Effect of quenching temperature on local ordering in Al₈₅Ni₅Co₂Y₈ metallic glass

The effect of quenching temperature on local atomic structure of Al₈₅Ni₅Co₂Y₈ metallic glass has been investigated in the present study. With increasing quenching temperature from 1273 K to 1573 K, the amount of medium range order (MRO) tends to decrease, while the structural unit size remains almost constant. The higher amount of MRO leads to movement of the crystallization nose of time-temperature-transformation (TTT) curve to a longer time scale by raising the viscosity of the liquid. On the other hand, quenched-in nuclei are present in the samples with higher quenching temperature, since the probability of intersecting the crystallization nose during cooling becomes higher with increasing quenching temperature. As a result, typical two types of as-quenched microstructure can be obtained, i.e. fully amorphous structure with higher amount of MRO and that with embedded quenched-in nuclei as well as relatively lower amount of MRO. The sample quenched at 1273 K without quenched-in nuclei exhibits the most fragile behavior, indicating that the fragility can be affected by the quenching temperature as well as the alloy composition in Al-based metallic glass.