2026年“核理安邦”联合博士生学术论坛

从表观熔合线到真实熔合区：F91/ERNiCr-3 堆焊界面分区及 PMZ 高温风险

Not scheduled

12m

地址：清华大学校内

口头报告 环、化、材、技、能源战略 环、化、材、技、能源战略

Speaker

Mr 罗 温伟 (清华大学核能与新能源技术研究院104室)

摘要

F91/ERNiCr-3异种金属堆焊界面存在显著的成分、组织、相结构及热物理性能梯度，是接头高温服役过程中的潜在薄弱区域。从微观尺度看，该界面并非单一几何线，而是具有一定空间尺度的熔合区或成分过渡区。其中，真实熔合线代表熔合区最靠近未熔化F91母材一侧的边界，是界定界面热历史、冶金分区及碳迁移行为的重要空间基准。然而，现有研究通常依据金相腐蚀或电解抛光后观察到的表观界面标定熔合线，其是否等同于真实熔化边界仍缺乏验证。
本研究结合FeCl₃腐蚀、电解抛光、硬度坑空间标记、EDS、EBSD、JMatPro 计算和高温原位实验，分析了 F91/ERNiCr-3堆焊界面的宏观偏析特征、真实熔合线位置及PMZ高温相稳定性。结果表明，TIG 堆焊界面并非均匀单一结构，而主要由无 PMZ 的普通界面和含PMZ的宏观偏析界面组成，二者沿界面长度占比分别约为24.2%和75.8%。FeCl₃ 腐蚀界面主要反映腐蚀响应差异，电解抛光界面主要对应bcc/fcc相界，二者均不应直接等同于真实熔合线。
通过硬度坑定位、EBSD晶粒形貌和EDS的Ni分布的联合分析发现，真实熔合线位于传统腐蚀界面更靠近 F91 母材的一侧，并揭示了CGHAZ与PMZ/TZ之间常被忽略的F91 UMZ。该区域具有凝固组织特征，其形成源于熔池边界层混合不足。进一步研究表明，PMZ虽在室温下保持bcc结构，但因Ni渗入导致Ac1降低至约300–400 ℃，低于典型服役温度541℃，并在高温原位实验中观察到疑似固态相变行为。该研究澄清了表观腐蚀界面、相界和真实熔合边界之间的差异，为F91/镍基焊材异种金属接头界面组织识别、碳迁移分析、高温铁素体残留机制解释及服役风险评估提供了更准确的冶金依据。

Abstract

F91/ERNiCr-3 dissimilar metal buttering interfaces exhibit pronounced gradients in composition, microstructure, phase constitution, and thermophysical properties, making them potential weak regions during high-temperature service. At the microscale, such an interface should not be regarded as a geometrically sharp line, but rather as a fusion region or compositional transition zone with a finite spatial extent. The true fusion line, defined as the boundary of this region closest to the unmelted F91 base metal, provides an essential spatial reference for interpreting the interfacial thermal history, metallurgical zoning, and carbon-migration behaviour. However, in previous studies, the fusion line has commonly been identified from the apparent boundary revealed by metallographic etching or electropolishing, although whether this boundary truly corresponds to the actual melting boundary remains insufficiently verified.
In this study, FeCl₃ etching, electropolishing, microhardness-indent spatial marking, EDS, EBSD, JMatPro calculations, and in-situ high-temperature observation were combined to investigate interfacial macrosegregation, the location of the true fusion line, and the high-temperature phase stability of the partially mixed zone (PMZ) in F91/ERNiCr-3 TIG buttering. The results show that the TIG-buttered interface is not a uniform single structure, but mainly consists of PMZ-free ordinary interface segments and PMZ-containing macrosegregated interface segments, which account for approximately 24.2% and 75.8% of the interfacial length, respectively. The boundary revealed by FeCl₃ etching mainly reflects differences in corrosion response, whereas the boundary observed after electropolishing primarily corresponds to the bcc/fcc phase boundary. Therefore, neither boundary should be directly equated with the true fusion line.
By correlating microhardness-indent markers with EBSD grain morphology and EDS Ni distributions, the true fusion boundary was found to lie on the F91 base-metal side of the conventionally etched boundary. This finding further reveals a previously overlooked F91 unmixed zone (UMZ) between the CGHAZ and the PMZ/TZ. This zone exhibits solidification-related microstructural features, and its formation can be attributed to insufficient mixing within the molten-pool boundary layer. Further analysis indicates that, although the PMZ retains a bcc structure at room temperature, local Ni enrichment lowers its Ac1 temperature to approximately 300–400 °C, below the typical service temperature of 541 °C. In-situ high-temperature observation also revealed microstructural changes indicative of possible solid-state transformation. This study clarifies the differences among the apparent etched boundary, the phase boundary, and the true fusion line, providing a more accurate metallurgical basis for interfacial microstructure identification, carbon-migration analysis, interpretation of retained high-temperature ferrite, and service-risk assessment of F91/Ni-filler dissimilar metal joints.