Phase Equilibria in Sm-Co-Ti Ternary System

Phase equilibria in the Sm-Co-Ti ternary system are very important for the design of high temperature Sm-Co-based permanent magnets. The isothermal sections in the Sm-Co-Ti ternary system at 1073 K and 773 K were determined using diffusion couples and equilibrated alloys by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), electronic probe microanalysis (EPMA) and x-ray diffraction (XRD) techniques. The ternary intermetallic compound SmTi x Co 12− x (τ) with a ThMn 12 -type structure was confirmed to be stable at 1073 K and 773 K. The composition range of this ternary compound was determined from 9.3 to 17.5 at.% Ti at 1073 K and from 9.4 to 15.6 at.% Ti at 773 K, respectively. SmCo 7 compound with a TbCu 7 -type structure that is a metastable phase in the Sm-Co binary system was found to be stable at 773 K in the Sm-Co-Ti ternary system due to the substitution of Co by Ti, while it was not found at 1073 K. The maximum solubility of Ti in SmCo 7 compound was measured to be about 3.2 at.% at 773 K.