Effect of heat treatment and cryo-treatment on dry tribological behavior of Inconel 718 fabricated using laser powder bed fusion

Abstract

Inconel 718 (In718) is a super alloy having FCC γ matrix reinforced with FCC γ′ phase, BCT γ′′ phase, δ phase (orthorhombic), and others. Each of these phases can influence the mechanical strength of the component. Inconel 718 alloy fabricated using Laser Powder Bed Fusion (LPBF) process is utilized in this study. In an attempt to analyze the effect of post-processing on the microstructural and tribological properties, the specimens were subjected to standard solution heat treatment at 1100 °C (2 h) with aging (720 °C for 8 h, 620 °C for 10 h). For cryogenic treatment, samples were soaked in liquid nitrogen (24 h) and tempered at 650 °C (2 h). It is observed from the results that the surface hardness of the solution heat-treated sample is higher than the as-printed and conventionally prepared In718 alloy due to the segregation of precipitates at the grain boundaries in the latter one. Tribological behaviour of LPBF In718 alloy is studied with 10, 20, 30, 40, 50 and 100 N normal loads. The microhardness of the LPBF HT and LPBF CT sample was 46.7% and 29.03% higher than as-printed LPBF sample. Worn surface analysis along with the counter body (wear track) is performed using optical microscope, 3D profilometer, SEM, and Raman's spectroscopy. Abrasive wear is found to be predominant in the LPBF samples even though plastic deformation and fractures are seen throughout the sample surfaces. The experiments were extended to conventionally prepared hot-forged Inconel sample for comparison.