CONTRIBUTION TO THE STUDY OF THE ALLOYS AND INTERMETALLIC COMPOUNDS OF ALUMINUM WITH THE RARE-EARTH-METALS

General properties of aluminium alloys of the rare earth metals are br iefly summarised. Their phase equilibria and the crystal structures of the different intermediate phases are presented and discussed. The re sults obtained in the experimental investigation of the Y-Al and Sm-Al systems are reported. The formation enthalpies of YAl2 and SmAl2 have been re-measured, resulting in -50.5 kJ/(mol at) and -55.0 kJ/(mol at ) at room temperature, in a good agree ment with literature data. Phas e equilibria investigation in the Sm-Al system has been carried out an d the results obtained via thermal analysis, micrographic examination, microprobe and X-ray diffraction analyses described and discussed in the framework of the general behaviour of the rare earth alloys. The e xperimental Sm-Al phase diagram, collated with previous literature dat a, is compared with the results of a thermodynamic optimisation. The f ollowing intermetallic compounds exist: Sm2Al (peritectic decompositio n, at 860 degrees C) SmAl (per.dec.960 degrees C), SmAl2 (melting poin t 1480 degrees C), SmAl3 (peritectoidal decomposition at 1130 degrees C), Sm3Al11 (melting point similar to 1380 degrees C). The following e utectic equilibria have also been determined or confirmed: 20 at% Al a nd 760 degrees C, 75 at% Al and 1340 degrees C, 97.0 at%Al and 635 deg rees C. A eutectoidal equilibrium occurs at 10 at% Al and 700 degrees C. (C) 1997 Elsevier Science Limited.