Dynamics of grain boundary premelting

Abstract

The mechanical strength of a polycrystalline material can be drastically weakened by a phenomenon known as grain boundary (GB) premelting that takes place, owing to the so-called disjoining potential, when the dry GB free energy $$\sigma _{gb}$$ σ gb exceeds twice the free energy of the solid–liquid interface $$\sigma _{sl}$$ σ sl . While previous studies of GB premelting are all limited to equilibrium conditions, we use a multi-phase field model to analyze premelting dynamics by simulating the steady-state growth of a liquid layer along a dry GB in an insulated channel and the evolution of a pre-melted polycrystalline microstructure. In both cases, our results reveal the crucial influence of the disjoining potential. A dry GB transforms into a pre-melted state for a grain-size-dependent temperature interval around $$T_m$$ T m , such that a critical overheating of the dry GBs over $$T_m$$ T m should be exceeded for the classical melting process to take place, the liquid layer to achieve a macroscopic width, and the disjoining potential to vanish. Our simulations suggest a steady-state velocity for this transformation proportional to $$\sigma _{gb} -2 \sigma _{sl}$$ σ gb - 2 σ sl . Concerning the poly-crystalline evolution, we find unusual grain morphologies and dynamics, deriving from the existence of a pre-melted polycrystalline equilibrium that we evidence. We are then able to identify the regime in which, due to the separation of the involved length scales, the dynamics corresponds to the same curvature-driven dynamics as for dry GBs, but with enhanced mobility.

Grain boundary diffusion of ferropericlase: Implications for the core-mantle interaction

“…melting point. This order-disorder transition is termed GB premelting (Torabi Rad et al, 2020) and has been observed in many materials (e.g., Glicksman & Vold, 1972;Dillon & Harmer, 2007;Frolov et al, 2013). Similar to the findings of Riet, Van Orman, and Lacks (2021) and , the GB in this quasi-liquid state exhibits considerable disorder nature and transport properties close to those of a supercooled liquid.…”

Surface induced melting of long Al nanowires: phase field model and simulations for pressure loading and without it

“…Good results have been obtained compared to previous experiments on temperaturedependent molten surface layer thickness for nanoparticles and size-dependent melting temperature [42,43]. The PFM is used for modeling the premelting of grain boundaries in pure materials [44][45][46]. Crystal-crystal PT is modeled via the PFM as a surface-induced virtual premelting [47].…”

Exploiting grain boundary diffusion to minimize dendrite formation in lithium metal-solid state batteries

“…The GB activation energies at high temperatures fall in the range of 0.2 to 0.4 eV, suggesting a different diffusion mechanism compared to low temperature diffusion. Prior studies 17,57–59 have reported that pre-melting can occur at GBs – i.e. , a disordered phase forms in the GB region at temperatures below the bulk melting temperature.…”