Microstructure evolution and mechanical behavior of additively manufactured CoCrFeNi high-entropy alloy fabricated via cold spraying and post-annealing

Abstract

In this work, equiatomic CoCrFeNi high-entropy alloy (HEA) was fabricated by solid-state cold spray additive manufacturing technology and then post-spray annealed at the temperature range of 500–1000 °C for 2 h. By adjusting the annealing temperature, four types of deposits (i.e., as-sprayed, recovered (500 °C), partially recrystallized (700 °C), and fully recrystallized (1000 °C) deposits) were obtained, and their microstructure, compressive and tensile properties were systematically explored. The as-sprayed deposit exhibited high compressive yield strength due to the dislocation strengthening and grain boundary strengthening effects but fractured within the elastic deformation regime in the tensile test. Such significant tension-compression asymmetry can be attributed to the difference in the sensitivity of the deposit to interior defects (i.e., pores and particle boundaries) under tensile and compressive loads. Only recover annealing hardly influenced the microstructure and mechanical properties of the deposits. While recrystallization annealing could trigger enhanced interface diffusion and the resultant metallurgical bonding, as evidenced by the improved deposit density and less visible interparticle interfaces. The partially recrystallized and fully recrystallized deposits exhibited an excellent combination of compressive strength and ductility. While the fully recrystallized deposit exhibited almost equal tensile and compressive yield strength and the best recovery of tensile ductility, indicating the weakened tension-compression asymmetry.