High-Temperature Tribological Performance of Additively Manufactured Inconel 718/Al2O3 Metal Matrix Composite Coatings

Abstract The wear mechanisms of an additively manufactured Inconel 718/Al2O3 metal matrix composite (MMC) coating under both the ambient and high temperatures are investigated. Firstly, a powder fed Laser Directed Energy Deposition (PF-LDED) technique is engaged to deposit the IN718/Al2O3 MMC coating. Thereafter, the tribological behavior of the coating was studied from ambient temperature (RT) to 600°C. At RT, the asperities of the coated surface offer more resistance against shear deformation, and the material gets removed through excessive brittle fracture and delamination. When the temperature increases from 100°C to 300°C, the asperities offer comparatively lower resistance against shear deformation owing to the partial thermal softening and that leads to the progressive increment in wear rate. The highest specific wear is found in the case of 300°C. This is ascribed to the excessive thermal softening of the surface asperities. When the temperature rises from 400°C to 600°C, the formation of a tribo-oxide layer indicates an alteration in wear mechanism from the mechanical abrasion to the oxidative wear. The degree of oxide formation increases significantly from 400°C to 600°C, and hence, an approximately 24 % decrement in wear rate is observed. During tribo-test at 600°C, the entire worn surface is almost covered with the stable and continuous tribo-oxide layer. Additionally, several metallic oxides (NiO, Cr2O3, and Fe2O3) and spinel oxides (NiFe2O4 and NiAl2O4) are formed. Nickel aluminate (NiAl2O4) is formed owing to the presence of Al2O3 in the Inconel matrix. Therefore, the lowest specific wear rate and friction coefficient are observed during the tribo-test at 600°C.