Effect of graphene nanoplatelets fraction on the microstructure and mechanical properties of Inconel 718 composites prepared by spark plasma sintering

Nickel-based superalloy, particularly Inconel 718, is a promising candidate in advanced structural and high-temperature applications, including turbine blades, combustors, and turbochargers. However, high-efficiency energy systems such as jet engines and land-based gas turbines demand increasingly high strength for advanced structural applications. Therefore, significant efforts are underway to enhance the strength of these materials. Reinforcement of graphene nanoplatelet (GNP), owing to its exceptional mechanical strength, lightweight, high aspect ratio, and high level of coherency with metal matrix, has been proposed as an effective way of incorporating high strength into the existing Inconel 718. In addition, the spark plasma-assisted heating process is an emanating technique for fusing materials within a short duration and at a lower temperature. Thus, diffusion bonding of composites based on GNP dispersion in IN718 has been processed via the spark plasma sintering (SPS) technique. This study presents a systematic approach for probing the effect of GNP fraction on the microstructure and mechanical properties of Inconel 718. The composites were prepared with varying fractions of GNP (i.e., 0.1 - 0.5 wt.%) at optimized processing parameters using high-energy ball milling followed by spark plasma sintering. Microstructural characterization and evaluation of mechanical properties of SPS-assisted samples were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Vickers indentation, and uniaxial tensile testing. The IN718-0.5 GNP sample showed a ∼29% increase in hardness, ∼64% in yield strength, ∼8% in tensile strength, and ∼18% elongation to fracture, achieving an excellent strength-ductility balance compared to pure IN718. The remarkable increase in mechanical properties of the IN718 is attributed to grain refinement, dislocation strengthening, solid-solution strengthening, and Orowan strengthening. Transmission electron microscopy (TEM) results indicated that NbxTiyC (∼Nb 1.5 Ti 0.5 C type precipitates) formed at the interface of the grain boundary after embedding GNPs in the IN718 matrix, resulting in increasing strength of the materials.