CONICET | Buscador de Institutos y Recursos Humanos

ABSTRACT A non-conventional bonding process, transient liquid phase bonding (TLBP), was applied to join Ni-based metals and aluminium. The process involves isothermal solidificationand homogenization of the interconnection zone. Although there is a large number of publications on TLPB, the fundamental mechanisms of diffusion-reaction processes for commercial alloys, its microstructure evolution and their effects on technological properties are still unclear. Knowledge of equilibrium phase diagrams, kinetics and diffusion are required to understand the phase transformations, thermal stability and phase formation sequence during this process.TLPB was developed for superalloys, whose applications involve high temperatures, high mechanical stresses and corrosive environments. In this work, two nickel based substrates were joined with high purity aluminium foils used as filler metal. Inconel 718 and pure nickel were bonded to analyse the effect of alloying elements in the phase formation and growing mechanism in the final joint. Tests were carried out under protective atmosphere and different temperatures and times. Microstructural, chemical and crystallographicanalyses were conducted by means of optical and electron microscopy (SEM/EDS-EBSD). Additionally,the samples were tested using nano- and micro-hardness. Finally, phase formation sequence was determined. The bonding involves the formation of different phases depending on temperature and holding time. In general, the interconnection zone consisted of a biphasic layer adjacent to the substrate, Mo, Nb and Ti carbides and AlNi grains.Results were compared with analyses performed on pure Al-Ni joints in order to correlate the observed growth mechanisms. Concerning the base material, longer exposures above 900°C deteriorate its mechanical properties due to grain coarsening and precipitates aging.

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