Achieving ultrahigh strength in oxide-dispersion-strengthened CoCrNi alloy via in situ formation of coherent Y-Ti-O nanoprecipitates

Oxide-dispersion-strengthened CoCrNi alloys were fabricated via in situ oxidation by adding Ti and Y, and non-in-situ oxidation by direct addition of Ti and Y₂O₃, referring to as Y-ODS and Y₂O₃-ODS alloys, respectively. Transmission electron microscopy (TEM) and atom probe tomography (APT) characterizations reveal that both alloys consist of an ultrafine-grained face-centered-cubic (fcc) matrix, a high number density of nanoscale Y-Ti-O precipitates and a small number of (Cr_0.75Ti_0.25)₂O₃ oxides. However, the nanoscale Y-Ti-O precipitates in the two alloys show distinct phase and microstructure. The Y₂O₃-ODS alloy contains only incoherent orthorhombic Y₂TiO₅ nanoprecipitates, but the Y-ODS alloy also contains a high density of fully coherent pyrochlore Y₂Ti₂O₇ nanoprecipitates. The Y-ODS alloy achieves an ultrahigh yield strength of 1660 MPa, which is 320 MPa higher than that of the Y₂O₃-ODS one, but maintains the same ductility. Quantitative analysis of the strengthening mechanism indicates that such large difference in strength is mainly attributed to the presence of coherent Y₂Ti₂O₇ nanoprecipitates in Y-ODS alloy. This study should provide significant insight into the design of ODS high/medium-entropy alloys via in situ oxidation during mechanical alloying and consolidation. © 2023 The Authors.