Effect of thermal annealing on the local structure in ZrCuAl bulk metallic glass

The relaxation and crystallization behaviors of the ternary Zr50Cu40Al10 bulk metallic glass were investigated by the positron annihilation measurements and the extended X-ray absorption fine structure (EXAFS) analysis at the Zr K-edge. The result of positron annihilation coincidence Doppler broadening (CDB) for as-prepared specimen suggests that the fraction of Zr atom around free volume is greater than that of composition for alloy system. According to the results of CDB spectrum and Fourier transformed EXAFS spectrum, the isothermal annealing below the glass transition temperature (Tg) (structural relaxation) decreases the size of free volume, but it causes little change in the distribution of atoms, either around free volume or around Zr atoms. For the isothermal annealing above crystallization temperature (Tx), the XRD and EXAFS spectra clearly show the crystallization of specimens. The CDB result also suggests the crystallization. These results demonstrate that the chemical order around free volume is dissociated, and crystallized order is newly formed during the thermal annealing above Tx.