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The role of light elements in ceramic materials cannot be overestimated. By tuning their concentration, a whole multitude of mechanisms can be activated, directly influencing the material's functional properties. However, accurate determination of light element concentrations remains a challenge and is often, especially in superstoichiometric compounds, overlooked. In this work, superstoichiometric (Al,Cr)Nx coatings (x > 1) were deposited via high-ionisation magnetron sputtering (HIMS). By combining the results of experiments and ab initio calculations, we were able to identify the locations of excess nitrogen atoms in these coatings with a high degree of confidence. Below a critical nitrogen concentration of approximately x ≈ 1.06-1.08, excess nitrogen predominantly occupies interstitial sites and a strong (111) growth orientation is favoured. At higher nitrogen concentrations, x > 1.06-1.08, along with interstitial lattice sites also a substantial occupation of metal sites (anti-sites) can occur, and the rate of grain re-nucleation is significantly increased, disrupting columnar growth and inducing a shift in the growth orientation to (220). These structural changes significantly affect the mechanical properties. Specifically, the (Al,Cr)N1.08 coating, with nitrogen concentration close to the threshold, exhibits a 9% higher hardness (34.4 GPa) and superior abrasive resistance, while the (Al,Cr)N1.11 coating, with nitrogen concentration above the threshold, shows 9% higher fracture toughness (4.15 MPa√m) and enhanced microcracking and crack-branching ability. These findings underscore the advantages of superstoichiometric (Al,Cr)Nx coatings but also suggest broader potential applications of superstoichiometric nitrides and ceramics in advanced material systems.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: (Al,Cr)NSuperstoichiometry, Point defects, Microstructure, Hardness, Fracture toughness, Wear resistance

Date published: 2025-05-19

Publisher: Elsevier BV

Journal:

• Acta Materialia (ISSN: 13596454) vol. 294 121158

Funding:

• Innosuisse Swiss Innovation Agency 42220.1 IP-ENG

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.1016/j.actamat.2025.121158

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Updated at: 2025-07-23 16:30:23 +0900

Published on MDR: 2025-07-23 16:20:21 +0900