Plastic deformation capacity obtained by the process of strain delocalization in Hf_0.5Nb_0.5Ta_0.5Ti_1.5Zr multi-principal-element alloy

Multi-principal element alloys (MPEAs) with body-centered-cubic (BCC) structures composed of elements of IVB, VB, and VIB usually exhibit high compressive strength and superior high-temperature performance. However, premature necking under tensile loading at ambient temperature limits their applications. Herein, we report the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA with a single BCC phase, which performs considerable tensile plasticity by the process of strain delocalization. The formation of dispersed slip bands and two major strain localized regions suppress premature necking. The strain-localized region with a larger strain gradient realized strain delocalization during non-uniform deformation, resulting in considerable tensile plasticity (similar to 20%) with a yield strength of 922 MPa. Two dominated work hardening mechanisms were revealed. One is the geometrically necessary dislocations (GNDs) produced by non-uniform deformation which can coordinate deformation incompatibility, thus enhancing plastic deformation capability. The other is the lattice distortion which can provide an easy path for the cross slip of dislocations and realize strain delocalization. These two kinds of work-hardening mechanisms jointly contribute to the significant plastic deformation capacity of the Hf0.5Nb0.5Ta0.5Ti1.5Zr MPEA.