In-situ SEM fatigue testing is performed to investigate crack propagation through the heat affected zone as well as in the base material and deposited material in a wire and arc additive manufacturing (WAAM) low-carbon steel part. The slip band formation and development prior to crack initiation and the crack growth rate are monitored in-situ and compared using fatigue testing specimens sampled from the base material, heat affected zone, WAAM zone, and cross-weld zone. Results show that the cross-weld zone specimen has the lowest crack growth rate, followed by the heat affected zone specimen and the two base material specimens. The effect of banded pearlite, acicular ferrite, and grain boundary and orientation is discussed with the aid of optical metallographic images, SEM, and EBSD maps. The mechanisms of the lowest rate observed in the cross-weld zone specimen are the pearlite bands preventing slip transfer, the high angle grain boundary of ultra-fine acicular ferrite hindering the crack propagation, as well as the basketweave structure promoting a zigzag growth path.

中文翻译：

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WAAM 低碳钢中疲劳裂纹通过交叉焊缝区域扩展的原位 SEM 研究以及微观结构在扩展行为中的作用


进行原位 SEM 疲劳测试，以研究裂纹在热影响区以及线材和电弧增材制造 （WAAM） 低碳钢零件中基材和沉积材料中的扩展。原位监测裂纹萌生前滑带的形成和发展以及裂纹扩展速率，并使用从基材、热影响区、WAAM 区和交叉焊缝区取样的疲劳试样进行比较。结果表明：交叉焊缝区试件的裂纹扩展速率最低，其次是热影响区试件和两个母材试件。借助光学金相图像、SEM 和 EBSD 面分布图，讨论了带状珠光体、针状铁素体以及晶界和取向的影响。在交叉焊缝区试样中观察到的速率最低的机制是防止滑移转移的珠光体带、阻碍裂纹扩展的超细针状铁氧体的高角度晶界以及促进锯齿形增长路径的篮式编织结构。