The Irradiation Effect Of Nickel And Nickel-based Alloy

Nickel-based alloy is selected as the candidate material of molten salts reactor?MSR?because of its good high temperature mechanical properties and excellent corrosion resistance.The structural materials in MSR are inevitably faced neutron irradiation,making their microstructure and mechanical properties changed,which has effects on their lifetime and even the safety of the reactor.Due to the disadvantage of neutron-irradiation research,such as high expense,treating with the radioactive samples and so on,the irradiation effect of nickel-based alloys is studied via ion irradiation.The mechanical properties of nickel-based alloys were investigated by nano-indentation;while the microstructure of the alloys by transmission electron microscopy?TEM?and slow positron technology.The mechanism of microstructure evolution of pure Ni was also studied.The mechanical properties of nickel and nickel based alloys irradiated by 7 MeV Xe²⁶⁺ and 0.5 1.9 MeV He⁺ were studied.Irradiation hardening was observed in nickel,GH3535 and Ni-W-Cr alloys,which is ascribed to the formation of dislocation loop,defect cluster and helium bubble under ion irradiation.The damage dose dependence of hardness in alloys is described by the Makin and Minter's equation,where the effective critical volume of obstacles can be used to represent the resistance of the irradiation hardening of the alloys.Moreover,the result also shows that Ni-W-Cr alloy has better irradiation hardening resistance than GH3535 alloy.The microstructure evolution of nickel and nickel based alloys irradiated by 1 MeV Xe²⁰⁺ and 30 keV He⁺ was investigated.The decoration of the intrinsic dislocation with interstitial loops was observed in Hastelloy N alloy under 1 MeV Xe²⁰⁺ ion irradiation.With increasing the irradiation damage,the intrinsic dislocation density decreases due to the climbing of the intrinsic dislocation by the absorption of interstitials under the ion irradiation.Moreover,the in situ annealing experiment reveals that the small interstitial loops induced by the ion irradiation are stable below 600 oC.In addition,under 30 keV He⁺ irradiation,the interstitial loops with Burgers vectors b =(62< 110 > were observed in nickel.The formation of the loop is ascribed to the assistance of He atom.The loop size increases with the irradiation temperature.The effect of the solute atoms on irradiation response of nickel based alloys was investigated by using 30 keV He⁺ ions.Cr and Mo in the alloys suppress the growth of loops.The volume size factors and alloying of solute atoms are related to the density and size of the loop.This is ascribed to the effect of solute atoms on the chemical disorder of the alloys,the diffusion of the solute cluster and point defect at cascade,the recovery of the defect and the migration of the defect towards surface.Moreover,the helium bubbles induced by irradiation at high temperature are distributed homogeneously in the matrix of the nickel-based binary alloys,and the size of the helium bubble produced during irradiation increases with the temperature.It is concluded that the solute atoms are the key factor for helium bubble formation;that the binding energy between helium and solute atoms play an important role in the size and density of the helium bubbles induced by ion irradiation in the nickel-based binary alloys.