Effects of grain boundary constraint on properties of polycrystalline materials.

Grain boundary networks are engineered by increasing the fraction of boundaries which exhibit improved properties. Favourable boundaries have either low grain boundary misorientation or they are special boundaries, such as coincident site lattice boundaries. Significant improvement in properties such as corrosion resistance, critical current in superconductors and mechanical strength and toughness occur, provided percolating grain or grain boundary structures can be engineered. We develop computational models for grain boundary engineered polycrystals and demonstrate that grain boundary constraints modify the behaviour near the percolation threshold. We postulate that this is due to an enhanced clustering of weak boundaries induced by grain boundary constraints. In random grain structures the fraction of strong grain boundaries may be measured in two ways, either the length fraction, c, or the edge fraction ce. We find that grain boundary constraint shifts the length fraction threshold, c*, of Potts model polycrystals to higher values, while the edge fraction, ce*, remains almost the same in both correlated and uncorrelated grain structures. [ABSTRACT FROM AUTHOR]