Melt Superheat and Gas Pressure Calibration for Tool Steels
Melt superheat fixes metal viscosity while gas pressure sets atomization shear energy, directly controlling powder size, cooling rate, and carbide morphology.
Recalescence
Meaning
Solidification phenomena in undercooled molten metals or semiconductors represent the sudden temperature rise caused by the rapid release of latent heat during crystallization. In industrial manufacturing of alloy powders or semiconductor substrates, recalescence occurs when the rate of latent heat release exceeds the rate of heat extraction to the surroundings. This temperature surge temporarily shifts the solidifying system back toward its equilibrium melting point.
Thermal Mechanism
Liquid metal cooled below its equilibrium freezing temperature remains in a meta-stable liquid state until nucleation starts. Once nucleated, the rapid phase transition to a solid releases latent heat of fusion, which drives the local temperature upward. This surge of recalescence is completed when the system temperature matches the solidus temperature or when heat extraction dominates again.
Microstructural Effect
High rates of heating during this transition alter the local solidification path and determine the final grain size of the material. Because the sudden temperature rise reduces the local undercooling, the growth rate of the solid phase slows down and can lead to coarser dendritic structures or altered phase distributions. In atomized precursor powder production, minimizing this effect is necessary to maintain a uniform, fine-grained microstructural state.
This prevention of coarse grains directly improves the chemical homogeneity and performance of subsequent battery materials.
Process Control
Spray cooling parameters and cooling gas selection are adjusted to maximize heat extraction rates during droplet solidification. Increasing the convective heat transfer coefficient allows the surrounding gas to absorb the released latent heat before the temperature of the droplet rises. This rapid heat extraction is essential when producing spherical alloy powders.
Solidification Dynamics of Rapidly Solidified Droplets in Battery Powder Synthesis
Rapid droplet solidification dynamics dictate grain size, microsegregation, and sphericity in battery powder synthesis, setting tap density and yield.