Nanoindentation and orientation imaging analysis of high entropy Ti–Nb–Zr–Ta–Mo alloys exhibiting dendrite microstructure

Refractory high entropy alloys (RHEAs), particularly Ti–Nb–Zr–Ta–Mo, are promising materials because of their high mechanical properties at elevated temperatures. Although a unique solid-solution phase characterizes these materials, the dendrite structure exhibits a clear element segregation when prepared by liquid route, leading to a different composition between dendrite and interdendrite. This study investigates the local mechanical properties of dendritic and interdendritic regions and the effect of adding Mo on the segregation and hardness. Two alloy compositions, i.e., Ti 25 Nb 25 Zr 25 Ta 25 and Ti 30 Nb 20 Zr 20 Ta 20 Mo 10 (at.%), were produced by copper mold suction casting. Characterization was carried out by XRD, EBSD, and nanoindentation mapping. It was observed that Mo reduces the lattice difference between the dendrite and interdendrite; both play different roles during plastic deformation, as interdendrites accumulate higher dislocation density. The alloys did not show any strain hardening after the compression test. Finally, Mo plays a key role in increasing the mechanical properties by solid solution hardening.