Development of IN718 Coating for Repair Applications by High-Pressure Cold Spraying Followed by Heat Treatment

Abstract

This study investigates the feasibility of using cold spray for repair of Inconel 718 (IN718) components. The effect of cold spray parameters on the particle velocity, splat morphology, deposition efficiency (DE), thickness, and porosity was evaluated. Thick coatings of approximately 4 mm were deposited onto ground and polished IN718 substrates using N₂ gas heated to 1000 °C with gas pressure of 5 and 7 MPa. The coatings were subjected to standard double aging (DA) and a combination of solutionizing and double aging (STDA) heat treatment. The microstructure, hardness, porosity, tensile strength, and adhesive strength of as-sprayed and heat-treated coatings were evaluated. Additionally, the tensile properties of the coating–substrate combination (sandwich samples) were also evaluated. It was observed that higher gas pressure led to increased particle velocity, decreased porosity, enhanced hardness, and improved adhesion/tensile strength. The splat size increased with higher particle velocity, indicating greater particle deformation. The DE decreased with increase in number of deposited layers and increased with increase in gas pressure. The AS coating microstructure exhibited a deformed powder microstructure having fine dendritic/cellular structure. Following the DA treatment, the dendritic features were preserved, accompanied by the precipitation of γ′, γ′′, and δ phases. After STDA treatment, a homogeneous microstructure with the presence of γ′, γ′′, and Nb and Ti carbides without any δ phase was observed. The most favorable outcomes were achieved with the 7 MPa STDA sample, yielding a minimal porosity level of 0.4 ± 0.1% and a tensile strength of 1325 ± 10 MPa with a failure strain of 6.1 ± 0.6%. The tensile strength of 7 MPa sandwich sample was found better (1049 ± 8.5 MPa) compared to stand-alone coating (965 ± 24 MPa) after DA treatment.