Positron annihilation and nano-indentation analysis of irradiation effects on the microstructure and hardening of A508-3 steels used in Chinese HTGR

The irradiation and annealing behavior of Chinese A508-3 reactor pressure vessel (RPV) steel (0.04 wt% Cu) after 3 MeV Fe-ion irradiation ranging from 0.1 to 20 dpa at room temperature (called RTRPV) and high temperature (250?°C, called HTRPV) was studied by positron annihilation Doppler broadening (PADB) spectroscopy and nano-indentation hardness. PADB showed that the density of vacancy-type defects was higher for low-temperature irradiations. The higher hardness was found after high-temperature irradiation because of the formation of solute clusters during irradiation. Positron annihilation measurements revealed the interaction and clustering of vacancies with solute clusters which were introduced by Fe-ion irradiation. For both RTRPVs and HTRPVs, the positron defect parameter and positron diffusion length showed the recovery of the irradiation-induced defects. Total recovery was observed after annealing at 450 °C.     

氦对Fe-Cr-Ni合金和Fe-Cr-Mn合金辐照损伤的影响

利用超高压电镜与高能离子加速器连接装置 ,研究了氦 (He)对Fe Cr Ni和Fe Cr Mn两类奥氏体型合金辐照损伤行为的影响。观察了辐照过程中二次点缺陷的演变、空洞的形成以及辐照诱导晶界处溶质元素浓度的变化。实验结果表明 :He能促进两类合金空洞核心的增加 ,但空洞尺寸和密度不同 ;He能有效抑制辐照诱起晶界元素偏析 ,但对不同原子尺寸的溶质原子抑制效果不同。该差别是由于He的注入提高空位移动激活能和改变点缺陷与溶质原子相互作用的效果     

双束同时辐照对低活性Fe-Cr-Mn(W,V)合金相稳定性影响

采用电子束 /He+ ion束同时复合辐照方式 ,研究了低活性Fe Cr Mn(W ,V)合金高温长时时效后组织稳定性 ,评价了He对辐照相稳定性影响。结果表明 ,单独电子辐照 ( 10a-1 )只引起相界面低密度空洞形成。而双束同时辐照对组织损伤具有协同效果 ,加剧相稳定性发生变化 ,如 :促进相间溶质原子扩散 ,导致析出相长大 ;新相的形成 ;发生结构无序化 ,促进析出相改性。从He原子与晶体辐照点缺陷与溶质原子相互作用和扩散等机制 ,讨论了辐照相稳定性发生变化的原因。     

Void Swelling of Solution-Annealed Type 316 Stainless Steel under Long Time Proton Irradiation

Solution-annealed type 316 stainless steel was irradiated by 150 keV proton to a dose of about 6 dpa at the irradiation temperature ranging 450–700°C. To examine the effect of aging during irradiation, the present proton irradiation was carried out for about 25 h at a low dose rate of 7×10–^?5dpa/s. The specimens without He preinjection showed much smaller void swelling than those preinjected with He to the content of 10 at.ppm. Similarly to the case of neutron irradiations, the void swelling in the He preinjected specimens showed the temperature dependence with double peaks, and the peak swelling temperatures were about 550 and 650°C. In these specimens with He preinjection. void number density decreased and average void diameter increased with the increase of irradiation temperature in the range of 450–600°C, but these trends were reversed between 600 and 650°C. The volume of the grain boudary M₂₃C6 precipitates increased with the increase of irradiation temperature from 600 to 700°C, and it was concluded that the decrease of soluble carbon due to the precipitation of M₂₃C6 caused the second swelling peak at 650°C.     

Hardening and microstructural evolution in A533B steels under neutron irradiation and a direct comparison with electron irradiation

A533B steels irradiated at 290 °C up to 10 mdpa in the Kyoto University Reactor were examined by hardness, positron annihilation and atom probe measurements. Dose dependent irradiation hardening and formation of Cu-rich clusters were confirmed in medium Cu (0.12% and 0.16%Cu) steels whereas neither hardening nor cluster formation was detected in low Cu (0.03%Cu) steel. No microvoids were formed in any of the steels. Post-irradiation annealing in medium Cu steels revealed that the hardening recovery at temperatures above 350-400 °C could be attributed to compositional changes and dissociation of the Cu-rich clusters. Compared to electron irradiation at almost the same dose and dose rate, KUR irradiation caused almost the same hardening and produced Cu-rich clusters, more solute-enriched with larger size and lower density. Considering lower production of freely-migrating vacancies in neutron irradiation, the results suggested that cascades enhance the formation of Cu-rich clusters.     

Effect of trapping on interstitial cluster nucleation at the onset of irradiation

Kinetic calculations have been carried out to study heterogeneous nucleation of interstitial clusters at solute trapping sites during the transient period from the onset of irradiation until the vacancy and interstitial concentrations approach their “quasi” steady-state values. The irradiation rate, temperature, and interstitial-solute binding energy were the primary parameters varied. It has been reported earlier that, for reasonable cluster binding energies, interstitial clusters nucleate homogeneously in high concentrations at the lower temperature range of void swelling and their concentration decreases with increasing temperature. In the present calculations it is found that the decrease in the free interstitial concentration due to trapping reduces the homogeneous nucleation but, except at very high interstitial-solute binding energies, this decrease is more than offset by heterogeneous nucleation, yielding a net increase in nucleated interstitial clusters. These effects are greater at lower temperatures and lower irradiation rates.     

The effect of primary recoil spectrum on radiation induced segregation in nickel-silicon alloys

Segregation of silicon to the surface of Ni-12.7 at% Si alloys during 2.0-MeV He and 3.25-MeV Kr irradiations was measured using Rutherford backscattering spectrometry. For equal calculated defect production rates the Kr irradiation was < 3 % as efficient as the He irradiation for promoting segregation in the temperature range, 450 °C–580 °C. It was further observed that Kr preirradiation of specimens dramatically reduced segregation during subsequent He irradiation. A model for cascade annealing in Ni-Si alloys is presented which qualitatively explains the segregation results. The model assumes that small interstitial-atom-clusters form in individual cascades and that these clusters become trapped at silicon solute atoms. The vacancy thereby becomes the more mobile defect. The model should also have relevance for the observation that void swelling in nickel is suppressed by the addition of silicon solute.     

Synthesis of atom probe experiments on irradiation-induced solute segregation in French ferritic pressure vessel steels

Microstructural changes due to neutron irradiation cause an evolution of the mechanical properties of reactor pressure vessels (RPV) steels. This paper aims at identifying and characterising the microstructural changes which have been found to be responsible in part for the observed embrittlement. This intensive work relies principally on an atom probe (AP) study of a low Cu-level French RPV steel (Chooz A). This material has been irradiated in in-service conditions for 0–16 years in the frame of the surveillance program. Under this aging condition, solute clustering occurs (Cu, Ni, Mn, Si, P, …). In order to identify the role of copper, experiments were also carried out on Fe–Cu model alloys submitted to different types of irradiations (neutron, electron, ion). Cu-cluster nucleation appears to be directly related to the presence of displacement cascades during neutron (ion) irradiation. The operating basic physical process is not clearly identified yet. A recovery of the mechanical properties of the irradiated material can be achieved by annealing treatments (20 h at 450°C in the case of the RPV steel under study, following microhardness measurements). It has been shown that the corresponding microstructural evolution was a rapid dissolution of the high number density of irradiation-induced solute clusters and the precipitation of a very low number density of Cu-rich particles.     

Evolution of nanoscopic iron clusters in irradiated zirconium alloys with different iron contents

We investigate the distribution of alloying elements in irradiated Zr alloys with different Fe contents using atom probe tomography. Our results showed dense nanoscale regions (clusters) of Fe formed in the matrix. The average diameter of the Fe clusters in alloy with a high Fe content increased under a higher neutron fluence. Conversely, the number density of Fe clusters remained similar in all the Zr alloy specimens. Energy-dispersive X-ray spectrometry showed that the maximum cluster size depended on the Fe content in the secondary phase particles. Fe clusters gathered along the basal plane of the Zr alloys at high fluence, indicating that irradiation defects influence Fe clustering. The solute concentration of Fe was estimated to be approximately 0.1 at%, which is the Fe concentration in the matrix exclusive of Fe clusters.     

Effects of stress on radiation hardening and microstructural evolution in A533B steel

Bent specimens of A533B steel (0.16 wt% Cu) were irradiated at 290 °C to 1 dpa with 6.4 MeV Fe³⁺ ions. Calculated tensile stresses at the irradiated surface were set to 0, 250, 500 and 750 MPa. The specimens were subjected to hardness measurements, transmission electron microscopy (TEM) observations and three-dimensional atom probe (3DAP) analysis. The radiation-induced hardening decreased with increasing stress to 500 MPa which was near the yield strength. TEM and 3DAP results showed that well-defined dislocation loops and solute clusters were formed. The diameter of dislocation loops increased and the number density decreased when the stress was applied, whereas the diameter and number density of solute clusters decreased. The hardening was mainly attributed to solute cluster formation. Application of tensile stress would control hardening by suppressing the solute cluster nucleation and growth.     

硅外延平面NPN双极晶体管的总剂量辐射损伤缺陷研究

本文针对国产NPN双极晶体管开展了不同偏置下的总剂量辐照试验。试验结果表明,辐照主要导致双极晶体管的基极电流增加和电流增益降低。同时,NPN晶体管在反向偏置下表现出较零偏下更严重的退化。分析发现,双极晶体管性能退化主要来源于辐射诱生缺陷导致的复合电流增加。最后,基于深能级瞬态谱开展了NPN晶体管发射结的缺陷测试,发现辐射会导致缺陷密度的增加和缺陷能级的改变。     

Effects of solute elements on hardening and microstructural evolution in neutron-irradiated and thermally-aged reactor pressure vessel model alloys

Nanometer-sized Cu-enriched solute clusters containing Mn, Ni, and Si atoms are considered as the primary embrittling feature in reactor pressure vessel steels. In order to understand the effects of solute atoms Mn, Ni, and Si on hardening and cluster formation, reactor pressure vessel model alloys FeCu, FeCuSi, FeCuNi, and FeCuNiMn were irradiated at 290 °C in a research reactor. Thermal ageing at 450 °C was also carried out to compare with the results in the neutron irradiation. The addition of Mn resulted in larger hardening and higher cluster number density in both thermal ageing and neutron irradiation. In FeCu0.8NiMn alloy, the size distribution of Cu-enriched clusters formed in 62-h thermal ageing (almost peak hardening) was very similar to that formed in the neutron irradiation, indicating they are on a similar growing stage. But the average Ni and Mn composition in clusters formed in neutron irradiation was higher. A good linear relationship between hardening and the square root of cluster volume fraction for both neutron irradiation and thermal ageing data was found.     

双束（H+/e-）辐照下氢对12Cr-ODS铁素体钢组织损伤影响研究

利用氢离子（H⁺）束和电子（e^-）束双束（H⁺/e^-）同时辐照用化学浸润法制备的新型12Cr-ODS铁素体钢，研究其辐照损伤效应及组织变化。实验结果表明：由于氧化物的钉扎，基体内保持低密度位错网络；辐照初期随辐照剂量的增加，缺陷团在位错线上及其周围形成，尺寸增加，密度不断增大，并形成间隙型位错环；不同温度下辐照均产生小尺寸高密度的空洞，随辐照剂量的增大，空洞长大速度降低，空洞密度缓慢减小；不同温度下，辐照剂量达15dpa时，空洞肿胀均小于0.15%。对辐照产生的点缺陷与氢相互作用进行理论分析，12Cr-ODS铁素体钢在623~823K经双束辐照后，表现出良好的抗辐照损伤性。     

He ion irradiation damage in Fe/W nanolayer films

We report on the evolution of microstructure and mechanical properties of Fe/W multilayers subjected to helium ion irradiations. Sputtered Fe/W multilayers with individual layer thickness, varying from 1 to 200 nm, were subjected to He⁺ ion irradiation with a peak displacement per atom value of 6 at ambient temperatures. Helium bubbles, 1-2 nm in diameter, were observed in Fe and W, and more so along layer interfaces. The magnitude of hardness variation after radiation depends on the individual layer thickness. Radiation hardening is observed in specimens with individual layer thickness of ?5 nm. At smaller layer thickness, the hardness barely changes. Analysis indicates that radiation hardening may originate mainly from dislocation loops and partially from He bubbles.     

急性、分次及慢性γ线照射诱发猕猴生物效应的比较研究

本文就高剂量率急性一次(223mGy/min)、分次累积(223mGy/min,每周照射一次,0.25Gy/次)及低剂量率慢性连续(每周照射5天,50mGy/d)γ射线照射时,在0—2Gy 累积剂量范围内,对猕猴造血、免疫及细胞遗传学方面某些生物效应进行了比较研究。不同方式照射时机体损伤程度和特性不一,急性照射组各类效应均比其它受照组明显;而分次和慢性照射组的剂量-效应规律则比较相似。在低剂量率慢性照射情况下,PHA 激活淋巴细胞微核、淋巴细胞染色体无着丝点断片及总断裂数在累积剂量为0.25Gy 时就出现了明显增高(p<0.05),且与受照剂量呈线性正相关。它们的剂量-效应曲线尾部(在1—2Gy 区)均呈现有“坪”的现象。停照后一年中动态观察的结果表明,各照射组动物受照时所诱发的效应,绝大多数是可恢复的。急性组恢复至正常所需时间较其它组长,其中免疫和造血机能的恢复呈显著波动性,而细胞遗传学效应随停照后时间的延长逐步恢复。     

钨中自间隙原子团簇扩散行为的分子动力学模拟

钨被视为未来聚变堆中最有可能全面使用的面对等离子体材料。而在未来聚变堆真实环境下,氘氚聚变反应产生的14 MeV高能中子辐照将在材料中产生严重的原子离位损伤和各种缺陷积累。其中自间隙原子（SIA）及其团簇是中子辐照损伤中最常见的缺陷种类。本文采用分子动力学模拟系统研究钨中1/2〈111〉和〈100〉 SIA团簇的稳定结构和形成能,发现SIA团簇最稳定结构是1/2〈111〉 SIA团簇结构,SIA团簇聚集后会稳定存在。并研究了不同尺寸1/2〈111〉 SIA团簇的动力学扩散行为,发现单个SIA在温度高于700 K时易扩散和转向,而两个以上的SIA团簇在300~900 K时主要表现为一维方向的运动。为准确描述各种尺寸SIA团簇的动力学行为,给出了一套计算SIA团簇跃迁频率的经验参数。相关结果将为更大尺度的动力学蒙特卡罗和团簇动力学模拟提供准确和完备的输入参数,为正确掌握和评价钨中子辐照行为提供依据。     

Understanding of copper precipitation under electron or ion irradiations in FeCu0.1 wt% ferritic alloy by combination of experiments and modelling

This work is dedicated to the understanding of the basic processes involved in the formation of copper enriched clusters in low alloyed FeCu binary system (FeCu0.1 wt%) under irradiation at temperature close to 300 °C. Such an alloy was irradiated with electrons or with ions (Fe⁺ or He⁺) in order to deconvolute the effect of displacement cascades and the associated generation of point defect clusters (ion irradiations), and the super-saturation of mono-vacancies and self-interstitial atoms (electron irradiation). The microstructure of this alloy was characterised by tomographic atom probe. Experimental results were compared with results obtained with cluster dynamic model giving an estimation of the evolution of point defects (free or agglomerated) under irradiation on the one hand and describing homogeneous enhanced precipitation of copper on the other hand. The comparison between the results obtained on the different irradiation conditions and the model suggests that the point defect clusters (dislocation loops and/or nano-voids) created in displacement cascades play a major role in copper clustering in low copper alloy irradiated at 573 K.     

The effect of neutron irradiation on mechanical properties of YAG laser weldments using previously irradiated material

The objective of this study is to make clear the effect of neutron irradiation on mechanical properties of laser weldments using irradiated material. This estimation is necessary for the application to joining coolant piping of the ITER blanket. Irradiation testing was performed at Japan Material Testing Reactor (JMTR). On the irradiation condition for weldments using irradiated material, fast neutron fluence was 1.4 × 10²⁴ n/m², which corresponds to a displacement damage rate of 0.26 displacement per atom (dpa) and irradiation temperature 200 °C. The results of this study show that tensile properties of all weldments changed into that of base material by the effect of neutron irradiation. The results of hardness tests show that irradiation hardening at an irradiation damage dose of 0.3 dpa is almost same as that at irradiation damage 0.6 dpa. It is concluded that irradiated weldments using irradiated material were moved toward irradiated base material on tensile and hardness properties up to 0.6 dpa. On the other hand, tensile properties of base material were changed by the effect of neutron irradiation up to about 0.3 dpa, and with much less change from 0.3 dpa to 0.6 dpa. It is inferred that the effect of neutron irradiation of SS316LN-IG almost saturated up to 0.3 dpa.     

Irradiation induced clustering in low copper or copper free ferritic model alloys

In order to determine the formation mechanism of solute cluster in ferritic steels under irradiation, Cu and Cu free ferritic model alloys (FeCuMnNiP and FeMnNiP) were irradiated with electrons and ions. Their microstructures were characterized by atom probe tomography and the evolution of the population of point defects was estimated with a model of cluster dynamic. The comparison between experimental results and predictions of the model suggests that the formation of the solute clusters is heterogeneous, on the point defect clusters. The comparison between the experimental results obtained on these two alloys shows that the absence of copper slows down the kinetics of precipitation. Moreover, by comparing the results obtained on the FeCuMnNiP alloy with previous results obtained on binary alloy FeCu, it appears that the presence of manganese, nickel and/or phosphorus slows down the kinetics of precipitation. Finally, the comparison between this study and results obtained by other authors on similar alloys irradiated with neutrons reveals a strong flux effect on the kinetic of precipitation of solute clusters.