Thermal stability of AlCoCrCuFeNi high entropy alloy thin films studied by in-situ XRD analysis

High entropy alloys (HEAs), containing five to thirteen metallic elements, with a concentration in the range of 5 to 35% for each element, exhibit very interesting properties (mechanical, tribological, formability, magnetism...). Their high mixing entropy promotes the formation of random solid solutions, amorphous alloys or nanocrystallized structures. Bulk pieces of these alloys are known to be stable at relatively high temperature (until 800 °C). We study the stability of AlCoCrCuFeNi thin film at temperatures in the range 110–810 °C. HEA thin films are deposited by magnetron sputtering from mosaic targets. In-situ X-ray diffraction (XRD) performed during annealing evidences damages of the film above 510 °C depending on the initial structure (or chemical composition) of the as-deposited HEA. Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) analysis carried out before and after annealing show that partial evaporation of the thin film, crystalline phase transformation and chemical reaction with the substrate may take place during annealing.