Investigation on annealed Fe43Co43Hf7B6Cu1 amorphous alloy by positron annihilation spectroscopy

Amorphous Fe43Co43Hf7B6Cu1 alloy prepared by melt-spun technique were annealed at temperature 200 ℃, 300 ℃, 400 ℃ and 500 ℃ for 30 min. The structure and structural defects in annealed specimens were investigated by positron annihilation lifetime spectra, X-ray diffraction (XRD) and Mssbauer spectroscopy (MS), etc. . The results show that in the as-quenched amorphous alloy, more than 85% of the positrons are localized at vacancy-sized free volumes in the amorphous based phase, annihilation lifetime τ1=158.4 ps, and the other 11.9% of positrons are trapped by microvoids, with lifetime τ2=397 ps. After annealing at temperature 200 ℃, 300 ℃ and 400 ℃ for 30 min, the atomic short range diffusion will give rise to the migration and annihilation of vacancy-like defects. The major component τ1 will be reduced continuously. The value of τ1 will decrease to 149 ps at 400 ℃, their relative intensities I1 decreases and reaches 80.8%. Meanwhile the annihilation lifetime of positrons in the microvoids τ2 will change from 353 ps to 364 ps, their relative intensities I2 are increased to 18.0%. When annealed at temperature 500 ℃ for 30 min, new trapping centers of positrons are produced owing to the crystallization of amorphous phase, I2 increases drastically to 26.7%.