During machining of single-crystal silicon, material removal involves two modes ductile shear-based removal and brittle fracture-based removal. Ductile shear-based chip removal occurs when fracture is suppressed due to local stress conditions along with reduced chances of defect involvement and is desirable for achieving better surface integrity of the machined silicon wafer. Whereas brittle fracture-based removal involves cracks and fractures in the newly formed surface. In this work, we use charged particle emissions to identify mode of material removal (ductile or brittle) during scratching of a silicon wafer. Linear varying-depth scratching tests were performed in a Vertical Machining Center (VMC) and rotational scratching tests were performed using a pin-on-disc tribometer setup. Both the scratching tests were performed using a conical diamond tip indenter. Linear scratching tests were performed at a velocity of 50 mm/min and rotational scratching at a velocity of 4260 mm/min.

The charged particles emitted during the material deformation were collected using a Faraday plate mounted in the vicinity of the indenter and the ion-current intensity of the charged particles were measured as signals using a sensitive femto/picoammeter. Post scratching, the mode of fracture was identified by examining the scratch in a scanning electron microscope. It is seen that, for a linear scratch which has an only ductile region, the ion-current intensity signal is almost constant and for a linear scratch which has an only brittle region, the ion-current intensity signal is highly fluctuating between -200 pA to +200 pA. Similarly, during scratching, ion current intensity due to only positive or negative ions has also been captured by biasing the Faraday plate. In a linear varying-depth scratching test, which has ductile, transition and brittle zones in a single scratch, a trend is observed for the ion-current intensity due to only the negative ions.

In rotational scratching tests at higher speeds, the varying-depth scratch test was performed in such a manner that both ductile-to-brittle and brittle-to-ductile modes occur in a single scratch test. From the results, a positive ion-current intensity was observed for the ductile mode of scratching and a highly varying ion-current intensity signal is observed during brittle mode of scratching. So, for various scratching tests performed, the signal is able to distinguish ductile and brittle mode of scratching. The present work indicates the suitability of employing charge emission signals to detect the mode of material removal during scratching of silicon. This work can be field-tested by conducting diamond turning experiments of silicon in a real-time machining environment further testing the scope of use of charged particle emission to monitor real-time machining process.