Phase equilibrian and thermodynamics of rare earth-iron systems

Sammanfattning: The present thesis was initiated by a quest for knowledgeabout the Fe-Tb-Dy system and is focused on the basicthermodynamics of the rare-earth systems with primarily iron.The final aim is to create a thermodynamic database for rareearth-iron systems, a database from which all phase diagramsand thermodynamic properties of interest may be calculated. Theemphasis is on the iron-rare earth systems but occasionallyother systems are considered, e.g. when a more systematic studyis performed in order to extrapolate necessary properties.In the thesis calculations, empirical predictions, e.g.based on the atomic number, and assessments are combined withexperimental investigations. During this work many questions ofmore fundamental nature appeared and some of them are tackledin the thesis. One may mention particularly:- In the Fe-Dy and Fe-Tb systems, the lack of thermodynamicdata led to several questions. For example, is it possible toobtain reliable values for the enthalpies of formation for theintermetallic phases by considering trends in the periodictable? Thus a systematic study, to predict the enthalpies offormation of the Laves phases, including the rare earth- iron,cobalt and nickel systems was performed, and the enthalpies forthe intermetallic phases in the Fe-Dy and Fe-Er systems weremeasured.- The solubility of Fe in Dy and Dy in Fe are determined bythe so-called lattice stabilities. These quantities arepredicted in the thesis by assessing intra rare earthsystems.- The transformation between the different close-packedstructures, e.g. dhcp and hcp, is controversial. Is there atwo-phase field between dhcp and hcp in the phase diagram orcan the two phases gradually transform into each? According tothe latest review article in the field such a gradualtransformation is indeed possible. However, when criticallyexamining the crystallographic relations and studying the earlyarticles on the Nd-Sc system the present author concluded thatthe transformation must always be first order, i.e. there mustbe a two-phase field.- The Fe2Dy phases is a ferrimagnetic compound. The effectof the magnetism on the thermodynamic properties isconsidered.Key Words:Rare earth metals, Terfenol-D, Laves phase,Enthalpy, experiment, Magnetostrictive material, intra rareearth systems, Fe-Tb, Dy-Fe, Dy-Fe-Tb, Er-Ho, Dy-Ho, Ho-Tb,Er-Tb, Dy-Er, Gd-Sc, Nd-Sc, Sc-Y, Heat capacity, Thermodynamic,Phase Equilibria