TerfenolD

Terfenol-D is a magnetostrictive alloy of terbium (Tb), dysprosium (Dy), and iron (Fe). It is notable for large strains produced by magnetic fields, enabling conversion between magnetic and mechanical energy. The typical composition is Tb0.3Dy0.7Fe2, with variations used to tune temperature stability and mechanical properties.

Terfenol-D shows one of the largest magnetostrictive effects among metallic alloys. Under magnetic fields of tens of kilooersteds, it can develop strains in the thousands of parts per million, with strong anisotropy. Maximum strain occurs along the magnetically soft axis. Performance declines with temperature and mechanical stress, and the material is brittle.

Fabrication usually yields rods, bars, sheets, or molded shapes. The material is brittle and machining is difficult, so components are oriented to align the magnetostrictive axis and often coated to prevent oxidation; annealing is used to optimize magnetic properties.

Applications include actuators, sensors, ultrasonic and sonar transducers, and vibration control. Limitations are brittleness, temperature sensitivity, and cost from rare-earth elements. Despite these, Terfenol-D remains a leading material for high-force, compact magnetostrictive devices.