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

• Applicant: Professor Dr.-Ing. Frank Walther
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264915567

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.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Wolfgang Tillmann