Scratching of Copper and Silicon: Acoustic Emission Analysis

The effect of scratching as one of the dominant modes of grinding, cutting, mechanical, and abrasive wear on the parameters of acoustic emission (AE) is considered in the present work. A connection between the AE signals emitted during the scratching associated with elastic or plastic shear stress due to material removal, plastic deformation, and damage development is studied. Cu and Si samples were scratched by a Knoop indenter at a load of 0.1 N and the rubbing velocities V = 1 and 100 µm/s. In order to evaluate the effect of ploughing on the AE parameters during scratching of Cu, rolling tests were also carried out. The AE parameters as the number of counts (HITs), frequency range, energy, and energy rate were evaluated, and the waveforms were analyzed. The AE waveforms during scratching and rolling of Cu present a low-amplitude wide noisy high-frequency range band. The low-frequency range in the scratching of Cu is associated with the ploughing. Brittle fracture of Si is accompanied by accumulation of the shear stress waves leading finally to the formation of shear bands, cracking around and inside the scratch track, and microchip formation. Scratching of brittle Si is characterized by scrubbing damage at the nanoscale (depth of scratching is 50–100 nm) and the development of microchips formed in the track, each 40–50 µm. Two typical signals under the scratching of Si were revealed: the first is a burst–shape waveform corresponding to the formation of microchips and microcracking damage; and the second presents the separated individual bursts of relatively high amplitude, associated with scrubbing and local fracture at the nanoscale. The effect of sliding velocity on the AE parameters during the scratching of Cu and Si was analyzed. It was found that practically all the AE parameters were larger under scratching with low velocity, V = 1 µm/s, in comparison to a relatively high velocity, 100 μm/s. Damage and the distance between the microchips were also larger under the scratching of Si with a minimal velocity, V = 1 µm/s.