Abstract
This paper reveals the 3D character of the intermetallic layer at the aluminum-steel interface which pops up above the original sample surface during annealing. Popping out of the intermetallics was proven using atomic force microscopy.
The phase expands out of the plane due to the exothermic formation of the Al5Fe2 phase and the feasibility of surface diffusion. Milling by a focused ion beam enabled the comparison of the chemical composition of the surface layer with the bulk interface, showing no difference.
The growth direction is both towards aluminum and steel - the main diffusion flux is from aluminum towards steel, and the new intermetallic phase emerges at the steel side. The shortage of Al atoms causes a shift of the intermetallic as a whole towards aluminum.