多层膜离子束混合研究亚稳合金形成和理论模型的进展(英文)

PROGRESS ON FORMATION AND THEORETICAL MODELING OF METASTABLE ALLOYS STUDIED BY ION MIXING OF MULTILAYERED FILMS

迄今为止，已经研究了大约90个二元金属系统的多层膜离子束混合，获得了许多非晶态合金（金属玻璃）。离子束混合不仅能在负生成热的，通常认为是易玻璃化的系统中合成金属玻璃，而且在正生成热的非玻璃系统，甚至在正生成热很大的互不固溶系统中也合成了金属玻璃。对此，用Miedema的生成热模型构造了二元金属系统的自由能图。在考虑了多层膜中的界面自由能后，提出了一个统一的热力学模型。对正生成热的系统，界面自由能使多层膜提高到比非晶相高的能态，从而有可能形成玻璃。而界面能对于负生成热提供的非晶化驱动力的影响可以忽略。另外，离子束混合也获得了五种结构类型的亚稳晶相（MX）。并从实验观察到的MX相和母相之间晶体学关系推导出MX相形成的原运动机制。自由能图包括了计算的MX相的自由能曲线后就更为完整了，可以用来预言离子束混合中有关合金相的形成。作者提出了用稳态退火实验来校验计算的自由能图在一些重要成份点的相对能态的合理性。实验表明，合金相的演化次序与计算推演的结果符合得很好，从而证实了Miedema理论的适用性。界面的概念也适用于同样开始于多层膜的固态反应技术。在一些正生成热的系统中，通过适当设计使多层膜中包含足够份额的界面，稳态退火确实获得了新的金属玻璃?

Up-to-now, some 90 binary metal systems have been studied by ion mixing with a multilayered films scheme and a great number of amorphous alloys(metallic glasses) have been obtained.Ion mixing is capable of synthesizing metallic glasses not only in those known as glass-forming systems usually with a negative heat of formation (△Hf), but also in those recognized as non-glass systems with a positive △Hf, and even in some immiscible systems with an extremely large positive △Hf. Miederna's theory was employed to construct the free energy diagram of the binary metal systems. Taking into account of the interfacial free energy stored in the multilayered films, a unified thermodynamic model was proposed.For the positive △Hf systems, the interfacial free energy elevated the multilayered films to a energetic state higher than that of the amorphous phase, leading to a situation possible for glass formation.While the effect of interface on the driving force originating from the negative △Hf was in a negligible manner. In addition, a number of metastable crystalline (MX) phases have also been obtained by ion mixing and they can be classified into five structural categories. The mechanism of atomic motion for MX phase formation was deduced through the observed crystallographic correlation between the newly formed MX phases with their matrix. By including the calculated free energy curves for the MX phases,the free energy diagrams became close to a complete one and could be employed to predict the related alloy phase formation upon ion mixing. Steady state thermal annealing was proposed by the authors as a means to check the relevance of the calculated free energy diagrams at some important compositions.The results showed that the phase evolution sequence matched well with that deduced by the calculation,thus confirming the applicability of the Miedema's theory.The interface concept was also applicable to another glass forming technique, i.e. solid-state reaction,which began also with multilayers. By properly designing the multilayers to include enough fractions of the interfaces, metallic glasses were indeed obtained in some positive △Hf systems by thermal annealing under appropriate experimental condition.