Mechanical performance of (NbTaW)1−xMox (x = 0, 0.05, 0.15, 0.25) refractory high entropy alloys: Perspective from experiments and first principles calculations

Abstract

NbMoTaW refractory high entropy alloy (RHEA) possesses superior high temperature mechanical strength while the very low plastic strain at room temperature limits its practical applications. In present work, the method of adjusting composition was employed to improve the mechanical properties of (NbTaW)1−xMox (x = 0, 0.05, 0.15, 0.25) alloys especially the plasticity at room temperature by the combination of experiments and first-principles calculations. Phase composition of the (NbTaW)1−xMox alloys identified using experiments and theoretical prediction were all single-phase solid solution. Microstructure and elements distribution of the alloys were characterized by SEM and EDS. All the as-casted alloys had dendrite structures and the grain size firstly increased (x < 0.15) and then decreased (x > 0.15) with the increase of Mo content. The compressive properties and the analysis of fracture surface demonstrated that strength and ductility of (NbTaW)1−xMox alloys were obviously enhanced with the decrease of Mo content. NbTaW MEA had the maximum mechanical strength (1460 MPa) and ductility (16.2%) in the designed alloys. Both the mechanical strength and plasticity at room temperature were greatly improved compared with that of NbMoTaW RHEA. The experimental results well agreed with that of first-principles calculations. The elastic anisotropy and microhardness of these alloys were also predicted. The orders of elastic anisotropy were (NbTaW)0.75Mo0.25< (NbTaW)0.85Mo0.15< (NbTaW)0.95Mo0.05< NbTaW. The hardness of (NbTaW)1−xMox alloys were increased with increasing of Mo content. Optimizing composition was demonstrated to be an effective method to improve the mechanical properties of NbMoTaW refractory high entropy alloy.