Evaluation of rhenium carbide as a prospective material for hard coating G. Soto ⁎, H. Tiznado, J.A. Díaz, E.C. Samano, A. Reyes-Serrato Universidad Nacional Autónoma de México, Km 107 carretera Tijuana-Ensenada, Ensenada Baja California, México abstract article info Article history: Received 27 May 2009 Received in revised form 30 November 2010 Accepted 6 January 2011 Keywords: Rhenium carbide Hard coatings X-ray diffraction Nanoindentation Pulse laser deposition The literature reveals that interstitial alloys based on rhenium as a precursor might be extremely hard, becoming suitable to be used as hard coatings. In this work, we have produced rhenium carbide (ReC x ) films by the reactive pulsed laser deposition method. Nanoindentation has been performed to estimate hardness. The maximum hardness value for ReC x films resulted to be 22.5 GPa. We found no evidence that ReC x films have hardness, or plasticity, higher than competitive hard coating materials. Our results and the fact that rhenium is expensive and scarce, suggest that preceding reports are overoptimistic on the prospective use of rhenium carbide as hard coatings. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The term of Hard Coatings is appropriate for materials that once applied as thin films, improve the wear resistance and extend the lifetime of the covered device [1]. Hard coatings are often applied to cutting tools, automotive engine parts, turbine blades, structural components, etc. Hard coatings are widely based on hard transition metal nitrides and their carbides; like TiN, CrN, WC, and in the last two decades, there has been a vast increase of multicomponent coatings (TiAlN), multilayer coatings (TiN/TiAlN) and diamond like carbon- based coatings as well [2]. The performance requirements for hard coatings were raised after their frequent application in dry high-speed machining and cutting processes. High hardness at high temperatures, self-lubrication, and the possibility to process ferrous alloys are the most requested attributes for hard coatings employed in industrial machining. Accordingly, the search for materials to be used as hard coatings is an active research field. From the scientific point of view, the key figures of merit for hard materials are: (a) high valence- electron density in bonding states, (b) covalence of bonds and (c) small bond distances along the principal axes. Materials with good resistance to shear are expected to be attained if these three requisites are simultaneously satisfied [3]. Heavy metals, like W, Re, Os, Ir and Pt intrinsically meet with the criterion given in (a) since they have high valence-electron densities [4,5]; consequently, they show high bulk modulus and are thus highly incompressible [6]. However, they do not exhibit plastic deformation due to its omnidirectional metallic bonding. To meet with the (b) requirement, hardness of metals is enhanced by adding interstitial atoms of moderate electronegativity; like boron, carbon or nitrogen, to provide covalence of bonds within the metallic lattice. However, these light atoms must be incorporated into their lattices without expanding it to meet with the (c) condition too. All three requisites have to be satisfied in a prospect material to reach superhardness standards [3]. Rhenium is a good candidate since it has an electronic density of 4.76 × 10 23 electrons cm -3 , second after osmium as pure metals. Recent research papers about the synthesis of rhenium–boron and rhenium–carbon give some indication that rhenium alloys are promising as hard coatings [7,8]. The mechanical properties have to be extraordinarily superior to make profitable coatings out of materials based on Re because this metal is scarce and expensive [9]. For this reason, the aim of this paper is to explore the possibility to manufacture hard coatings from rhenium as a precursor. We specifically did rhenium carbide films (ReC x ) by the laser ablation method. The Pulsed Laser Deposition (PLD) technique in the reactive mode (RPLD) is an efficient method for growing high quality alloyed films [10]. The incorporation of nonmetallic atoms is associated to the reactive partial gas pressure; subsequently, the film composition can be customized by controlling the deposition pressure [11]. In this report, we explore the issues of ReC x films growth by RPLD and its spectroscopic, structural and mechanical characterizations. As a matter of fact, we have already reported the growth of rhenium nitride films by this same method [12]. 2. Experimental details Rhenium carbide film deposits were accomplished by laser ablating a high purity solid Re target, ~99.9 wt.%, in a CH 4 reactive atmosphere at several pressures. Films were grown simultaneously on both (100)-silicon wafers and TiAl6V4 polished substrates placed Thin Solid Films 519 (2011) 3236–3241 ⁎ Corresponding author. E-mail address: gerardo@cnyn.unam.mx (G. Soto). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.190 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf