声场助蓝宝石外延反应连接机理及焊缝结构与力学行为

Interface bonding and residual stress are two primary factors that affect the mechanical performance of sapphire (monocrystalline α-Al2O3) joints. Here we propose a novel method to make brazed joints with a "Sapphire/Composite/Sapphire" structure, based on the epitaxial reaction on sapphire, which requires relatively low brazing temperature and produces sapphire brazed joints with low residual stress. As a result of cavitation induced by ultrasound in liquid aluminum, a peculiar physical and chemical environment forms on the surface of the sapphire, where the transient reaction between aluminum and oxygen that comes from the ambient atmosphere is enhanced. The products of the reaction deposit on the sapphire and epitaxially grow on it. In the later stage of the growth, the liquid aluminum and the alumina particles around it stick together and become a "particle enhanced aluminum based composite" structure. The final structure of the joints is "Sapphire/epitaxy layer/composite layer/epitaxy layer/Sapphire". The residual stress and lattice mismatch between the epitaxy layer and sapphire is minimum. The research covers the regularity of the formation, depositon and growth of the alumina in the ultrasound field, and the relation between the micro structure of the joints and their mechanical properties. In this study, we will explore a new method to braze sapphire and new technological path to make sapphire joints with high mechanical performance and low stress.

界面接合和残余应力是决定蓝宝石（单晶α-Al2O3）连接接头力学性能的两个重要因素。本研究提出一种基于蓝宝石表面外延反应形成"蓝宝石/铝基复合材料/蓝宝石"钎焊缝结构的方法，实现一种低温、低应力钎焊蓝宝石的新工艺。利用超声波空化作用，在蓝宝石表面形成极端的物理化学环境，加速液态铝与其内部、来源于空气中氧的瞬时反应，在固体蓝宝石表面外延生长蓝宝石层；在生长的后期剩余少量铝与周围的氧化铝颗粒形成复合材料结构，形成的接头结构是由"母材/蓝宝石外延层/铝基复合材料层/蓝宝石外延层/母材"组成，其外延生长蓝宝石层与母材晶格和应力错配很小。主要研究超声场下液态铝中氧-铝化合物的形成、沉积和外延反应规律，以及复合材料结构的焊缝的微观结构与蓝宝石连接接头力学性能之间的关系。探索蓝宝石钎焊的新工艺，为实现高强度、低应力蓝宝石的可靠连接探索新的技术途径。

蓝宝石在很多领域中都有广泛的应用前景，实现高强度、低成本和低应力的蓝宝石连接是扩展蓝宝石进一步应用的关键。本研究以蓝宝石为研究对象，提出了一种利用超声空化作用实现蓝宝石表面外延反应结合的方法，并揭示了外延层的生成过程与机制，结果发现，短时间超声作用蓝宝石表面先形成非晶氧化铝薄层，随后发生部分晶化，最终形成了由纳米晶和非晶构成的混合层结构。为了实现蓝宝石高强度、低应力连接，分别利用了铝基和锌基钎料，并基于热氧化法和溶解法制备了两种“母材/蓝宝石外延层/复合材料层/蓝宝石外延层/母材”复合结构的蓝宝石焊接接头，并揭示了复合层结构、接头残余应力与接头力学性能之间的关系。基于超声辅助外延反应的机理，开发了多种低熔点的含Al钎料，获得了低温条件下蓝宝石低应力焊接的新工艺。