Thermal and microstructural effects of welding metallic glasses by self-propagating reactions in multilayer foils

We have previously demonstrated that Zr-based metallic glass components can be welded using the heat produced by self-propagating exothermic reactions in multilayer metallic foils. Here, we examine the evolution of the temperature field during reactive joining of bulk amorphous Zr57Ti5Cu20Ni8Al10, as well as the microstructure of the resulting joints. Numerical simulations predict that the metallic glass near the glass/foil interface heats very rapidly )~107 K s^-1) to temperatures of~1350 K, well above the liquidus temperature of the amorphous alloy (~1115 K), followed by rapid cooling (~105 K s^-1) once the reaction front has passed. The maximum temperature, heating rate, and cooling rate of the glass all decrease with increasing distance from the interface. Infrared measurements of the temperature of the metallic glass components during joining show that the cooling rate exceeds the critical cooling rate of the alloy. Optical and scanning electron microscopy reveal no evidence of crystallization of the glass components due to the joining process.