Microstructural Study of Containerless Solidification of Al–20wt%Ce Alloy

Containerless solidification of Al–20wt%Ce is investigated experimentally using the electromagnetic levitation (EML) and impulse atomization (IA) techniques. In the processed EML samples, small primary undercooling and minimal eutectic undercooling are shown. The microstructure consists of large primary Al₁₁Ce₃ dendrites surrounded by an α-Al–Al₁₁Ce₃ eutectic. Phase fractions determined by neutron diffraction are similar to the values obtained from a Scheil–Gulliver solidification simulation. Larger IA powders (between 425 and 1000 μm) show a microstructure qualitatively similar to that of EML samples, implying that they follow a similar solidification path. Quantitatively, microstructural features are finer due to the higher cooling rates involved in the solidification process. Atomized particles with a size lower than 425 μm show a strikingly different microstructure, with a very fine eutectic giving way to large intermetallic plates surround by a regular eutectic. Microhardness testing of the structures shows a significant increase in hardness as the sample size decreases, going from 45.8 ± 3.6 HV for the EML sample (lowest cooling rate) to 142.2 ± 12.0 HV for particles in the 106–150 μm range (highest cooling rate).