Ductile alloys offering 100 MPa tensile strength at 2,400 °C

Extreme applications call for materials that are not only strong to withstand thermomechanical loads at temperatures in excess of 2,000 °C (refs. ^1-3), but also highly formable at room temperature to allow for processing into complex-shaped parts. The latter excludes brittle ceramics⁴ and intermetallic compounds⁵, limiting the selection to highly ductile metals and their alloys, but for them, an adequate strength at ultrahigh temperatures seems unreachable. Here we show a breakthrough in casting alloys that achieve both simultaneously. A boron-stabilized HfO₂-strengthened Ta-based alloy was carefully crafted using a new boron-intervened in situ oxidation reaction, producing about 50-nm diameter oxide particles dispersed densely and uniformly in the grain interior. The new alloy fills the blank at ultrahigh temperatures in terms of tensile yield strength, around 200 MPa at 2,000 °C and 100 MPa at 2,400 °C, while simultaneously possessing an excellent strength-ductility balance at room temperature (ultimate tensile strength >800 MPa, elongation-to-failure of about 35%), a property combination surpassing all previous refractory (including multi-principal-element) alloys. Moreover, the boron segregation around the oxide nanoparticles imparts excellent thermal stability against coarsening at 2,000-2,400 °C. Our strategy thus goes beyond traditional oxide-dispersion strengthening to enable highly ductile refractory alloys that are capable of load-bearing applications at extreme temperatures.