Heterostructure effect at the interface of maraging steel deposited upon carbon steel via directed energy deposition

To study the mechanical behavior of the interface region that appears when dissimilar metals are deposited by additive manufacturing process, maraging steel was deposited on S45C carbon steel via directed energy deposition. A 3.3 mm-thick plate obtained from the deposition containing four different regions in the vicinity of the interface (substrate/HAZ/dilution layers/feed material) was subjected to uniaxial tensile deformation parallel to the interface. The strength of the layered structure exceeded the theoretical strength calculated through the rule of mixture, while elongation to failure was almost the same as the carbon steel and yield point phenomena disappeared. The synergetic heterostructure effect of the layered structure was attributed to the formation of strain gradient and back stress strengthening effect due to the mechanical incompatibility between each region in the layered structure. Applying 220 °C preheating reduced the layered structure's elongation by assigning different strengths and residual stresses to each layer. The current result suggested that the mechanical incompatibility between domains in the interface region, including the residual stress field distribution, should be carefully controlled to improve the mechanical behavior of the interface region.