Evaluation of Solid-State Diffusion Bonded Inconel 718 Mechanical Properties

Leila Ladani; Preston Regg Angell

Abstract

Nickel based polycrystalline superalloys, designed for high temperature applications, are extensively used in the aerospace industry for the materials excellent mechanical properties at elevated temperatures. The relatively low intrinsic diffusivity of nickel-based alloys make them infamously difficult to diffusion bond. This study attempts to experimentally achieve solid state bonding of nickel-based superalloys, without the aid of an interlayer material, with complete grain coalescence while maintaining tensile properties of the base material. A design of experiments was conducted using Inconel 718 as base material bonded to itself in a hot press vacuum furnace, while key process parameters are iteratively varied. Mechanical properties of diffusion welded samples, subjected to a precipitation heat treatment, were compared against base material properties with the same precipitation heat treatment. The data collected indicates that diffusion bonding atmosphere, surface preparation, and thermal cycle are significant contributors in maintaining tensile properties. Tensile strength results of diffusion bonded samples were approximately 10–30% lower than the base material. The low tensile values are theorized to be a result of grain growth as outlined by the Hall-Petch theory. Elevated temperatures promote diffusion aiding successful bonding but also foster grain growth and coarsening of undesired secondary precipitates.

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