Formation And Properties Of The Novel Pr-based Bulk Metallic Glasses

This work focuses on analysis and studying of the newly discovered Pr-Cu-Ni-Al bulk metallic glasses (BMGs), including its glass forming range, glass forming ability (GFA) and thermal properties. We choose the model system-Pr60Cu20Ni10Al10 BMG sample, which has the highest glass forming ability, to study its crystallization kinetics, glass transition and relaxation using ultrasonic method and differential scanning calorimeter.The critical section thickness of the paramagnetic Pr60Cu20Ni10Al10 composition is 5 mm in diameter for die cast, which exhibits a distinct glass transition and a wide supercooled liquid region (SLR). The glass transition temperature is only 409 K.The glass forming range of the Pr-Cu-Ni-Al BMGs moves in the Pr-poor direction with increasing Al concentration, meanwhile the Cu-Ni concentration exhibits a stepwise decrease. If Al concentration is too high (≥40 at %) or too low (≤10 at %), the glass forming range becomes very small, even vanish. The glass forming ability indicated by several mostly used criterions does not accord with that from experimental results. This may suggests that there is no universal criterion for glass forming alloys up to now. The ultrasonic experiments show that the Pr60Cu20Ni10Al10 BMG exhibits small moduli compared with that of some other typical BMGs, while its Poisson's ratio is comparable to that of these BMGs. This indicates that the Pr60Cu20Ni10Al10 may have a similar ability to prevent the atom rearrangement and long range movement to these BMGs. In addition, the apparent activation energy for glass transition and crystallization are also smaller than that of the other typical BMGs, which means a larger possibility to get enough energy to evolve into a more stable state in energy landscape. According to the value of the fragility of the BMG (m=31), it can be classified into the strong category. Finally, we clarified qualitatively the glass transition in thermal analysis experiments by free volume theory, the "overshoot" is observed in experiments.