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

Abstract

This study investigates the microstructure across the interconnection zone of an IN718/Al/IN718 couple 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 on a thin lamella (FIB) 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 a increases until a maximum of 2.9407 Å and then decreases with the annealing time, suggesting that the chemical composition of AlNi changes with time at constant temperature. This trend is related with the formation of two distinctive layers of AlNi with different chemical composition: Al-rich AlNi and Ni-rich AlNi. The split of the AlNi phase indicates that a chemical partition takes place when Ni and Al concentration equals. The growth kinetics of both layers are controlled by diffusion but 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.