Simulation of deformation behavior in Al₂Nb₄₈Ta₂₅Ti₂₀Hf₅/Ti2AlNb heterogeneous interface and study on the strengthening/toughening mechanisms of the Ti2AlNb joint

A high-entropy interlayer alloy with a composition of Al₂Nb₄₈Ta₂₅Ti₂₀Hf₅ was developed to improve the strength and ductility of Ti2AlNb diffusion-welded joints. However, the fundamental strengthening and toughening mechanisms at the heterogeneous interface remain unclear. Therefore, in this paper, finite element simulation was employed to investigate the distribution of strain, stress (back stress), and dislocation density in the heterogeneous interface, and Scanning Electron Microscopy-Digital Image Correlation (SEM-DIC) experiments were conducted to validate the strengthening effect of back stress at the grain boundaries. Based on this, design criteria for the Ti2AlNb joint microstructure were proposed. The simulation results show that during tensile deformation, a strain gradient (SGR) forms at the grain boundaries between coarse and fine grains in the heterogeneous microstructure. The intensity of the strain gradient peaks at the grain boundaries and increases significantly with the increasing tensile strain, resulting from the difference in deformation capability between coarse and fine grains. As the strain increases to 10 %, the back stress accounts for approximately 25 % of the joint's strength. The combined effect of back stress and forward stress coordinates dislocation strengthening and fine grain strengthening, which not only strengthens the recrystallized grains but also induces plastic deformation in the surrounding fine-grained structure. This alleviates stress concentration at the grain boundaries, effectively enhancing the joint's strength and ductility. Furthermore, it is proposed to use the intensity, width, and distribution of the strain gradient at the coarse/fine grain boundaries as microstructural control parameters. When the joint forms a hetero-structure with fine grains enveloping coarse grains, the strain is uniformly distributed throughout the joint, effectively improving the mismatch problem between strength and plasticity of the Ti2AlNb joint.