The phase diagram of the terbium–gold alloy system

The terbium-gold phase diagram has been investigated in the 0–100 at% Au field by differential thermal analysis (DTA), X-ray diffractometry (XRD), optical microscopy (LOM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Eight intermetallic phases were found, namely: Tb2Au orthorhombic oP12–Co2Si, peritectic decomposition at 1000°C, TbAu, L.T. form, orthorhombic oC8–CrB type and H.T. form, cubic cP2–CsCl type, congruent melting at 1590°C, Tb3Au4 trigonal hR42–Pu3Pd4 type, peritectic decomposition at 1340°C, Tb7Au10 tetragonal tI136–Gd7Au10 type, peritectic decomposition at 1210°C, TbAu2 tetragonal tI6–MoSi2 type, congruent melting at 1265°C, TbAu3 orthorhombic oP8–TiCu3 type, congruent melting at 1215°C, Tb14Au51 hexagonal hP65–Gd14Ag51 type, peritectic decomposition at 1175°C, and TbAu6 tetragonal tP56–SmAu6 type, peritectic decomposition at 855°C. Four eutectic reactions were found to occur at 880°C and 20.0 at% Au, at 1195°C and 62.5 at% Au, at 1160°C and 71.0 at% Au and finally at 805°C and 89.0 at% Au. A catatectic reaction occurs in the Tb-rich region. The experimental results are discussed and compared with the general behaviour of the other R–Au systems.