Microstructure and high temperature oxidation resistance of nickel based alloy GH4169 irradiated by high current pulsed electron beam

The surface of nickel-based superalloy GH4169 was irradiated by high-current pulsed electron beam (HCPEB). Oxidation test of the irradiated specimens was conducted at 900 °C in air for 80 h. The microstructure evolution and surface morphology of the irradiated surface were analyzed by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM). XRD result showed that the width of peaks had a broadened trend, indicating grain refinement was obtained in the rapid-quenched. Microstructure observations revealed that a compact remelted layer was formed on the sample surface after HCPEB irradiation, inside which were mainly nanocrystallines with their size smaller than 100 nm. Besides, high-density dislocations and deformation twins were also formed in remelted layer. The observations after oxidation test showed that the oxide film on 20-pulsed sample surface was more continuous and compact than that on the initial sample surface, and the protection mechanism of 20-pulsed sample surface changed from the combined action of outer NiCr2O4 spinel layer and inner Cr2O3 oxide film layer into outer Cr2O3 oxide film and inner Al2O3 oxide film. The results indicated that the irradiated sample had much higher oxidation resistance than the initial one, among which 20-pulsed sample own the best oxidation resistance.