FRACTURE MECHANISMS OF THIN AMORPHOUS-CARBON FILMS IN NANOINDENTATION

The nanoindentation fracture of amorphous carbon films on silicon subs trate was studied. Load-displacement curves were obtained during inden tation in conjunction with the scanning electron microscope (SEM) obse rvations of fractured surfaces at different loads. The Fracture proces s was found to progress in three stages: (1) first ring-like through-t hickness cracks form around the indenter by high stresses in the conta ct area; (2) delamination and buckling occur around the contact area a t the film/substrate interface by high lateral pressure; and (3) secon d ring-like through-thickness cracks and spalling are generated by hig h bending stresses at the edges of the buckled film. The strain energy release in cracking was estimated from a step observed during the loa ding cycle of the load-displacement curve. An equation for calculation of fracture toughness of thin films is introduced based on the analys is of the energy release rare. The methodology is used to obtain the f racture toughness of thin films. The results show that the calculated Values are in good agreement with those measured by conventional metho ds. (C) 1997 Acta Metallurgica Inc.