Study On Mechanical Properties Of SS316L/BNi-2 Brazing Joint Based On The Nanoindentation Method

Heat exchanger based on plate-fin structure is more and more favored in high temperature integration system due to its compact and high efficient characteristics. In the new generation of high temperature gas cooled reactor, plate-fin structure is not only the most feasible form of heat exchanger unit, but also directly determines the energy conversion efficiency of the reactor. As the two core indexes of heat exchanger equipment, high efficiency and structure reliability always complements and restricts each other. The properties of filler alloy and brazing structure determine the safety and reliability of the heat exchange equipment and even the whole system performance. Therefore, there is a great significance of mechanical properties study of both brazing alloy and brazing structures.Theoretical analysis, numerical simulation and nanoindentation experimental research are proposed to test the mechanical properties of as-cast solder and the stainless steel brazing joint. The main research work and the related conclusions are as follows:(1) Based on the nanoindentation theory, the hardness and modulus of brazing alloy are obtained. It is confirmed the feasibility of testing material mechanical properties by using nanoindentation compared to tensile experiment. The plastic parameters of the as-cast BNi-2 brazing alloy are obtained using M. Dao’s model. Combining with finite element simulation and experimental research, the accurate stress-strain constitutive relationship is gotten.(2) SS316L/BNi-2 brazing joint is studied using the same method on the basis of the study of as-cast BNi-2 brazing alloy. The features and properties of the micro-area in brazing joint have been analyzed combining with microstructure analysis.(3) The finite element model of the micro-area of brazing joint is established. And the stress-strain relationship in different zones of the joint and the mechanical properties of the SS316L/BNi-2 brazing joint are acquired combined with the nanoindentation experiment. It is established the relationship between the different regions of brazing joint.(4) The influence of indenter tip radius and the friction between the indenter and the material have been investigated. It has been studied the influence of the indentation size effect on as-cast BNi-2 and the micro zone of SS316L/BNi-2 brazing joint and the reason of the formation of indentation size effect has been explained from micromechanism.