| FeCr-based stainless steel materials have been widely used as nuclear reactor structure materials due to their excellent mechanical properties.As important nuclear reactor structure materials,FeCr-based alloys in the long service process inevitably bear high doses of radiation damage,resulting in radiation hardening,helium evolution and swelling.Because helium in the metals has an extremely low solubility,it's easy to migrate,nucleation grow,and cause a series of problems such as helium brittleness,that resulting in degradation of material properties,and affecting the service and safety of the reactor.Some studies have pointed out that oxide dispersion strengthening(ODS)is an effective method to improve the anti-radiation properties of materials.Through the addition of trace nano-Y2O3 particles(0.1%?0.5%wt)not only prevent dislocation movement,improve the high temperature mechanical properties of the materials,but also enhance the anti-radiation properties of materials owning to the effective decrease of radiation defects.At the same time,matrix structure refinement is considered as one of the effective way to optimize material strength and toughness.Mainly because of the existence of high density solid-solid interface in fine-grained materials which can absorb and annihilate the point defects generated by radiation,grain refinement can thus greatly improve materials anti-radiation ability.In this paper,ODS-FeCr-based films with different helium concentrations were prepared by magnetron sputtering method,the microstructures and mechanical properties of the films were analyzed by FESEM,XRD,XPS,ICP,HTDS and Nanoindentator.The optimum conditions for the preparation of stainless steel films were investigated by changing the sputtering parameters such as sputtering power,working pressure and substrate temperature in a high purity argon atmosphere by magnetron sputtering.It was found that when the working pressure was at 1 Pa,the sputtering power was about 70W,and the substrate temperature was in 200?,the performance of FeCr-based thin films was the best.On this basis,ODS-FeCr-based films with different Y2O3 contents were prepared under the optimal sputtering conditions to analysis the effect of the Y2O3 content on the mechanical properties of the material.The results show that the prepared ODS-FeCr-based thin film is a nanostructured columnar structure with a particle size about 7?12 nm,and the density of columnar changes largely.Based on the XPS analysis,the Y element in the ODS film is existed as the form of Y2O3.Adjusting the Y2O3 concentration in the composite target to control the Y content varies from 0 to 1.01 at%.The concentration of Y2O3 increased,the hardness of the ODS-FeCr based film raised gradually,and the hardness was as high as 16.5GPa when the Y content was at 1.01 at%,which was about 59%higher than that of pure FeCr film.About the ODS-FeCr film with different helium concentration,increasing the helium ratio made the columnar of ODS film more refinement and more density.Changing the He/Ar ratio can effectively control the He concentration and film hardness in the ODS film,where He/Ar = 4,the hardness of the ODS film reached to 12.75GPa.The effects of annealing on the growth of helium bubbles and film structure were studied by high temperature aging method.It was found that high temperature annealing could lead to the transformation from columnar crystals to equiaxed grains.For helium bubble growth,it can't promote the combination of helium clusters or small-sized helium bubbles due to the low migration of helium in low temperature annealing,and only small-sized helium bubbles can be formed with the size less than 1 nm.With the increase of annealing temperature,helium atoms are caught by vacancies in high temperature,affected by vacancy and gap diffusion mechanisms,helium atoms and small-sized helium bubbles migrated and accumulated.As the suggested Ostwald Ripening mechanism,the helium bubble finally grew up to 2 nm.Along the grain boundaries,which act as a fast channel of helium migration,the helium bubble arranged like a chain.Due to the further diffusion of helium bubbles along the grain boundary,the form of helium bubbles eventually elongated in the grain boundary direction.When the temperature is further increased to 1000?,the helium bubbles exposed undergoing thermal dissociation. |
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