钛合金/钢异质金属真空钎焊过程中多组元合金元素协同扩散及反应机理

Vacuum brazed dissimilar metals structure between titanium alloy and steel appeals a breakthrough in key industrial fields such as energy manufacturing. Sound titanium alloy/steel dissimilar metal joint could be achieved by using Ag-based filler materials or by making composite coating on steel surface before welding, although the former technology is expensive and the latter one involves complicated techniques, because the conventional Ti-Cu-Ni series filler cannot fulfill the requirement. This project will explore the composition rules of Ti-Cu-Ni-Zr-V alloy, develop Ti-Cu-Ni-Zr-V alloy foil with proper thickness and width, and appropriate strength and ductility. This proposal will investigate the effect of brazing temperature, heating rate, duration time and filler thickness on the microstructure and mechanical properties of vacuum brazed dissimilar metals joint between titanium alloy and steel. The diffusion kinemics and reaction mechanism of alloying elements during brazing process will be revealed. The evolution mechanism of microstructure in brazed seam and interface will be explained. The failure mechanism of the titanium alloy/steel dissimilar metals joint will be clarified. The synergistic diffusion kinetics model of multi-component alloying elements will be established, enriching the theory of welding metallurgy in joining of dissimilar metals. The research results of this project will provide theoretical basis and experimental support for independent development of low-melting point filler materials for vacuum brazing of dissimilar metals joint between titanium alloy and steel by breaking through the technical bottlenecks of titanium alloy/steel dissimilar metals vacuum brazing.

钛合金/钢异质金属真空钎焊结构在发动机制造等关键领域亟待实现技术突破。为获得优质高效钛合金/钢异质金属钎焊接头，常采用银基钎料或在钢表面镀复合层，前者价格昂贵，后者工艺复杂，而常规Ti-Cu-Ni系列合金钎料不能满足要求。本项目拟探索Ti-Cu-Ni-Zr-V合金的成分规律，自主研发宽度和厚度适当、强度和韧性合适的Ti-Cu-Ni-Zr-V合金薄带钎料。研究钎焊温度、加热速率、保温时间、钎料厚度等对钛合金/钢异质金属真空钎焊接头微观组织和力学性能影响规律，阐明合金元素在钎焊时的扩散动力学和反应机理，揭示钎缝及界面层的微观组织演变机制，解析钛合金/钢真空钎焊接头失效机理，建立钎焊过程中多组元合金元素的协同扩散动力学模型，完善异质金属焊接冶金理论。突破钛合金/钢真空钎焊技术瓶颈，为实现适用于钛合金/钢异质金属真空钎焊的低熔点合金钎料自主研发提供理论基础和实验支撑。

钛/钢异种金属真空钎焊结构在发动机制造等关键领域亟待实现技术突破。本项目自主设计了新型Ti-Cu-Zi-Zr-V合金箔带钎料，研究了钎焊工艺参数对钛/钢异质金属真空钎焊接头微观组织和力学性能影响规律，阐明了合金元素在钎焊过程中的扩散动力学和反应机理。主要研究内容和结论如下：.（1）基于钎料团簇式[Ti-Cu6Ti8]Cu3，采用相似元素替换规则，设计了Ti33.3Zr16.7Cu50-xNix、Ti50-xZrxCu39Ni11和Ti38.8-xZr11.2VxCu39Ni11三种Ti-Cu基非晶钎料箔带。.（2）表征了TC4钛合金/Ti-Cu基钎料/316L不锈钢真空钎缝物相结构和界面组织特征。钎缝界面结构为：钛合金母材/扩散区/钎缝/界面区/不锈钢母材。扩散区由魏氏体和β-Ti转变区组成；钎缝区包含钎料组元残留区和FeTi反应层；Fe2Ti、FeCr和α-Fe三个反应层依次在界面区形成。.（3）探讨了接头内主要反应区随钎焊工艺参数和钎料中Ni、Zr和V含量的演变规律。钎焊温度升高和钎焊时间延长都会促进钎料中Ti原子向不锈钢母材远距离扩散，加剧Cr元素上坡扩散和偏聚，导致界面区厚度增加，其中钎焊温度是影响FeTi反应层厚度的主要工艺参数。Ni含量增加抑制了钎料和不锈钢之间的相互扩散和反应，FeTi和界面区厚度均减小。Zr和V替换钎料中的Ti，导致FeTi界面层厚度减小；钎料向不锈钢母材扩散的Ti量减少，界面层变薄。.（4）基于断裂处界面晶格结构揭示了钎焊接头断裂行为，建立了界面组织-力学性能的对应关系。钎焊过程中，FeTi/Fe2Ti界面为固/液界面，残余应力较大，二者之间难以构成晶粒取向关系，导致该处为接头主要裂纹源。Fe2Ti和FeCr反应层具有相近的纳米压痕和弹性模量，二者之间晶面和晶向错配度较小，因此裂纹在该处的扩展行为相似。钎料成分优化后，Ni、Zr和V含量分别为11 at.%、16.7 at.%和5.8 at.%。在990 oC/10 min下，采用Ti33.3Zr16.7Cu39Ni11非晶钎料制备的接头最大剪切强度为318 MPa。.（5）本项目还研究了不同焊丝成分对TC4钛合金/304不锈钢钨极氩弧焊接头微观组织和力学性能的影响机理，设计了TC4钛合金/304不锈钢熔焊Cu+Ni复合填充层，接头平均抗拉强度达432MPa。