Diffusion kinetics of transient liquid phase bonding of Ni-based superalloy with Ni nanoparticles: A molecular dynamics perspective

Transient liquid phase (TLP) bonding has been broadly utilized to join and repair Ni-based superalloy components; however, the understanding of its diffusion kinetics is still in infancy due to challenges in in situ experimental characterization under high operating temperatures. In this research, we examine detailed diffusion kinetics of Ni-based superalloy bonding with Ni nanoparticles employing molecular dynamics (MD), aiming to advance TLP bonding by achieving a desirable diffusion-induced joint microstructure. Diffusion kinetics of TLP bonding is compared with traditional constant heating method (CHM) bonding, by examining diffusion behaviors and microstructure. Self-diffusivity of each specific element is firstly calculated using MD, demonstrating a good agreement with the reported experimental values. The nanoscale size of Ni fillers and high operating temperature induce a large mobility, thus less porosity, while a slower diffusion in TLP bonding than CHM leads to a more crystallized microstructure with nano-sized grains. In addition, non-uniform diffusivity distribution of the surrounding elements influences diffusion pathway and joint microstructure. Therefore, desirable bonding properties can be achieved through Ni nano-filler, optimal temperature, as well as effective composition of atomic surroundings.