Characterisation of the corrosion fatigue behaviour of brazed AISI 304L/BNi-2 joints in synthetic exhaust gas condensate
Characterisation of the corrosion fatigue behaviour of brazed AISI 304L/BNi-2 joints in synthetic exhaust gas condensate
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DOI：
10.1007/s40194-018-0557-y
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发表时间：
2018-02
影响因子：
2.1
通讯作者：
A. Schmiedt;M. Manka;W. Tillmann;F. Walther
中科院分区：
文献类型：
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作者：
A. Schmiedt;M. Manka;W. Tillmann;F. Walther
采用钎焊热交换器的废气再循环（EGR）是减少汽车柴油机nox排放的常用方法。由于在运行过程中，由于腐蚀性废气的腐蚀作用，钎焊EGR冷却器的疲劳载荷叠加在一起，因此钎焊接头的腐蚀疲劳行为与部件设计有关。在本研究中，钎焊AISI 304L/BNi-2接头在合成废气冷凝液K2.2中进行循环测试，使用腐蚀池，以及在预腐蚀acc后的空气中进行循环测试。至VDA 230-214，老化持续时间长达6周。在2 × 106次循环中，叠加腐蚀疲劳载荷的疲劳强度降低了43%，连续腐蚀疲劳载荷的疲劳强度降低了22%。在经过长时间和高成本的预腐蚀后，原位测试的试样的恒流阳极极化成功地有效地再现了腐蚀疲劳行为。在这种情况下，采用一种新的测试策略，使用新开发的延伸计进行局部应变测量，以及电气和电化学测量，以精确评估钎焊接头的腐蚀疲劳。利用扫描电镜对微结构相关的腐蚀疲劳损伤机制进行了评价。
Exhaust gas recirculation (EGR) with brazed heat exchangers is commonly used for the reduction of NOxemissions of automotive diesel engines. Since the fatigue loading of brazed EGR coolers during the operation is superimposed by corrosive attack due to aggressive exhaust gases, the corrosion fatigue behaviour of brazed joints is relevant for the component design. In the present study, brazed AISI 304L/BNi-2 joints were cyclically tested in the synthetic exhaust gas condensate K2.2, using a corrosion cell, as well as in air after pre-corrosion acc. to VDA 230–214 with ageing durations of up to 6 weeks. A significant reduction of the fatigue strength at 2 × 106cycles down to 43% was determined for superimposed and down to 22% for successive corrosion fatigue loading. A galvanostatic anodic polarisation of the specimens tested in situ was applied successfully for an efficient reproduction of the corrosion fatigue behaviour after the long-time and cost-intensive pre-corrosion. In this context, a novel test strategy with local strain measurements, using a newly developed extensometer, as well as electrical and electrochemical measurements was established for a precise corrosion fatigue assessment of the brazed joints. Microstructure-related corrosion fatigue damage mechanisms were evaluated using scanning electron microscopy.