铜锆基金属玻璃中液态-液态相变机制的原位研究

The excellent glass forming ability (GFA) of alloys is the prerequisite for unique applications of their bulk metallic glasses (BMGs) in 3D printing. It was proposed that glass-forming metallic liquids undergo a transition between liquids with different density and ordering, which is known as the liquid-to-liquid transition (LLPT). LLPT occurs before the the liquid-to-glass phase transition during vitrification. The nature of GFA can be better understood by studying the atomic scale origin of LLPT. Our study focuses on the study of atomic scale origin for LLPT. However, the experiment of studying LLPT can be easily disrupted by intervening crystallization. In the past, a levitation is usually a must for the study of LLPT in the important temperature regime of undercooled multi-components metallic liquids. Meanwhile, data analysis is also very difficult due to LLPT’s complex chemistry.Recently, the occurrence of LLPT was reported in binary and ternary Cu-Zr-based alloy system above melting temperature, which provides some possibilities to avoid the aforementioned difficulties. Inspired by this discovery,we propose to conduct in-situ high energy synchrotron X-ray scattering studies of LLPT in excellent glass-forming Cu-Zr-based alloys with simple chemistry above melting temperature during heating and cooling. The development of a special sample holder for molten alloys with appropriate geometry for scattering experiment is one of the innovations. Structure evidence for LLPT in metallic liquids will be determined by characterizing the multi-scale structural evolution. We intend to observe the changes in total scattering patterns when LLPT occurs. We will also study the alloying effect on LLPT and GFA, which would shed light on developing novel BMGs and promoting their application in 3D printing.

合金优异玻璃形成能力是实现其大块金属玻璃在3D打印上独特应用的前提。合金玻璃化过程会发生不同密度和有序度液体之间的转变，即液态-液态相变。揭示这一相变原子层面微观机制将加深我们对玻璃形成能力本质的认识。然而当前液态-液态相变微观机制悬而未决且具有争议。以往，多元合金体系液态-液态相变研究须使用悬浮设备以排除过冷液体结晶的干扰，同时组分过多导致结构数据分析困难。最近研究发现，简单的二元和三元铜-锆基金属玻璃液态-液态相变发生在熔点温度以上不受结晶干扰，符合常规实验条件要求。受此启发，本研究将通过原位同步辐射散射检测二元和三元铜-锆基熔融合金液体加热和冷却过程中多尺度原子结构的演变，以期获得金属玻璃中液态-液态相变的有力结构证据。符合散射实验要求的熔体样品容器的应用是本研究的特色之一。本研究还将探讨合金化对液态-液态相变和玻璃形成能力的影响，为金属玻璃的研发及其在3D打印上的应用提供重要参考。

本项目利用先进的原位中子及同步辐射散射手段，辅以透射电子显微镜等先进手段研究了具有优异玻璃形成能力的合金体系液态-液态相变原子及纳米尺度的微观机制及其与玻璃形成能力的关联。主要研究内容及重要成果包括以下几个方面：1）在项目执行期内针对铜-锆基金属玻璃及其形成液体的液态-液态相变展开了原位中子和同步辐射散射、透射电子显微镜等分析，并挖掘出液态-液态相变的证据，为这一有争议性的课题提供了重要参考。2）基于铜-锆基的结果，我们同时针对钯基合金的液态-液态相变行为进行了研究，并由此为解决该体系困扰非晶合金领域逾四十年的一个难题提供了合理解释，提出一系列具有异常放热峰的非晶合金体系在超过冷液相区均可能会发生液态-液态相变。3）在项目执行期内将铜-锆基金属玻璃的液态-液态相变与“雪崩”形核联系起来，探讨了此种联系与玻璃形成能力之间的关联。4）基于液态-液态相变的研究，我们通过合金元素的添加，研究了具有热稳定性、高塑性的铜-锆基金属玻璃体系，为研发新型的非晶合金提供了新的思路和有价值的参考。项目组成员在Nature Communications、Acta Materialia等SCI期刊上发表论文共15篇，其中一作或通讯论文7篇，包括SCI一区论文4篇，所有成果均有标注。项目组共申请专利3项，获授权1项。项目执行期共培养7名研究生。项目执行期内，组织国际知名戈登研讨会中子散射会议1次，在国内外会议上做项目相关报告9次，其中国际会议5次。本项目成果被国内外媒体广泛报道，被基金委网站首页以要闻报道，同时获自然通讯杂志冶金专栏珍藏。非晶合金中液态-液态相变直接证据的挖掘为清除该领域的争议提供了重要参考，其微观机制研究为通过相变调控非晶合金原子及纳米尺度的微观结构，以及为研发具有优异力学性能的超稳非晶合金提供新的思路，还可为大块金属玻璃未来在3D打印上的应用提供独特视角。