The microstructure and distribution of the elements have been studied in thin films of a near-equimolar CrNbTaTiW high entropy alloy (HEA) and films with 8 at.% carbon added to the alloy. The films were deposited by magnetron sputtering at 300°C. X-ray diffraction shows that the near-equimolar metallic film crystallizes in a single-phase body centered cubic (bcc) structure with a strong (110) texture. However, more detailed analyses with transmission electron microscopy (TEM) and atom probe tomography (APT) show a strong segregation of Ti to the grain boundaries forming a very thin Ti–Cr rich interfacial layer. The effect can be explained by the large negative formation enthalpy of Ti–Cr compounds and shows that CrNbTaTiW is not a true HEA at lower temperatures. The addition of 8 at.% carbon leads to the formation of an amorphous structure, which can be explained by the limited solubility of carbon in bcc alloys. TEM energy-dispersive X-ray spectroscopy indicated that all metallic elements are randomly distributed in the film. The APT investigation, however, revealed that carbide-like clusters are present in the amorphous film.

A detailed microstructural evaluation was executed on the crystallographic texture as well as the mechanisms for nucleation, phase transformation, and grain growth in a Al0.7CoCrFeNi high-entropy alloy. The microstructure and crystallographic orientations were characterized by electron backscatter diffraction, and the chemical composition variations by energy-dispersive X-ray spectroscopy. The cast Al0.7CoCrFeNi alloy started in the BCC phase and partially transformed into the FCC phase. It was found that the Pitsch orientation relationship (OR) dominates the nucleation mechanism of the FCC phase; however, deviations with respect to the Pitsch OR are observed and are attributed to the differently sized atoms forming an ordered B2 phase in the alloy causing lattice distortions. The dual phase BCC–FCC microstructure contains FCC Widmanstätten plates oriented parallel to the {110}BCC planes of the parent grain. It was found that the crystal orientation distribution after the BCC–FCC phase transformation is confined and is explained as a product of the governing mechanisms.

A CrMnFeCoNi high-entropy alloy was investigated by nanoindentation from room temperature to 400 °C in the nanocrystalline state and cast plus homogenized coarse-grained state. In the latter case a 〈100〉-orientated grain was selected by electron back scatter diffraction for nanoindentation. It was found that hardness decreases more strongly with increasing temperature than Young’s modulus, especially for the coarse-grained state. The modulus of the nanocrystalline state was slightly higher than that of the coarse-grained one. For the coarse-grained sample a strong thermally activated deformation behavior was found up to 100–150 °C, followed by a diminishing thermally activated contribution at higher testing temperatures. For the nanocrystalline state, different temperature dependent deformation mechanisms are proposed. At low temperatures, the governing processes appear to be similar to those in the coarse-grained sample, but with increasing temperature, dislocation-grain boundary interactions likely become more dominant. Finally, at 400 °C, decomposition of the nanocrystalline alloy causes a further reduction in thermal activation. This is rationalized by a reduction of the deformation controlling internal length scale by precipitate formation in conjunction with a diffusional contribution.

Al1.3CrFeNi eutectic high entropy alloy was designed and prepared by arc-melting to investigate the microstructure and oxidation behaviors at 1000 °C. The XRD pattern shows that this alloy had a double bcc/B2 structure. SEM images indicates that the microstructure of the alloy is composed of two precipitates of [Cr, Fe] solid solution and NiAl intermetallic, which form the typical eutectic structure. To explore the thermal application of Al1.3CrFeNi alloy, the oxidation behavior of Al1.3CrFeNi alloy at 1000 °C was investigated. From XRD and SEM results, it could be concluded that Al2O3 and Cr2O3 were the predominant oxides during the oxidation process. In addition, spinel like FeCr2O4 was also observed in the oxide scale. According to the analysis of oxide precipitates, the whole process of oxides’ formation was discussed and a simplified oxidation dynamic model of Al1.3CrFeNi alloy at 1000 °C was obtained. This could promote the development of thermal applications in multi-component alloys field.