In situ Correlative Observation of Humping-Induced Cracking in Directed Energy Deposition of Nickel-Based Superalloys
In situ Correlative Observation of Humping-Induced Cracking in Directed Energy Deposition of Nickel-Based Superalloys
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DOI：
10.1016/j.addma.2023.103579
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发表时间：
2023-04
影响因子：
11
通讯作者：
Tristan G. Fleming;David Tien Rees;S. Marussi;T. Connolley;R. Atwood;M. Jones;J. Fraser;Chu Lun;Alex Leung;P. D. Lee
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文献类型：
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作者：
Tristan G. Fleming;David Tien Rees;S. Marussi;T. Connolley;R. Atwood;M. Jones;J. Fraser;Chu Lun;Alex Leung;P. D. Lee
定向能量沉积（DED）是一种有前途的用于修复的增材制造技术;然而，DED易于在薄壁截面中产生表面波纹（隆起），这会增加残余应力和裂纹敏感性，并降低疲劳性能。目前，由于缺乏具有高时空分辨率的可操作监测方法，DED中的裂纹形成机制还没有得到很好的理解。在这里，我们使用内联相干成像（ICI）光学监测表面拓扑结构和原位检测裂纹，再加上同步加速器X射线成像观察亚表面裂纹愈合和生长。ICI第一次实现了离轴对准（相对于激光器成24°），能够集成到DED机器中，而无需更改激光传输光学器件。我们使用单元件MEMS扫描仪和定制校准板在ICI测量和激光束位置之间实现了横向（<10 µm）和深度（<3 µm）的精确配准。ICI表面拓扑结构通过相应的射线照片（相关性>0.93）进行验证，直接跟踪表面粗糙度和波度。我们有意在镍高温合金CM 247 LC的薄壁结构中播种隆起，在表面谷中局部诱导开裂。使用ICI原位观察到小至7 µm的裂纹开口，包括亚表面信号。通过量化驼峰和开裂，我们证明ICI是一个可行的工具，在原位裂纹检测。
Directed energy deposition (DED) is a promising additive manufacturing technique for repair; however, DED is prone to surface waviness (humping) in thin-walled sections, which increases residual stresses and crack susceptibility, and lowers fatigue performance. Currently, the crack formation mechanism in DED is not well understood due to a lack of operando monitoring methods with high spatiotemporal resolution. Here, we use inline coherent imaging (ICI) to optically monitor surface topology and detect cracking in situ, coupled with synchrotron X-ray imaging for observing sub-surface crack healing and growth. For the first time, ICI was aligned off-axis (24° relative to laser), enabling integration into a DED machine with no alterations to the laser delivery optics. We achieved accurate registration laterally (<10 µm) and in depth (<3 µm) between ICI measurements and the laser beam position using a single-element MEMS scanner and a custom calibration plate. ICI surface topology is verified with corresponding radiographs (correlation >0.93), directly tracking surface roughness and waviness. We intentionally seed humping into thin-wall builds of nickel super-alloy CM247LC, locally inducing cracking in surface valleys. Crack openings as small as 7 µm were observed in situ using ICI, including sub-surface signal. By quantifying both humping and cracking, we demonstrate that ICI is a viable tool for in situ crack detection.