Emergent behavior of nano-multilayered coatings during dry high-speed machining of hardened tool steels

A multi-functional nano-multilayered Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N physical vapor deposited (PVD) adaptive hard coatings is presented. This novel coating consists of alternating layers with variable chemical composition but similar crystal structure and hardness.A comprehensive investigation of the microstructure and properties of the coating was performed. The structure of the coating before and after service has been characterized by high-resolution transmission electron microscopy (HRTEM). Various micro-mechanical characteristics (hardness, impact fatigue fracture resistance, and low cycling wear resistance) of the coating have been investigated. Oxidation resistance of the coating has been studied using Thermogravimetric–Differential Thermal Analysis (TG-DTA) within a temperature range of 25–1200°C in air.Wear performance of the novel TiAlCrSiYN/TiAlCrN coating was evaluated through tool life studies, cutting forces measurements and identification of chips characteristics. To determine the causes of improvement in wear performance, the worn surface of the coated cutting tools was investigated using SEM/EDS. The characteristics of the surface tribo-films that were formed on the worn surface were studied using, X-ray photoelectron spectroscopy (XPS) and Extended Energy-loss Fine Spectroscopy (EELFS). One of the major features of this coating is enhanced formation of tribo-oxide films on the surface during friction. These oxides possess a sapphire and mullite structure with superb protective ability that acts simultaneously with high temperature lubricious Si–O and Cr–O phases.Due to emergent properties, the developed adaptive coating behaves as a higher ordered system under operation, capable of sustaining extreme operating conditions.