Abstract
In this review, we analyze the structure of multicomponent alloys without principal components (they are also called high entropy alloys—HEAs), containing not only metals but also hydrogen, nitrogen, carbon, boron, or silicon. In particular, we discuss the phenomenon of grain boundary (GB) wetting by the melt or solid phase. The GB wetting can be complete or incomplete (partial). In the former case, the grains of the matrix are completely separated by the continuous layer of the second phase (solid or liquid). In the latter case of partial GB wetting, the second solid phase forms, between the matrix grains, a chain of (usually lenticular) precipitates or droplets with a non-zero value of the contact angle. To deal with the morphology of GBs, the new GB tie-lines are used, which can be constructed in the two- or multiphase areas of the multidimensional HEAs phase diagrams. The GBs in HEAs in the case of complete or partial wetting can also contain hydrides, nitrides, carbides, borides, or silicides. Thus, GB wetting by the hydrides, nitrides, carbides, borides, or silicides can be used in the so-called grain boundary chemical engineering in order to improve the properties of respective HEAs.
Highlights
The investigation of high-entropy alloys (HEAs) started in 2004 with the works of Cantor et al and Yeh et al [1,2]
We provided several examples of grain boundary (GB) wetting in HEAs containing hydrogen, nitrogen, carbon, boron, and silicon and, hydrides, nitrides, carbides, borides, and silicides
The given cases do not exhaust all possibilities of such GB wetting phenomena in HEAs
Summary
The investigation of high-entropy alloys (HEAs) started in 2004 with the works of Cantor et al and Yeh et al [1,2]. The interest in the inhomogeneous HEAs has gained momentum This is because the presence of a second (third, etc.) phase can, for example, increase the strength of HEA and prevent the grain growth and the following softening at elevated temperature, etc. This review is devoted to the important type of inhomogeneity in HEAs, namely to the GB phase transformations. Such phase transitions include GB wetting with a liquid phase or a second solid phase and the appearance of different thin GB phases [14,15,16,17]. The GB wetting phenomena strongly depend on the temperature, pressure, and composition in a multicomponent system They become especially interesting in HEAs including non-metallic elements such as nitrogen, carbon, boron, silicon, or hydrogen. Similar microstructures can frequently be seen in papers devoted to HEAs
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