Ductile-brittle transition of cutting behavior in diamond turning of single crystal Si

Diamond turning of single crystal silicon disks with round-nosed diamond tools has been studied by interrupting the turning and observing the surface of shoulders formed between the turned regions and original surface. The observation of such a shoulder surface reveals a distinct transition from the very smooth, crack-free zone on the top side of the shoulder. The location of the boundary between the two zones moves up or down or out of the shoulder depending on the feed rate, depth of cut, crystallographic orientation and cutting fluid. Such a distinct transition seems to indicate a change in the cutting mode or material removal process from ductile plastic deformation of the work material in front of the cutting tool to brittle crack propagation and fracture. The location of such a transition zone seems determined by the ''uncut chip thickness''. Experimental details and possible explanations for cutting mode transition will be discussed in detail during the presentation.