Thermal stability and thermomechanical behavior of CrFeCoNi compositionally complex alloy thin films
CrFeCoNi thin films are deposited by magnetron co-sputtering at RUB with a precise control of thickness and composition. The thin films are investigated for the formation of secondary phases, microstructure evolution, thermal stability and thermomechanical properties. Our results show that films have a homogenous composition with predominantly fcc phase. However, the presence of a small fraction of Cr rich s phase has been detected which so far has been reported only for bulk counterparts after long annealing treatment or severe plastic deformation . This has been attributed to a finer microstructural length scale (grain size <50 nm) of thin films. Further, we show that single phase fcc films could be formed by fine tuning the composition, while we report a large thermal stability up to ~800°C.
The films deposited on c-sapphire grew epitaxially with the orientations relationships similar to pure fcc metals. The hardness of the dense films ranges from 6.5 to 8 GPa in agreement with literature values for bulk nanocrystalline CCA. Future research directions aim to establish the mechanical behavior of single phase alloy thin films that remains scarcely studied compared to pure metal thin films.