Surface nanostructure of a directionally solidified Ni-based superalloy DZ4 induced by high intensity pulsed ion beam irradiation

A high intensity pulsed ion beam (HIPIB) was used to irradiate directionally solidified nickel-based superalloy DZ4 with the following parameters: ion content consisting of Cn+ (30 at.%) and H+(70 at.%), an accelerating voltage of 250 kV, a pulse duration of 70 ns, a beam current density of 100 A/cm2, irradiation times of 15. As revealed by SEM and TEM, the thermal effect was confined in a ∼1.3 μm thick surface zone, in which rapid melting and cooling occurred. A two-phase nanostructured layer of ∼10 nm thick was formed on the outmost surface. The component phases are the γ phase and the carbide with a particle size of ∼5-10 nm. The presence of dense dislocation networks was observed in depth in the substrate metal, for instance ∼20 μm away from the sample surface, which is caused by shock wave impact.

► DZ4 superalloy was irradiated by HIPIB. ► The microstructure of alloy in the depth was analyzed by TEM and SEM. ► Polycrystalline nano surface layer was composed of γ phase and carbides. ► The γ′ phase was dissolved in the melted layer that reached about 1.3 μm. ► Dislocation was enhanced due to shock waves over a much deeper depth range.