Abstract

Professor Anthony D. Rollett
Department of Materials Science and Engineering
Carnegie Mellon University

Seminar: October 30, 2006
3:30-4:30pm
Mechanical Engineering, Room 339

An Update on Grain Boundaries and their Properties

Grain boundary energy used to be described in the context of coincident site lattice theory to explain or predict which types of boundaries will have low energies. However, evidence has accumulated that grain boundary energies are more closely related to the energies of the two surfaces that comprise the boundary. Given this simple and elegant basis for a property, it is interesting to compare this result with the situation for grain boundary mobility. Experimental measurements using stored energy as a driving force suggest that the dependence on boundary type is similar to that observed by the Aachen group for curvature driving force. For example, at low temperatures, the sigma-7 boundary type is the most mobile type whereas at higher temperatures, the peak shifts to higher angles. The variation in activation energy with misorientation (angle) is similar although the absolute levels are different for the different driving forces. When compared to theoretical estimates of mobility derived from simulations, the crystallographic anisotropy is again similar, except that the activation energies found in simulation are much smaller than the experimental values. Solute drag in experiments is presumed to account for the difference: this still leaves us the challenge of finding an appropriate scaling of mobilities as a function of composition. Finally, the importance of grain boundary properties is illustrated with the example of texture development during recrystallization.

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