Improved toughness of layered architecture TiAlN/CrN coatings for titanium high speed cutting

Abstract

Fracture toughness is an important characteristic for coatings for high speed cutting of titanium. This study focuses on improving the fracture toughness of the coatings using a layered design method. TiAlN/CrN multilayer coatings with bilayer periods between 12nm and 270nm were prepared by reactive magnetron sputtering. XRD results show the multilayer coatings have face-centred cubic structures. When the bilayer period of multilayer coating decreases from 270nm to 25nm, the coating hardness decreases from 24.5GPa to 18.1GPa. Increased fracture toughness and adhesion strength of multilayer coatings are observed with decreasing bilayer periods. A maximum fracture toughness (KIC) of 3.6MPam1/2 and adhesion strength of 107 N were obtained with a 25nm bilayer period. The inhibition of crack propagation is the main reason for the high fracture toughness values in multilayer coatings. However, when the bilayer period is decreased further (12nm), the coating hardness begins to increase rapidly to 23.4GPa, and the fracture toughness and adhesion strength begin to decrease. Titanium cutting results show that an improvement in cutting performance is obtained with a TiAlN/CrN_25 multilayer coating.