Modelling Microstructural Development in Spray Forming: Experimental Verification

Abstract

Experiments to determine the sticking efficiency of droplets in spray forming and the as cast porosity in two different spray formed geometries (tubes and billets) have been carried out in two alloys, guided by modelling of different aspects of spray forming. Two major results were found. For a given geometry a single parameter, the liquid fraction f ₁ in the spray appears to control the process, independent of the alloy used. For billets the highest sticking efficiencies were obtained at f ₁ of about 0·3 and the deposits made with this liquid fraction, and higher, had minimum porosity. Second, this optimum value of f ₁ was found to increase, however, to about 0·55–0·6 for tubes. It is argued that this distinction between the geometries arose since f ₁ on the top surface of the deposit was significantly lower for the tube geometry than for the billet geometry. This result suggests that the critical control parameter is actually the liquid fraction on the deposit surface. It was also found that the sticking efficiency increased as the tube rotation rate was reduced and that the material failing to stick to the deposited billets was partially solid and partially liquid at the moment of leaving the deposit. PM/0754