Increasing the cutting speed to an ultra-high level usually gives rise to a chip flow transition from continuously serrated to discontinuously segmented, which is one of the most fundamental and challenging problems in metal cutting. In this work, we experimentally performed the ultra-high-speed cutting on Ti-6Al-4V with a maximum cutting speed of 210 m/s, focusing on the physical phenomena accompanying the discontinuously segmented chip flow. It reveals that the discontinuously segmented chip flow can be attributed to the shear fracture induced by the fully matured shear banding, and there exists a ductile-brittle transition of the shear fracture as the cutting speed increases to an ultra-high level. In addition, the critical condition for the onset of segmented chip flow is presented using the momentum diffusion-based shear band evolution model, which gives good prediction for the chip segmentation.