Monte Carlo Potts Investigation of the Role of Sparse
Recrystallization in Dynamic Abnormal Grain Growth
By: Alan Williamson
Advisors: Professor Jean Pierre Delplanque
Dynamic abnormal grain growth (DAGG) is a type of abnormal grain growth discovered in Molybdenum that occurs during dynamic straining. Specifics about DAGG initiation and propagation are dependent on the processing conditions. A theory proposed for explaining DAGG is through the nucleation and growth of a sparse number of recrystallized grains. These recrystallized grains could grow abnormally using their strain energy driving force advantage. This theory is investigated numerically by modeling dynamic recrystallization using the Monte Carlo Potts method.
Dynamic recrystallization is studied to answer whether sparse recrystallization is possible, if sparse recrystallization can cause abnormal grain growth and under what conditions sparse recrystallization is accomplished. Viable sparse recrystallization can be achieved and will cause DAGG-like behavior through the nucleation and rapid growth of a single recrystallized grain. The conditions to achieve sparse recrystallization are examined using the relationship recrystallization has with strain energy and microstructural parameters. Results show that a critical strain energy of 6 grain boundary area sections of non-dimensional (n.d.) energy is needed to allow viable nucleation of recrystallized grains. This value can be reduced to 5 n.d. with the inclusion of external solid-vapor surfaces. Sparse recrystallization is possible by minimizing the availability of nucleation sites and the rate new nucleation sites are formed.
This is accomplished by minimizing strain energy, while still above the critical value, coupled with a coarse microstructure. The inclusion of non-ideal microstructural features can assist in achieving sparse recrystallization. Anisotropic grain boundary energy and an external solid-vapor boundary will reduce the availability of viable nucleation sites, and nano-sized pinning particles will reduce the rate new nucleation sites can be created.
Date(s) - 01/22/2015
5:00 pm - 6:00 pm