In-situ SEM observation of crack propagation in brazed joints during bending tests
摘要
Understanding the fracture mechanisms in brazed joints offers opportunities to improve joint design and brazing processes. Traditional ex-situ methods cannot capture the material behavior in real-time, making in-situ observation during mechanical testing, such as in SEM, invaluable. In the present work, in-situ bending tests were used to observe the crack propagation in brazed joints exhibiting both ductile and brittle fracture mechanisms. Samples were prepared with precise geometries and notched to initiate cracks in the joining zone. These in-situ tests provide valuable data on the mechanical behavior of brazed joints, offering insights into their failure processes. Three different joints were analyzed: AISI 304 brazed with AgCu filler metal, Mar M 509 brazed with Co-based filler metal and mixed joints of AA 6082 and AISI 304 brazed with AlGeSi filler metal. In the medium strength joint brazed with Ag 272 filler metal, the fracture occurred by slipping through the eutectic. In the high strength joint brazed with Co 900 filler metal, the crack propagated transgranularly through the intermetallic phases and stopped at the interface between the intermetallic and Co solid solution. The AA 6082 / AISI 304 joint was studied using an overlap geometry, showing that microcracks formed as the bending stress increased, finally leading to a failure at the Al7Fe2Si intermetallic layer, a critical microstructural feature. The used test procedure is suitable for further observations on the fracture mechanism in joints brazed in specific geometries as well as using different brazing process parameters and comparing the results with existing investigations.