Synergetic strengthening in HfMoNbTaTi refractory high-entropy alloy via disordered nanoscale phase and semicoherent refractory particle

We propose a novel strengthening strategy that involves the introduction of a high-entropy nanoscale phase (HENP) and semicoherent refractory nanoparticle into the A2 matrix of an as-cast equimolar HfMoNbTaTi refractory high-entropy alloy (RHEA). Based on the design concept of low difference in elemental melting points, equiaxed grains with slight segregation were obtained. The HENP was characterized as a disordered near-coherent structure with a composition significantly similar to the matrix that differed from traditional coherent intermetallics. The heterogeneous nucleation was attributed to the aggregation of the largest Hf atoms and interstitial complexes in the locally distorted matrix. Moreover, the refractory nanoparticle was inferred to be hafnium nitride, possessing high thermal stability and establishing a semicoherent interface with the matrix. Notably, the interface was lined with a Ti film of one or two atomic layers. Furthermore, owing to the high melting point and precipitation strengthening, a highest yield strength (851 MPa) was obtained at 1200 °C compared with those reported cast RHEAs. At room temperature, a high yield strength (1713 MPa) was revealed mainly due to the combined effect of solid-solution strengthening and precipitation strengthening. The present study provides a new pathway for the future design of HEAs.