Abstract: Rare-earth (RE) elements, known as “industrial vitamins”, have permeated modern lives, especially in high-tech applications. Although the RE elements possess close chemical similarities and have been treated as “one element” in the periodic table, their characteristics differ from each other. The RE micro-alloying effect is the crux to ameliorate the physicomechanical and thermochemical properties of materials, thereby the study of RE-related phase diagrams becomes indispensable to the design and optimization of RE-containing materials. However, in reality, the knowledge base in this area is considerably scarce compared with that of other commonly-used elements. In this work, the phase equilibria, phase diagrams, phase transformations, and some recent examples of RE-containing materials design are summarized, with which one can predict the RE solubilities, the RE precipitates, as well as the corresponding service behaviors. The attainment of enhanced materials' properties suggests that the thermodynamic rules extracted from the phase diagrams could serve as fundamental criteria for the successful development of novel RE-containing materials.

Key words: Rare-earth elements, Phase diagrams, CALPHAD, Phase transformations, Materials design