Time-dependent changes in the mechanical properties of diamond-like carbon films

A number of workers have reported the degradation of hydrogenated diamond-like carbon films at elevated temperatures generally graphitisation rapidly occurs at temperatures above 250 degrees C. However, changes in properties due to structural relaxation at lower temperatures have been much less well studied. The residual stress measured in an ion-beam-assisted diamond-like carbon (DLC) film is much greater just after deposition than when remeasured some months later. Nanoindentation measurements on DLC films produced by ion-beam-assisted deposition and plasma-assisted chemical vapour deposition have been made within a few weeks of coating and then repeated after allowing the coatings to age for several years. There is a reduction in both the hardness and the Young's modulus of the coating. These results are discussed in light of the structure of DLC and how this changes during ageing. (C) 1999 Elsevier Science S.A. All rights reserved.