Abstract
In-situ TEM-heating study of the microstructural evolution of CrFeCoNiCu high entropy alloy (HEA) thin films was carried out and morphological and phase changes were recorded. Post annealing investigation of the samples was carried out by high resolution electron microscopy and EDS measurements. The film is structurally and morphologically stable single phase FCC HEA up to 400 °C. At 450 °C the formation of a BCC phase was observed, however, the morphology of the film remained unchanged. This type of transformation is attributed to diffusionless processes (martensitic or massive). From 550 °C fast morphological and structural changes occur, controlled by volume diffusion processes. Fast growing of a new intermetallic phase is observed which contains mainly Cr and has large unit cell due to chemical ordering of components in <100> direction. The surface of the films gets covered with a CrO-type layer, possibly contributing to corrosion resistance of these.
Highlights
High entropy alloys (HEAs) are multi-component alloys in which at least five elements of concentration between 5 and 30 at % are combined [1]
Detailed structural investigations of bulk HEA have shown that some ordered solid solutions as well as intermetallic compounds can precipitate from the homogeneous matrix at room temperature (RT) and at elevated temperatures as well
These results show that separation of the components in the originally single phase, homogeneous solid solution HEA film took place during the annealing above 600 °C
Summary
High entropy alloys (HEAs) are multi-component alloys in which at least five elements of concentration between 5 and 30 at % are combined [1]. The basic idea is to reduce the Gibbs free energy through maximizing the configuration entropy, which facilitates the formation of random solid solution rather than a complex microstructure built up by intermetallic compounds [2,3]. Detailed structural investigations of bulk HEA have shown that some ordered solid solutions as well as intermetallic compounds can precipitate from the homogeneous matrix at room temperature (RT) and at elevated temperatures as well. The size and the lattice parameter of these BCC grains have been found to be of the order of ten micrometers and 0.289 nm respectively, regardless of their composition
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