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

废气承载部件中的钎焊结构的操作行为受到钎焊接头的腐蚀疲劳行为的显著影响，例如用镍基填充金属钎焊的奥氏体AISI 304 L。在第一个资助期内，首次将一种新的测试系统应用于钎焊AISI 304 L/BNi-2接头，以便在10 Hz的测试频率下验证合成废气冷凝物的疲劳行为。由于腐蚀过程是时间依赖性的，因此预计所应用的测试频率会产生重大影响。目前，缺乏基于微观结构的理解测试频率对钎焊接头的腐蚀疲劳行为的影响，以及用于有效表征和预测排气冷凝物中频率相关疲劳特性的损伤模型。此外，奥氏体AISI 304 L接头的研究结果的可转移性和有效性，钎焊与耐腐蚀镍基钎料，是未知的，因为合金依赖的微观结构的影响，在废气冷凝物的腐蚀疲劳行为尚未研究。在第二个资助期内，计划对试验频率对奥氏体接头腐蚀疲劳性能的影响进行系统和基于机制的表征，该接头采用两种镍基钎料钎焊。其目的是一个微观结构为基础的理解的影响的频率和时间依赖性的腐蚀的变形和损坏机制，以澄清腐蚀和机械损坏机制之间的因果关系。基于微观结构，它将被评估，如果使用硼还原的镍基填充金属，是否以及如何可以防止扩散区的腐蚀损伤和频率依赖的腐蚀疲劳性能可以得到改善。最后，结果将被应用到开发一个合金依赖的损伤模型的时间和成本效益的表征频率依赖的腐蚀疲劳行为的钎焊接头。

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.