Satellite formation mechanism in gas atomised powders

摘要

An Al-1Li alloy along with tin (under argon and helium) and pure copper powders (under helium) were produced in a pilot plant gas atomizer. The pressure of the atomizing gases used was 1.85 MPa, except that of argon gas in Sn powder production(l.56 MPa). The atomizing agents were used in a confined design nozzle operating vertically upwards. The morphology, size, size distribution, and surface features of the powder particles used in the present study (i.e. Al, Al-Li, Cu, Mg, and Sn powders)were examined by scanning electron microscopy and by dry sieving in order to size the powders. It was observed that for satellite formation in gas atomized powders there is a need for both coarse and fine particles. Under turbulent atomization conditionsthese two families of particles of different size and mass must interact with each other. The probability of this interaction increases not only when the amount of fine particles is high, arising from efficient secondary breakup depending on the type ofatomizing gas used and its pressure, but also when the shape of the coarse particles is irregular and the surface texture is rough. If this probability of interaction results in welding of finer particles to larger ones during in flight collisions thenthis increases the true satellite formation process. When the susceptibility of the material being atomized to oxidation is high, the oxygen potential of the atomization environment and the atomizing gas pressure are effective in controlling the shapeirregularity of the coarse powders produced. The inhomogeneity of the surface oxide film thicknesses influences the surface roughness.