Haris Doumanidis

Abstract:

Crystallite size is a primary determinant of the mechanical properties in solidified alloy deposits, and thus it is in need of predictive modeling. This project reports on employing uniform droplet spraying (UDS) [1] as a paradigm for solidification modeling of mono-size solid droplets in an oil bath, as well as planar and globular splats on a cooling substrate for AZ₉₁D and Mg₉₇ZnY₂ alloys [2]. The model combines a nucleation and dendrite fragmentation description from solidification theory with a framework for constrained growth of crystalline domains confined by adjacent developing ones [3]. The latter is based on differential attributes of the dynamic temperature field during solidification, derived from semi-analytical expressions for the simple droplet and splat geometries above. The model parameters are calibrated and its predictions are validated against measured domain size distributions on section micrographs, and found to be within a -10% to +14% estimation error range. Further improvement of the model via numerical thermal descriptions for off-line material design and optimization in additive manufacturing is discussed [4], along with its use as a real-time structural observer for closed-loop control based on temperature measurements in UDS-based processes.

[1] Chun, J.-H., Passow, C.H., " Production of Charged Uniformly Sized Metal Droplets ", Massachusetts Institute of Technology, US Patent 5,266,098 (1992).
[2] Fukuda, H, "Droplet-Based Processing of Magnesium Alloys for the Production of High-Performance Bulk Materials", PhD Thesis, MIE Dept, Northeastern University, Boston, MA (2009).
[3] DiVenuti, A.G., Ando, T., " Free Dendritic Growth Model Accommodating Curved Phase Boundaries and High Peclet Number Conditions " Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 29A (12) (1998): 3047-3056.
[4] Wang, P., Sun, H., Wong, P.Y., Fukuda, H., Ando, T., " Modeling of Droplet-Based Processing for the Production of High-performance Particulate Materials Using Level Set Method ", Proc. of IMECE2008, ASME, Boston, MA (2008).