Huazhong Univ Sci & Technol, State Key Lab Plast Forming Stimulat & Die & Moul, Wuhan 430074, Peoples R China
; Beihang Univ, Dept Mat Sci & Engn, Beijing 100083, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Lab Nucl Anal & Technol, Beijing 100039, Peoples R China
In this paper, positron annihilation spectroscopy and differential scanning calorimetry were applied to study the structural relaxation of Pd40Cu30Ni10P20 bulk metallic glass during long-time annealing at 523 K. It was found that the relaxation of the alloy follows a two-stage process. In the initial stage, with increasing annealing time, the height of the glass transition peak (namely Delta c(p)) increased, while the average positron lifetime decreased. The isothermal relaxation kinetics obeys a Kohlrausch law with exponent of beta = 0.5 +/- 0.03. However, when the annealing time is beyond 32 h, the height of the glass transition peak (Delta c(p)) decreased, and the average positron lifetime increased. This is possibly due to the enhancement of the topological short-range ordering, which results in the generation of new defects on the interfaces between the solid-like regions and the liquid-like regions in amorphous phase. The experimental results were tentatively discussed in terms of free-volume theory and percolation theory.