Investigating the Strengthening and Deformation Behavior of B2-strengthened High Entropy Alloys with High Co and Al Contents

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 degrees C was investigated. The alloy annealed at 700 degrees 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 degrees C (denoted as A900), the FCC matrix has been full-recrystallized, and the grain size of FCC matrix increases from 0.21 mu m to 2.8 mu m. 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.