PhD Thesis Colloquium: Mr.Shubham P. Karmokar (23/09/25)
Thesis title:
Selection of Dendritic Microstructures across a Wide Range of Thermal Gradients and Cooling Rates: A Cellular Automata Study
Faculty advisor(s):
Prof. Pikee Priya
When?
23rd September, 2025 (Tuesday), 4:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract:
Lipton–Glicksman–Kurz (LGK) and Kurz–Giovanola–Trivedi (KGT) are classical analytical models for dendritic growth, widely used to describe the evolution of equiaxed and columnar dendrites under isothermal conditions. The LGK model treats solidification as an equilibrium diffusion-controlled process, incorporating solutal and curvature-driven tip undercoolings, whereas the KGT model introduces off-equilibrium solute trapping and an additional kinetic undercooling that becomes significant at high tip velocities. The resulting velocity–undercooling relationships are central to predicting microstructural evolution and columnar-to-equiaxed transition (CET), traditionally modeled using a Johnson–Mehl–Avrami type evolution of spherical equiaxed grains that block advancing columnar fronts. The applicability of LGK and KGT models to non-isothermal solidification has been revisited. The analytical CET criterion has been correlated to the evolution of dendritic shaped equiaxed grains. In this work, we systematically investigate solidification microstructure evolution over a broad spectrum of processing conditions—from conventional casting to additive manufacturing—using a Cellular Automata (CA) framework. Based on these simulations, we propose a CET criterion and microstructure selection map expressed in terms of experimentally accessible parameters: thermal gradient (G) and cooling rate (Ṫ). The constructed map is further validated against analytical formulations. A key outcome of this study is a new methodology for estimating the interface width in CA simulations, revealing that LGK dendritic tips exhibit a more diffuse interface (~1 µm), while KGT tips are considerably sharper, of the order of a few Å.