U.S. Department of Energy integrated manufacturing predoctoral fellowships: Fellows` annual report 1997--1998
In the uniform droplet spray (UDS) process, a jet of liquid metal is broken up into uniform droplets by applying a periodic perturbation to the jet at a specific frequency and amplitude. The droplets are electrically charged to the same polarity to prevent in-flight merging. As a result of the uniform droplet size distribution, the dynamic and thermal states of the droplets can be precisely controlled in the UDS process. Before the UDS process can be applied to the production of aluminum sheets, the thermal history of the droplets must be understood. The incoming thermal state of the droplets at impact with the substrate significantly affects the degree of droplet consolidation as well as the microstructural grain size, which in turn determine the final material properties of the sprayed part. Therefore, the first step in this research was to simulate and measure the droplet thermal state during flight. The thermal state of a solidifying droplet is defined by its temperature and volume fraction of solid. To predict the temperature and solid fraction of the droplets as functions of flight distance, a thermal model was developed for aluminum binary alloy droplets by assuming Newtonian cooling, no undercooling, and local equilibrium at the solid/liquid interface during solidification. Experiments to validate the droplet thermal model were made with Al-4.5 wt% Cu and Al-4.3 wt% Fe droplets, 275 {micro}m and 250 {micro}m in diameter, respectively. The droplets were quenched at different flight distances and their microstructures were examined metallographically using SEM analysis. By observing the change in microstructure from a fully liquid droplet to a fully solid powder, the solid fraction of the droplet as a function of flight distance can be measured.
- Research Organization:
- National Center for Manufacturing Sciences, Ann Arbor, MI (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- FG02-93ER14370
- OSTI ID:
- 656800
- Report Number(s):
- DOE/ER/14370-T1; ON: DE98006447; TRN: AHC29817%%359
- Resource Relation:
- Other Information: PBD: 22 May 1998
- Country of Publication:
- United States
- Language:
- English
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