有色金属工程（有色金属（中英文））

以铸造近α钛合金为研究对象，通过系统设计的锻造、固溶、热轧及两种热处理工艺，制备出两种组织模式的三态组织合金材料。该三态组织由长条状初生α相(α_p)、等轴状α_p相以及次生α相(α_s)共同构成，其晶粒形貌与微观结构均显著区别于传统双态组织。直接时效处理获得的三态组织-1呈现显著细化的晶粒结构，并富含细长条状α_p相。即使在α_p相含量较高的情况下，其抗拉强度仍由双态组织的956 MPa提升至1 070 MPa，同时保持10.2%的良好延伸率；三态组织-2的晶粒尺寸与α_p相含量与双态组织相近，但强度仍提升至1 008 MPa。通过对比分析三种组织模式的性能差异，表明位错强化与细晶强化是强度提升的关键机制。更重要的是，与拉伸方向平行的长条状α_p相能够有效维持位错的平面滑移特性，从而进一步强化材料性能。

With the continuous advancement of the aerospace industry,increasingly stringent demands are being placed on the performance of titanium alloys,particularly requiring higher strength while maintaining sufficient ductility to ensure safety,reliability,and extended service life under extreme environments. Near-α titanium alloys,which are widely utilized in high-temperature structural components of aero-engines and airframes,typically exhibit four classical microstructural types:equiaxed,bimodal,widmanst??tten(lamellar),and basket-weave structures. Despite their wide application,these microstructures often encounter an inherent strength-ductility trade-off,which limits further improvement of comprehensive mechanical properties. To address this limitation and meet the evolving requirements of aerospace engineering,the development of novel microstructures that can simultaneously enhance strength and maintain or improve ductility has become an urgent research focus in the field of advanced titanium alloys. In this study,a cast near-α titanium alloy was selected as the research material,and a systematically designed thermomechanical processing route was employed to develop near-α titanium alloys with targeted microstructural configurations that aim to overcome the strength-ductility trade-off. Initially,through carefully controlled forging and solution treatment processes,appropriate bimodal microstructures were obtained,providing a foundation for subsequent microstructural tuning. Building upon these bimodal structures,a meticulously designed rolling process was applied to develop specific rolling-induced microstructures,followed by two distinctly different heat treatment strategies to ultimately obtain two types of tri-modal microstructures within the near-α titanium alloy system. Detailed microstructural characterizations were conducted using optical microscopy,electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM) to compare the differences among the three microstructural configurations,including the baseline bimodal and the two developed tri-modal structures. The tri-modal structures consisted of elongated primary α(α_p) phases,equiaxed α_p phases,and secondary α(α_s) phases,with the overall grain morphology and microstructural features differing significantly from those observed in the conventional bimodal structure. The tri-modal structure obtained through direct aging treatment(tri-modal-1) exhibited significantly refined grains,a higher volume fraction of α_p phases,and an abundance of elongated,lath-like α_p phases distributed along the rolling direction. Remarkably,even with a relatively high α_p phase content,the tensile strength of the alloy increased from 956 MPa in the bimodal structure to 1 070 MPa while maintaining a favorable elongation of 10.2%. The second tri-modal structure(tri-modal-2),which underwent a short-duration,high-temperature heat treatment,presented grain sizes and α_p phase content similar to those of the bimodal structure but still exhibited an enhanced tensile strength of 1 008 MPa. Further analysis revealed that the tri-modal-1 structure exhibited larger aspect ratios in the elongated α_p phases,finer grain sizes in the α_s phases,and higher dislocation densities within the matrix. This was primarily attributed to the processing route employed,where the absence of high-temperature recovery and recrystallization in tri-modal-1 helped retain high dislocation densities and refined grains. In contrast,the tri-modal-2 structure underwent more pronounced recovery and partial recrystallization during the high temperature heat treatment,leading to changes in grain size,morphology,and a significant reduction in dislocation density. It is noteworthy that all three microstructures underwent the same aging treatment,which resulted in similar precipitation behavior of the primary strengthening phases within the alloy. This consistency in precipitation strengthening across the different microstructures indicates that the observed improvements in mechanical properties are primarily due to differences in the grain structure and dislocation configurations rather than differences in precipitate hardening. Through comprehensive comparative analysis of the microstructures and mechanical properties across the three configurations,it was demonstrated that dislocation strengthening and grain refinement are the critical mechanisms contributing to the enhanced strength of the near-α titanium alloy. Furthermore,the presence of elongated α_p phases aligned parallel to the tensile loading direction was found to play a significant role in maintaining planar dislocation slip during deformation,thereby facilitating strain accommodation while preserving strength. This alignment effectively hinders the operation of cross-slip and the formation of detrimental stress concentrations,which are typically responsible for premature failure in high-strength alloys. Overall,the study highlights that the strategically designed tri-modal microstructures developed through systematic thermomechanical processing can significantly enhance the strength of near-α titanium alloys while maintaining sufficient ductility,offering a promising pathway for the development of next-generation high-performance titanium alloys for demanding aerospace applications.