Ripening of L12 nanoparticles and their effects on mechanical properties of Ni28Co28Fe21Cr15Al4Ti4 high-entropy alloys

Abstract The coarsening behaviors of γ′ particles in Ni28Co28Fe21Cr15Al4Ti4 high-entropy alloys and their influences on mechanical properties were analyzed. The lattice constant of the matrix decreased with the increase in aging time due to the precipitation of L12 nanoparticles. The increase in annealing time led to a continuous growth of both face-centered cubic grains and L12 particles. Both yield strength and microhardness exhibited age hardening, which varied with the holding time at 800 °C. When the holding time was in the range of 0–24 h, the yield strength and hardness increased with the aging time and dislocation cutting through particle mechanism dominates during deformation. When the holding time exceeded 24 h, the strength and hardness gradually decreased with the increase in aging time and Orowan dislocation looping was the dominant strengthening mechanism. Upon the aging at 800 °C for 24 h, the age hardening reached a peak, which provided an excellent combination of yield strength (855 MPa) and ultimate tensile strength (1031 MPa). The age hardening was related to the precipitation and ripening of spherical L12 nanoparticles. The ripening rate of L12 precipitates was calculated to be 0.31 × 10−27 m3/s. Our results can guide the designs of tough high-entropy alloys for various applications and heat treatments for a good combination of mechanical properties.