A new indentation cracking method for evaluating interfacial adhesion energy of hard films

Abstract

The linear dependency of interfacial crack length on indentation load in a spherical brale C indentation (the so-called indentation cracking test), d P/d c, has been generally used as the criterion of adhesion for a hard film on a soft substrate. However, this criterion is a relative yardstick that is valid only in materials of same kind. For a more reliable evaluation of adhesion, the energy release rate concept was introduced to relate the dependence of interfacial crack on indentation load to the release of stored energy in the film; here the stress distribution around the indentation is required. The stress state in the film was deduced using the condition of strain continuity at the interface from the stress state in the substrate and then the critical energy release rate G c was obtained as an analytical function of d P/d c and material properties. This method was applied to the adhesion measurement of diamond-like carbon film deposited on AISI D2 steel. The effects of deposition condition and residual stress on adhesion were discussed on the basis of the G c results.