High temperature decomposition and age hardening of single-phase wurtzite Ti$_{1-x}$Al$_{x}$N thin films grown by cathodic arc deposition

TL;DR

This study explores the high temperature decomposition of wurtzite Ti$_{1-x}$Al$_{x}$N thin films, revealing nanoscale phase separation and age hardening effects through experimental and computational methods.

Contribution

It provides new insights into the decomposition behavior and phase stability of wurtzite Ti$_{1-x}$Al$_{x}$N films at high temperatures, combining first-principles calculations with experimental observations.

Findings

Decomposition occurs after annealing at 950°C.

Nanoscale chemical modulations form with Ti-rich and Al-rich regions.

Age hardening of 1-2 GPa is observed due to spinodal decomposition.

Abstract

We investigated the high temperature decomposition behavior of wurtzite phase Ti$_{1-x}$Al$_{x}$N films using experimental methods and first-principles calculations. Single phase metastable wurtzite Ti$_{1-x}$Al$_{x}$N (x = 0.65, 0.75, 085 and 0.95) solid solution films were grown by cathodic arc deposition using low duty cycle pulsed substrate-bias voltage. First-principles calculated elastic constants of the wurtzite Ti$_{1-x}$Al$_{x}$N phase show a strong dependence on alloy composition. The predicted phase diagram shows a miscibility gap with an unstable region. High resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950$^{\circ}$C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semi coherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1-2 GPa.