Time-Dependent Deformation Behavior of Amorphous Nitrogen-containing Carbon Films

An indentation creep test has been performed to investigate the nanostructure changes in nitrogen-containing carbon films showing a relatively high hardness value. The time-dependent indentation depth of the hard films indicates a monatomic increase at the initial stage of the creep procedure and thereafter, remains constant. Using the results of the slope of the time-displacement relation at the initial stage of the creep procedure, the strain rate sensitivity exponent m is obtained. Several experiments were conducted under various applied forces, ranging from 20 to 600 mN, to confirm the differences in the viscous flow characteristics of samples with various nitrogen contents. The results revealed that viscous flow of the sample began only when the applied force was increased beyond a critical value. The critical loading force rapidly dropped with increasing extent of nitrogen-carbon bonding in the film.