Double heterogeneous structures induced excellent strength–ductility synergy in Ni40Co30Cr20Al5Ti5 medium-entropy alloy

•Through an ingenious mechanical heat treatment process, a double heterogeneous structure alloy composed of heterogeneous grain structure and heterogeneous size phase was designed.•The double heterogeneous structure alloy simultaneously increases strength and ductility, demonstrating a remarkable strength–ductility synergy.•Double heterostructure alloys have superior mechanical properties compared to other high performance heterostructure alloys.