SOLIDIFICATION PROGRESS AND HEAT-TRANSFER ANALYSIS OF GAS-ATOMIZED ALLOY DROPLETS DURING SPRAY FORMING

In order to predict gas and droplet velocities, droplet temperature, a nd fractional solidification with flight distance during spray forming , the Newtonian heat transfer formulation has been coupled with the cl assical heterogeneous nucleation and the specific solidification proce ss. It has been demonstrated that the thermal profile of the droplet i n flight is significantly affected by process parameters such as dropl et size, initial gas velocity, undercooling, and superheat. With incre asing droplet size or initial gas velocity, the onset and completion o f solidification are shifted to greater flight distances and the solid ification process also extends over a wider range of flight distances. It has been found that the corresponding solid fractions formed durin g recalesced, segregated, and eutectic solidifications are linearly re lated to the degree of undercooling and that those solid fractions are insensitive to droplet size, initial gas velocity and superheat.