Optimization of temperature-/time-cycles in brazing through thermodynamic calculations

摘要

Brazing with nickel-based filler materials is an established joining process. In this context the formation of brittle phases in the joint is a significant difficulty. An increased proportion of these phases influences the mechanical properties of the joints negatively. This effect gains strong influence if a continuous band of brittle phases is formed. In order to avoid formation of brittle phases, small brazing gaps are necessary. Subsequent heat treatment is partially able to reduce the proportion of brittle phases. In this paper thermodynamic simulations are applied in order to calculate phase transformations and diffusion processes during brazing of commonly used materials. The simulations are performed by using Thermo-Calc and TC Dictra, as well as an analytical model. Different temperature-time-cycles are examined in order to characterize their influence on the formation of brittle phases. Additionally, experiments were executed with the materials of interest. Nanoindentation is used to determine local values of YOUNG's modulus and hardness. Miniature tensile tests are applied to examine the tensile strength. The evaluated data is used to specify correlations between the properties of brittle phases in the joint and of its global mechanical properties.