Grain boundary engineering methods improve materials properties by modifying the composition and connectivity of grain boundary networks. A quantitative understanding of grain boundary network characteristics and their impact on materials properties was therefore desirable for both scientific and practical purposes. Here, attention was focussed upon the case of Coble creep, a viscous deformation mechanism prevailing at intermediate to high temperatures. Using computer simulations, the creep viscosity was characterized as a function of the fraction of slow-diffusing so-called special grain boundaries in a 2-dimensional honeycomb grain-boundary network. This basically defined a new class of percolation problem where mass diffusion and force equilibrium were coupled in a complex way. The percolation threshold and scaling exponents were extracted from the simulation data and analyzed in the context of correlations and energy balance on the network. Stress concentrations induced by the grain boundary character distribution, the effect of crystallographic constraints, and an empirical effective-medium equation that could be used with classical creep constitutive laws in order to predict the viscosity of a heterogeneous material were also explored.

Coble Creep in Heterogeneous Materials - the Role of Grain Boundary Engineering. Y.Chen, C.A.Schuh: Physical Review B, 2007, 76[6], 064111 (13pp)