A precipitation-hardened medium-entropy alloy with low thermal expansion and high ductility

Alloys with low thermal expansion are vital for precision components in aerospace, cryogenics, optics, and electronics, where dimensional stability under thermal cycling is essential. As these applications face harsher mechanical and thermal conditions, materials must offer not only low thermal expansion but also high strength and ductility. Achieving all three remains difficult, as their underlying microstructural requirements often conflict. Here, we present a medium-entropy alloy, Fe54Ni34Co6Ti3Al3 (at.%), designed to overcome this challenge through tailored precipitation engineering. The alloy forms coherent L12 nanoprecipitates that not only provide substantial precipitation strengthening but also modulate the composition of the face-centered cubic matrix. This tuning induces a low coefficient of thermal expansion and metastability in the matrix, enabling transformation-induced plasticity that enhances ductility and strain hardening. As a result, the alloy achieves a tensile yield strength of (1036±21) MPa, uniform elongation of 18.4%±1.1%, and a coefficient of thermal expansion of 5.8×10−6 °C−1. This work demonstrates a precipitation-driven pathway to reconcile strength, ductility, and thermal stability, offering a new strategy for designing multifunctional structural materials for advanced engineering environments.