The evolution of compositional and microstructural heterogeneities in a TaMo0.5ZrTi1.5Al0.1Si0.2 high entropy alloy

Highlights: • Original compositional heterogeneity of RHEA is created by solidification. • Annealing results in evident phase decomposition and elemental redistribution. • Zr tends to be repelled from the parent phase during solidification and annealing. • Dynamical recrystallization occurs in RHEAs after compression at 1000 °C. • Necklace microstructures are formed in RHEAs compressed at high temperatures. We report the chemical segregation and the phase decomposition as well as the microstructural response upon plastic deformation in a TaMo_0.5ZrTi_1.5Al0.1Si_0.2 (at.%) refractory high entropy alloy (RHEA) by combining the thermodynamic calculation and the multiple experimental characterization techniques down to near-atomic scales. The alloy's compositional and microstructural heterogeneities under different processing conditions, including casting, annealing and room/high temperature compression, are emphasized. Results show that casting creates the original compositional heterogeneity with evident dendritic microstructures. The dendrite consists of a single body-centered-cubic (BCC) phase enriched with Ta and Mo. The interdendritic region is delineated by Zr, Ti, Al and Si, with the formation of rod-like BCC/silicide eutectics. After annealing at 1300 °C for 48 h, both dendritic and interdendritic BCC phases experience evident phase decomposition and elemental redistribution. This leads to the increase of compressive strength at room temperature to ~2050 MPa, which is ~300 MPa higher compared to that of the as-cast material. Strain softening of the annealed alloy occurs when subjected to compression at 1000 °C, which is associated with the formation of a heterogeneous necklace microstructure composed of dynamically recrystallized grains