When a molten metal droplet hits a solid plate and freezes, the shape of the flattened, solidified splat that is formed depends on the temperature of the plate. Figure 1 shows aluminum splats produced by wire arc spraying, a widely used coating process in which an electric arc is struck between the tips of two continuously fed wires. A high velocity air jet directed at the gap between the wires strips off droplets of molten metal and propels them onto the surface being coated. In the study 1 from which Fig. 1 was taken droplet diameters ranged from 16 to 25 μm and velocities from 100 to 125 m/s. Droplets that landed on a polished stainless steel plate at 25°C formed irregular shaped splats (Fig. 1(a)), while those impinging on a plate heated to 350°C produced almost perfectly circular splats (Fig. 1(b)).

Why does surface temperature affect splat...

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