Contribution to the study of the alloys and intermetallic compounds of aluminium with the rare-earth metals

Abstract

General properties of aluminium alloys of the rare earth metals are briefly summarised. Their phase equilibria and the crystal structures of the different intermediate phases are presented and discussed. The results 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 agreement with literature data. Phase equilibria investigation in the SmAl system has been carried out and 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 experimental Sm-Al phase diagram, collated with previous literature data, is compared with the results of a thermodynamic optimisation. The following intermetallic compounds exist: Sm2Al (peritectic decomposition, at 860 °C) SmAl (per.dec.960 °C), SmAl2 (melting point 1480 °C), SmAl3 (peritectoidal decomposition at 1130 °C), Sm3Al11 (melting point ~1380 °C). The following eutectic equilibria have also been determined or confirmed: 20 at% Al and 760 °C, 75 at% Al and 1340 °C, 97.0 at% Al and 635 °C. A eutectoidal equilibrium occurs at 10 at% Al and 700 °C.