Origins of HDI Stress in Copper–brass Laminates with Dual-Heterostructured Interfaces

In this work, a copper - brass hetero-laminate with dual-heterostructured interfaces was fabricated by diffusion welding in combination with cold deformation and annealing. These dual-heterostructured interfaces possess the characteristics of both gradient interface and sharp interface. The evolutions of geometrically necessary dislocations (GNDs) and local strains near these dual-heterostructured interfaces were investigated by in -situ and quasi in -situ tests. By employing a constitutive model, the evolutions of GND density and the HDI synergistic strengthening mechanism were systematically explored. The results demonstrated that the distribution of GNDs and local strains near the coarse/fine-grained interface exhibited a gradient feature, without any obvious concentrations of GNDs and strains, which can be attributed to the transition effect of the gradient interface. Furthermore, the density of sample -scale GNDs accumulated near the coarse/fine-grained interface was found to be at least one order of magnitude lower than that of grain -scale GNDs accumulated near grain boundaries. Both the constitutive model and experimental results confirmed that grain -scale GNDs serve as the primary origins of significant HDI stress, rather than the sample -scale GNDs.