异种钛合金扩散连接层合结构疲劳增寿及机理研究

Titanium alloys have become an important material as main structure of modern aircraft. However, high fatigue crack sensitivity results in short crack growth life of titanium alloy components, which seriously affects long-term safety of the aircrafts. Nowadays, although unbonded or weakly-bonded zones introduced in diffusion bonded laminate of same titanium alloy can improve fatigue resistance, they prominently deteriorate static mechanical properties. Therefore, diffusion bonded laminate of different titanium alloys is proposed in this study. Its fatigue crack growth is evidently inhibited due to the existence of bonding interface of different materials and different layer properties. Furthermore, the static properties are not reduced. The diffusion bonding process and fatigue behavior of two-layer laminate for different titanium alloys are firstly investigated. The fatigue life prediction model and fatigue constitutive model of bonded interface of different materials are proposed. Then diffusion bonding process of laminate is investigated for fatigue life improvement. Suitable diffusion bonding process parameters and laminate parameters are selected. Mechanism model and accumulated plastic strain criterion of fatigue crack growth are also established. Finally, fatigue crack growth in a typical diffusion bonding laminate component of different titanium alloys is discussed by extended finite element simulation model. Regulation mechanisms of bonded interface of different materials and layer property difference on stress and plastic strain fields of crack tip are analyzed. This research provides a new idea for improving fatigue life of titanium alloys. The application of new diffusion bonded laminate components can be of great benefit to significant progress in aircraft safety.

钛合金已成为现代飞机主体结构的重要材料，然而高疲劳裂纹敏感性使得钛合金构件裂纹扩展寿命很短，严重影响其长期安全使用，目前同种钛合金扩散连接层合结构中引入未焊合区或弱焊合区，虽然提高了抗疲劳性能，却显著降低其静态力学性能，因此提出异种钛合金扩散连接层合结构，由于异质界面的存在和层间不同的材料性能，对疲劳裂纹扩展具有显著的抑制作用，且不降低静态性能。首先研究异种钛合金两层结构扩散连接工艺及疲劳行为，建立疲劳寿命预测模型和异质界面疲劳本构模型；研究异种钛合金层合结构疲劳增寿的扩散连接工艺，制定合适的工艺参数和层合结构参数，建立疲劳裂纹扩展机理模型和累积塑性应变判据；最后建立典型异种钛合金扩散连接层合结构件疲劳裂纹扩展的扩展有限元仿真模型，分析异质界面和层间性能差异对裂尖应力场与塑性应变场分布的调控机理。该研究为钛合金疲劳增寿提供了新思路，而新型扩散连接层合结构件的应用有利于飞机安全性的明显改善。

钛合金已成为现代航空航天主体结构的重要材料，然而高疲劳裂纹敏感性使得钛合金构件裂纹扩展寿命很短，严重影响其长期安全使用。本项目重点研究了TC4/TB8、TC4/TB5、TC4/TA15异种扩散连接过程中的组织结构、相变规律、微观机理和动力学特征等多个方面内容，分析了TC4/TC4、TC4/TB8、TC4/TA15层合结构的疲劳裂纹扩展行为和机理，揭示了扩散连接热循环对钛合金振动疲劳性能的影响规律与机制，验证了利用异种钛合金扩散连接层合结构解决疲劳裂纹扩展速率快、损伤容限性能差等关键科学问题的可行性。对于扩散连接的TC4合金层合结构，在低温、高压条件下制备的试样疲劳裂纹扩展寿命比高温、低压条件的提升84%。扩散连接的TB8钛合金高层合结构比低层合结构的疲劳裂纹扩展寿命提高了9.4%。因此，采用合适的扩散连接工艺参数与层合结构参数均能提高钛合金的疲劳寿命，该研究为满足新一代飞机、航空发动机关键构件的目标服服役寿命要求提供理论和技术基础。