MODELING MICROSTRUCTURAL DEVELOPMENT IN SPRAY FORMING - EXPERIMENTAL-VERIFICATION

Experiments to determine the sticking efficiency of droplets in spray forming and the as cast porosity in two different spray formed geometr ies (tubes and billets) have been carried out in two alloys, guided by modelling of different aspects of spray forming. Two major results we re found. For a given geometry a single parameter, the liquid fraction f(1) in the spray ai,pears to control the process, independent of the alloy used. For billets the highest sticking efficiencies were obtain ed at f(1) of about 0.3 and the deposits made with this liquid fractio n, and higher, had minimum porosity. Second, this optimum value off, w as found to increase, however, to about 0.55-0.6 for tubes. It is argu ed that this distinction between the geometries arose since f(1) on th e top surface of the deposit was significantly lower for the tube geom etry than for the billet geometry. This result suggests that the criti cal control parameter is actually the liquid fraction on the deposit s urface. It was also found that the sticking efficiency increased as th e tube rotation rate was reduced and that the material failing to stic k to the deposited billets was partially solid and partially liquid at the moment of leaving the deposit. (C) Osprey Metals Ltd.