Exceptional strength and ductility in 18Ni300/316 L heterogeneous bionic structures through laser additive manufacturing

Compared to single-phase materials, heterogeneous structural materials exhibit significant potential in achieving an excellent combination of strength and ductility. To harness this potential, 18Ni300/316 L layered heterogeneous structural materials were fabricated through a controlled laser direct energy deposition strategy. Samples with a higher content of the relatively softer 316 L exhibited fracture elongation of up to 31.7 %. In contrast, samples with a higher content of the relatively harder 18Ni300 exhibited higher tensile strength, reaching 812 MPa, with only a slight reduction in ductility (28.5 %). The microstructure of the 18Ni300/316 L samples transformed from dendritic, equiaxed grains to columnar grains, consisting of martensite and austenite phases. The austenite grains extended from the 316 L region into the 18Ni300 region, exhibiting characteristics of epitaxial growth. During tensile testing, the “soft” (316 L layer) and “hard” (18Ni300 layer) regions at the interface underwent uneven deformation. The harder region induced normal stress, while the softer region induced back stress, leading to heterogeneous deformation-induced strengthening of the material. The novel implementation of the heterogeneous structure process may provide a new solution for overcoming the trade-off between strength and ductility.