Abstract
Near eutectic Al-Cu droplets were rapidly solidified by Impulse Atomization. A wide range of microstructural scales was obtained at different cooling rates and undercoolings. The micrographs of the investigated samples revealed two distinct zones of different structural morphologies: An undulated eutectic morphology developed during recalescence following the single grain nucleation and a regular lamellar eutectic morphology resulting from the solidification of the remaining liquid post recalescence. The volume fraction of each zone was measured as a function of the droplet diameter, and the nucleation undercooling was deduced using the hypercooling limit equation. Scanning Electronic Microscopy imaging and microhardness measurements were used to evaluate the microstructural scale, and mechanical properties.
Highlights
High undercooling / cooling rate associated with rapid solidification of metallic alloys results in various beneficial microstructural features
The micrographs of the investigated samples revealed two distinct zones of different structural morphologies: An undulated eutectic morphology developed during recalescence following the single grain nucleation and a regular lamellar eutectic morphology resulting from the solidification of the remaining liquid post recalescence
This paper present the observations made on rapidly solidified Al-Cu droplets of eutectic composition, obtained by Impulse Atomization (IA)
Summary
High undercooling / cooling rate associated with rapid solidification of metallic alloys results in various beneficial microstructural features. These include minimal segregation, grain refinement, solubility extension and the formation of metastable phases [[1]][[2]][[3]][[4]]. It is sometimes difficult to relate the observed microstructure with process parameters due to experimental difficulties. These include, measurements of variables such as cooling rate, undercooling and solidification rate, which are very well known to control the final solidification microstructure. A regular lamellar eutectic structure, consisting of alternate α-Al and θ-Al2Cu lamellae, is formed. Al-Cu eutectic solidifies into degenerate / anomalous eutectic structure consisting of irregular θ-Al2Cu precipitates embedded in an α-Al matrix or into undulated eutectic
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