In this research, the relationship among TLP bonding microstructures, mechanical properties and fracture mechanism of IN 718 / BNi-2 /AISI 316L joint was studied. In the first step, by changing TLP variables e.g. time and bonding temperature in the range 30-60 min and 950-1050 0 C respectively, characteristics of each type of microstructures including formation of destructive phases and homogeneity of microstructures were studied. In the second step, in order to investigate the mechanical properties and their fracture surface morphology, hardness and shear tests were accomplished. In the next stage, based on diffusion behavior of alloying elements, the relationship among microstructure, mechanical properties and fracture mechanism was studied. Results show that microstructures of bonding region were classified in three types. Type I: solid state bonding microstructure, Type II: Athermal – isothermal solidification microstructure, and Type III: isothermal solidification microstructure. It was observed that for each specific microstructure, there is one fracture mechanism or there are more that are dimples fracture resulting from precipitations within matrix, quasi-cleavage fracture resulting from dual microstructure of eutectic – isothermal solidification and dimple-tearing fracture resulting from tiny precipitations within bonding region. Copyright © VBRI Press.