高性能薄壁件激光冲击表面强韧化机理及精准调控技术

Thin-walled parts are widely used in various fields of aerospace, defense, vehicle, equipment and power. High strength, high hardness, high fatigue resistance, high resistance corrosion, and high maintain performance of causative precision is the main manufacturing target of this kind of parts. Laser shock peening technology can not only introduce the residual compressive stress in parts surface, but also introduce high-density nanocrystals. So, laser shock peening is an important means of strengthening thin-walled parts. For the problems of macro-deformation, crack, stress relaxation, and microstructure degradation in laser peened aeronautical thin-walled parts, the phenomenon of nonlinear strong coupling, multi-scale effect, and strong temporal-spatial variation on the strength effect during laser peening and aging process are analyzed. And the analysis is based on the theory of thermal-stress-wave coupling, material flow stress regulation and shock wave guidance. The relationship between laser shock wave energy, acoustic impedance matching, peening temperature, ageing parameter and surface characteristics/characteristic micro-structure is quantitative descripted. Laser shock peening prototype of improving micro-structure/residual-stress stability is presented. That is the laser shock peening technology with temperature controlling and post aging, which based on the pinning effect. By means of the path optimization, strain wave guidance, and dynamic strain aging, the strength-toughness property improving and it’s stability of thin-walled parts will be solved.

薄壁类零件广泛应用于航空航天、国防、运载工具、动力、装备等各个领域，这类零件以高强度、高硬度、高疲劳性能、高抗腐蚀性能、使役精度保持性等物理性能为主要制造指标。激光冲击强化技术在零件表层不仅能引入残余压应力，还能引入致密的纳米层，因而是强韧化薄壁件的重要手段。针对航空薄壁件激光冲击强化中凸显的宏观变形、组织开裂、应力松弛和特征微结构退化等深层次问题，基于“热-力-波”耦合、材料流变应力调控与冲击波疏导理论，分析激光冲击与时效过程中多种非线性强耦合、多尺度效应、强时空变化现象对强韧化效果的影响规律，建立激光冲击波能量、声阻抗匹配、强化温度、时效与零件表面性能/特征微结构间的定量描述，提出提高激光冲击特征微结构/残余应力稳定性的技术原型—基于钉扎效应与后时效处理的温控激光冲击强化，采用路径优化、应变波疏导、动态应变时效等手段，解决薄壁件强韧性能稳固与再提升的新技术与新方法。

薄壁类零件广泛应用于航空航天、国防、运载工具、动力、装备等各个领域，这类零件以高强度、高硬度、高疲劳性能、高抗腐蚀性能、使役精度保持性等物理性能为主要制造指标。针对航空薄壁件激光冲击强化中凸显的宏观变形、组织开裂、应力松弛和特征微结构退化等深层次问题，基于“热-力-波”耦合、材料流变应力调控与冲击波疏导理论，分析激光冲击与时效过程中多种非线性强耦合、多尺度效应、强时空变化现象对强韧化效果的影响规律，建立激光冲击波能量、声阻抗匹配、强化温度、时效与零件表面性能/特征微结构间的定量描述，提出提高激光冲击特征微结构/残余应力稳定性的技术原型—基于钉扎效应与后时效处理的温控激光冲击强化，采用路径优化、应变波疏导、动态应变时效等手段，解决薄壁件强韧性能稳固与再提升的新技术与新方法。研究结果表明，正面残余应力随厚度增加而增大，反面残余应力随厚度增加先增大后减少。对于显微硬度，当厚度为4mm时，正面显微硬度最大，为440.2HV。厚度为2mm时，反面显微硬度最大，为416.1HV。冲击波在不同声阻抗接触面下产生的拉伸波与压缩波对残余应力场的分布规律有着较大的影响。采用所建立的冲击波压力空间分布精确模型预测的残余应力场与传统模型相比有着更高的精度。当搭接率为62.5%的情况下，强化效果和加工效率均较好。当激光光束平顶光强范围占比在40%-50%之间时，加工面积大且中心区域残余应力洞程度较小，零件的强化效果和加工效率均较好。当工艺温度为200℃时，强化效果最佳。试样经过WLSP（200℃）处理后，材料内部生成了高密度位错缠结，形成了位错网络、位错胞等复杂的位错结构。随后以表面残余应力和微观组织结构变化为表征指标，研究了不同时效温度和时效时间下温激光冲击强化GH4169合金的热稳定性。结果表明，与LSP相比，WLSP试样表面残余应力松弛量和松弛速率较小，材料内部位错密度更高、更加均匀，且无明显的δ相析出，具有更高的热稳定性。研究的结果可以为薄壁件工艺优化提供参考。