Interlayer orientation effects on mechanical response of wire-arc additive manufactured multi-grade steel hybrid sandwich structures

Abstract

In this study, multi-grade steel hybrid sandwich structures with interlayer orientation were designed and fabricated using additive manufacturing (AM) technology. This design effectively combines the high strength from high-grade steel (HGS) and the superior ductility provided by low-grade steel (LGS). Macroscopic digital image correlation (DIC) and in-situ electron backscatter diffraction (EBSD) analyses reveal that the tensile co-coordinated deformation mechanism of two steels is mainly based on staged deformation. During the stretching process, HGS layer is first used to increase the strength of the structure, followed by LGS layer to provide significant deformation capacity. Furthermore, when the deposition direction of both steel layers aligns with the loading direction, the structure completes coordinated deformation only through staging. When there are interlayer orientation differences, coordinates deformation of structure not only through staging, but also relies on the interlayer strain gradients, which drives 66–75 MPa strengthen. On this basis, when the deposition direction of HGS layer is at an angle of 0° to the force direction, it allows cracks to propagate transversely through the martensitic laths, fully exploiting the mechanical advantage of the lath martensite (LM). When the deposition direction of LGS layer is at an angle of 45° to the loading direction, it promotes dislocations to slide along the boundaries, reduces the degree of grain rotation and allows cracks to extend into the ferrite in an inclined manner, maximising the deformability of the material.