声-电-力耦合协同表面强化方法与机理研究

Key components in the national economic field required high fatigue property and long service life, aiming at this point, amplitude and depth of compressive residual stress layer, surface microstructure and roughness were the key factors in surface strengthening. Due to skin effect and electro plastic effect of high-frequency pulsed electric field, Ultrasonic shockwave and static force would be focused on the skin layer, on the other hand, the surface deformation resistance was reduced, further more the skin layer depth was decided by electric parameters, it was beneficial to improve and control the amplitude and depth of compressive residual stress layer. Meanwhile, the combination of Ultrasonic Rolling surface strengthening and pulsed electric field was beneficial to reduce surface microstructure and roughness. Therefore, this project proposed a surface strengthening method based on multi fields coupling coordination of ultrasonic energy field, pulsed electric field and static load field. According to the analysis of effect of multi fields coupling coordination on the surface state, compressive residual stress layer with high amplitude and large depth could be obtained, nano-crystallization of surface microstructure and roughness could be realized. And multi fields coupling coordination strengthening theory of ultrasonic energy field, pulsed electric field and static load field would be established, this would set up a theoretical and technology foundation for its application in key components.

针对国民经济领域关键构件高疲劳性能和长使用寿命的需求，提高材料表层残余压应力幅值和深度以及降低表面粗糙度和表层晶粒尺寸是表面强化的关键因素。由于高频脉冲电场的“集肤效应”和“电致塑性效应”，一方面可以将超声冲击波和静载力的作用集中于集肤层，另一方面可以降低表层的变形抗力，并且通过电场参数调整集肤层深度，有利于实现表层残余压应力幅值和深度的提高与控制，同时，还可以将超声滚压降低表面粗糙度的优势与脉冲电流促进再结晶的作用相结合，有利于表层组织、表面粗糙度的降低。因此，本项目提出了基于超声能场、脉冲电场和静载力场多场耦合协同作用的表面强化方法。通过深入系统地研究脉冲电流、超声能场两种特殊能场与静载力场耦合协同的作用机制，实现高幅值、大深度残余压应力层的控制和表层组织、表面粗糙度的“双纳米化”，并建立脉冲电流、超声能场和静载力场耦合协同驱动的强化理论，为其在关键构件上的应用奠定理论和技术基础。

针对航空钛合金构件高疲劳性能的需求,本文采用多场耦合表面强化技术强化TC4钛合金表面，对其强化前后的表面粗糙度、三维形貌、显微硬度及残余应力分布等表面状态进行分析，并在疲劳性能评价的基础上,探索了失效机理。结果表明，表面强化后，钛合金表面发生塑性变形，改善表面状态，在优化的工艺参数下，表面粗糙度可以达到0.044μm，表面显微硬度达到HV462.6，较之母材，分别提高83.4%和44.1%，获得的表面残余压应力层层厚650μm，应力最高达到-500MPa。另外，强化后的钛合金疲劳极限达到570MPa，较之母材，提高10%。通过失效断口分析，表面粗糙度的改善，避免应力集中产生疲劳裂纹源，另外表层组织的硬化以及残余压应力层的引入，导致材料的疲劳源从表面转移到次表面，从而提高了材料的疲劳性能。