Influence of Thermomechanical Processing on Microstructure and Mechanical Properties of NiCo-Based Superalloys

Abstract:

A novel grain structure was developed in a NiCo-based superalloy by short-term annealing and aging treatment. Results show that the novel grain structure consists of residual deformed grains, fine recrystallized grains, and multi-scale L1₂-γ' precipitates. Compared with the conventional heat-treated alloy (yield strength of 1106 MPa; elongation of 18.8%), the alloy with a partially recrystallized microstructure exhibits a significantly higher yield strength of 1371 MPa while maintaining the elongation of 13.3%. This high strength is attributed to synergistic effects from dislocation strengthening (induced by prior cold rolling), fine grain strengthening, and precipitation reinforcement by γ' phases. In contrast, the fully recrystallized alloy demonstrates a yield strength of 1390 MPa and an elongation of 14.3%, primarily due to the uniform fine-grained structure and homogeneously diffused γ' precipitation. The underlying deformation mechanisms are thoroughly investigated, revealing that in addition to precipitates, the dislocation activity, nanotwins, and Lomer-Cottrell locks are also critical for the outstanding mechanical properties. This research provides a practical and cost-effective processing strategy for developing high-performance NiCo-based superalloys for demanding engineering applications.