Microstructure-based understanding of the test frequency influence on the corrosion fatigue behaviour of austenite AISI 304L joints brazed with nickel based filler metal

废气输送部件中的钎焊结构的工作性能受钎焊接头的腐蚀疲劳性能的影响很大，例如用镍基钎料钎焊奥氏体AISI 304L。在第一个资助期内，首次将一种新的测试系统应用于AISI 304L/BNI-2钎焊接头，以表征在10赫兹测试频率下合成废气冷凝液中的疲劳行为。由于腐蚀过程是时间相关的，预计施加的试验频率会产生重大影响。目前，对试验频率对钎焊接头腐蚀疲劳行为的影响以及有效表征和预测废气冷凝液中随频率变化的疲劳性能的损伤模型缺乏基于微观结构的理解。此外，奥氏体AISI 304L接头用耐蚀镍基钎料钎焊的研究结果的可转移性和有效性尚不清楚，因为合金化相关的微观组织对废气冷凝液中腐蚀疲劳行为的影响尚未得到研究。在第二个资助期内，计划对试验频率对用两种镍基钎料钎焊的奥氏体接头的腐蚀疲劳性能的影响进行系统和基于机理的表征。其目的是从微观结构上理解频率和时间相关的腐蚀对变形和损伤机制的影响，以澄清腐蚀和机械损伤机制之间的因果关系。根据显微组织，将评估是否以及如何能够防止扩散区的腐蚀损伤，以及如何改善频率相关的腐蚀疲劳性能。最后，这些结果将被应用于开发合金相关损伤模型，以时间和成本高效地表征钎焊接头的频率相关腐蚀疲劳行为。

The operational behaviour of brazed constructions in exhaust gas carrying components is significantly influenced by the corrosion fatigue behaviour of the brazed joins, such as austenite AISI 304L brazed with nickel-based filler metal. Within the first funding period, a novel test systematics was applied to brazed AISI 304L/BNi-2 joints for the first time, in order to characterise the fatigue behaviour in synthetic exhaust gas condensate at a test frequency of 10 Hz. As corrosion processes are time-dependent, a significant influence of the applied test frequency is expected. Currently, a microstructure-based understanding of the test frequency influence on the corrosion fatigue behaviour of brazed joints as well as damage models for the efficient characterisation and prediction of the frequency-dependent fatigue properties in exhaust gas condensate are missing. Further, the transferability and validity of research results on austenite AISI 304L joints, brazed with corrosions-resistant nickel based filler metal, is unknown, because the alloying-dependent microstructure influence on the corrosion fatigue behaviour in exhaust gas condensate was not yet investigated. Within the second funding period, a systematic and mechanism-based characterisation of the test frequency influence on the corrosion fatigue properties of austenite joints, brazed with two nickel based filler metals, is planned. The aim is a microstructure-based understanding of the influence of the frequency- and time-dependent corrosion on the deformation and damage mechanisms in order to clarify the cause-effect relationship between corrosive and mechanical damage mechanisms. Based on the microstructure, it will be evaluated, if and how the corrosive damage of the diffusion zones can be prevented and the frequency-dependent corrosion fatigue properties can be improved, if a boron-reduced nickel-based filler metal is used. Finally, the results will be applied to develop an alloying-dependant damage model for a time- and cost-efficient characterization of the frequency-dependant corrosions fatigue behaviour of brazed joints.