Investigation of Strain Stabilization in Aluminium-based High Entropy Sublattice Nitride Films

Abstract

Hard protective coatings allow for increased lifespan of machining tools and more versatile fields of application. Less than two decades ago the world of material science was introduced to the so called “high entropy alloys” (HEAs), a field that has since seen explosive growth in popularity. Consisting of a solid solution of at least five primary elements in near equiatomic composition, these materials show remarkable promise. Based off Density Functional Theory calculations several Al based high entropy nitrides systems were chosen, which showed, through strain stabilization, to delay the onset of wurtzite AlN phase after being subjected to prolonged high temperature conditions in vacuum and in ambient atmosphere. Five different material combinations were chosen to be synthesized via reactive magnetron sputtering as nitrides, oxynitrides and Si-alloyed nitrides. The primary investigation focused on how the mechanical properties such as hardness and fracture toughness of the nitride coating changed after vacuum annealing for up to 50 hours, how the oxynitrides related to those results, and whether the formation of the wurtzite phase could be detected. The secondary investigation was aimed towards the oxidation resistance of the coatings, and if the additional silicon could delay the oxidation process. Their characterization includes X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, nanoindentation and cube-corner indentation.