高温服役构件蠕变状态的多参数化表征与剩余寿命预测

In the chemical engineering and petroleum plants, energy and power plants, and aeronautics & astronautics fields, many structural components are often exposed to elevated temperature and subjected to the long term sustained loading. Under these service environments, the elevated-temperature creep becomes one of the most critical factors determining the structural integrity and safe operation of components. Due to the great progress in the nonlinear ultrasound (NLU) and electromagnetic acoustic resonance (EMAR), they have been powerful tools to study the elevated-temperature creep state of structural component. Meanwhile, the continuum creep damage mechanics (CDM) has attracted much attention in recent years owning to its explicit expression. However, the single physical parameter is usually adopted by previous researches, which made it very difficult to build the effective relationship between the adopted parameter and the damage state. Because the creep of metal materials is time-dependent and its microstructure evolution has the multi-scale feature, an innovative approach in the present research is provided to evaluate the elevated-temperature creep state of structural components and to predict the remaining life by the combination of nondestructive evaluation (NDE) techniques of multi-parametric characterization and the improved CDM model. From the view of microstructure evolution caused by creep, the NDE methods of nonlinear ultrasound and electromagnetic acoustic resonance are used to characterize the creep state of metal components under elevated-temperature service comprehensively and reliably. Based on these results, the quantitative predication of the remaining life for metal components with complicated service histories can be achieved.

石油化工、能源动力和航空航天等众多领域，许多金属构件长期服役在高温、高压条件下，使得蠕变成为制约其完整性和安全运行的一个重要因素。非线性超声和电磁声谐振等无损检测技术的不断发展,近年来成为研究高温构件蠕变状态的有力工具。同时连续介质蠕变损伤力学CDM模型由于其明确的表达形式，近来也越来越受到重视。然而现有研究采用的参数往往比较单一，未能建立起所选参量与传统CDM中损伤程度之间的量化模型。因此，针对金属材料蠕变过程具有的时间相关性和内部微结构演化的多尺度特点，本项目拟提出基于多参数化表征（非线性超声纵波参数和横波电磁声谐振超声衰减系数）的无损检测技术与改进蠕变损伤本构模型的有机结合用于服役构件蠕变状态与剩余寿命的研究，从蠕变过程内部微结构演化的角度探讨用非线性超声和电磁声谐振等技术如何全面、准确地表征服役构件的蠕变状态，在此基础上实现对复杂服役历史条件下高温服役构件蠕变剩余寿命的定量预测。

本项目以石油化工、能源动力和航空航天等众多领域发生的高铬耐热钢构件蠕变破坏现象为研究对象，首先在580℃、600℃和620℃条件下分别进行了多个应力水平的持久蠕变和间断蠕变实验（总计100个）。随后，应用TTP参数法（包括Larson-Miller参数法、OSD参数法以及Wilshire模型等）、基于蠕变曲线的改进Theta法模型和具有单一损伤因子的K-R模型分别对长时蠕变寿命进行了外推预测。接着，采用非线性超声NLU法、传统超声UT法和电磁谐振EMAR等方法对所有蠕变试样进行了无损检测实验，同时利用IF内耗测量、XRD、SEM以及EBSD等手段从多个角度分析了不同蠕变状态下表征参数的变化规律。在此基础上，通过引入位错动力学和连续损伤力学等相关理论，结合Orawan方程构建了基于内部多尺度微观结构演化行为的高铬耐热钢蠕变本构模型（具体由6个未知参数和9个常微分方程组成），并对已获得的蠕变数据成功实施了反向求解。上述结果表明，无论是TTP参数法、改进Theta法还是K-R模型，在外推长时蠕变寿命时都存在估计精度不够问题。其次，非线性超声NLU的表征参数在蠕变第一阶段和第二阶段发生显著增加。相比之下，EMAR、UT两种方法的超声衰减系数均在蠕变第三阶段快速递增。此外，利用上述本构模型从组织演化的角度成功阐明了所用多表征参数随蠕变状态变化的微观物理机制，并对复杂服役历史条件下的蠕变剩余寿命进行了定量分析。这些成果均为上述领域内高温、高压服役构件的健康状况评价提供了重要数据与理论依据，同时也为进一步提高已有高温耐热钢材料的蠕变强度进行了有益探索。