热机械加工对NiCo基高温合金微观组织和力学性能的影响

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

摘要:

通过短时退火与时效处理，在镍钴基高温合金中构建出一种新型晶粒结构。结果表明：该新型晶粒结构包含残余变形晶粒、细小再结晶晶粒及多尺度L1₂-γ'析出相。与传统热处理态合金（屈服强度1106 MPa；延伸率18.8%）相比，具有部分再结晶显微组织的合金屈服强度显著提升至1371 MPa，同时保持了13.3%的延伸率。这一高强度特性源于位错强化（由前期冷轧引入）、细晶强化与γ'相沉淀强化的协同作用。与之相对，完全再结晶态合金的屈服强度为1390 MPa、延伸率为14.3%，其性能优势主要得益于均匀的细晶组织与弥散分布的γ'析出相。还深入探究了材料的内在变形机制，表明除析出相外，位错运动、纳米孪晶及Lomer-Cottrell位错锁对合金卓越力学性能的实现也起到了关键作用。本研究为研发面向严苛工程应用的高性能镍钴基高温合金，提供了一种实用且成本效益高的加工策略。

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.