Diffusion brazing, as the name implies is a brazing procss which lasts long enough so that the liquid brazing alloy interacts (with dissolution/solidification/interdiffusion) with the solid materials to be joined and eventually solidifies under isothermal conditions. Copper-Silver alloys are well known is this context and a paper by T.B. Massalski and co-workers illustrates how equilibrium and kinetic information can be combined to understand the kinetics of the diffusion brazing process in this simple binary system. This presentation starts with a review of a selection of some theories of diffusion brazing and continues with two applications, one ancient (again with the copper-silver system) and one contemporary with nickel based brazing alloys. The first application deals with ancient counterfeiting. A. Deraisme and co-workers recently figured out which techniques were used to make forgeries of coins in Roman Gaul in the third century. To understand how craftsmen of the time made the coins, the supposed technique was recreated in modern laboratory by heating copper cylinders that had been coated with thin silver layers at different temperatures and for varying lengths of time. Four minutes and 950°C led to the composition and structure closed to that of the counterfeit coins. The interpretation of EMPA composition profiles of counterfeit coins and recreations relies mostly on the work by Massalski et al. The contemporary application is that of nickel based brazes. A classical application is the repair of nickel base superalloys components of aero gas turbines and a not so classical one is the joining of ferritic stainless steel Fe20Cr5Al (wt%) by nickel chrmium silicium commercial brazing alloys in the form of powders. Laboratory studies include differential thermal analysis and diffusion experiments combined with EMPA (microanalysis) of the diffusion couples and actual diffusion brazed joints.

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1. Continuous casting and processing of copper alloys containing tin : an illustration of the applicability of phase stability rules and data