Mechanical properties of VMoNO as a function of oxygen concentration: toward development of hard and tough refractory oxynitrides

TL;DR

This study investigates how oxygen incorporation affects the mechanical properties of VMoN alloys, revealing that VMoNO oxynitrides maintain high hardness and ductility even at high oxygen levels, which is promising for wear-resistant coatings.

Contribution

It provides a theoretical analysis of VMoNO oxynitrides' mechanical behavior as a function of oxygen content, highlighting their potential for durable, tough ceramic coatings.

Findings

Oxidation does not significantly degrade mechanical properties.

Oxygen reduces covalent bonding but preserves ductility.

High oxygen content alloys retain high hardness and toughness.

Abstract

Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem which may compromise material properties and performance. Here, we explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx solid solutions as a function of the oxygen concentration x. Elastic-constant and intrinsic hardness calculations show that oxidation does not degrade the mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate that the presence of oxygen reduces the covalent bond character, which slightly lowers the alloy strength and intrinsic hardness. Nevertheless, the character of metallic d-d states, which are crucial for allowing plastic deformation and enhancing toughness, remains unaffected. Overall, our results suggest that VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high intrinsic hardness, while still being ductile.