Nanomechanical tests to investigate Diamond-Like Carbon (DLC) coating abrasive wear behavior were carried out under different load and strain rate conditions. Nanomechanical tests performed include nanoindentation, single and multi-asperity scratching tests. Characterization methods used are confocal optical microscopy, SEM/EDS, and (high-resolution) AFM. The counterpart material used is diamond.
Results show that DLC abrasive wear behavior is predominantly plowing. Increasing normal load results in wear debris at the edge and inside the wear scar. Failure occurs between DLC and substrate (in this case SiC), upon further increasing the normal load which is in agreement with the literature. In addition, it is found that strain rate influences DLC wear behavior with increasing normal load. This implies that DLC/SiC interfacial adhesion strength presents strain rate dependency rather than DLC itself. This is supported by nanoindentation measurements, where no strain rate dependency was observed. Therefore, for a DLC coating operating under high loading (≥100mN per asperity) in an engineering application, single-asperity testing is not representative of the engineering application. This is caused by the limitations of single-asperity test setup reaching strain rates close to that of the engineering application.
Further, it is reported that in multi-asperity scratching tests increasing the normal load affected the scratch density rather than scratch depth and width. This implies that there is a range of macroscopic normal loads that corresponds to similar single-asperity wear behavior. Scratching tests performed at the edge of DLC/SiC wafers showed that edge wear depends on the rate of change of asperity interference (ω ̇) during collision with the edge. Moreover, an analytical model was developed which predicts that minimization of the impact force (and thus wear) is accomplished when ω ̈ takes minimum value. Based on this criterion minimized edge wear takes place when the asperities are relatively sharp (~1μm) and their initial interference does not exceed 30% of the coating thickness.