一体化核反应堆内直流蒸发器用钛合金的高周多轴腐蚀疲劳性能研究

The heat transfer components of one-through steam generator for intergrated nuclear reactor are usually caused to fail due to the interaction of temperature, mechanical loading and corrosion, which affects the running security of the whole nulcear equipment. However, no design standard concerning this problem has been accomplished in the world. In this project, the titanium alloy TA16 used in nuclear steam generator was chosen as the research object, and the high-cycle multiaxial fatigue test as well as the microscopic failure mechanism will be performed under high temperature (325℃), high pressure (10.5MPa), hot steam and hot salt environment. The influence of high-cycle multiaxial loading on the deformation and damage mechanism will be illustrated, and the effects of multiaxial stress, temperature and corrosion on the local plastic strain accumulation will be clarified, the dynamic hardening rule in the crystal plastic model will be modified and implemented in finite element software, and the macroscopic stress strain response of the titanium alloy will be described by CP-FEM. Finally, the high-cycle multiaxial corrosion fatigue criterion with considering stress gradient and random distribution of defects will be proposed to accurately predict the fatigue life of titanium heat transfer components. The project will hopefully clarify the rule of high-cycle multiaxial corrosion fatigue failure and establish a prediction method for the heat transfer components in intergrated nuclear reactor, and the achievements will provide a theoretic support for long-life design of nuclear one-through steam generator.

一体化反应堆内直流式蒸汽发生器的传热组件经常由于经受温度、机械载荷、腐蚀的交互作用而导致失效，影响整个核电装备的安全运行，但国内外对此没有设计标准。本课题以核电蒸发器用材料TA16钛合金为研究对象，开展高温（325℃）、高压（10.5MPa）、热蒸汽和热盐环境下钛合金的高周多轴疲劳试验及失效机理研究，阐明高周多轴载荷对钛合金微观变形与损伤机制的影响，澄清多轴应力、温度、腐蚀对局部塑性应变累积的影响规律，修正晶体塑性模型的随动强化率并嵌入有限元软件，建立晶体塑性-有限元模型（CP-FEM）对钛合金宏观应力应变响应进行描述。最后，提出考虑应力梯度与缺陷随机分布的高周多轴腐蚀疲劳判据，精确预测钛合金换热组件的疲劳寿命。本项目有望阐明一体化反应堆内换热组件的高周多轴腐蚀疲劳失效规律并建立预测方法，其研究成果为核电直流蒸汽发生器的长寿命设计提供理论支持。

换热管作为核反应堆蒸汽发生器中的重要构件，其在经受温度、机械载荷、腐蚀交互作用下的结构完整性是小型堆长周期安全可靠运行的重要课题。本项目围绕换热管材料TA16钛合金在高温、多轴复杂应力等极端工况下的疲劳失效行为开展研究，揭示了温度对高周疲劳损伤机制的影响，阐明了多轴载荷对钛合金微观变形机制的影响规律，发展复杂应力作用下的晶体塑性-有限元模型(CP-FEM)，结合疲劳微观损伤累积规律，提出了相应的疲劳判据，实现了对疲劳寿命和裂纹萌生位置的预测；同时还开发了内壁滚压强化技术以提高其疲劳性能。具体研究内容和结论如下：.（1）开展了室温及服役高温下TA16管材的高周疲劳实验，高温下热激活破坏了短程有序结构，促进了多滑移行为，位错交割引起较高水平的硬化，从而导致晶粒裂纹萌生平面由主导滑移面转换为沿最大拉应力平面。.（2）分析了TA16钛合金单轴及双轴变形的微观变形机制，单轴变形下材料以柱面单滑移为主，而双轴变形条件则大量激活了多滑移和交滑移；开展了TA16厚壁管结构在压扁试验过程中的应力分析，阐述了其集中应力区的详细变形机理。.（3）开展了TA16钛合金热机疲劳实验，并对其宏观力学响应、疲劳断口、截面微裂纹进行分析。在热机耦合条件下，同相位热机疲劳实验寿命高于恒温疲劳，而反相位热机疲劳实验寿命低于恒温疲劳。.（4）开发了基于EBSD的晶体塑性建模方法，系统比较了CP-FEM预测和SEM-DIC测量得到的全场位移和应变数据，确定了基面滑移和柱面滑移的临界分切应力比值R=4，模拟结果和DIC结果呈现出较好的一致性。.（5）开展了不同幅值下的中断疲劳实验，监测并分析穿晶、沿晶和准穿晶裂纹的形核机理，开发了结合应变不相容参数的新型疲劳指示因子及孪生-退孪生模型结合，成功预测了疲劳裂纹形核位置。.（6）开发了小规格后壁管内壁滚压强化技术，开展了滚压强化后管材的高周疲劳及热机疲劳实验，梯度结构中纳米晶及纳米孪晶层抑制了裂纹萌生及扩展，裂纹萌生从表面位置向亚表面转移，从而提高了疲劳寿命。