Numerical and Experimental Study of Residual Stress of Multilayer Diamond-Like Carbon Films Prepared by Filtered Cathodic Vacuum Arc Deposition

The high-hardness diamond-like carbon (DLC) films synthesized by filtered cathodic vacuum arc (FCVA) deposition may have high residual stress, which will cause the DLC film/substrate interfacial crack and film failure. Therefore, it is essential to analyze and control the residual stress during the DLC deposition. In this paper, the low-hardness DLC monolithic layer films (rich in sp² content, soft DLC), the high-hardness DLC monolithic layer films (rich in sp³ content, hard DLC), and a series of soft/hard DLC multilayer films with modulation ratio of 1 : 1 and modulation periods ranging from 70 to 280 nm are deposited, respectively, on Si (100) wafer and Ti-6Al-4V by FCVA technology with periodic adjustments of the substrate negative bias. The effects of modulation periods (bilayer thickness) on residual stress and wear resistance of multilayer DLC films are studied. The results show that the residual stress decreases in soft/hard multilayer DLC films with decreasing modulation periods, and the films with modulation period of 140 nm have excellent wear resistance. ANSYS finite-element software is used to simulate the residual stress generation during FCVA deposition in the DLC film on a silicon substrate. The result of the finite-element simulation is consistent with that of the experiment, and the finite-element technique has a potential application in the optimization process of DLC multilayer films.

I. Introduction

Diamond-Like CARBON (DLC) films have been widely studied because of their unusual and promising properties such as high hardness, a low friction coefficient, wear resistance, and excellent chemical stability [1], [2]. These unique properties make DLC films very attractive for a wide range of tribological and mechanical engineering applications [3], [4]. In addition, the combination of the excellent tribological properties, corrosion resistance, and good biological compatibility [5], [6] of DLC films also offers promising opportunities for biomedical applications in blood-contacting devices, particularly for medical implants or surgical prostheses [7]–[9]. Many techniques have been applied to deposit DLC multilayer films. Among them, the filtered cathodic vacuum arc (FCVA) technique is one of the most promising methods [10], [11]. It has been reported that the content of DLC films prepared by the FCVA technique can be up to 88% and that their microhardness can be more than 60 GPa [10]. However, the major drawback of DLC films is its high internal compressive stress, which will cause the DLC film/substrate interfacial cracking and film failure and limit practical applications of the DLC film.