Forming high-strength and softening-resistant AlxHf0.5Mo0.5NbTa0.5TiVZr dual-phase refractory high-entropy alloys

Refractory high-entropy alloys AlxHf0.5Mo0.5NbTa0.5TiVZr with the addition of different amounts of low-density aluminum were developed to improve the strength and softening resistance at elevated temperatures. The microstructure and phase formation were investigated, and the mechanical properties and deformation behavior at various temperatures were studied. The primary dendrites consisted of body-centered cubic (Mo,Nb,Ta)-rich multicomponent phase, and the latter solidified interdendrites contained Al-(Hf,V,Zr)-rich second phase initiating from grain boundaries. With an increased aluminum content, the size of dendrites decreased, and the portion of the network-like second phase increased. The hard precipitates improved the yield strength and softening resistance but sacrificed the ductility of the alloys. At an appropriate aluminum content of x = 0.5, the Al0.5Hf0.5Mo0.5NbTa0.5TiVZr alloy showed promising softening resistance at 600 degrees C with a retained strength of 1240 MPa and a compressive strain of 13 %. A large number of dislocations formed a tangled dislocation forest than glided in a planar way, additionally enhancing the work hardening and improving the softening resistance. However, an excessive accumulation of dislocations at the phase boundaries caused the brittle fracture in the latter stage.