Abstract
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.
Highlights
The advent of high-entropy alloys (HEAs) as introduced by Yeh et al (2004) has given an impetus to the design of multicomponent alloy systems, which are mechanically stable at elevated temperatures
The same microstructural picture is observed for many other BCC parent grains and, it is easy to conclude that the FCC grains must have a plate-like shape
We may state that electron backscatter diffraction (EBSD) observations provide considerable statistics for orientation relationship (OR) between the FCC phase and BCC phase, which could be used for a precise orientation estimation based on an assumption of Gaussian error distribution in crystal orientation measurements
Summary
The advent of high-entropy alloys (HEAs) as introduced by Yeh et al (2004) has given an impetus to the design of multicomponent alloy systems, which are mechanically stable at elevated temperatures. In recent years considerable attention has been paid to the microstructure, alloy preparation, and mechanical performance of various HEAs (Zhang et al, 2014). This interest was caused by the extraordinary properties of HEAs compared with their principal elements and other known alloys. Despite the rather extended literature dealing with processing, almost no detailed work has been reported concentrating on the crystallographic orientation relationships (ORs) and distributions in multiphase HEAs. Needless to say, to fully understand the structure–property– performance relationships detailed information about the OR, which influences the materials’ microstructure, is a critical issue and of major concern
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