Thermal annealing affected microstructure evolution and creep behavior in amorphous TaTiZr medium-entropy alloy

Abstract

The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation. In this work, the near-equiatomic TaTiZr amorphous medium-entropy alloy (AMEA) was prepared via the magnetron sputtering to investigate the microstructural thermostability and nanoindentation creep behavior. Thermal annealing below the glass transition temperature gave rise to the microstructural heterogeneity due to the positive mixing enthalpy in TaTiZr AMEA, which became increasingly enhanced with raising the annealing temperature. Correspondingly, there appeared a monotonic increase in hardness as well as the elastic/shear modulus, yet a reduction in strain-rate sensitivity m or an increment in shear transformation zone volume with annealing temperature. Meanwhile, the indentation morphology measured by atomic force microscope exhibited a significant transformation from pile-up to sink-in, demonstrating the degradation of plastic deformability with enhancing the microstructural heterogeneity. Based on the relaxation time spectra for Maxwell-Voigt model, the microstructural heterogeneity can restrain the activation of internal defects associated with the operation of flow units during creeping, further triggering the strain-strengthening behavior and improved creep resistance in the annealed samples. This work provides significant guidance for the structural design of high-performance amorphous alloys.