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.

Grain-direction dependent oxidation at the surface of polycrystalline Fe-Cr steel is not well understood, as most of the described systems in literature focus on single crystals of either Fe or Cr. We found through electron backscatter diffraction that surface oxidation in air at temperatures between 260 and 450°C depends severely on grain orientations at the outer surface. Subsequently electron microscopy was combined with X-ray photoelectron spectroscopy (XPS) and X-ray Diffraction (XRD) to characterize the oxide film further in detail. In particular we have observed the following sequence in oxidation rate of crystal planes parallel to the surface for Fe-Cr steel, {0 0 1} < {1 1 1} & {1 0 1}, which was not reported in literature before.