Effect of thermal conditions on microstructural features during spray forming

Abstract

The evolution of fine-grained microstructure, during spray forming is a noteworthy feature and it is achieved by properly designed parameters. These parameters include the thermodynamic properties of the gas and the material and the important process variables like superheat temperature, gas pressure, metal flow rate and flight distance. In the present investigation, fundamental characteristics of droplet dynamics and heat flow pattern have been analysed during the process. It has been indicated that the heat transfer coefficient at the droplet–gas interface is strongly influenced by the size of the droplets and their relative velocity with the gas stream. The droplet dynamics and the thermal state during deposition accordingly govern the microstructure evolution in the deposit. The solidification structure along peripheral to central regions of spray deposits, obtained using a spray atomization and deposition facility available at NPL in conical and flat disc shapes, has been evaluated. On the basis of preliminary observations, the analysis of process parameters during atomization and deposition and their consequences on the scale of microstructure in atomized droplets and spray deposits has been compared and discussed.