Microstructural, Mechanical, and Tribological Evaluation of HVAF-Sprayed Inconel 718 Coatings

Abstract

This study evaluates the mechanical and wear properties of IN718 coating on IN625 substrates deposited using the HVAF-spraying technique. The deposited coating was characterized by SEM, EDS, EBSD, Raman, nanoindentation, and microhardness. The integrity and adhesion of the coating were assessed using scratch tests aided by acoustic emission spectroscopy. The tribological evaluation was performed using a dry sliding wear test with a ball-on-coated disc configuration using alumina as the counterface. The coating microstructure comprises mostly unmelted particles with a small fraction of melted, with a porosity level < 1.5% and about 8.4% oxidation. Both the microhardness and nanoindentation show the anisotropy in the coating. The elastic modulus is at the same level as bulk IN718 when measured perpendicularly to the thickness direction, but it is lower when measured along the thickness. The average compressive stress of 608 MPa and the Bauschinger effect influence the anisotropy observed in the coatings. ISO 27307 scratch tests reveal that coatings have good cohesion and adhesion strength. Wear tests were performed at room temperature, 400 °C and 600 °C. The room temperature wear is high and abrasive, while the high-temperature wear was lower and determined to be oxidative. Porosity is detrimental to the abrasive wear at room temperatures, which leads to localized chipping.