Fracture mechanisms of thin amorphous carbon films in nanoindentation

The nanoindentation fracture of amorphous carbon films on silicon substrate was studied. Load-displacement curves were obtained during indentation in conjunction with the scanning electron microscope (SEM) observations of fractured surfaces at different loads. The Fracture process was found to progress in three stages: (1) first ring-like through-thickness cracks form around the indenter by high stresses in the contact area; (2) delamination and buckling occur around the contact area at the film/substrate interface by high lateral pressure; and (3) second ring-like through-thickness cracks and spalling are generated by high bending stresses at the edges of the buckled film. The strain energy release in cracking was estimated from a step observed during the loading cycle of the load-displacement curve. An equation for calculation of fracture toughness of thin films is introduced based on the analysis of the energy release rare. The methodology is used to obtain the fracture toughness of thin films. The results show that the calculated Values are in good agreement with those measured by conventional methods. (C) 1997 Acta Metallurgica Inc.