Formation and deformation mechanism of the hierarchical diffusion layer in the laminated Ti/Ti–50Nb alloy

The diffusion layer is commonly formed in laminated metal composites (LMCs) and it continuously coordinates the deformation inconsistency between components of LMCs during deformation. By adjusting the phase structure of the diffusion layer, the mechanical properties and deformation behavior of the LMCs can be optimized. In this study, hierarchical diffusion layers with different multiphase architectures, caused by elemental gradients, are obtained in the investigated laminated Ti/Ti–50Nb (laminated Ti–TiNb) alloy by adjusting the cooling rate. TEM and EBSD were applied to investigate the microstructure evolution before and after the tensile deformation. The results indicate that the phase structure of the diffusion layer significantly affects the properties of laminated Ti–TiNb and the strain distribution during deformation. Compared with the “hard” diffusion layer accompanied by fine α phase precipitation, the “soft” diffusion layer with a large amount of α′′ phase precipitation is more conducive to the strain transfer between Ti and TiNb components. Each region in the “soft” diffusion layer exhibites different deformation behavior due to the difference in Nb element content and phase constitution. At last, the formation and deformation mechanism of the “soft” diffusion layer are analyzed in detail. This work provides a new strategy to develop high-performance laminated metal composites by structural design.