Rotational twinning endows B2 multi-principal element intermetallic alloys with excellent strength and ductility

Abstract

The synergistic enhancement of strength and ductility remains a critical challenge for B2 intermetallic alloys due to their intrinsic room-temperature brittleness. Herein, using the Ni–Ti system with its highly tunable composition and sensitive phase stability as an ideal model, we designed Ni50Ti16.7Zr16.7Hf16.6 and Ni25Co25Ti16.7Zr16.7Hf16.6 alloys via a multi-principal element approach. Multiscale characterization and first-principles calculations show that the Co-free alloy adopts a brittle B19′ martensitic structure at room temperature, with a fracture strain of ∼13%. In contrast, Co-doping induces changes in the structural ground state, which facilitates the stabilization of the monolithic B2 phase. The Ni25Co25Ti16.7Zr16.7Hf16.6 alloy shows an exceptional combination of strength and ductility, with a yield strength of 1527 MPa, an ultimate compressive strength of 3099 MPa, and a compressive strain of ∼40%. This distinctive feature stems from a deformation mechanism in which <110>-oriented rotational twinning mediates strain accommodation, maintains long-range structural order, and facilitates screw dislocations cross-slip. This twinning-induced plasticity within ordered structures provides a generalizable pathway for designing high-performance B2 intermetallic alloys.