High-entropy transition metal nitride thin films alloyed with Al: Microstructure, phase composition and mechanical properties. (July 2022)

• Record Type: Journal Article
• Authors: Pshyk, A.V.; Vasylenko, A.; Bakhit, B.; Hultman, L.; Schweizer, P.; Edwards, T.E.J.; Michler, J.; Greczynski, G.
• Is Part Of: Materials & design. Volume 219(2022)
• Publication Date: 2022-07
• Subjects: High-entropy nitride -- HiPIMS -- Mechanical properties -- Hardness -- Yield strength; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2022.110798
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: (TiHfNbVZr)1- x Al x N and (TiHfNbVZrTa)1- x Al x N high-entropy nitride thin films are synthesised utilizing a hybrid PVD method. The hexanary and heptanary thin films are based on single-phase fcc-NaCl structured solid solution. Al concentration in high-entropy nitride thin films determines hardness, yield strength, toughness, and plastisity. The solid solution is stable up to x~0.51-0.61 and up to x ~0.45-0.64 for the hexanary and heptanary films, respectively. Mechanical properties are determined by deformation mechanisms arising from the electronic structure and phase composition. 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 -x Al x N and x ∼ 0.45–0.64 in (TiHfNbVZrTa)1 -x Al x N 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.