Author Description

The Ti-6Al-4V (Ti64) alloy has been widely used as a light-weight structural material due to its excellent corrosion resistance and high strength even at elevated temperatures. However, the poor machinability of Ti64, leading to higher costs, has severely limited its application. The formation of segmented chips rather than smooth continuous chips, caused by the intrinsic low thermal conductivity of Ti64, is of great interest and significance for investigation.Ti64 bars with various microstructures, namely mill-annealed (MIL), elongated (ELO), solution treated and aged (STA), and lamellar (LAM), were machined at 61, 91, and 122 m/min. The chips were collected, and their microstructures were characterized by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). The morphology of these chips was also measured, and observations of the smooth and segmented sides were also made and compared.For STA chips, nano-indentation and EBSD were used to investigate local shear strain phenomena. An existing continuum model based upon material constants and mechanical properties was used for shear band width prediction at various cutting speeds and the predicted values were compared with the measured values and discussed. In addition, a model based on the morphology of the segmented chips was adopted to calculate the homogeneous shear strains in the segments and catastrophic shear strains within the shear bands. Representative examples of chips were characterized by EBSD and analyzed using the stress tensor obtained from finite element numerical simulation. Finally, the chips were annealed at 500, 600 and 650 ℗ʻC to investigate their response to annealing, revealing effects of the chip deformation history. For LAM, a few EBSD scans were also carried out to show the correlation between chip morphology and local orientations.Overall, the work presented in this study demonstrates an approach to investigating the℗ formation of segmented chips and the severe d