Nanoscale Exploratory Research: Dispersion of Nanopowders in Solidifying Molten Metals and Formation of High-Strength Nano-Composite Solders

纳米级探索性研究(NER)项目是一项探索性研究，旨在了解纳米颗粒在熔融金属中分散的关键物理机制，以及纳米颗粒增强熔体金属的伴随凝固过程，从而形成具有高强度、耐用性和可靠性的纳米颗粒增强复合焊料。将进行精心策划和计划的实验，以商业锡铅和无铅焊料混合物为基础，与纳米粉末很好地混合，生产纳米颗粒增强复合焊料。在这项研究的第一阶段，将选择铜、铁、钼和镍的纳米粉末，在接下来的阶段，将选择纳米二氧化钛和氧化铝。经过多次试验和错误试验后，将开发创新的技术，以建立一种将纳米粉末与微米级焊料粉末混合的有效方法，从而使熔融焊料混合物具有接近均匀的纳米颗粒分散。将进行定量测量，以表征复合熔融焊料混合物的凝固动力学。使用光学显微镜和扫描电子显微镜进行金相观察，以表征固有显微组织特征的性质、形态和分布，以及微孔和宏观孔洞、空洞和微观裂纹等伪迹的存在和分布。将进行包括显微硬度、拉伸变形和循环疲劳在内的力学测试，以证明纳米颗粒增强复合焊料的力学性能组合的整体优势。预计这项研究的结果将为设计高强度材料提供一种可行的解决方案，将微量的纳米粉末添加到凝固的熔融金属中，形成纳米颗粒增强复合材料。这种工程化的复合焊料将具有极具吸引力的强度、耐损性和耐用性的组合，同时提高了可靠性，从而增加了其在微电子和光电子设备和组件中使用的可能性。这项研究的结果也将产生深远的影响，而不仅仅是焊接材料。预计这项研究还将阐明与纳米颗粒增强金属甚至非金属复合材料的形成有关的几个基本问题。研究纳米颗粒对晶体形核动力学和微观组织发展的影响，有助于加深对现代凝固理论的理解。

This Nanoscale Exploratory Research (NER) project is an exploratory study aimed at understanding the key physical mechanisms governing the dispersion of nano-particles in molten metals and the concomitant solidification of the nano-particle-reinforced molten metals resulting in the formation of nano-particle reinforced composite solders having attractive combinations of strength, durability and reliability. Carefully orchestrated and planned experiments will be performed to produce nano-particle reinforced composite solders based on commercial tin-lead and lead-free solder mixtures blended well with nanopowders. In the first phase of this research nanopowders of copper, iron, molybdenum and nickel will be chosen and in the follow phase nanopowders of titanium dioxide and aluminum oxide will be the candidates. Innovative techniques will be developed after several trial and error experimentation to establish an efficient means for blending the nano-powders with the micron-size powders of the solder resulting in a molten solder mixture having a near uniform dispersion of nanoparticles. Quantitative measurements will be conducted to characterize the dynamics of solidification of the composite molten solder mixture. Metallurgical observations using both optical microscopy and scanning electron microscopy will be made to characterize the nature, morphology and distribution of intrinsic microstructural features and the presence and distribution of artifacts such as micro and macro porosity, voids and microscopic cracks. Mechanical tests, to include microhardness, tensile deformation and cyclic fatigue, will be conducted to demonstrate the overall superiority combination of mechanical properties of the nano-particle reinforced composite solders. It is anticipated that the findings of this research study will provide a viable solution to engineering high strength materials by adding trace amounts of nanopowders into a solidifying molten metal to form nano-particle reinforced composite. The engineered composite solders will have attractive combinations of strength; damage tolerance and durability coupled with improved reliability thereby enhancing the probability of its use on in a spectrum of microelectronic and opto-electronic devices and assemblies. Results of this research exercise will also have far reaching consequences beyond soldering materials. It is expected that the study would also shed light on several fundamental issues related to the formation of nanoparticle-reinforced metallic and even non-metallic composites. A study of the influence of nano-particles on crystalline nucleation kinetics and microstructural development will contribute to enhancing our understanding of modern solidification theory.