Al alloying-driven spinodal decomposition enables ultra-strong cast refractory high-entropy alloys

Strengthening in refractory high-entropy alloys (RHEAs) can be achieved through the formation of “compositional heterogeneity” at the atomic scale. Here, we chose Zr₄₅Ti₁₅Nb₂₀Ta₂₀ alloy with a single-phase body-centered cubic (BCC) structure as a matrix and added a small amount of Al to promote a unique spinodal decomposition. The results show that the introduction of Al-X negative mixing enthalpy induces the RHEAs spinodal decomposition to form a nanocubic structure in the form of a basket-like fabric morphology with a characteristic periodicity of 12 nm. Nanocubic structures consist of (Nb, Ta)-rich cubes and Zr-rich channels as well as generate strong localized strain fields at the interfaces. Spinodal decomposition strengthening enables the as-cast RHEA to achieve a yield strength of 1405 MPa. Periodically distributed nanostructures make dislocations move slowly, causing plugging and cross-slip, facilitating dislocation interactions, multiplication, and accumulation. In summary, the chemical heterostructure produced by spinodal decomposition has been remarkably effective in improving the strength of RHEAs.