Strengthening and deformation mechanisms of selective laser melted CoCrNiNb_0.12 multi-principal element alloy by constructing δ nano-precipitate and stable cellular structure

CoCrNi multi-principal element alloys (MPEAs) exhibit excellent fracture toughness in a cryogenic environment, while their insufficient yield strength remains a key limitation, thereby hindering broader engineering applications. In this study, a Nb-added CoCrNi MPEA (i.e., CoCrNiNb_0.12) was fabricated via the selective laser melting technology to construct a stable Nb-enriched cellular structure and δ nano-precipitates for strengthening. The as-deposited alloy exhibits a Nb-segregated cellular structure with a characteristic size of ∼0.44 μm. After annealing at 750 °C for 10 h, the cellular structure remains stable, while δ nano-precipitates preferentially form along cellular boundaries. At 298 K, the TM-750 specimen shows a yield strength of 1002 MPa and an elongation of 5.6%, whereas at 77 K these values increase to 1292 MPa and decrease to 3.2%, respectively. The strength improvement is mainly attributed to δ precipitates strengthening and dislocation interactions with the cellular structure. At room temperature, partial shearing of δ precipitates by stacking faults alleviates stress concentration, whereas at cryogenic temperatures, the δ precipitates hinder the propagation of stacking faults and deformation twins, resulting in reduced ductility. These results demonstrate that the introduction of δ nano-precipitates and a stable cellular structure provides a viable strategy for achieving high yield strength in additively manufactured CoCrNi-based MPEAs from room to cryogenic temperatures.