Surface and Coatings Technology 154 (2002) 232–236 0257-8972/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0257-8972 Ž 02 . 00007-5 Analysis of nano-scratch behavior of diamond-like carbon films Li-Ye Huang , Ke-Wei Xu *, Jian Lu , Bruno Guelorget a,b a, b b State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, PR China a LASMIS, Universite de Technologie de Troyes, 10010 Troyes, France b Received 14 August 2001; accepted in revised form 3 January 2002 Abstract The nano-scratch behavior of diamond-like carbon films prepared on Ti alloy substrates by r.f. PECVD was analyzed using a Nano Indenter XP system with the attachment of lateral force measurement in order to understand the deformation mechanism  of the films. It was concluded that the three processes that occur successively with the increase of load during the scratching are fully elastic recovery, plastic deformation, and delamination of the films. In the first regime, no damage could be found on the surface of the films. In the second regime, due to the asynchronous recovery of the films and the substrates, a trace-like fish bone composed of tiny cracks along the track of the indenter was formed. It was only in the third regime when the critical load was obtained that the partial spallation of the films was detected with careful examination. It was determined that the film spallation originated from the fish bone cracking, and the fish bone was just a profiling of the Berkovich indenter.  2002 Elsevier Science B.V. All rights reserved. Keywords: Diamond-like carbon (DLC); Nano-scratch; Nanoindentation 1. Introduction Diamond-like carbon (DLC) films have desirable characterization and properties, such as high optical transparency in the infra-red, high electrical resistivity, high thermal conductivity, high chemical inertness, good biocompatibility, high hardness, low friction coefficient and high wear resistance w1x. These properties make these films suitable for a wide range of applications in the fields of optical, electric, thermal management, biomedical and tribological applications during the last two decades w2x. In certain applications, some scratch performances on the surface of DLC protective films do exist, for instance, the damage on the surface of the prosthesis caused by the wear debris on the main articulating surface w3x, the performance occurring in head-disk interface or MEMS device interface w4x, and the scratching of the optics caused by particles in the air. How to appropriately evaluate the scratch resistance of the films at light load has been the center of attention *Corresponding author. Tel.: q6-29-266-8914; fax: q6-29-323- 7910. E-mail address: kwxu@mail.xjtu.edu.cn (K.-W. Xu). because it would be difficult to directly observe the scratch behavior of small particles on the surface of DLC films, including the process control of both load and scratch process, and how to characterize the surface damage. Therefore, simulated experiments should be applied to examine the scratch resistance of DLC films. The nano-scratch apparatus equipped in a Nano Indenter XP system can apply a fairly controlled low  load to the tip and precisely control the movement of the tip relative to the film. By using a diamond tip to translate on the surface of the films, accompanied with applying loads in the range of micronewtons, contact situations quite similar to those occurring in the inter- faces between DLC films and particles can be achieved. It provides a simple, versatile and rapid means of assessing the scratch resistance of the films. At present, the nano-scratch test may be one of the best ways to evaluate the scratch resistance of the films at low load w5x. As far as we know, several groups have studied the performance of DLC films by nano-scratch w6,7x. Li et al. w6x have systematically investigated the effect of the thickness on the scratch performance of their thin amorphous carbon films using a nanoindenter with a