Grain boundary excess free volume—direct thermodynamic measurement

The grain boundary excess free volume (BFV) along with the surface tension determines the major thermodynamic properties of grain boundaries. The BFV controls to a large extent the evolution and stability of polycrystals. Unfortunately, our knowledge about the BFV is completely restricted to data generated by computer simulations, which, in turn, are strictly limited to grain boundaries in the vicinity of special misorientations. We developed a special technique that makes it possible to measure the BFV for practically any grain boundary and provides a way of estimating the BFV for grain boundaries of different classes with high accuracy. A knowledge of the BFV is especially important for fine grained and nanocrystalline systems where it opens new possibilities to design the physical properties and microstructure of such polycrystals.