Evolution of 3D chip morphology and phase transformation in dry drilling Ti6Al4V alloys

Drilling as one of the most complex manufacturing processes covers a large variety of titanium alloys applications. However, a comprehensive characterization of morphology and microstructural behavior of chips generated in titanium alloys drilling process is significantly lacking. For this purpose, a new 3D schematic has been conducted to fully understand the chip formation and morphology in dry drilling Ti6Al4V alloys process. It is found that spiral chips are easily generated in drilling with four regions: initial spiral cone, steady-state spiral cone, transition between spiral cone and folded long ribbon, and folded long ribbon. Compared with cutting speed, the feed rate plays a more important role in chip macro morphology. The length of chip decreases with feed increasing, while there is no big difference with cutting speed increasing. The microstructural analysis shows that severe phase deformation and transformation occur in the adiabatic shear band (ASB) and second shear band: the β phase experiences an extremely plastic deformation and an allotropic transformation into martensitic phase.