High-entropy transition metal nitride thin films alloyed with Al: Microstructure, phase composition and mechanical properties

Abstract

Deviation from equimolar composition in high-entropy multielement ceramics offers a possibility of fine-tuning the materials’ properties for targeted application. Here, we present a systematic experimental and theoretical study on the effects of alloying equimolar pentanary (TiHfNbVZr)N and hexanary (TiHfNbVZrTa)N high-entropy nitrides with Al. Although being predicted to be metastable by ab initio density-functional theory calculations, single-phase fcc NaCl-structured solid solution thin films with Al solubility limits as high as x ∼ 0.51–0.61 in (TiHfNbVZr)1-xAlxN and x ∼ 0.45–0.64 in (TiHfNbVZrTa)1-xAlxN are synthesised utilizing a hybrid deposition technique that offers dynamic mixing of film atoms from Al+ subplantation and non-equilibrium growth conditions leading to quenching of the desired film structure. In experimental studies supplemented with density-functional theory calculations, it is demonstrated that Al concentration in alloys with the multielement compositions of high-entropy nitride thin films determine hardness, yield strength, toughness, and ability to deform plastically up to fracture due to different deformation mechanisms arising from the electronic structure and phase compositions.

Keywords

• High-entropy nitride
• HiPIMS
• Mechanical properties
• Hardness
• Yield strength