A Brief Review on He Ion Irradiation Research of Steel and Iron‑Based Alloys in Nuclear Power Plants

Nuclear power plays a key role as renewable energy in alleviating the worldwide energy shortage.The material degradation caused by high-temperature and high-flux neutron irradiation is the most concerning issue for nuclear reactor safety.A large number of He atoms produced through the(n,α)transmutation reaction diffuse and migrate in metals and accumulate to form He bubbles because of the extremely low solubility of He atoms in metal materials.The helium bubbles gather at the grain boundary or grain to cause swelling,hardening,embrittlement,and other damages to the in-core structural components.This paper mainly summarizes the research progress on He irradiation in steel and iron-based alloys,including the diffusion and accumulation of He atoms,the nucleation and growth of He bubbles,and the microstructure and macroscopic degradation of material performance caused by He irradiation.The mechanism of helium irradiation-induced corrosion in steel and iron-based alloys in recent years is reviewed as well.Moreover,the investigations on irradiation performance in additive manufactured stainless steels are summarized,and the mechanism of irradiation resistance is prospected.

One-step accurate synthesis of shell controllable CoFe2O4 hollow microspheres as high-performance electrode materials in supercapacitor

Multi-shelled CoFe2O4 hollow microspheres with a tunable number of layers （1-4） were successfully synthesized via a facile one-step method using cyclodextrin as a template, followed by calcination. The structural features, including the shell number and shell porosity, were controlled by adjusting the synthesis parameters to produce hollow spheres with excellent capacity and durability. This is a straightforward and general strategy for fabricating metal oxide or bimetallic metal oxide hollow microspheres with a tunable number of shells.

Effect of Heat Treatment on the Microstructure,Mechanical Properties and Corrosion Resistance of Selective Laser Melted 304L Stainless Steel

The influence of heat treatment holding temperatures from 600 to 1300℃ on the microstructure,mechanical properties and corrosion resistance in selective laser melted(SLMed)304L stainless steel is investigated in this work.The results reveal that there is no remarkable microstructure change after holding at 600℃ for 2 h,while recrystallization leads to a slight decrease in grain size in the temperature range of 700–900℃.The heat treatment at temperatures from 1000 to 1300℃ for 2 h obviously affects the morphology of grains in SLMed 304L stainless steel.Combining effects of grain coarsening,delta-ferrite(δ)phases reduction and residual stress release during heat treatment lead to the reduction of yield strength and an increasing elongation.The elongation of the samples heat treated at 800℃ for 2 h is,however,significantly decreased due to the increase in the amount of sigma(σ)phase.A remarkable increase in the amount ofδferrite results in an increase in yield strength but a decrease in ductility after heat treatment at 1300℃ for 2 h.The corrosion resistance of the samples heat treated at 1300℃ is significantly improved due to the substantial reduction of brittle phase(σ).There is no obvious effect of the presence ofδferrite on corrosion behavior.

Helium Bubble Growth in He^(+) Ions Implanted 304L Stainless Steel Processed by Laser Powder Bed Fusion During Post-Irradiation Annealing at 600℃

The abundancy of defect sinks in the microstructure of laser powder bed fusion(LPBF) processed austenitic stainless steels was found to be beneficial for helium resistance.In the current study,the influence of the novel microstructure in LPBF processed 304 L on the helium bubble growth behaviour was investigated using transmission electron microscopy in samples implanted with He^(+) ion and post-irradiation annealing treated at 600℃ for 1 h.Two variants of LPBF processed 304 L samples were used,one in as-built condition and the other solution-annealed.The comparison between the two samples indicated that the helium bubble growth was inhibited and remained stable in the as-built sample but coarsened significantly in the solution-annealed sample.The sub-grain boundaries and oxide nano-inclusions acted as defect sinks to trap helium atoms and inhibited the growth of helium bubble in the as-built sample under the post-irradiation annealing conditions used.