties at the interface due to sliding for films with varying silver content. Both the experimental characterization and the theoretical modeling showed that silver content affects friction and wear, through the role of silver in film reconstruction during sliding. The results suggest that the relative amount of silver may be used to tune film performance for a given application. V C 2014 AIP Publishing LLC. It is well established that high temperature working environments are still a major challenge for the tribology community. Oxidation of the commonly-used solid lubricants, such as MoS 2 and graphite, has hampered their use at elevated temperatures due to the degradation of material properties. 1 Solid lubricants that have been reported in the literature as well as used in industry when the temperature exceeds $300 C include noble metals, alkaline halides, Magn eli phases, and ternary oxides (also termed binary metal oxides).2 These systems usually exhibit friction coefficients in the range of 0.1-0.4, depending on the selected material, working temperature, and load. For more detailed information on the properties of these materials as high temperature solid lubricants, the reader is encouraged to refer to the following review articles. [3][4][5][6] Very recently, silver tantalate (AgTaO 3 ) was reported to be a promising lubricant material at elevated temperatures. 7,8 The measured coefficient of friction (CoF) at 750 C was found to be as low as 0.04-0.06 in two recent studies conducted by our group. Additionally, transmission electron microscopy (TEM) revealed that the AgTaO 3 phase produced clusters of silver surrounded by Ta 2 O 5 near the surface, where the applied stress was presumed to attain its maximum values. These features were reproduced in molecular dynamics (MD) simulations, 8,9 and results indicated that the lubricious nature of AgTaO 3 at high temperatures was enabled by the joint contributions of the hard Ta 2 O 5 phase and lubricious silver clusters in the shear-and temperature-induced surface layer. Theoretical and experimental cross-sectional images of the coatings in the wear track revealed that the presence of Ta 2 O 5 and silver increased dramatically closer to the interface whereas the remainder of the coating consisted primarily of AgTaO 3 with a very small amo...

No abstract

No abstract