| Abstract Scope |
This work presents a detailed investigation of the microstructural evolution and mechanical properties of an autogenous electron-beam-welded joint between Alloy 718 and Alloy 718Plus, aged at 760 °C for up to 1000 h. The fusion zone exhibits pronounced chemical heterogeneity due to dendritic solidification and Nb segregation, leading to Laves-phase formation in interdendritic regions. Microstructural characterization using SEM, high-resolution TEM/STEM-HAADF, and three-dimensional FIB-SEM tomography, supported by CALPHAD simulations, revealed that the metastable Laves phase decomposes diffusion-controlledly into ä, ç, and ó phases during aging. The decomposition products form a complex interconnected interdendritic network. High-resolution TEM confirmed crystallographic orientation relationships and partially coherent interfaces between the ã matrix and secondary phases. Simultaneously, ã′ precipitation initially increased hardness, followed by softening associated with precipitate coarsening and TCP phase formation. The results demonstrate that aging at 760 °C promotes complex phase evolution rather than microstructural homogenization, significantly affecting welded joint stability. |
