This study employs the direct energy deposition method to fabricate functionally graded materials (FGMs) using GH3536 and GH4169 alloys. The approach achieves a seamless linear gradient transition in the FGMs, progressing from GH3536 alloy to GH4169 alloy. Additionally, the impact of a solid solution twin-aging process on the properties of the FGMs was investigated. The findings reveal that variations in the powder content of GH3536/GH4169 alloy exhibit minimal impact on the microstructure of the deposited FGMs, with columnar crystals predominantly growing along the <001> direction. The direct energy deposition process induces an exceptionally high temperature gradient and cooling rate, preventing the timely precipitation of the second strengthening phase (γ", γ', δ), as well as M6C and M23C6 in the FGMs. Furthermore, the formation of the Laves phase (Ni2Nb, Cr2Mo) diminishes the overall performance of the FGMs. In correspondence with the linear variation of GH3536/GH4169 alloy powder content, the hardness of each layer within the deposited FGMs exhibits an initial increase followed by a subsequent decrease. Following the solution aging treatment, complete dissolution of the Laves phase and δ phase occurs, leading to the formation of a secondary chain phase (M23C6) along the grain boundaries. Simultaneously, needle and granular δ phases disperse within the grain structure, contributing to enhanced performance in the FGMs and ensuring uniform hardness throughout.