Acceleration of Grain Boundary Cracking in Ni-Base Alloy 617 Under Creep-Fatigue Loading at 800°C
Acceleration of Grain Boundary Cracking in Ni-Base Alloy 617 Under Creep-Fatigue Loading at 800°C
复制标题
800°C 蠕变疲劳载荷下镍基合金 617 的晶界开裂加速
DOI：
10.1115/imece2020-23738
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Miura Hideo
中科院分区：
文献类型：
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作者：
Ishihara Kenta;Luo Yifan;Miura Hideo
近年来，为了解决全球气候变暖问题，先进火电厂的运行温度都在试图提高热效率和减少CO2排放。然而，在高温蠕变和蠕变疲劳条件下，发现诸如在约750°C下具有高强度和良好耐腐蚀性的Ni基合金617等耐热合金的有效寿命急剧下降。其主要原因是裂纹萌生和扩展路径由穿晶向沿晶转变。因此，理解和表达晶界开裂的判据是很重要的。在这项研究中，电子背散射衍射（EBSD）分析被施加到合金中的晶界质量的退化过程的可视化。在蠕变和蠕变疲劳试验过程中，连续监测晶粒和晶界的结晶度的变化。结果表明，空位和位错的积累降低了晶界的结晶度，从而降低了晶界的强度。蠕变过程中，在由施密德因子差异较大的晶粒组成的特定晶界附近发生堆积。另一方面，它发生在蠕变疲劳载荷下的所有晶界。因此，在蠕变疲劳载荷下，缺陷的积累明显加速。晶间裂纹的临界图像质量（IQ）值几乎是相同的，无论加载模式。当损伤晶界的IQ值降低到临界值时，晶界处开始发生沿晶开裂。
In recent years, in order to solve the global warming issue, the operating temperature of advanced thermal power plants has attempted to improve thermal efficiency and reduce CO2emissions. Under the creep and creep-fatigue conditions at elevated temperature, however, the effective lifetime of heat-resistant alloys such as Ni-base Alloy 617, which has high strength and good corrosion resistance at about 750°C, was found to decrease drastically. Main reason for this short lifetime was attributed to the change in the crack initiation and propagation paths from transgranular one to intergranular one. Therefore, it is important to understand and express the criteria for grain boundary cracking. In this study, electron back-scatter diffraction (EBSD) analysis was applied to the visualization of the degradation process of the quality of grain boundaries in the alloy. The change in the crystallinity of grains and grain boundaries were continuously monitored during creep and creep-fatigue tests. It was found that accumulation of vacancies and dislocations degraded the crystallinity of grain boundaries and thus, their strength. The accumulation occurred around the specific grain boundaries which consisted of grains with large difference of Schmid factor during creep test. On the other hand, it occurred around all grain boundaries under the creep-fatigue loading. Thus, the accumulation of defects was clearly accelerated under the creep-fatigue loading. The critical image quality (IQ) value of intergranular cracking was almost the same regardless of the loading mode. Once the IQ value of the damaged grain boundaries decreased to a critical value, intergranular cracking started to occur at the grain boundaries.