Influence of heat-treatment and cryo-treatment on high temperature wear performance of LPBF Inconel 718

Abstract

The present study discusses the high temperature tribological performance of Laser Powder Bed Fused (LPBF) Inconel 718 (In718) using a pin-on-disk tribometer. Inconel being an age hardenable alloy with γ′ and γ′′ phases can be manipulated to with-stand elevated environments and thus, the tribology can be improved. This study involves homogenization heat treatment at 1100 °C treatment with and without a two-step aging process (720 °C for 8 h and 620 °C for 10 h). Fine dendritic structure is identified in microscopy after homogenization with the dissolution of δ phase. The microhardness of the sample is influenced by the presence of γ′ and γ′′ phases as the hardness increased by 53.2% and 56.2% respectively after homogenization and cryo-treatment. Tribology of LPBF In718 is evaluated at room temperature (RT), 100, 200, 300, 400, 500 and 600 °C and the worn surfaces were characterized. Wear rate decreased steadily with temperature and became negligible at 600 °C which is caused by the formation of protective NiFe2O4 and other oxidative film formation. The transient formation and abrupt rupture and peeling away of the oxide film causes fluctuation in friction coefficient even at elevated temperature giving a non-uniform frictional behavior.