Brazed joints evaluation and computer modelling of mass transport in multi-component systems in the Au–Ni solder-14-5 PH joints

Vacuum brazing tests were carried out on the age-hardened steel of the 14-5 PH type using the 82Au–18Ni solder. It has been found that structure of the joint consisted of two kinds of Au–Ni solid solutions: one is rich in gold and the other rich in nickel. The influence of roughness of the surfaces to be joined and the distance between them as well as duration of the brazing on the joint structure and properties have been determined. The maximum tensile strength (Rm = 1260 MN/m2) was obtained for the joints of polished surfaces without any distances elements, brazed in temperature 1273 K for 7.2 ks and aged in temperature 723 K for 7.2 ks. In the further part of this paper the interdiffusion in the 14-5 PH steel/Au–18Ni solder system is analyzed. A special attention is put on the Ni–Au system which is a base of the brazed joints. The objective of this study is to calculate the intrinsic diffusivities of Au and Ni which have been used for modelling of mass transport during vacuum brazing. The generalized darken method (GDM) of interdiffusion and the inverse method (IM) have been used for the calculations of the effective intrinsic diffusivities of Au, Ni and other elements. These diffusivities have subsequently been employed to compute the concentration profiles in the 14-5 PH steel/Au–18Ni solder system and been compared with the experimental results.