Microstructural Analysis and Integrity of Drilling Surfaces on Titanium Alloy (Ti–6Al–4V) Using Heat-Sink-Based Cryogenic Cooling

Abstract

Low thermal conductivity of titanium alloy tends to increase the cutting temperature and tool wear, which can thereafter adversely affect the integrity of machined surfaces. Therefore, EBSD was performed dry and various cryogenic chilling procedures to characterize the microstructure and mechanical properties of the drilled surfaces on the titanium alloy. The heat-sink channel was used during drilling for effective heat dissipation by flowing the cryogenic coolant through it. Dry and heat-sink-based cryogenic cooling was used for drilling trials, with cutting speeds of 65 m/min and 95 m/min, feed rates of 0.1 mm/rev and 0.2 mm/rev, and cryogenic temperatures of − 25 °C, − 50 °C and − 75 °C. A whole indexing of the grain structure was observed under the drilling edge using cryogenic cooling with a heat-sink. The cryogenic cooling also gave the smallest machining affected zone of 6 μm, and the strain in the grain of 0.4 and 1.1 at the feed rate of 0.1 mm/rev and 0.2 mm/rev, respectively, resulted in the uppermost standardized image quality value which denotes the highest defect-free microstructure on the drilled surfaces, the least value of low-angle boundaries of grains and kernel average misorientation and a higher value of nano-hardness of 8 GPa as compared to dry drilling.