Rare Earth Elements in Advanced Engineering Materials: A Critical Review of Applications, Thermodynamic Behavior, Processing and Mechanical Performance

Rare earth elements (REEs) consist of a group of 17 elements, including the lanthanides together with scandium and yttrium, which are chemically similar yet critically important due to their wide range of applications. Classified as light and heavy rare earth elements, this group has become indispensable in modern high-technology products owing to their unique magnetic, optical, catalytic, electrical, and mechanical properties. Although some REEs are relatively abundant in the Earth’s crust, they are referred to as “rare” due to difficulties in extraction and separation as well as their distinctive geochemical behavior.The global energy transition has significantly increased the demand for rare earth elements, driven by the rapid expansion of electric vehicles, wind turbines, and renewable energy technologies. In particular, elements such as neodymium, praseodymium, dysprosium, and terbium play a critical role in the production of permanent magnets. NdFeB- and Sm–Co-based magnets provide high efficiency in electric motors, generators, defense systems, wind turbines, and electronic devices.In conclusion, rare earth elements hold strategic importance in improving energy efficiency, enabling environmentally friendly technologies, and advancing modern engineering materials. Due to increasing demand and supply risks, recycling, alternative material development, and sustainable mining approaches are expected to become increasingly important in the future.