热机械加工对NiCo基高温合金微观组织和力学性能的影响

The influence of thermomechanical processing on the microstructure and mechanical properties of NiCo-based superalloys

摘要:

高效实现优异的强塑协同效应是先进结构材料的核心研发目标。本研究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 —— 该结构包含残余变形晶粒、细小再结晶晶粒及多尺度 L1?-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。研究还深入探究了材料的内在变形机制，结果表明：除析出相外，位错运动、纳米孪晶及 L-C 位错锁（L-C locks）对合金卓越力学性能的实现也起到关键作用。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:

Achieving an optimal strength-ductility synergy efficiently is a critical objective for advanced structural materials. This study developed a novel grain structure in a NiCo-based superalloy, consisting of residual deformed grains, fine recrystallized grains, and multi-scale L12-γ′ precipitates, using a short-term annealing and aging treatment. Compared to the conventional heat-treated condition (yield strength: 1,106 MPa; elongation: 18.8%), the alloy with a partially recrystallized microstructure exhibited a significantly higher yield strength of 1,371 MPa, while maintaining a ductility 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 variant demonstrated a yield strength of 1,390 MPa with an elongation of 14.3%, primarily due to a uniform fine-grained structure and homogeneous γ′ precipitation. The underlying deformation mechanisms were thoroughly investigated, re-vealing that dislocation activity, nano-twins, and L-C locks, in addition to the precipitates, are critical for the outstanding mechanical properties. This work provides a practical and cost-effective processing strategy for developing high-performance NiCo-based superalloys for demanding engineering applications.