Effect Of Nanoparticles On The Irradiation Evolution Of ODS Steel And Vanadium Alloy

Structural materials are one of the key technologies for the future development and application of fusion reactor.ODS steel and vanadium alloys are considered as important candidates for fusion reactor structural materials due to their excellent properties.However,there is no unified conclusion on the structure stability of ODS steel under irradiation.Besides,the irradiation evolution of vanadium alloy is still in early.In this paper,above quesitions are studied using high voltage electron microscopy(HVEM),ion irradiation,nanoindentation,and transmission electron microscopy(TEM).The main research contents are as follows:In situ electron irradiation and high-resolution transmission electron microscopy(HRTEM)is used to investigate the stability of nano particles(NPs)in 12Cr-ODS steel at room temperature,300? and 500?.Using HRTEM instead of typical two-beam images can effectively identify NPs without the miscalculation caused by irradiation-induced dislocation loops.The results show that most NPs are stable at room temperature with the dose up to 1.52 dpa,and only a few coarsened.The precipitation of some new Y-Ti-O NPs are observed.The sphere-cubic transformation of NPs is observed in 300? aged TEM sample resulting in coherent YTiO3 NPs.This kind of NPs coarsened obviously at 300?and 500?,the coarsening rate is positively correlated with irradiation temperature.The cubic of NP's size has a linear relationship with the irradiation dose with constant irradiation damage rate,which confirms that the Ostwald ripening mechanism dominates the coarsening process.The electron irradiation on He+pre-implanted sample shows that He can reduce the diffusion of Y and indirectly improve the stability of NPs.Special diffraction streaks appear in the FFT image of 12Cr ODS steel electron irradiated at 300? and 500?.HRTEM analysis shows that the diffraction streaks is related to the special precipitates at NPs/matrix interface.During irradiation,the defect trap at NP/matrix results in the precipitation and growth of precipitates along the interface.The kinetic study shows that the formation rate of precipitates is higher at 500?,which indicates that the formation rate is positively correlated with irradiation temperature.Compared with the radiation induced Cr precipitates in Fe-Cr alloy,precipitation in ODS steel is less dependent on the pre-implantation of H+because H is not need to coordinate lattice distortion.Based on the results of HRTEM,two hypotheses are proposed.The one is a single layer Cr precipitation the other is single layer YTiO3 precipitation.D+ implantation at room temperature and nano indentation are used to study the irradiation harding as well as radiation induced dislocation loops of V-4Cr-4Ti and V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy containing NPs.The resutls indicate that V-4Cr-4Ti-1.8Y-0.4Ti3SiC2 alloy has lower hardening rate.It is found that V-4Cr-4Ti alloy has abnormal radiation hardening,in which radiation hardening from nanoindentation test far exceed the theoretical values.The analysis shows that the abnormal hardening is closely related to the size evoluation of Ti(CNO)precipitates.In order to verify the above conclusions and eliminate the possible interference of C,which is introduced by Ti3SiC2,a series of V-4Cr-4Ti alloys with different Y contents are prepared by mechanical alloying and spark plasma sintering.A new way to improve the plasticity of vanadium alloy is explored,where Y is used as deoxidizer to reduced the content of excess oxygen in vanadium by internal oxidation resulting in the effectively improvement on the plasticity.The deoxidation products are Y2O3 and YVO4 NPs.The optimum parameters of mechanical alloying and spark plasma sintering are obtained as follows:ball milling at 240 rpm for 40 h with a ball to material ratio of 10:1,sintering temperature is 1150? with a pressure of 40 MPa and a holding time of 5 min.A new boundary condition of sintering temperature for ZrO2 ball and vials is proposed.The results of ion irradiation experiments show that the irradiation hardening of these alloys is mainly caused by dislocation induced loops excluding the effect of Ti(CNO)precipitation.Compared with ordinary V-4Cr-4Ti alloy,the V-4Cr-4Ti alloy containing NPs has lower dislocation density and lower radiation hardening.However,the existence of NPs will lead to the segregation of Ti around the NPs.