钛合金激光焊/超塑成形接头均匀性行为及机理研究

Laser welding / superplastic forming technology, which can further expand the application range of welding / superplastic forming technology, has the widespread application prospect of lightweight structure manufacture in the field of aviation and aerospace. The current study shows that laser welding / superplastic forming can be used in manufacturing three layer, four layer titanium alloy structure, but the joint has obvious uneven deformation problems. Therefore, the microstructure and deformation inhomogeneity of joint is the key problem in application of laser welding / superplastic forming technology. Based on the the characteristics of hydrogen can be adjusted on the microstructure of titanium alloy, hydrogen - heat treatment is proposed to adjust the organization uniformity of the joint, and improve the deformation uniformity. The project suggests that the superplastic deformation process not only contains equiaxial process of a single regional non ideal tissue, but also contains the coupling of different regional tissue homogenization behavior. By observing the microstructure state among different regions at different deformation, the regional organizations coupled uniform mechanism of joint in the deformation process will be deducted. The mechanical and fatigue performance will be tested on forming joints with different deformation. This project could provide design theory basis for manufacturing of lightweight structure with laser welding / superplastic forming technology. And can also provide experimental basis for superplastic deformation mechanism study of the inhomogeneous tissue.

激光焊/超塑成形技术可进一步拓宽焊接/超塑成形技术的应用范围，在航空航天等领域的轻量化结构制造中具有广泛的应用前景。现有研究表明钛合金能够采用激光焊/超塑成形技术制造三层、四层结构，但是接头处存在明显变形不均匀的问题。因此接头的组织及变形不均匀性是制约激光焊/超塑成形技术实际应用的关键问题。基于置氢可以对钛合金组织进行调整的特点，项目提出氢-热联合处理的方法，调整接头各区域组织的均匀程度，提高其变形均匀性。项目认为钛合金激光焊接接头超塑变形过程不仅包含单个区域非理想组织的等轴化过程，还有不同区域组织的耦合均匀化行为。拟通过观察不同变形量时接头各区域间的组织状态，推演接头在变形过程中各区域的组织耦合均匀化机理。并对不同变形量下的成形接头进行力学及疲劳性能测试，为激光焊/超塑成形技术制造轻量化结构提供设计依据和理论基础。项目还可以为非均匀组织的超塑性变形机理的研究提供试验基础。

项目通过氢热处理来调整TC4钛合金接头的组织性能，提高接头的超塑性变形均匀性，采用变形均匀系数K（母材和焊缝截面收缩率之比）来表征横向焊缝在超塑性变形过程中变形均匀性，针对接头超塑性变形行为和机理展开研究，并对变形后接头的常温力学性能和疲劳性能进行了检测。研究发现：置氢处理可降低接头整体β相转变温度，同时氢化物作用于接头各区域，从而提高接头组织和性能均匀性；淬火可以使母材组织转变为针状马氏体，向焊缝的网篮状组织靠拢，且淬火温度越高于相变温度，接头各区域组织越一致；氢热联合处理结合两者优点，不仅使得母材的组织向针状组织转变，同时β相晶粒的尺寸较小，接头组织均匀性良好，同时接头的显微硬度差异更小，为接头超塑性均匀变形提供了良好的基础。超塑性变形后，随淬火温度的增加，钛合金激光焊接头的K增大，淬火处理TC4钛合金激光焊接接头在淬火温度1000℃、940℃、10-4s-1条件下K值达到0.9269；随置氢量的增加，K值增大，置氢处理TC4钛合金激光焊接接头在置氢量0.37%、920℃、10-4s-1条件下K值达到0.85；在氢热处理中，随着氢含量的增加，钛合金激光焊接头的K先增大后减小，随着淬火温度越高，K值增大，氢热处理TC4钛合金激光焊接接头在置氢量0.16%、淬火温度960℃、920℃、10-4s-1条件下K达到0.989。置氢和淬火均可以可以调节TC4钛合金接头的显微组织，接头中β相含量增加，初生α相减少。超塑性变形的进行，接头内部相组成发生α′→α+β的相变，接头组织发生动态再结晶，组织不断等轴化。仅置氢处理，超塑性变形后接头的抗拉强度和屈服强度降低明显，在低应力疲劳循环中疲劳寿命较高；仅淬火处理，超塑性变形后接头的抗拉强度和屈服强度未发生明显改变，但是同样低应力疲劳循环中疲劳寿命较高；氢热联合处理，变形后接头的抗拉强度和屈服强度有所降低，低应力疲劳循环中疲劳寿命较高。本研究为TC4钛合金接头的实际应用提供了数据支持。项目支助发表论文10余篇，其中2篇待刊载。培养硕士研究生4名，3名已毕业，1名在读。