Laser-based directed energy deposition (LDED) enables rapid near-net-shape fabrication of large-scale titanium components for aerospace applications. However, the poor tensile ductility of most as-deposited titanium alloys, particularly near-α alloys, hinders their wide usage for critical load-bearing structures. Here we report that a high density of microscale shear bands (MSBs) can be activated in an LDED-produced Ti-6Al-2Zr-1Mo-1V alloy with dispersed microscale α colonies to enhance its tensile ductility. Using high-speed nanoindentation and in situ scanning electron microscopy tensile tests, we correlate the local micromechanical properties and global mechanical behavior of such a LDED-produced titanium alloy: (i) The soft α colonies with a hardness of ∼3.3 GPa produce slip bands (SLBs) with basal and prismatic <a>-slips; (ii) The surrounding hard α colonies or individual laths with a hardness of ∼4.4 GPa are plastically deformed by activating MSBs, which are assisted by pyramidal <a>- and <c + a>-slips. Our results suggest that the nucleation of MSBs relies on the degree of local shear stress acting on the hard domains. The local shear stress is determined by the domain size, spatial orientation, and mechanical contrast with vicinal soft domains. The propagation of MSBs can be arrested by the boundaries between hard and soft domains, suppressing the evolution of MSBs into macroscale catastrophic shear bands and, therefore, enhancing tensile ductility. Our study demonstrates that activating the MSBs provides a new opportunity to effectively enhance the ductility of LDED-produced titanium alloys and expedite the adoption of this additive manufacturing technology for critical structural applications.

基于激光的定向能量沉积 (LDED) 可实现用于航空航天应用的大型钛部件的快速近净成形制造。然而，大多数沉积态钛合金，特别是近α合金的拉伸延展性较差，阻碍了它们在关键承载结构中的广泛使用。在这里，我们报告说，可以在 LDED 生产的 Ti-6Al-2Zr-1Mo-1V 合金中激活高密度的微尺度剪切带 (MSB)，该合金具有分散的微尺度 α 菌落，以增强其拉伸延展性。使用高速纳米压痕和原位扫描电子显微镜拉伸试验，我们将这种 LDED 生产的钛合金的局部微观力学性能和整体力学行为联系起来：（i）硬度为 ∼3.3 GPa 的软α 菌落产生滑带（SLBs），基底和棱柱 < > - 滑倒；(ii) 周围的硬α菌落或硬度为~4.4 GPa 的单个板条通过激活 MSB 发生塑性变形，这由锥体 < a >- 和 < c  +  a辅助>-滑倒。我们的研究结果表明，MSB 的成核依赖于作用在硬域上的局部剪切应力的程度。局部剪切应力由域大小、空间方向和与相邻软域的机械对比决定。MSB 的传播可以通过硬域和软域之间的边界来阻止，从而抑制 MSB 演变为宏观尺度的灾难性剪切带，从而提高拉伸延展性。我们的研究表明，激活 MSB 为有效提高 LDED 生产的钛合金的延展性和加快在关键结构应用中采用这种增材制造技术提供了新的机会。