Thin film growth and mechanical properties of CrFeCoNi/TiNbZrTa multilayers

Abstract

Multilayers of high entropy alloys (HEA) are picking up interest due to the possibility of altering material properties by tuningcrystallinity, thickness, and interfaces of the layers. This study investigates the growth mechanism and mechanical properties of CrFeCoNi/TiNbZrTamultilayers grown by magnetron sputtering. Multilayers of bilayer thickness (Λ) from 5 nm to 50 nm were grown on Si(100) substrates. Images taken by transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed that the layers were well defined with no occurrence of elemental mixing. Multilayers with Λ < 20 nm exhibited an amorphous structure. As Λ increased, the CrFeCoNi layer displayed a higher crystallinity in comparison to the amorphous TiNbZrTa layer. Themechanical properties were influenced by thecrystallinity of the layers and stresses in the film. The film with Λ = 20 nm had the highest hardness of approximately 12.5 GPa owing grain refinement of the CrFeCoNi layer. An increase of Λ ≥ 30 nm resulted in a drop in the hardness due to the increase in crystal domains of the CrFeCoNi layer. Micropillar compression induced shear in the material rather than fracture, along with elemental intermixing in the core of the deformed region of the compressed micropillar.