Structure characterization and tribological study of magnetron sputtered nanocomposite nc-TiAlV(N,C)/a-C coatings

Abstract

Grown by reactive unbalanced magnetron sputtering in a mixed N2 and CH4 gaseous medium, heterogeneous nanocomposite coatings in the Ti-Al-V-N-C system show extraordinarily excellent tribological performance of coated machining tools. Using analytical high resolution TEM, EELS, FEG-SEM, XRD, and Raman spectroscopy, this paper reports detailed structural and chemical characterization of the coatings grown at various CH4: N2 ratios. Meanwhile, the mechanical and tribological properties were also measured, including hardness, Young's modulus, residual stress and the dry-sliding friction and wear at varying environmental humidity. When CH4 gas was introduced in the deposition, the structure of the coatings has been found to experience a change from nano-scale TiAlN-VN multilayer architecture to a complex mixture of columnar grains of nc-TiAlV(N,C)/a-C nanocomposites and inter-column network of sp 2 -type amorphous carbon. Carbon incorporation and segregation also shows remarkable influence on the columnar growth model by leading to finer grain size. As compared to the carbon-free nitride coating, the nanocomposite coatings showed substantially reduced residual stress owing to the freecarbon precipitation, whereas the coatings maintained comparable hardness to the carbon-free TiAlN/VN. Their tribological properties were found to be strongly dependent on the environment. In humid air at RH > 30%, the coatings showed low friction coefficient less than 0.4 and extremely low wear rate at a scale of ~10 -17 m 3 N -1 m -1 .

Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

“…[1][2][3][4][5][6][7][8][9][10] However, their limitations are low toughness and high internal stress levels. [11][12][13] Thus, the design and development of high hardness, high wear resistance, low friction, good toughness and low internal stress level coatings, which will result in a significant increase in the lifetime of mechanical components, are of most importance in fundamental research and industrial applications.…”

Electron Microscopy and Spectroscopy in the Analysis of Friction and Wear Mechanisms

“…Such tribofilm exhibited varied friction coefficient highly dependent on the testing temperature and on the relative humidity. Such environment-dependent friction behaviour has also been found in carbon-containing nitride coating TiAlV(N,C)/a-C [28]. The characterization of wear debris and tribofilms has provided explanations to these phenomena.…”

“…In view of the wear property, tribofilms have also been found to change the stress distribution on the wear contact zone and to be associated with the deformation of the top worn surface [15][16][17][18][19][20]. The friction behaviour of the tribofilms is related not only to the sliding materials themselves, but also to the participation of environmental species, such as oxygen and hydro-oxygen (water) [11,27,28].…”

“…In particular, TEM provides a powerful analytical tool in the characterization of nano-structured transition metal nitride coatings, such the multilayer TiAlN/VN coatings [41][42][43][44][45]. In addition, TEM based spectroscopic chemical analyses are superior to SEM-EDX in detecting light elements, including EDX and electron energy loss spectroscopy (EELS) [14,23,25,27,28,[46][47][48][49][50]. Therefore, TEM has become a platform of several advanced nano/atomic scale characterizations.…”

From Micro to Nano Scales -Recent Progress in the Characterization of Nitrided Austenitic Stainless Steels

“…Recently, the present author has employed EELS and ELNES in the characterization of nanocomposite coatings and wear induced tribo-chemical reactions [95][96][97][98], which not only demonstrated energy resolution in detecting light elements, like carbon, nitrogen and oxygen, but also evidenced the occurrence of sliding-induced oxidation of the nitrides. Therefore, we expect that EELS or ELNES analysis will be a useful tool in characterization of nitride steels.…”