TEM and Synchrotron X-ray Study of the Evolution of Phases Formed During Bonding of IN718/Al/IN718 Couples by TLPB

This study investigates the microstructure across the interconnection zone of IN718/Al/IN718 couples obtained by the Transient Liquid Phase Bonding (TLPB) process at temperatures ranging from 800 °C to 1000 °C. The crystal structure and the chemical composition of the phases formed, including the AlNi intermetallic, were evaluated using TEM-EDS. The evolution of the AlNi layer as a function of bonding time was studied by in situ high energy synchrotron x-ray diffraction. The AlNi lattice parameter increases up to 2.9401 Å and subsequently decreases with the annealing time due to changes in the chemical composition of AlNi. This behavior is related to the formation of two distinct layers of AlNi: Al-rich AlNi and Ni-rich AlNi. The split of the AlNi phase indicates that a chemical partition takes place when Ni and Al atomic concentrations are approximately equal. The growth kinetics of both layers are controlled by diffusion with different growth rate constants. These results contribute to the understanding of the solid-state transformations occurring in a multicomponent and multilayered TLP bond under isothermal conditions.