ANALYSIS OF SOLIDIFICATION IN SPRAY ATOMIZED AND CODEPOSITED METAL-MATRIX COMPOSITES .1. ATOMIZATION

Fluid mechanics, heat transfer and liquid-to-solid phase transformatio n are assessed in optimizing the spray atomization and codeposition pr ocess parameters for size refinement and microstructural uniformity of the deposited material. Atomization gas velocities, atomized droplets velocities, convective heat transfer coefficients, thermal histories of the solidifying droplets, freezing rates, fraction solid evolution and solid-liquid interface propagation velocity are calculated, The in fluence, on the deposit microstructural features, of process parameter s like the atomization gas pressure, the pouring tube orifice: diamete r, the geometrical features of the atomization device, the potency of, pre-existing or injected;as reinforcement, nucleation sites, the wett ing angle between the liquid melt and impurity particles acting as pre ferred nucleation sites, the in-flight distance of the solidifying dro plets in the atomization chamber, is evaluated. As a result of the eva luation, appropriate choice of the adjustable process parameters for t he production of powders and/or deposits with desired grain size and m icrostructure, can be made.