Study On The Diffusion Behavior Of Elements On Interface Of SS316L/BNi-2 Brazed Joint

High temperature vacuum brazing has become the only appropriate process for thin-walled structures such as compact heat exchangers used in high-temperature gas-cooled reactor (HTGR) systems. During the typical brazing process, major attention should be paid to the isothermal solidification stage which has the most important influence on joint quality. However, the isothermal solidification process is controlled by the diffusion behavior of melting point depressant (MPD) elements, and only thorough diffusion of MPD elements into the base metal can result in the formation of the full solid-solution brazed joints. However the bonding mechanism of brazing joints based on diffusion is not perfect, it is urgent to establish suitable Multi-Diffusion to predict the actual diffusion behavior in bonding process.According to the above problems, interface characteristic and multi-component diffusion behavior of SS316L/BNi-2 brazed joints were studied, through vacuum brazing experiments and diffusion analytical model. Based on the diffusion ability of joint elements, main element and follow elements were divided in this study. The main research contents are as follows:1) Based on the new type of wedge-shaped brazing specimen by vacuum brazing experiments, IRZ, DAZ, MBC values of SS316L/BNi-2 brazed joint under different process parameters were acquired, joint regional characteristics were also studied.2) Based on the Fick's second law, through using the migrate solid-liquid interface model and Arrhenius equation, the diffusion coefficient and diffusion activation energy of the main element B were obtained. Moreover, the effect of brazing time and brazing temperature on the diffusion behavior were also discussed.3) Obtained the concentration distribution curves and its regularity of follow elements under different brazing parameters, the average contents at the feature region of brazed joint were calculated, and the Boltzmann function was used to fit the elements concentration distribution curves so that the components concentration curve can be quantitative analyzed. Furtherly, the Boltzmann-Matano method was adopted to calculate the diffusion coefficients of follow elements which is useful for establishing Multi-component diffusion model.