High entropy alloys (HEAs) are a new class of metallic materials with at least four principal elements. Recently, intensive studies in HEAs have led to the discovery of a number of attractive properties. The concept of non-equiatomic HEAs has greatly expanded the compositional space for HEA design, and work on these compositions has achieved unparalleled properties. In the development of traditional structural metals and alloys, the properties are essentially determined by the microstructure achieved via processing. For this reason, it is of great importance to explore the relationship between properties and microstructures in HEAs.
In the non-equiatomic FeNiCoAl-based HEAs, Cr is effective on the enhancement of <001>recrystallization texture through proper thermomechanical processing, and the ductility of specimens is improved with strong recrystallization texture.
Design of heterogeneous lamella structure in non-equiatomic HEAs towards synergy of high strength and ductility is successfully made. This precipitation-controlled method for tuning the microstructure of non-equiatomic FeNiCoAl-based HEAs provides an opportunity to modify mechanical properties within a strength and ductility window perhaps more effectively than a large number of existing metals and alloys. The heterogeneous lamella HEA has demonstrated better mechanical properties over fine grained and coarse grained HEAs due to the back-stress strengthening mechanism.
A new class of non-equiatomic FeNiCoAlTaB (HEA) is introduced, which exhibits tunable properties from cryogenic/ambient superelasticity to ultra-high strength through controlling the nature or type of martensite. This alloy system can help to expand the application domain of HEAs, for example into high-damping applications, robust actuators, space exploration and other structural material applications.
For the precipitation behavior of tantalum (Ta) and NiAl along grain boundaries of polycrystalline FeNiCoAlTaB superelastic alloy, it is found that Ta precipitates at grain boundary triple-junctions first, then along grain boundaries, and acts as nuclei for β-NiAl phase formation. The superelasticity can be improved through suppressing the precipitation of Ta and NiAl along grain boundaries.