Investigating the correlation between nano-impact fracture resistance and hardness/modulus ratio from nanoindentation at 25-500 °C and the fracture resistance and lifetime of cutting tools with Ti1−xAlxN (x = 0.5 and 0.67) PVD coatings in milling operations

A novel laboratory technique, nano-impact testing, has been used to test Ti_1−xAl_xN (x = 0.5 and 0.67) PVD coated WC-Co inserts at 25-500 °C. Cutting tool life was studied under conditions of face milling of the structural AISI 1040 steel; the end milling of hardened 4340 steel (HRC 40) and TiAl6V4 alloy. A correlation was found between the results of the rapid nano-impact test and milling tests. When x = 0.67 improved resistance to fracture was found during milling operations and also in the nano-impact test of this coating compared to when x = 0.50. The coating protects the cutting tool surface against the chipping that is typical for cutting operations with intensive adhesive interaction with workpiece materials such as machining of Ti-based alloys. The results give encouragement that the elevated temperature nano-impact test can be used to predict the wear and fracture resistance of hard coatings during milling operations. At 500 °C nanoindentation shows there is a lower H/E_r ratio for the PVD coatings compared to room temperature, consistent with reduced fracture observed at this temperature in the nano-impact test.