Formation of coherent BCC/B2 microstructure and mechanical properties of Al-Ti-Zr-Nb-Ta-Cr/Mo light-weight refractory high-entropy alloys

The present work investigated the formation of coherent body-centered-cubic (BCC)/B2 microstructure in Al-Ti-Zr-Nb-Ta-Cr/Mo refractory high-entropy alloy system, in which three alloys with the composition of Al2Ti6Zr2Nb3Ta2(Cr/Mo)(1) were designed. These as-cast alloy ingots were homogenized at 1573 K for 2 h and then aged at different temperatures for 24 h. It is found that the BCC/B2 coherent microstructure with cuboidal BCC nanoprecipitates into the B2 matrix would be formed in 873 K-aged Al2Ti6Zr2Nb3Ta2Cr0.5Mo0.5 alloy with half Cr and half Mo, which is ascribed to a moderate lattice misfit (epsilon = 0.94%) between BCC and B2 phases. It is due to the special coherent microstructure that results in a prominent mechanical property with the highest compressive yield strength (sigma(Ys) = 1314 MPa) and good plasticity among these alloys, while coarse Cr2Ti and Zr5Al3 particles are existed in 873 K-aged alloy with Cr-1. After 1073 K aging, all these alloys with Cr-1, Cr0.5Mo0.5 and Mo-1 consist of BCC, B2 and Zr5Al3, in which BCC/B2 coherent microstructure is destabilized. The strengthening mechanism of BCC/B2 coherent microstructure in 873 K-aged alloy with Cr0.5Mo0.5 was also discussed.

Automated summary

This study investigated the formation and strengthening mechanism of coherent BCC/B2 microstructure in Al-Ti-Zr-Nb-Ta-Cr/Mo refractory high-entropy alloy system. It found that the alloy with Cr0.5Mo0.5 exhibited the best mechanical performance after aging at 873 K.