Microstructural Characterization of Chip Segmentation Under Different Machining Environments in Orthogonal Machining of Ti6Al4V

Abstract

Segmented chips are known to form in machining of titanium alloys due to localization of heat in the shear zone, which is a function of machining environment. To investigate the correlation between machining environments and microstructural aspects of chip segmentation, orthogonal turning experiments were performed under three machining environments, viz., room, LN2, and 260 °C. Scanning electron and optical microscopy of chip roots show that the mechanism of chip segment formation changes from plastic strain and mode II fracture at room temperature, to predominant mode I fracture at LN2 and plastic strain leading to shear band formation at 260 °C. The chip segment pitch and shear plane length predicted using Deform™ matched well with the experimental values at room temperature. The microstructural analysis of chips show that higher shear localization occurs at room temperature than the other two temperatures. The depth of machining affected zone (MAZ) on work surfaces was lower at the two temperatures than that of at the room temperature at a higher cutting speed of 91.8 m/min.