Spinodal-modulated solid solution delivers a strong and ductile refractory high-entropy alloy

Body-centered-cubic (BCC) refractory high-entropy alloys (RHEAs) are being actively pursued due to their potential to outperform existing superalloys at elevated temperatures. One bottleneck problem, however, is that these RHEAs lack tensile ductility and, hence, processability at room temperature. The strategy previously invoked to sustain ductility in high-strength HEAs is to manage dislocation movements via incorporating dispersed obstacles; this, however, may also have embrittlement ramifications. Here, a new strategy is demonstrated to achieve ductile BCC HfNbTiV, via decomposing the BCC arrangement (beta phase) into a beta(BCC1) + beta*(BCC2) arrangement via spinodal decomposition, producing chemical composition modulations and, more importantly, elastic strain on a length scale of a few tens of nanometers. The periodically spaced beta*, with large lattice distortion, is particularly potent in heightening the ruggedness of the terrain for the passage of dislocations. This makes the motion of dislocations sluggish, causing a traffic jam and cross-slip, facilitating dislocation interactions, multiplication, and accumulation. Wavy dislocations form walls that entangle with slip bands, promoting strain hardening and delocalizing plastic strain. A simultaneous combination of high yield strength (1.1 GPa) and tensile strain to failure (28%) is achieved; these values are among the best reported so far for refractory high-entropy alloys.

Automated summary

A new strategy is demonstrated to achieve ductile BCC HfNbTiV by decomposing the BCC arrangement into two different phases via spinodal decomposition, resulting in chemical composition modulations and elastic strain on a length scale of a few tens of nanometers. The periodically spaced beta* with large lattice distortion is particularly effective in hindering dislocation movement, leading to strain hardening and enhancing plastic strain delocalization, ultimately achieving high yield strength and tensile strain to failure.