Comparative Investigation of the Mechanical and Wear Properties of Multilayer Si-DLC/DLC Films

Abstract

In this study, multilayer diamond-like carbon films 1 µm thick with different numbers of multilayer repetitions were deposited onto austenitic stainless steel SUS304 substrates using different source gases. The influence of the gas and the difference in the number of multilayer repetitions on the adhesion strength and wear resistance of the films was subsequently investigated. The samples were subjected to cross-sectional microstructure observations, elemental analysis by glow-discharge optical emission spectroscopy, nano-indentation tests, Rockwell indentation tests, friction and wear tests, and delamination tests. The nano-indentation tests showed that the films prepared using C2H2 gas were harder than those prepared using CH4 gas. In addition, irrespective of the gas used, the film hardness was improved when four layers rather than two layers were deposited. However, the hardness of the eight layers film decreased. The Rockwell indentation tests showed no improvement in adhesiveness when the gas or the number of multilayer repetitions was varied. The wear tests revealed that the friction coefficient of the films prepared using C2H2 gas was smaller than that of films prepared using CH4 gas. No difference was observed with increasing number of multilayer repetitions. The delamination tests showed that the distance until delamination of the films prepared using C2H2 gas was longer than that of the films prepared using CH4 gas. In addition, the distance until delamination was improved by changing the number of multilayer repetitions from two layers to four layers for both gases but decreased when the number of repetitions was extended to eight layers. In this study, the value of H/E (hardness/Young’s modulus) increased and various characteristics improved with increasing number of multilayer repetitions.