Changes in the Elastic-Stress State and Phase Composition of TiAlN Coatings under Thermal Cycling

Abstract

By means of XRD structural analysis and transmission electron microscopy, changes in the microstructure of TiAlN coatings deposited via magnetron sputtering after thermal cycling procedures (140 cycles) have been investigated. The thermal cycling procedure consisted in heating to 900°C and further cooling to room temperature. The sputtered target represented a 60 Ti–40 Al (at %) alloy. The coatings were deposited either onto a quenched austenitic steel substrate or onto the same substrate after preliminary Ti ion beam treatment. It is established that a layer of Ti and Al oxides with microcrystalline structure is formed on the coating surface in the course of thermal cycling. Compressive macrostresses under the oxide layer in the TiAlN coating decrease, whereas the heterogeneity of the Al distribution in the Ti_1–хAl_хN phase exhibits an increase. The preliminary Ti ion beam treatment of the substrate leads to an improvement of the coating thermal stability, to a decrease in the oxide layer thickness for the same number of thermal cycles, and to a wider Al concentration range in the Ti_1–хAl_хN phase of the surface coating layers.