Refractory high entropy alloy thin films with controlled oxygen addition
Résumé
Developing new materials with high strength and ductility that can withstand harsh environments remains a key challenge for microelectromechanical systems (MEMS) and energy storage applications. Refractory high entropy alloys (RHEAs) with a BCC structure can represent promising materials for these industrial applications due to their high strength, oxidation, and corrosion resistance [1]. However, these alloys often exhibit low ductility at room temperature [2]. To overcome this drawback, one approach consists of adding ductile FCC elements to the BCC phase to promote the formation of a dual-phase (BCC-HCP) structure, balancing strength-ductility [3]. Another strategy is the addition of small amounts of nonmetallic elements, particularly oxygen, which form ordered oxygen complexes that act as dislocation pinning points and help mitigate brittle behavior [4]. However, most of these studies focus on bulk RHEAs, while there are limited studies on thin film counterparts (RHEA-TFs, thickness < 1µm), especially their relationship between microstructure and mechanical properties. Firstly, I will present some preliminary results on Fex(CoCrNi)100-x HEA-TFs deposited by magnetron sputtering, with Fe content varying from 13 to 29 at.%. CoCrNi showed a dual FCC-HCP phase, contributing to a hardness of 9.7 GPa and an elastic modulus of 204.4 GPa, while the FCC phase was stabilized with Fe addition. Then, I will present the core research of my PhD thesis, focusing on the deposition of TiZrHf RHEA-TFs via magnetron sputtering with a progressive addition of Al (up to 25 at.%) and O (up to 15 at.%), to investigate film growth mechanisms, atomic structure evolution, and microscale mechanical properties using a scale-bridging approach from the nm up to the µm scale. [1] C.H. Chang et al., Adv. Eng. Mater., 8,2018; [2] O. N. Senkov et al., Intermetallics, 19, 2011; [3] L. Rogal et al., Sci. Rep., 7, 2017; [4] Z. Lei et al., Nature, 563, 2018.