Effect of local interference on the surface microstructure of FGH96 alloys in quenching process

Effect of local interference (holding devices) on the surface microstructure of FGH96 alloys in quenching process was studied by optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), microhardness, and numerical simulation. The results show that, the holding devices used in quenching produce the chilling effect at the surface of FGH96 alloys, which changes the cooling mode of the connect points and then affects the precipitation and growth behavior of γ′ phases. After the low corrosion, the γ′ phases with the different size and morphology exhibit the visual color difference, leading to the corrosion circles. The maximum diameter of corrosion circles is ~10 mm, and the section depth is ~3 mm. The secondary γ′ phases inside the corrosion circles are fine and spherical, and the average size is ~100 nm. The secondary γ′ phases on the corrosion circles are polygonal distributed, and the average size is ~350 nm. The secondary γ′ phases outside the circles are spherical in distribution, and the average size is ~150 nm. The different size and morphology of the secondary γ′ phases result in the fluctuation of microhardness inside and outside the corrosion circles. The average microhardness is ~HV 450 outside the circles, and that of ~HV 485 inside the circles. The grain structure difference and the element segregation near the corrosion circles are not found.