超声冲击处理改善奥氏体不锈钢抗应力腐蚀疲劳性能的微观机理研究

Microscopic mechanism on stress corrosion fatigue performance improvement of austenitic stainless steel treated by ultrasonic impact treatment (UIT) is a multiscale and multilevel problem. According to this problem, the project will establish a mathematical-physical model to describe the dynamic response of the material treated by UIT. The mapping relationships between UIT parameters and results induced by treatment as gradient nanostructure, residual stress distribution, etc will be constructed. Effects of gradient nanostructure and transfer behavior among different layers on the electrochemical behaviors and passive film characteristics of grains within different layers will be analyzed. The scale effect caused by gradient nanostructure and the effect of compressive residual stress distribution on the characteristics and propagation behaviors of stress corrosion fatigue crack will also be studied. The normalized damage parameter D will be put forward to describe the interaction damage effects induced by stress corrosion and corrosion fatigue, and a theoretical model will be established to predict the growth rate of stress corrosion fatigue crack in the gradient nanostructure layers of stainless steel. The quantitative relations between ‘UIT parameters - microstructures – stress corrosion fatigue performance improvement’ will be determined, and the whole scheme on optimization of the UIT parameters to improve stress corrosion fatigue performance will be proposed. The project will widen the application of UIT technology and provide the basic theoretical foundation and scientific method to solve austenitic stainless steel stress corrosion fatigue of major equipments.

超声冲击处理改善奥氏体不锈钢抗应力腐蚀疲劳性能的微观机理是一个多层次、多尺度的复杂问题。针对该问题，本项目建立超声冲击处理材料动态响应过程的数学物理模型，获得超声冲击参数与处理后表层梯度纳米结构、残余应力分布等的映射关系。分析梯度纳米结构及层间传递效应对材料电化学行为、钝化膜特性的影响，以及梯度变化晶粒带来的尺度效应、残余压应力分布对应力腐蚀疲劳裂纹特征与扩展行为的影响；提出描述应力腐蚀和腐蚀疲劳交互作用下材料归一化的损伤参量D，建立描述超声冲击后应力腐蚀疲劳裂纹在不锈钢梯度纳米层内扩展速率的模型。确立奥氏体不锈钢冲击处理后“超声冲击参数—微观结构—抗应力腐蚀疲劳性能”之间的定量关系，提出强化不锈钢抗应力腐蚀疲劳性能的超声冲击参数优化准则的整体方案。本研究将进一步拓宽超声冲击处理技术的应用领域，为解决重大装备奥氏体不锈钢应力腐蚀疲劳问题提供理论基础和科学方法。

超声冲击处理改善奥氏体不锈钢抗应力腐蚀疲劳性能的微观机理是一个多层次、多尺度的复杂问题。针对该问题，本项目建立了超声冲击处理材料动态响应过程的数学物理模型，获得了超声冲击参数与处理后表层梯度纳米结构、残余应力分布等的映射关系。分析了梯度纳米结构及层间传递效应对材料电化学行为、钝化膜特性的影响；考虑梯度变化晶粒带来的尺度效应、残余压应力带来的裂纹闭合效应以及腐蚀膜附加应力，建立了预测奥氏体不锈钢GNG层内应力腐蚀疲劳裂纹扩展速率的“力-化学”模型，实现了超声冲击处理后GNG/CG 304不锈钢应力腐蚀疲劳寿命的科学预测。确立了奥氏体不锈钢冲击处理后“超声冲击参数—微观结构—抗应力腐蚀疲劳性能”之间的定量关系，提出了强化不锈钢抗应力腐蚀疲劳性能的超声冲击参数优化准则的整体方案，并通过现场挂片实验进行了验证与技术推广。. 本项目已发表一作SCI论文三篇，相关内容与成果作为 “特种表面冲击强化抗应力腐蚀与疲劳技术及应用”一部分获得了 2018 年国家科学技术进步奖二等 1 项，研究成果可进一步拓宽超声冲击处理技术的应用领域，为解决重大装备奥氏体不锈钢应力腐蚀疲劳问题提供理论基础和科学方法。