On the kinetic mechanism of grain boundary wetting in metals

The thermodynamic condition characteristic of grain boundary wetting (GBW) causes an imbalance between grain boundary (GB) and solid–liquid interphase surface tensions ${\gamma }_{\mathrm{GB}}$ and ${\gamma }_{\mathrm{SL}}.$ This creates in turn a force acting at the root of the GB groove, and pointing into the solid. The “indentation” action of this force is suggested to cause stress-driven self-diffusion into the GB. This process removes the solid atoms from the groove cavity and causes their deposition along the GB (“internal solution”). Assuming that the GB acts as a perfect sink, this “self-indentation-internal solution” mechanism can account for a number of GBW features: the non-Mullins grooving morphology and linear kinetics, the origin of the singular stress field at the wetting front, the expansion of the solid under GBW, the influence of external stress on GBW, the GBW transitions with temperature, and the fast atomic penetration of the liquid metal ahead of the groove root.