Origin of back stress generation during tensile deformation of a heterostructured titanium alloy: An in-situ EBSD study on local slip system activation
Ling-Jian Meng, Yuyue Wang, Xin Li, Zhihua Wang, Zhengyi Jiang, Jingwei Zhao
Abstract
Revealing the origin of back stress generation is important for the design of heterostructured metals and alloys. Here, we study the back stress generation during tensile deformation in a heterostructured Ti-6Al-4V alloy via in-situ scanning electron microscopy/electron backscatter diffraction characterization and slip trace analysis. The co-effects of grain size gradient, slip system compatibility, subgrain formation, and multiple slip system activation on back stress generation are clarified. The results show that the dislocation accumulates and back stress generates around the grain boundary owing to the inhomogeneous deformation behavior between large and small grains. For back stress generation, grain size gradient is the initial requirement and the subgrain formation within large grains will not suppress the back stress generation. Besides, low slip system compatibility of the adjacent large/small grains must be strictly satisfied for back stress generation. Otherwise, the grain boundary may provide limited hindering effect on dislocation motion, leading to the easy slip transfer. As a result, the dislocation density gradient at two sides of the grain boundary is diminished, and the back stress becomes not significant. In addition, the multiple slip system activation within one specific large grain may suppress back stress generation, as it promotes the motion and annihilation of dislocations.