Hang Zang

Irradiation-induced grain growth in nanocrystalline reduced activation ferrite/martensite steel

In this work, we investigate the microstructure evolution of surface-nanocrystallized reduced activation ferrite/martensite steels upon high-dose helium ion irradiation (24.3 dpa). We report a significant irradiation-induced grain growth in the irradiated buried layer at a depth of 300–500 nm, rather than at the peak damage region (at a depth of ∼840 nm). This phenomenon can be explained by the thermal spike model: minimization of the grain boundary (GB) curvature resulting from atomic diffusion in the cascade center near GBs.

Irradiation Induced Microstructure Evolution in Nanostructured Materials: A Review

Nanostructured (NS) materials may have different irradiation resistance from their coarse-grained (CG) counterparts. In this review, we focus on the effect of grain boundaries (GBs)/interfaces on irradiation induced microstructure evolution and the irradiation tolerance of NS materials under irradiation. The features of void denuded zones (VDZs) and the unusual behavior of void formation near GBs/interfaces in metals due to the interactions between GBs/interfaces and irradiation-produced point defects are systematically reviewed. Some experimental results and calculation results show that NS materials have enhanced irradiation resistance, due to their extremely small grain sizes and large volume fractions of GBs/interfaces, which could absorb and annihilate the mobile defects produced during irradiation. However, there is also literature reporting reduced irradiation resistance or even amorphization of NS materials at a lower irradiation dose compared with their bulk counterparts, since the GBs are also characterized by excess energy (compared to that of single crystal materials) which could provide a shift in the total free energy that will lead to the amorphization process. The competition of these two effects leads to the different irradiation tolerance of NS materials. The irradiation-induced grain growth is dominated by irradiation temperature, dose, ion flux, character of GBs/interface and nanoprecipitates, although the decrease of grain sizes under irradiation is also observed in some experiments.

Evolution of Defects and Defect Clusters in β-SiC Irradiated at High Temperature

Abstract A molecular dynamics study has been performed to investigate the generation and evolution of damage states in irradiated β-SiC at high temperature. It is found that most of the C antisites (SiC) are created during the early collisional phase, while the Si antisites (CSi) are significantly produced during the thermal spike phase. A modified near-neighbor point defect density (NPDD) is introduced to study the spatial aggregation of different defects during the displacement cascades, and feature of defect clusters evolution is analyzed in details. The dominated types of vacancy clusters after the displacement cascades are two- and three-size chainlike ones. And the vacancy NPDD (V-NPDD) decreases as the recoil energy increases. Furthermore, after the thermal spike phase, there is an additional annealing process during which the interstitials and antisites turn into defect clusters, respectively.

Modeling of long-term defect evolution in heavy-ion irradiated 3C-SiC: Mechanism for thermal annealing and influences of spatial correlation

Based on the parameters from published ab-initio theoretical and experimental studies, and combining molecular dynamics and kinetic Monte Carlo simulations, a framework of multi-scale modeling is developed to investigate the long-term evolution of displacement damage induced by heavy-ion irradiation in cubic silicon carbide. The isochronal annealing after heavy ion irradiation is simulated, and the annealing behaviors of total interstitials are found consistent with previous experiments. Two annealing stages below 600 K and one stage above 900 K are identified. The mechanisms for those recovery stages are interpreted by the evolution of defects. The influence of the spatial correlation in primary damage on defect recovery has been studied and found insignificant when the damage dose is high enough, which sheds light on the applicability of approaches with mean-field approximation to the long-term evolution of damage by heavy ions in SiC.

Re-evaluation of neutron displacement cross sections for silicon carbide by a Monte Carlo approach

Neutron displacement cross sections for SiC are re-evaluated by a Monte Carlo approach, with damage energies of primary recoils calculated by the stopping and range of ions in matter (SRIM) code. The validity of the Monte Carlo model is examined by the case of iron, and the results show good agreement with the reference values. Neutron displacement cross sections for SiC at energies up to 100 MeV are calculated, and averaged over the neutron spectra of a fusion DEMO reactor, the high flux test module of the International Fusion Materials Irradiation Facility, and typical fission test reactors. Gas production is also calculated for those neutron irradiation facilities. Finally, the suitability of the displacement cross sections is discussed. The results on comparison among neutron irradiation of different facilities by the current displacement cross sections are similar to those by results of the previous work. Moreover, since neutron displacement cross sections in this study are calculated with damage energies of primary recoils calculated by SRIM, neutron damage evaluated by our displacement cross sections is suitable for correlation with damage by heavy ions calculated by SRIM.

Magnetoelectric memory effect of paramagnetic nonpolar phase in Co4Nb2O9

A polarization memory effect of the paramagnetic nonpolar phase is observed in magnetoelectric antiferromagnet Co4Nb2O9, which has a magnetic field induced polarization in the antiferromagnetic phase. Following magnetoelectric poling in the polar phase, the nonpolar paramagnetic state retains a strong memory of polarization. When reentering the polar phase without applying the electric field, a polarization along the initial poling direction is recovered. If the applied magnetic field while staying in the paramagnetic phase is weakened, the memory effect is enhanced. With reversing this magnetic field, the polarization is also reversed when reentering the polar phase. The memory effect can be attributed to the ferroelectric seeds forming in the nonpolar phase due to short-range magnetic ordering as evidenced by magnetic entropy data.A polarization memory effect of the paramagnetic nonpolar phase is observed in magnetoelectric antiferromagnet Co4Nb2O9, which has a magnetic field induced polarization in the antiferromagnetic phase. Following magnetoelectric poling in the polar phase, the nonpolar paramagnetic state retains a strong memory of polarization. When reentering the polar phase without applying the electric field, a polarization along the initial poling direction is recovered. If the applied magnetic field while staying in the paramagnetic phase is weakened, the memory effect is enhanced. With reversing this magnetic field, the polarization is also reversed when reentering the polar phase. The memory effect can be attributed to the ferroelectric seeds forming in the nonpolar phase due to short-range magnetic ordering as evidenced by magnetic entropy data.

Switching the magnetically induced polarization of Co4Nb2O9 by dielectric-relaxation-related internal electric field

The possibility of switching the magnetically induced polarization (MIP) in magnetoelectric antiferromagnet Co4Nb2O9 by a dielectric-relaxation-related internal electric field was investigated. The MIP at a lower temperature is more difficult to be reversed, and this can be explained based on the Landau-Ginzburg-Devonshire theory as well as the domain nucleation and growth theory.

Primary Total Ionizing Dose Effect Studies on Xilinx SoC Irradiated with 60Co γ Rays

We designed radiation effect experimental system including current measurement section and functional test section for Xilinx Zynq-7010 System on chip (SoC) and performed the Total Ionizing Dose (TID) experiment irradiated by Co60 γ-source on the chip. At the dose rate of 0.04 Gy(Si)/s, the total dose of 1.69 kGy(Si), the current value in the experiment increased first and then decreased. The test board got functional interruption at the gamma dose of 1.69 kGy(Si). The function of the board normalized after room temperature annealing and 70°C high temperature annealing except that the current value decreased by 28% compared to the current before irradiation. The mechanisms for the first TID test results on Xilinx SoC were deduced and discussed.

Modification of Fe/Cu Multilayers under 2-MeV Xe20+ Irradiation

Two kinds of Fe/Cu multilayers with different modulation wavelength were deposited on cleaved Si(100) substrates and then irradiated at room temperature using 400 keV Xe20+ in a wide range of irradiation fluences. As a comparison, thermal annealing at 300-900 degrees C was also carried out in vacuum. Then the samples were analyzed by XRD and the evolution of crystallite structures induced by irradiation was investigated. The obtained XRD patterns showed that, with increase of the irradiation fluence, the peaks of Fe became weaker, the peaks related to Cu-based fcc solid solution and Fe-based bcc solid solution phase became visible and the former became strong gradually. This implied that the intermixing at the Fe/Cu interface induced by ion irradiation resulted in the formation of the new phases which could not be achieved by thermal annealing. The possible intermixing mechanism of Fe/Cu multilayers induced by energetic ion irradiation was briefly discussed.