Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondary α-phase (αs) from β-matrix but often compromise ductility due to the conventional strength-ductility trade-off. In this study, a new strategy based on β-subgrains-mediated hierarchical α-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe (wt.%) alloy through a unique combination of hot rolling, short-term solid solution, and aging treatment, i.e., RSST+A. Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of ∼1581 MPa and decent ductility of ∼8.4 %, surpassing ∼1060 MPa and ∼2.7 % of the corresponding RSST counterparts without final aging treatment. This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting of β-subgrains-mediated hierarchical α-precipitates as a result of our specific processing approach. The designed short-term solution introduces abundant β subgrains that are transformed from the retained intensive dislocations during hot rolling. The β subgrain boundaries subsequently promote a dramatic precipitation of α allotriomorphs (αGB) and Widmanstätten side-plates (αWGB), which effectively subdivides β grains into numerous tiny independent deformation units. Consequently, plastic strain is uniformly partitioned into a large number of small aged β subgrains during tension, which strongly impedes strain localization that would typically occur across multiple β subgrains in the fashion of long straight slip bands in the case of the RSST samples. Furthermore, the hierarchical α structure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining. These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing high-strength titanium alloys in the precipitation-hardening state.

中文翻译：

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通过β亚晶粒介导的分层α沉淀增强亚稳态 β-Ti 合金的强度-延展性协同作用


钛合金可以通过对β基体的次级 α 相 （αs） 进行沉淀硬化来实现超高强度，但由于传统的强度-延展性权衡，通常会损害延展性。在本研究中，设计了一种基于 β-亚晶粒介导的多级α析出的新策略，通过热轧、短期固溶和时效处理的独特组合来平衡 Ti-6Al-2Mo-4Cr-2Fe （wt.%） 合金中的冲突，即 RSST+A。拉伸测试表明，RSST+A 样品表现出 ∼1581 MPa 的超高强度和 ∼8.4% 的良好延展性。 超过 ∼1060 MPa 和 ∼2.7 % 的相应 RSST 对应物，未经最终老化处理。这种显着的强化和违反直觉的管道化归因于我们特定的加工方法，β-亚晶粒介导的分层α沉淀物的结构。设计的短期解决方案引入了丰富的β亚晶粒，这些亚晶粒是从热轧过程中保留的密集位错转化而来的。β亚晶界随后促进了α同种异体 （αGB） 和 Widmanstätten 侧板 （αWGB） 的戏剧性沉淀，从而有效地将β晶粒细分为许多微小的独立变形单元。因此，在张力过程中，塑性应变被均匀地分成大量小的老化β亚晶，这严重阻碍了应变定位，在 RSST 样品的情况下，通常以长直滑带的方式在多个β亚晶中发生。此外，分层α结构还可以推迟无法控制的开裂，即使结构损坏发生在应变的最后阶段。 这些发现表明，通过精心设计加工路线来适当操纵微观结构，可以在沉淀硬化状态下意外地实现高强度钛合金的管道化。