Trends in Grain Boundary Mobility: Frequency of new and existing mechanisms

Grain boundary (GB) motion in polycrystalline materials is expected and observed to be dominated by thermally activated processes. This has important implications for properties influenced by the presence of GBs. Here, the GB motions of a catalog of 388 simulated nickel boundaries reveal a rich set of behaviors, which demonstrate that the temperature dependencies of GB mobility are far more complex than originally believed. In the set of 388 boundaries, four different general classes were observed with the following percentages: (I) ~57% exhibited traditional thermally activated mobility; (II) ~20% exhibited non-thermally activated mobility, where mobility was either independent of temperature or mobility decreased with increasing temperature (i.e., not thermally activated); (III) ~14% exhibited mixed modes of mobility, where different trends were exhibited over different temperature regimes (e.g., thermally activated at low temperature and non-thermally activated at high temperature); and (IV) ~9% exhibited unclassifiable mobility trends or were immobile over the studied temperature range. Thus, although the studied set of boundaries is not statistically representative of all GBs, it indicates that we must expand our preconceived notions to include new and interesting phenomena.
The full article can be obtained at doi:10.1007/s11837-013-0801-2