Abstract: Aiming at low strength due to the obvious interface formed by the connection of IN718 and 316L, the direct and gradient connected IN718/316L components are manufactured by laser directed energy deposition (LDED) process. Scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) are used to observe the microstructure at the interface of directly and gradient connected heterogeneous metals. In addition, the digital image correlation (DIC) in situ tensile technology is used to investigate the overall strength of directly connected and gradient connected IN718/316L components, as well as the strain distribution at the interface during the tensile process. The results show that there is an obvious interface between directly connected IN718/316L components, and the microstructure of 316L and IN718 regions near the interface is quite different. Elements like Fe are significantly increased at the interface, while elements including Ni and Nb are significantly decreased from the IN718 to 316L region. There is no obvious interface in gradient connected IN718/316L, and the there is a trend of transformation from cellular crystal to columnar dendrite in microstructure along the graded direction from pure 316L to pure IN718. In addition, the tensile strength of gradient connected IN718/316L is increased by 28.77% compared with that of direct connection method. The elimination of obvious interface between heterogeneous metals, the gradual element distribution and significant improvement of the tensile strength are realized by the gradient connecting of heterogeneous metals.

Key words: laser direct energy deposition, In718/316l, functionally graded material, tensile property, microstructure