Alloying-related trends from first principles: An application to the Ti--Al--X--N system

TL;DR

This study uses first-principles calculations to analyze how adding early transition metals to Ti-Al-N systems affects their structural and electronic properties, providing insights into alloying trends for protective coatings.

Contribution

It offers a systematic first-principles analysis of alloying trends in Ti-Al-N with early transition metals, highlighting effects on lattice parameters, chemical strengthening, and decomposition tendencies.

Findings

Lattice parameters deviate more than 2.5% from Vegard's estimation with Y addition.

Chemical strengthening is most pronounced for Ta and Nb.

Y, Zr, and Nb increase mixing enthalpy, suggesting earlier spinodal decomposition.

Abstract

Tailoring and improving material properties by alloying is a long-known and used concept. Recent research has demonstrated the potential of ab initio calculations in understanding the material properties at the nanoscale. Here we present a systematic overview of alloying trends when early-transition metals (Y, Zr, Nb, Hf, Ta) are added in the Ti$_{1-x}$Al$_x$N system, routinely used as a protective hard coating. The alloy lattice parameters tend to be larger than the corresponding linearised Vegard's estimation, with the largest deviation more than 2.5% obtained for Y$_{0.5}$Al$_{0.5}$N. The chemical strengthening is most pronounced for Ta and Nb, although also causing smallest elastic distortions of the lattice due to their atomic radii being comparable with Ti and Al. This is further supported by the analysis of the electronic density of states. Finally, mixing enthalpy as a measure of the driving force for decomposition into the stable constituents, is enhanced by adding Y, Zr and Nb, suggesting that the onset of spinodal decomposition will appear in these cases for lower thermal loads than for Hf and Ta alloyed Ti$_{1-x}$Al$_x$N.