The aim of the present work is growing CoCrCuFeNi HEA thin films of 40–50 nm thickness
and annealing them in-situ in the electron microscope for a better understanding and
controlling the early stages of phase and compositional instability of as deposited
films at temperatures up to 550 °C. Carrying out in-situ electron microscopic experiments
of isochronal annealing at temperatures of 450 °C and 550 °C we could follow the structural
changes in thin (40–50 nm thick) CoCrCuFeNi MPEA films. We observed that at temperatures
450 and 550 °C the first change in the structure is the martensitic transformation
of the FCC to BCC phase. We have shown by EDS mapping of the transformed area that
no compositional changes occur during this process and, specific for martensitic transformation
orientation, relationships between the two phases are present. The changes occur after
about 20 min annealing time at these temperatures. Longer anneals at the same temperatures
lead to separation of components. Above 40 min annealing time at 450 °C voids appear
in the film, Cr will be partly bonded to oxygen (impurity in the vacuum system) in
the form of a thin surface oxide layer. The other components tend to form binary like
compositions of Cu-Ni and Fe–Co pairs. We also estimated the diffusion coefficient
at 450 °C in this alloy to be around ~6 × 10−19 m2/s.
