拘束效应和残余应力耦合下的核电异种金属焊接接头环境致裂研究

To satisfy the demand of defect assessment and repair of dissimilar metal welded joints in light water reactors, the aim of this project is to address the fracturing properties and environmentally assisted cracking behavior of welded joints under coupling of constraint effect and residual stress. The following issues will be focused in the present project: . (1) Developing the quantitative characterization of the welded joint local zones. This research can be used to clarify the mechanism of constraint effect on welded residual stress release and re-distribution mechanism; . (2) Describing the interaction of residual stress and environmentally assisted cracking of dissimilar metal welded joints. The influence rules of residual stress redistribution, temperature and microstructure of interface materials on the material fracture mechanism and toughness can be clarified; . (3) Analyzing the coupling influence of constraint effect and initial residual stress on the fracture toughness of welded joint local zones. The correlation of high-constraint specimens to actual welded joints of three-dimensional constraint can be built. The defect assessment method of dissimilar metal welded joints in nuclear power plants contains constraint effect and residual stress parameters can be constructed. . The mechanical, material and chemical analyses were included in this cross-domain program. Through the accomplishment of this project, the environmentally assisted cracking behavior of dissimilar metal welded joints in high temperature water environment can be explained through the view point of mechanics and materials analysis. Some scientific insights can be provided for the defects assessment methods establishment of the dissimilar metal welded joints for engineering application.

面向轻水堆异种金属焊接接头缺陷评估和修复的需求，针对拘束效应和残余应力耦合作用下的接头断裂性能和环境致裂行为开展研究。主要包括：(1) 定量表征接头各微区拘束效应控制参量，澄清拘束效应对焊接残余应力释放及重新分布的作用机制；(2) 探明残余应力与接头环境致裂裂纹扩展的相互影响规律，研究残余应力重新分布、温度、界面材料微观组织等因素对材料断裂机理和韧性的影响规律；(3) 分析拘束效应和初始残余应力耦合对焊接接头各微区断裂韧性的影响，建立高拘束试样与实际核电焊接接头三维拘束的统一关联，构建包含拘束效应和残余应力参量的核电异种金属焊接接头的缺陷评定方法。本项目体现了力学、材料、化学等多学科领域的交叉，有望从力学-材料角度阐明高温水环境中核电异种金属焊接接头的环境致裂行为，为建立具有实际工程意义的异种金属焊接接头缺陷评定方法提供科学支持。

核电设备中存在着大量急需评估、修复和预测的异种金属焊接接头。为进行准确的核电焊接接头结构完整性评定和寿命预测，需要纳入拘束效应和残余应力的影响。本项目通过探索拘束效应和残余应力耦合作用下的接头断裂性能，从力学-材料角度对高温水环境中核电异种金属焊接接头的环境致裂行为进行了研究，完成的主要工作内容和研究结果如下：(1) 研究了拘束效应对高温水环境中不锈钢及镍基合金应力腐蚀裂纹扩展速率的影响，选取了统一表征面内/面外拘束的新拘束参数；(2) 探究了残余应力和工作载荷交互作用下的焊接接头裂纹扩展行为和异种金属焊接接头界面裂纹的扩展特性；(3) 讨论了晶粒取向对双晶体晶界处应力状态的影响；(4) 研究氧化膜对镍基合金应力腐蚀行为的影响，讨论了基体金属裂纹扩展方向两侧的高应力应变对氧化膜破裂的促进作用。.本项目的研究为澄清残余应力-拘束效应耦合与接头环境致裂裂纹扩展的相互影响规律，以及最终建立具有实际工程意义的异种金属焊接接头缺陷评定方法奠定了一定的基础。特别是通过本项目的研究，我们与海洋腐蚀与防护国防科技重点实验室建立了比较深入的合作关系，申请获得了该实验室2019 年度的开放基金资助1项，获得2016年度陕西省优秀博士学位论文奖1项，并协助指导3名硕士生顺利毕业。本项目的部分研究成果已发表在国内外相关学术期刊和会议上。