叠层材料过渡液相扩散焊+GMAW结构稳定性及界面组织与性能的研究

This investigation is focused on the key technique and application fundament about new Super-Ni/Ti3Al laminated composite materials with light-metal application prospect, based on advanced transient liquid phase diffusion bonding (TLPDB)+GMAW combined welding. The effect of middle transient alloy, interface diffusion, welding parameters match and control on the interfacial bonding, formation of brittle phase, interfacial microstructure and joint strength-toughness properties. The relativity of microstructure evolution and performance of Super-Ni/Ti3Al laminated composite structure TLPDB+GMAW combined joint is researched by means of combination of advanced dynamic high-speed numeral video, static micro-magnify analysis, micro-shear test, scanning electron microscope analysis. The qualitative and quantitative evaluation method on microstructure and properties of laminated composite materials TLPDB+GMAW combined joint is put forward. This investigation aims to illustrate the distribution and control mechnasim of stress in laminated composite TLPDB+GMAW lightweight welding structure and to reveal the inner correlation between microstructure evolution and performance stability. This project has important significance in promoting the application of TLPDB+GMAW combined welding technique for laminated composite in manufacturing modern vehicle (such as aviation, naval vessels and high-speed train) and improving the stability of lightweight welding structure.

针对有轻量化应用前景的Super-Ni/Ti3Al新型叠层复合材料，提出采用过渡液相扩散焊（TLPDB）+GMAW组合方法开展叠层复合材料焊接性的应用基础研究。通过研究中间过渡合金、界面扩散、参数匹配及过程控制等对界面结合、脆性相形成、界面组织结构与强韧性等的影响，将“动态高速数码摄像+静态显微图像放大分析”和微剪切试验、扫描电镜分析结合在一起，阐明叠层复合材料扩撒焊+GMAW组合焊接头区组织结构演变与性能的相关性，揭示内在作用的科学规律。提出针对叠层复合材料TLPDB+GMAW组合接头区组织性能进行定性和定量评价的方法。研究叠层复合材料TLPDB+GMAW轻量化焊接结构应力分布和控制机制，揭示焊接接头区组织性能演变与质量稳定性的内在联系。这对推进叠层复合材料组合焊接技术在航空、舰船、能源动力等现代运载工具制造中的应用和提高轻量化焊接结构的安全性有重要的意义。

本项研究是针对叠层复合材料与TC4钛合金扩散连接界面的显微组织、相结构与界面结合性能的相关性进行研究。Super-Ni/NiCr叠层材料与钛合金热物理性能差异很大，结构形式特殊（Super-Ni叠层仅0.2-0.3mm，NiCr基层2.0mm），难以采用传统焊接工艺进行直接连接。本课题采用加Cu-Ti复合中间层的过渡液相扩散焊（TLD）对Super-Ni/TC4钛合金以及Ni80Cr20/TC4进行连接，促进界面过渡液相的生成，提高界面原子扩散速率，改善叠层材料与钛合金的界面结合。揭示了叠层材料与TC4钛合金复合中间层扩散焊接头的组织演变规律，Cu+Ti复合中间层过渡液相的等温凝固反应主要为：L → TiNi + TiCu + Ti2Cu，L + TiNi → Ti2Ni + Ti2Cu，L + Ti2Cu → Ti2Ni + β(Ti)，三元共晶及包晶组织的形成促进了界面组织均匀化和界面结合。延长保温时间促使界面增宽并引起Super-Ni叠层侧开裂。.Super-Ni/NiCr叠层材料与TC4钛合金扩散焊界面过渡区宽度与保温时间满足抛物线规律，Ni、Ti元素扩散系数的较大差异（DNi in Ti >> DTi in Ni）和后期形成的TiNi层对反应层中Ni、Ti的消耗，导致Ni80Cr20/TC4界面处形成贫镍富铬区。从高温界面物质形态转变和原子扩散路径的角度分析了Ni、Ti非对称扩散机理对元素分布的影响。Ti、Cu原子促进原始晶界液化形成过渡液相，晶界和过渡液相共同加剧了Ti元素扩散，形成Ti、Ni元素非对称扩散，Ti元素可扩散至Super-Ni叠层侧形成Ti-Cu-Ni反应层。保温时间90min 时，Super-Ni/Cu+Ti/TC4和Ni80Cr20/Cu+Ti/TC4扩散焊接头获得最大剪切强度。相对于无中间层和Cu中间层，Cu+Ti复合中间层可提高扩散焊接头剪切强度96%和57%。揭示了叠层材料与TC4钛合金扩散焊接头剪切断裂特征，扩散接头剪切断裂是在剪切应力作用下，界面附近显微组织内部的晶界发生滑移，形成滑移台阶。剪切载荷作用下Super-Ni的微观流变行为和TiNi3晶体脱落形成断裂表面的多面体坑特征。Super-Ni叠层有一定的塑性，沿剪切面可发生小距离的晶粒协调变形，当晶体面剪切应力达到界面结合强度时，扩散接头发生剪切断裂。