Investigating the strengthening and deformation behavior of B2-strengthened high entropy alloys with high Co and Al contents

Abstract

A never-ending challenge for materials scientists is to design alloys with excellent strength-ductility combinations. Here, a systematic study on B2 precipitation and mechanical behaviors of a high Co and Al content high entropy alloy (HEA) annealed at 700–1000 °C was investigated. The alloy annealed at 700 °C (denoted as A700) exhibited a high yield strength of 1820 ± 22 MPa and an ultimate tensile strength of 1884 ± 21 MPa, which can be mainly attributed to the dislocation, ultra-fine grain and B2-strengthening. With the annealed temperature increasing to 900 °C (denoted as A900), the FCC matrix has been full-recrystallized, and the grain size of FCC matrix increases from 0.21 μm to 2.8 μm. The volume fraction of the B2 phase decreases slightly from 58% to 53%. As a result, the A900 alloy displays a yield strength of 1038 ± 17 MPa and tensile ductility of 28 ± 2.3%. The deformation and strengthening mechanisms are investigated by microstructural characterization and theoretical calculations. This work will provide a basis for the composition and structural design of B2-strengthened HEAs.