The alumina former radiant coil is typically used as a high-temperature material. It is inevitable that the material undergoes deterioration after prolonged use. This deterioration is primarily caused by damage from the service environment and initiates carburization, resulting in a loss of its mechanical properties. Currently, the damage to the materials is only discovered when they are already broken and a precise non-destructive testing method to determine the extent of material deterioration before the damage occurs has not successfully been developed. Therefore, this research aims to study and analyze the deterioration and the causes of damage to alumina former radiant coil materials. Additionally, the study was conducted to establish a relationship between the extent of deterioration and the impedance phase angle using the eddy current test method. The experimental analysis included both as-received and in-service materials of alumina former radiant coil, which consisted of 45 % nickel by weight, 30 % chromium by weight and 4 % alumina by weight. The additional testing methods included microstructure and elemental analysis, deterioration distance measurement and impedance phase angle measurement. The results indicated that the deterioration was primarily caused by damage to the oxidation layer, facilitating the diffusion of carbon and initiating a carburization reaction on the surface of the coil. These factors unavoidably reduced the corrosion resistance of alumina former radiant coil materials. Furthermore, the reduction in chromium content as materials entered the deterioration stage led to increased hardness in the carburization zone and reduced hardness in the oxidation zone. This deterioration caused the material to exhibit ferromagnetic behavior. It was observed that as the area of deterioration increased, the size of the ferromagnetic regions also increased. Resulting in, the eddy current testing results show a variation in the impedance phase angle. Therefore, the relationship can be concluded that the impedance phase angle increases in the counterclockwise direction, corresponding to a greater extent of deterioration. The benefit of this paper is to forecast the level of the severity of deterioration quantitatively when using eddy current testing.

中文翻译：

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用于预测氧化铝前辐射线圈劣化阶段的涡流分析

氧化铝辐射线圈通常用作高温材料。长时间使用后，材料不可避免地会发生劣化。这种劣化主要是由使用环境的损坏引起的，并引发渗碳，导致其机械性能损失。目前，只有当材料已经破损时才会发现材料的损坏，并且尚未成功开发出在损坏发生之前确定材料劣化程度的精确无损检测方法。因此，本研究旨在研究分析氧化铝原辐射线圈材料的劣化及损坏原因。此外，还利用涡流试验方法建立了劣化程度与阻抗相位角之间的关系。实验分析包括氧化铝前辐射线圈的接收材料和使用中材料，其成分为按重量计 45% 的镍、按重量计 30% 的铬和按重量计 4% 的氧化铝。附加测试方法包括微观结构和元素分析、劣化距离测量和阻抗相位角测量。结果表明，劣化主要是由于氧化层受损，促进碳扩散并在卷材表面引发渗碳反应造成的。这些因素不可避免地降低了氧化铝辐射盘管材料的耐腐蚀性能。此外，随着材料进入劣化阶段，铬含量减少，导致渗碳区硬度增加，氧化区硬度降低。这种恶化导致材料表现出铁磁行为。据观察，随着劣化面积的增加，铁磁区域的尺寸也增加。结果，涡流测试结果显示阻抗相位角的变化。因此，可以得出这样的关系：阻抗相位角沿逆时针方向增大，对应于更大程度的劣化。本文的好处是在使用涡流检测时定量预测劣化的严重程度。