Tailored synthesis of TiC∕a-C nanocomposite tribological coatings

Abstract

Composite coatings made of nanocrystalline TiC ͑nc-TiC͒ particles and amorphous carbon ͑a-C͒ have been prepared in a double magnetron sputtering system using graphite and titanium targets under Ar bombardment. Chemical composition and microstructure of coatings were studied by transmission electron microscopy ͑TEM͒, electron energy loss spectroscopy ͑EELS͒, and x-ray diffraction ͑XRD͒ for a set of samples prepared varying the ratio and intensity of power applied to each magnetron. Changes in coatings microstructure, from a quasipolycrystalline TiC to a nanocomposite formed by nanocrystals of TiC embedded in an amorphous matrix of carbon ͑nc-TiC / a-C͒, are observed depending on the synthesis conditions. Tribological and mechanical properties of coatings were tested using a pin-on-disk tribometer and an ultramicrohardness indenter, respectively. Coatings with moderate hardness ͑7-27 GPa͒, low friction ͑0.1-0.2͒, and low wear rates ͑k ϳ 10 −7 mm 3 /N m͒ were obtained. A percentage between 15% and 30% of TiC is found as an optimum value to get a good compromise between good mechanical and tribological properties. Finally, a mapping of the mechanical and tribological properties of the nc-TiC / a-C system is presented for the synthesis conditions employed.

Microstructure evolution of Ti–Si–C–Ag nanocomposite coatings deposited by DC magnetron sputtering

“…Figure 5a, and reference 32 ). With increased C content for a given Ti content, the maximum C fraction in the TiC x phase (x ~0.47-0.97) [32,33] is exceeded, which triggers a phase separation into TiC and C, in the case of no Si [4,5,11] or SiC (in the present case). The observation from Figure 5 and XPS indicates that the amorphous SiC phase has a much more limited diffusivity of Ag and TiC than amorphous Si and C. Thus, the emerging TiC and Ag crystallites may become covered by the amorphous matrix more frequently.…”

“…TiC-based nanocomposites have been studied intensively during the last decade and are well known as tribological coatings [1,2,3,4,5,6]. They have recently also been adopted in electrical applications [ 7 , 8 , 9 , 10 ].…”

Control of crystallinity in sputtered Cr–Ti–C films

“…Typically, the group IV metals Ti, Zr, and Hf form crystalline films although the carbide often is present as nano-sized crystallites in an amorphous carbon (a-C) matrix, depending of the C content. The properties of these nanocomposites are typically affected by the relative amount of a hard carbide phase in a softer a-C matrix [4][5][6][7]. For the 3d transition metals, the tendency to form amorphous films increases with increasing number of d-electrons in the metal and sputtered Cr-C and Fe-C films are therefore often amorphous [8][9][10][11].…”

High-rate deposition of amorphous and nanocomposite Ti–Si–C multifunctional coatings

“…Another unsatisfactory condition is that electroplating of gold often requires preparation steps that are not environmentally friendly. TiC-based nanocomposite coatings are well known from tribological applications [5,6,7,8,9,10], but have only recently been adopted for electrical contacts [ 11,12,13,14,15 ]. Ti-Si-C based nanocomposites are particularly relevant, since these nanocomposites have been demonstrated to combine their known mechanical strength and low coefficient of friction [9,16,17,18,19,20,21] with high conductivity and low contact resistance [11,15].…”