Designing (TiZrHf)_100-xCu_x high entropy alloys with abnormal as-cast divorced eutectoid microstructure and balanced mechanical properties

Incorporating eutectoid transformation in high-entropy alloys (HEAs) breaks a new path to explore high-performance HEAs. Here, based on the binary eutectoid Ti–Cu system, we designed (TiZrHf)_100-xCu_x HEAs exhibiting as-cast Widmanstätten microstructures composed of Ti-rich and Hf-rich solid-solution laths and spherical (Ti,Zr,Hf)₂Cu nanoparticles. These microstructures are proved to be the products of divorced eutectoid transformation (DET) by combining experiments and thermodynamic calculations. The special DET in these chemical complex HEAs is induced by local segregations of Ti and Hf, as indicated by hybrid Molecular Dynamics/Monte Carlo simulations, and this DET cannot be realized in as-cast traditional eutectoid alloys (e.g. Ti–Cu alloys). The solid solution strengthening, hierarchical grain refinement induced by higher Cu contents, and (Ti,Zr,Hf)₂Cu nanoparticles endow as-cast (TiZrHf)_100-xCu_x HEAs with yield strengths up to ∼917 MPa, and the DET (Ti,Zr,Hf)₂Cu nanoparticles further plays a key role for retaining good tensile ductilities up to ∼7.2%. These property combinations are superior to as-cast Ti–Cu alloys.