Effects of helium ion irradiation on the high temperature oxidation resistance of Inconel 718 alloy

Abstract The Ni-based Inconel 718 alloy was irradiated using 50 keV helium ion to doses of 0.4, 4 and 40 dpa. The oxidation behaviors of un-irradiated and irradiated samples were studied under isothermal conditions at 900 °C. The phase constitution, oxide layer morphology and microstructure variation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM). It was found that the oxidation kinetics of un-irradiated and irradiated samples obeyed a parabolic law. The oxidation rate was lower in the sample with higher dose irradiation. The oxide layer was comprised of outer oxide scale (mainly Cr 2 O 3 ) and inner oxide layer (mainly Al 2 O 3 and TiO 2 ). Irradiation raised the surface layer's energy and facilitated the nucleation of fine oxide particles. While fine oxide particles improved the densification of outer oxide scale. Due to the irradiation-induced defects, fast-diffusion paths were provided for Cr to the surface. This accelerated the forming of dense outer Cr 2 O 3 oxide scale, and restricted the inward penetration of O. Therefore, the thickness of oxide layer especially the inner oxide layer significantly decreased. The enhanced oxidation resistance of irradiated samples was essentially attributed to the combination of improved surface layer's energy and irradiation defects.