Effects of Applied Heat and Stress on Structural Changes of DLC Film

Abstract

Diamond-like carbon (DLC) is considered to be predominantly amorphous, whereby small clusters of microcrystalline structures with sp3 and sp2 bonding, and an amorphous matrix, coexist. DLC film has some extraordinary properties such as high hardness, low friction, and high wear resistance. There is strong demand for the use of such DLC properties in a wide range of tribological applications, including cutting tools, mechanical elements of automobiles, die surfaces, and computer hard disks. On the other hand, it is widely known that changes in the structure of DLC film during sliding affect its tribological properties. However, the precise mechanism of the structural change remains unclear. In this study, the effects of applied heat and stress on the structural changes of DLC films were investigated to evaluate the predominant factor in this mechanism. DLC film was deposited on a steel substrate using plasma-based ion implantation and deposition. After heat treatment with applied force, structural changes of the DLC film were investigated by micro-laser Raman spectroscopy. Structural change was confirmed in DLC film annealed at temperatures over 648 K. This suggests that hydrogen evolution from the DLC film possibly caused the structural change. Greater hydrogen evolution was observed from the unloaded surface compared to the loaded area. Structural change was found to be dependent on the stress field: The tensile stress led to structural change, but the compressive stress field did not affect the structural change. These results indicate that a structural change in DLC film caused by heat treatment can be suppressed by preventing hydrogen evolution from the surface of the film.

Keywords

• dlc
• hydrogen
• coating
• heat treatment
• raman spectroscopy
• erda