Effects of substrate bias voltage on mechanical properties and tribological behaviors of RF sputtered multilayer TiN/CrAlN films Xiao Chen, Yeting Xi, Jie Meng, Xiaolu Pang, Huisheng Yang * School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China article info Article history: Received 28 July 2015 Received in revised form 30 September 2015 Accepted 8 October 2015 Available online 22 October 2015 Keywords: TiN/CrAlN films RF magnetron sputtering Substrate bias Mechanical properties Tribological properties abstract Multilayer brittle TiN/CrAlN films were prepared on polished silicon and high speed steel by RF magnetron sputtering technology with various substrate bias voltages ranging from 0 to 150 V. In this study, the main attention is targeting the correlation between the substrate bias voltage and the resulting mechanicaletribological properties. It is revealed that the films become much denser and more compact with increasing substrate bias, meanwhile, hardness and elastic modulus are correspondingly elevated. However, relatively decreased adhesion emerges when reaching the bias voltage of 150 V. The wear resistance is progressively enhanced while the deposition rate gradually declines as the substrate bias increases. Additionally, the mean values of dry friction coefficients sliding against Si 3 N 4 are in the range of 0.57e0.42, and the wear volumes are ranging from 23.97  10 3 to 13.93  10 3 mm 3 . Thus, it can be drawn that the film maintains more excellent mechanical and tribological properties, which is sputtered at the moderate substrate bias of 100 V. © 2015 Elsevier B.V. All rights reserved. 1. Introduction In this day and age, to protect the cutting tool surface and prolong the service life, transition metal nitride films have been prevalently used in the modern machining industry such as TiN, CrN, TiAlN films, which are attributed to their attractive properties such as oxidation resistance, high hardness, good wear resistance and low friction coefficient [1e5]. However, as modern industry rapidly and dramatically develops, practical operating environ- ments are gradually becoming much sterner including higher temperature and faster cutting speed. Thus, compared with con- ventional metal nitride films, the protected CrAlN multilayer films come into being due to more excellent performances such as su- perior mechanical and tribology properties [6e11]. Currently, an increasing amount of studies have focused on CrAlN multilayer films, which are promising to achieve a widespread applications in the high speed machining of cutting tools because the aluminum and chromium elements can produce complex oxides, which are considered an effective barrier of oxygen diffusion inward. Will- mann et al. [12] illustrated that CrAlN films obtain high thermal stability over 900  C in ambient atmosphere, which are ascribed to the formation of complex oxides (Cr, Al) 2 O 3 . CrAlN multilayer films can be prepared by means of physical vapor deposition techniques, such as cathodic arc ion plating [13,14], beam plasma-assisted physical vapor deposition [15] and unbalanced reactive magnetron sputtering [16,17]. In order to optimize the properties, numerous researchers have tried to tailor Cr/Al atom ratio and alter the deposition parameters such as total working pressure and substrate bias voltage. Several studies [18,19] have confirmed that the Al content in the Cr (1x) Al x N films is limited at x ¼ 0.6e0.7, obtaining more excellent performances. Additionally, CrAlN films exhibit great tribological properties up to 500  C [20]. Spain et al. [21] confirmed that the service life of CrAlN films can be prolonged by 8/3 times than TiN films. R. Escobar Galindo et al. [22] argued that adding TiN layer into multilayer CrAlN film, acting as an effective oxygen diffusion barrier layer reducing the inward diffusion, can promote the aluminium-rich oxides formation on the surface, thus enhancing the long-time oxidation resistance of the film. Meanwhile, multilayer system can enhance the adhesion. Therefore, TiN/CrAlN multilayer system is chosen in this study. As is well known, the structure and properties of multilayer films are strongly relying on the deposition conditions. Particularly, substrate bias voltage is an essential sputtered parameter which apparently influences the quality of the films due to the strong strength of adatom mobility and ion bombardment effect. The * Corresponding author. E-mail address: hsyang@263.net (H. Yang). Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom http://dx.doi.org/10.1016/j.jallcom.2015.10.076 0925-8388/© 2015 Elsevier B.V. All rights reserved. Journal of Alloys and Compounds 665 (2016) 210e217