Kinetic and structural insights into the grain boundary phase transitions in Ni-Bi alloys

First-principles study of grain-boundary wetting in Fe-Σ5(013)[100] tilt boundary

“…The nanoscale intergranular layer spontaneously forms as a first wetting step before eventually becoming much larger by dissolution diffusion phenomena. Another process where one observes GBW is by alloying several elements (often immiscible) followed by high-temperature annealing above the disordering or phase decomposition temperature [2]. After thermal annealing, the thermodynamic equilibrium state is reached with GB segregation of impurities or as a complexion of the GB [3].…”

“…Generally, when GBW occurs, in some cases above a transition temperature, it leads to detrimental mechanical properties with brittle fracture at the intergranular film. The known couples are Al/Sn, Cu/In, Al/Pb-Sn, Al/Ga, Al/Sn-Ga, Cu/Bi, Fe-Si/Zn, Mo/Ni, W/Ni, Zn/Sn and Ni/Bi [1,2]. The kinetics of such spontaneous processes can be truly astounding with GB penetration speed reaching hundreds of micrometers per second in the Al/Ga case or leading to disastrous brittle fracture or complete ruin of an otherwise ductile material like Cu/Bi [4,5].…”