钛合金/铁镍基高温合金电子束焊原位复合梯度焊缝形成及接头高温强化机理研究

Aeronautic and astronautic engine bodies made of high temperature titanium alloy and Fe-Ni base superalloy can exert the high specific strength of titanium alloy and excellent high- temperature properties of Fe-Ni base superalloy, which can significantly improve the thrust-weight ratio of aeronautic and astronautic aircraft. To meet the requirements of high temperature application, a combined strengthening thought of forming a weld with muti-gradient solid solution transition and in situ synthesis strengthening phases was proposed. According to metallurgical-thermal-mechanical matching and liquid-solid, solid-solid reaction thermodynamics computation and experiment optimization, compositions of the main and trace elements of gradient layers of the filler metal were designed，and proper electron beam welding heat input and postheat treatment modes were developed. Then, weld pool flow and mass transfer behavior were studied. In situ synthetic chemical reaction process and strengthening phase growth mechanism were also verified. As a result, the matter - energy criteria for the formation of in situ composite gradient weld were obtained. Relationship between characterization of in situ synthesis strengthening phase and high temperature properties of the joint was revealed, so that high temperature strengthening and toughening mechanism was unriddled. Research achievements of this project can promote the applications of the structures which were made of these two alloys in the lightweight manufacturing of aeronautic and astronautic engines, enrich the basic strengthening theories of electron beam welded dissimilar metal joints and provide a new method for the high quality welding of other dissimilar metals.

采用高温钛合金与铁镍基合金双金属结构的航空航天发动机机体，可以同时发挥钛合金比强度高及铁镍基合金高温性能优异的优势，极大提高航空航天飞行器的推重比。本项目面向高温环境应用需求，提出高温钛合金与铁镍基合金电子束焊缝多级固溶体梯度过渡与原位复合增强的联合强化思想。基于冶金-热-力匹配与液-固、固-固反应热力学计算及试验优化，设计填充金属梯度层主体和微量元素成分，开发合理的电子束焊接能量输入与后热作用模式。研究熔池流动及传质行为，探明原位合成化学反应过程及增强相成长机制，获得原位复合增强梯度焊缝形成的质-能条件，揭示原位合成增强相基本特性与接头高温性能的相关性，解明接头高温强韧化机理。项目研究成果可推动该双金属结构在航空航天发动机轻量化制造中的应用，丰富异种金属电子束焊接头强化基础理论，为其他异种金属的高质量焊接提供思路。

航空航天工业的飞速发展对发动机的推重比提出更高要求。采用钛合金作为结构材料可大幅降低结构重量，但钛合金在600℃以上高温性能明显下降，限制了其在发动机高温部件中的使用。镍基合金在1000℃仍可保持良好的高温性能。若采用高温钛合金与镍基合金双金属结构的发动机，则可在保证发动机推力的同时，大幅减轻发动机重量，提高发动机推重比。. 针对钛合金/镍基合金双金属结构制造中面临的焊接难题，本项目对Ti60钛合金与GH3128镍基合金的电子束焊接进行了研究。钛合金与镍基合金的直接电子束焊接试验表明，在焊缝内生成大量的TiNi、Ti2Ni脆性金属间化合物，限制了接头的有效连接。采用Cu、V单一组元作为填充层进行钛/镍电子束焊接，实现了两者的有效连接，焊缝组织由固溶体+化合物组成，固溶体的存在提高了焊缝的塑性，接头抗拉强度可达到228 MPa。但由于钛侧Ti-Cu化合物层和镍侧Ni-V化合物层的存在，增加了焊缝的脆性，限制了接头力学性能的提高。. 基于单一元素进行冶金调控存在的问题，分别采用CuCr合金和CuV合金，研究了二元合金元素对钛/镍电子束焊接冶金的影响，获得了以固溶体为主的组织形式，抗拉强度提高到264 MPa，但由于焊缝中存在较多的Ti-Ni-Cu三元相，导致接头的力学性能较差。为进一步提高钛/镍电子束焊接接头性能，利用Cu-Ni，V-Cu，V-Ti之间无金属间化合物形成，设计了V/CuV梯度填充层，对钛/镍电子束焊接冶金过程进行调控，抑制了化合物的大量生成，焊缝组织为Ti60/(Ti,V)+V(s,s)+TiCu/V(s,s)+Cu(s,s) /Ni(s,s)/GH3128的固溶体成分过渡形式，接头抗拉达到392 MPa，焊缝整体硬度水平明显降低。. 通过项目研究，阐明了冶金调控元素对异种金属焊接冶金过程的控制机理和过程，获得了工艺参数对冶金控制过程的影响，在避免焊接缺陷形成的前提下，尽量减小活性元素母材的熔化量。冶金调控元素的加入量要保证组织控制的效果，还要考虑其自身的熔化特性。研究结果对其他异种金属的焊接也有重要的指导意义。. 项目执行期间，共发表相关论文10篇，申请专利3项，授权1项，获科技奖励1项，培养博士研究生1人，硕士研究生3人。