The evolution of microcrystalline structures in supercooled metal powders

摘要: A numerical model has been developed to study the relative effects of nucleation and growth kinetics on evolution ultrafine grain structures observed in some supercooled metal powders. The thermal history during solidification is analyzed using a Newtonian heat transfer formulation coupled classical models for homogeneous continuous with diffuse interface. results indicate that decreasing particle size increases both supercooling prior excursion beyond temperature. After first nucleus appears, compctition established between formation new nuclei existing one(s). There range sizes which achievable supercoolings are high enough produce massive before any significant growth—and ensuing recalescence—can take place. probability multiple may be evaluated from dimensionless parameter combining characteristic frequencies nucleation, growth, processes at moment nucleation. Calculations Al Ni systems confirm experimental observation latter stronger tendency supercool develop microcrystalline structures.