Experimental investigation on chip morphologies in high-speed dry milling of titanium alloy Ti-6Al-4V

An experimental investigation of chip morphologies in high-speed dry milling of Ti-6Al-4V alloy was conducted over a variety of different cutting conditions. Observation on the multi-view characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using an optical microscope and a scanning electron microscope (SEM). The microstructural analysis indicated that the chip morphology when dry milling Ti-6Al-4V alloy in high-speed range exhibited a serrated shape for a wide range of cutting conditions. The degree of chip serration is more pronounced and evident with the increase in cutting speed, feed, and depth of cut. A significant variation in the microstructure of the chip including the thickness of the shear bands and the serrated tooth structure for different cutting speeds has been identified. The higher chip serration ratio (CSR) in high cutting speed range may facilitate appropriate machining condition for the occurrence of well-broken chips. Moreover, chip formation takes place by the mechanism of catastrophic thermoplastic shear from the observation of the shear bands using metallurgical analysis techniques. X-ray diffraction results indicated that no evidence of phase transformation was found in the shear localized chips. The variation in chip serration and metallurgical microstructure inside the shear bands and the tool/chip contact zone should be attributed to the reinforcement of coupled thermo-mechanical behavior in the cutting process with the increase in machining parameters.