Thermally-driven structural inhomogeneity and serrated plastic flow in TaTiZr amorphous medium-entropy alloy

Abstract

Thermally driven structural heterogeneity, plastic deformation and concomitantly serration flow behavior in an equiatomic TaTiZr amorphous medium-entropy alloy (AMEA) were investigated systematically via experiment and simulation methods. The element segregation induced structural heterogeneity and short/medium-range ordering could be dramatically enhanced during heating below glassy temperature, owing to the annihilation of atomic free volume and structural relaxation. The uniaxial compression of TaTiZr AMEA micropillars exhibited an increasing yield strength with raising the annealing temperature, corresponding to a transformation of deformation behavior from homogeneous-like multiple shear banding to highly localized shear banding. Moreover, the statistical and dynamic analysis on the serrated stress-time curves of the as-deposited and annealed TaTiZr AMEAs demonstrated that both the stress drop amplitudes and their time durations are gradually decreased with annealing temperature. However, the corresponding distribution changes from a power-law scaling to a Gaussian behavior, indicating the transformation of underlying dynamics from a self-organized criticality to a chaotic state and the plastic deterioration in AMEAs due to the structural heterogeneity. The plastic deformation behavior and physical mechanism contributing to the serrated flow dynamics are rationalized in accordance with the mean-field theory. Our findings are expected to facilitate the understanding of the dynamic mechanism tuning intermittent flow of AMEAs to achieve exceptional deformation stability.