An in-operando evaluation identified the oxidative failure mechanism of TiN hard coatings during extreme thermal cycling

We determine the definitive failure mechanism of passivated TiN films by in-operando monitoring extreme temperature (650 degrees C) induced microstructure, chemical, and mechanical changes. Films were in-operando characterized using Raman and optical microscopy, in air and argon, and post-mortem using nanoindentation, XPS, XRD, and microscopy. Initially, TiO2 anatase forms from pre-existing anatase-rich nucleation centers. These develop into domed bulges of condensed N2 gas in the sub-surface. This initial oxidation is limited to the surface. However, during cooling, cracks propagate from the bubbles, leading to wide-area delamination of the films. These cracks provide a pathway for further destructive bulk oxidation to rutile. This insight into failure mechanism provides deposition protocol for coatings operated under demanding conditions.

Automated summary

This study determines the definitive failure mechanism of passivated TiN films by monitoring their microstructure, chemical, and mechanical changes at extreme temperatures. The initial oxidation is limited to the surface, but cracks form during cooling and lead to wide-area delamination of the films, allowing for further bulk oxidation.