Effects of droplet thermal state on deposit microstructure in spray forming
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Lab. for Manufacturing and Productivity
- Tufts Univ., Medford, MA (United States). Dept. of Mechanical Engineering
Spray forming with mush uniform-droplets deposited onto a solidified deposit surface produced a fine, equiaxed microstructure in a Sn-5wt.%Pb alloy. The equiaxed grains are those of the Sn-rich phase and were delineated with thin films of the Pb-rich phase along the grain boundaries. No splat or spray boundaries were noted. The equiaxed microstructure evolved mainly from fragmented and randomly oriented crystals which originally formed in the droplets before impact. The lack of splat boundaries was explained by the local epitaxial growth of the grains in the prior splat and the oxide-free deposit surface maintained during the experiment. Use of mush droplets is the single most important requirement for the formation of equiaxed microstructures in a spray deposit. The thermal state of the deposit surface may play only a minor role. Molten droplets produced a rapidly solidified columnar microstructure by the epitaxial growth of the Sn-rich phase. No splat boundaries were produced. The primary Sn-rich phase columnar grains were contiguous through the entire deposit thickness of about 20 mm. A schematic process-microstructure map for the spray forming process is used to show the entire process window and expected microstructures for spray forming with uniform-droplet sprays.
- OSTI ID:
- 215339
- Journal Information:
- Scripta Materialia, Journal Name: Scripta Materialia Journal Issue: 5 Vol. 34; ISSN 1359-6462; ISSN XZ503X
- Country of Publication:
- United States
- Language:
- English
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