Gradient structure (GS) possesses a typical trans-scale grain hierarchy with varying internal plastic stability, and the mutual plastic accommodation plays a crucial role in its superior strength-ductility combination. Using the in-situ synchrotron X-ray diffraction (XRD) during tensile loading, we measured lattice strains sequentially from the nanostructured (NS) surface layer to the central coarsegrained (CG) layer to elucidate when and how plastic accommodation occurs and evolves within the GS, along with their roles in plastic deformation and strain hardening. Throughout the tensile deformation, two types of plastic incompatibility occur in the GS. One is an extended elastoplastic transition due to layer-by-layer yielding. The other is strain localization and softening in the NS layer, in contrast with the stable plastic deformation in the CG layer. Plastic accommodation thus occurs concurrently and manifests as both an inter-layer and intra-layer change of stress state throughout tensile deformation. This produces different micromechanical responses between layers. Specifically, the NS layer initially experiences strain hardening followed by an elastoplastic deformation. The hetero-deformation induced hardening, along with forest hardening, facilitates a sustainable tensile strain in the NS layer, comparable to that in the CG layer.

梯度結構是一種典型跨尺度微觀結構, 其內部不同尺度晶粒具有迥異的內稟塑性穩定性, 塑性協調是其獲得優異強韌性的關鍵微觀機制. 本研究採用同步輻射原位拉伸測試方法, 對梯度結構在拉伸變形過程中, 由表及裡不同深度結構層的點陣應變演化進行研究. 結果表明, 梯度結構拉伸時具有兩類塑性協調回應: 一是由逐層微觀屈服導致的瞬態彈-塑性變形, 使納米結構層的彈-塑性應變範圍延後和擴展; 二是納米結構表層的塑性局域化和軟化. 梯度結構塑性協調引起了層間和層內應力狀態的轉變, 導致層間微觀力學行為回應的顯著差異, 利用異質變形誘導應變硬化和林位錯硬化, 促使梯度結構中納米結構表層獲得與芯部粗晶層相當的拉伸均勻應變.