Effect of cryogenic treatment on the microstructure and the wear behavior of WC-Co end mills for machining of Ti6Al4V titanium alloy

Abstract

This paper compares some of the key machinability aspects acquired during milling of Ti6Al4V titanium alloy with uncoated and coated cryogenically treated end mills. Tool wear, coefficient of friction, cutting force, and chip morphology were the major criteria considered. Ti6Al4V is one of the titanium alloys that are widely used in aerospace and biomedical applications; however, it has a poor machinability and tribological properties. To evaluate the performance of cryogenically treated end mills, milling operations using a force dynamometer and dry sliding tests were conducted. The milling operations were conducted with a cutting speed of 90 m/min, a feed rate of 0.11 mm/tooth, a 1-mm axial depth of cut, and a 10-mm radial depth of cut under dry cutting conditions. The dry sliding tests were conducted using a tribometer with a ball-on-disk geometry under 10 N load and a speed of 5 cm/s. The milling test results showed that flank wear, chipping, and tool breakage were the wear mechanisms of the end mills. The cutting force measurements and the dry sliding tests showed that the cutting force and friction force values decreased when the cryogenic treatment time increased. As a result of the study, tools treated cryogenically for 36 h showed the best performance for the cutting force, friction force, and tool wear criteria. These improvements were characterized with hardness, fracture toughness, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) analyses.