金属玻璃异常放热现象与隐藏非晶相变研究进展

The progress of research on anomalous exothermic phenomenon and hidden amorphous phase transition in metallic glasses

金属玻璃因其简单的金属键结合及原子密堆积结构而成为研究非晶物理的理想材料模型。解开玻璃形成液体的微观结构可以探寻玻璃形成能力的秘诀。许多非晶合金体系在玻璃转变点以上、结晶温度以下表现出异常放热现象,暗示在超过冷液相区间隐藏着非晶相变,这一现象的微观结构本质困扰了学界逾四十年。近来,中子和同步辐射散射等大科学装置的发展为揭示隐藏非晶相变的机制提供了原位、无损以及从原子到纳米级别的多尺度"探针"。最新研究发现Pd-Ni-P这一典型的具有异常放热现象的原型非晶合金在临界转变温度处发生了重入超过冷液体转变,其内在微观机制为中程有序结构的演变所导致的液-液相变。同时通过恰当的热处理,人们可以方便地调控这一类非晶合金的微观结构。经过统计几种具有异常放热现象的典型金属玻璃体系的热物理参数,发现异常放热峰可能与玻璃形成能力有一定的关联。金属玻璃中的异常放热现象及其隐藏的非晶相变为开发新型非晶合金体系并改进合金的性能提供了新的思路。

Metallic glasses （MGs） provide ideal model systems for investigating amorphous physics including the secrets of glass- forming ability （GFA）. Many MGs were reported to exhibit an anomalous exothermal peak （AEP） in the supercooled liquid region, indicating the occurrence of a hidden poly-amorphous phase transition, The structure origin of the AEP has puzzled the metallic glass community over four decades, Recently, the development of cutting-edge scattering facilities in the world such as neutron and synchrotron sources provide opportunities to reveal the origin of the AEP using a suite of bulk, in-sit-u, non-destructive structure probes covering multiple time and length scales. The latest remits were found that Pd-Ni-P MGs, a prototypical glass with an AEP, underwent a reentrant supercooled liquid transition at a critical temperature. The origin was determined to be a liquid-liquid phase transition mediated by structure evolution at a medium-range length scale. We demonstrated that proper heat treatments could manipulate the mierostructure of the MGs of an AEP. We also summarized the thermophysical parameters of several typical MGs with an AEP. It was suggested that the AEP might correlate with the GFA, which sheds light on exploring new amorphous alloys.