Development of a novel Ni-based composite via in-situ reinforcement units formed by high-density hierarchical nanoscale precipitates

In the present work, we selected (CoCrFeNiMn)90Hf10 amorphous high-entropy alloys (AHEAs) as the added particle into pure Ni powder and prepared novel Ni-based composites by spark plasma sintering (SPS). Three kinds of in-situ nanoscale reinforcements with face-centered cubic structure are obtained by phase separation and crystallization of AHEA in the Ni matrix during SPS, possessing different formation mechanisms, distribution sizes, and existing regions. It allows the formation of hierarchical nanoprecipitates through the interaction of Ni matrix and appropriately added AHEA, bringing about reinforcement unit formation with core–shell types embedded in the matrix. Accordingly, a significant enhancement in the strength and ductility synergy compared to SPS-ed pure Ni bulk is achieved. The 20 vol% AHEA/Ni-based composite achieves the optimal yield strength, ultimate tensile strength, and elongation of 358 MPa, 561 MPa, and 24.1%, respectively. The different types of in-situ hierarchical nanoscale precipitates in the Ni matrix manifest unique pinning behaviors for various defect forms. The disordered interfacial nanolayer obtained along the grain boundary between matrix and nanoprecipitate verifies the large tensile ductility. Moreover, the hierarchical dimples exhibiting a uniform distribution involving in reinforcement unit and Ni matrix also decipher the basis of the strength-ductility trade-off.