MICROSTRUCTURAL CHARACTERIZATION OF AS-CAST RAPIDLY SOLIDIFIED Al-Sm, Al-Gd AND Al-Er BINARY ALLOYS.

Rapidly solidified ribbons of three aluminum-rare earth (lanthanide) alloys, Al-10wt/oSm; Al-11. 4wt/oGd and Al-11. 6wt/oEr, were prepared by melt spinning with little variation in the microhardness of the as-cast ribbons from system to system. Minor differences in the microstructural morphology occured which are attributed to changes in the direction of heat flow. The scale of the microstructure remained approximately the same, and indicated a cooling rate during solidification of about 10**5 K/s. X-ray and electron diffraction analysis confirmed the presence of metastable Al//4Gd and Al//4Sm, and the equilibrium phases Al//3Er and Al//3Sm. Positive identification of Al//4Gd has resolved a long-standing controversy concerning the existence of this phase, which was shown to be a function of the cooling rate during solidification from the melt.