[SY-I2] Microstructure Stabilization and the Herring Condition
Invited
Consistency of properties is critical for materials performance, and fundamentally depends on the stabilization of the microstructure. Existing stabilization techniques often rely on chemical modifications, with the solute preferentially segregating to the interfaces or precipitating as small second phase particles. The idea to instead stabilize a microstructure by modifying the crystallographic degrees of freedom is part of the broader subject known as grain boundary engineering. This has been most successful with materials that form low-energy annealing twins, though this severely restricts the materials to which the concept can be applied.
We propose that, rather than increasing the fraction of low-energy boundaries, grain boundary engineering can most effectively stabilize a microstructure by increasing the fraction of boundaries with boundary plane orientations at cusps in the energy landscape. The resistance of such boundaries to reorientation can pin boundary junction lines in two-dimensional materials and boundary junction points in three-dimensional materials. This is discussed in the context of the two-dimensional Herring condition and the three-dimensional analogue, which is apparently not widely known in the literature.
This leads to the idea that the microstructure of materials with arbitrary chemical compositions could be stabilized by introducing a misorientation distribution that makes many singular boundary plane orientations available; the material would then be allowed to evolve to a local minimum of the overall grain boundary energy, with the junction points pinned in metastable configurations. Simulation of such a process requires the implementation of accurate and general equations of motion for the junction points. We finally describe our ongoing development of a finite element-based microstructure evolution code for this purpose.
We propose that, rather than increasing the fraction of low-energy boundaries, grain boundary engineering can most effectively stabilize a microstructure by increasing the fraction of boundaries with boundary plane orientations at cusps in the energy landscape. The resistance of such boundaries to reorientation can pin boundary junction lines in two-dimensional materials and boundary junction points in three-dimensional materials. This is discussed in the context of the two-dimensional Herring condition and the three-dimensional analogue, which is apparently not widely known in the literature.
This leads to the idea that the microstructure of materials with arbitrary chemical compositions could be stabilized by introducing a misorientation distribution that makes many singular boundary plane orientations available; the material would then be allowed to evolve to a local minimum of the overall grain boundary energy, with the junction points pinned in metastable configurations. Simulation of such a process requires the implementation of accurate and general equations of motion for the junction points. We finally describe our ongoing development of a finite element-based microstructure evolution code for this purpose.