700℃含镍耐热钢多轴蠕变孔洞长大失效机制和应用模型研究

700℃-grade nickel containing heat resistant steel is a prerequisite to developing advanced ultra-supercritical power plant, the heat resistant properties of which has not been more abundantly studied than the low alloy steels used in traditional supercritical power plant, especially in creep mechanism. Due to the complexity of thermal-mechanical loading on high temperature turbine component, the problem of multiaxial creep damage and failure become increasingly serious. Essentially, the multiaxial creep damage results from creep rupture basing on cavity nucleation, growth and coalescence under complex stress and multi-mechanism. According to this point of view, this research project try to raise a new multiaxial creep model of cavity growth, which is fit for 700℃-grade nickel containing alloy. The methodology of combining theoretical derivation, numerical calculation and experimental investigation will be adopted in this research. Through the adopted method, the root cause will be disclosed with regard to the multiaxial creep failure of cavity growth. The cavity growth mechanism will be illustrated under creep condition, and then the relationship between cavity growth controlled by multi-mechanism and multiaxial creep failure behavior will be established corresponding to microstructure and macrostructure scale respectively. Through the newly developed model, it will provide theoretical support and technological approach to the creep life design on long life and large dimensional component.

700℃含镍耐热钢是发展先进超超临界发电机组的必要条件之一，其耐热性能包括蠕变机制的研究远不如传统超临界电厂低合金钢那样充分。由于汽轮机高温构件受复杂热-机械载荷作用，多轴蠕变损伤及失效问题日益突出，而多轴蠕变损伤实质上是在复杂应力状态和多种微观机制作用下材料孔洞形核、长大、聚合所引起的蠕变断裂。基于这样一种基本观点，本课题试图构建一种适合700℃含镍耐热钢高温构件的孔洞长大多轴蠕变模型，采用理论推导、数值计算、试验验证相结合研究方法，揭示700℃等级汽轮机耐热钢多轴蠕变孔洞长大失效本质，阐明材料在蠕变条件下孔洞长大的控制机制，确立微观-宏观尺度下多机制控制孔洞长大与多轴蠕变失效行为之间的内在联系，通过深入研究蠕变机制,发展适用的模型，进而为超长工作周期的大尺寸结构蠕变寿命设计提供更加完备的解决方法和理论支撑。

21世纪以来，环境与能源问题日益突出，可持续发展成为人们的共识，以清洁、高效、安全为特点的低碳经济与发展模式势在必行。根据热力学第二定理中卡诺循环可知，高温是提高能源装备与动力机械热效率的最重要途径之一。今后，无论是先进航空燃气轮机、超超临界火电、新一代核电，还是现代的煤、石油、天然气化工，其核心工艺与装备均以高参数（高温或高压）为基础。在高温下，金属材料的强度承受了很大的挑战。如果以700℃工作温度为界，传统的铁素体和奥氏体材料(如P91、P92)都不能胜任使用要求。超超临界发电主蒸汽温度提升至700℃，目前这一等级镍基耐热钢的需求已出现，但其耐热性能包括蠕变机制的研究还很欠缺。因此，本项目以In783/718材料为切入点，从孔洞长大过程微观物理机制入手，研究了700℃等级镍基合金的蠕变失效机制，揭示了700℃含镍耐热钢多轴蠕变孔洞长大失效本质，构建了具有坚实微观物理基础的理论模型，阐明了孔洞长大的控制机制，确立了微观-宏观尺度下多机制控制孔洞长大与多轴蠕变失效行为之间的内在联系，发展了适用的多轴蠕变应用模型，弄清楚了各参数对700℃含镍耐热钢多轴蠕变失效的影响，如应力水平、蠕变率、温度、应力三维度、微观结构。得到了多轴蠕变损伤实质上是在复杂应力状态和多种微观机制作用下材料孔洞形核、长大、聚合所引起的蠕变断裂。从应用上讲，借助了以上理论成果完成了对超长工作周期大尺度典型高温构件的多轴蠕变寿命设计，取得了较为满意的寿命及损伤预测结果。项目资助发表了SCI期刊论文10余篇，取得了10余项专利成果。项目资助培养硕士研究生4 名，协助培养博士4 名。项目投入直接经费20.00万元，支出19.97万元，各项支出与预算相符。