Atom probe tomography analysis of nanostructure evolution in Ni-Cr-Mo low alloy steel under neutron irradiation

Ni-Cr-Mo low alloy steels are being considered as alternative materials to replace the Mn-Mo-Ni low alloy steels used in reactor pressure vessels in nuclear power plants, because of their higher strength and toughness. However, the neutron irradiation occurring during reactor operation causes degradation of Ni-Cr-Mo low alloy steel. In this study, irradiation-induced clusters in a Ni-Cr-Mo model alloy irradiated in the High-flux advanced neutron application reactor (HANARO) research reactor were investigated via Atom probe tomography (APT). The irradiated specimens showed irradiation-induced hardening and embrittlement. The neutron irradiation caused Si clustering, and these spherical clusters were homogeneously distributed within the matrix. Ni was also clustered at the Si clusters. However, the other elements did not clearly exhibit clustering behavior. Si and Ni atoms were also located at the dislocations. To quantify the nano-sized clusters, a method based on the Density-based spatial clustering of applications with noise (DBSCAN) algorithm was implemented. The total number of clusters was calculated to be ~7 × 10^-4 n/nm³ and the average cluster radius was less than 2 nm. The APT approach was demonstrated to be well suited for discovering the irradiation defect structures.     

Statistical analysis of atom probe data: Detecting the early stages of solute clustering and/or co-segregation

Statistical analysis of atom probe data has improved dramatically in the last decade and it is now possible to determine the size, the number density and the composition of individual clusters or precipitates such as those formed in reactor pressure vessel (RPV) steels during irradiation. However, the characterisation of the onset of clustering or co-segregation is more difficult and has traditionally focused on the use of composition frequency distributions (for detecting clustering) and contingency tables (for detecting co-segregation).     

美国压水堆RPV延寿分析研究及中国RPV延寿之关键问题

以美国Point Beach-2 60年延寿执照更新为例,论述基于中子辐照脆化机理的时限老化分析——承压热冲击分析、上平台能量分析和压力-温度限值曲线计算分析;在介绍美国RPV延寿期内辐照监督要求和新技术开发应用的基础上,参照法国核电法规要求,重点分析了中国在RPV中子辐照脆化评估中的几个关键问题。     

High-resolution Transmission Electron Microscopy Characterization of the Structure of Cu Precipitate in a Thermal-aged Multicomponent Steel

High-dispersed nanoscale Cu precipitates often contribute to extremely high strength due to precipitation hardening,and whereas usually lead to degraded toughness for especially ferritic steels.Hence,it is important to understand the formation behaviors of the Cu precipitates.High-resolution transmission electron microscopy(TEM) is utilized to investigate the structure of Cu precipitates thermally formed in a high-strength low-alloy(HSLA) steel.The Cu precipitates were generally formed from solid solution and at the crystallographic defects such as martensite lath boundaries and dislocations.The Cu precipitates in the same aging condition have various structure of BCC,9 R and FCC,and the structural evolution does not greatly correlate with the actual sizes.The presence of different structures in an individual Cu precipitate is observed,which reflects the structural transformation occurring locally to relax the strain energy.The multiply additions in the steel possibly make the Cu precipitation more complex compared to the binary or the ternary Fe-Cu alloys with Ni or Mn additions.This research gives constructive suggestions on alloying design of Cu-bearing alloy steels.     

Sub-nanometre elemental analysis of Cu cluster in Fe-Cu-Ni alloy using aberration corrected STEM-EDS

In order to understand the mechanism of Cu clustering and Ni effects on Cu clusters, a sub-nano scale structural and elemental analysis of Cu-bearing steels was carried out through an aberration corrected scanning transmission electron microscope. Based on systematic observation condition adjustment by changing the electron scattered angle, we adopted an inner scattered semi angle of between 50 and 70 mrad for the scanning transmission electron microscope energy dispersive X-ray spectroscopy analysis. Under this condition, Cu precipitates such as 9R are clearly recognized through atomic scale scanning transmission electron microscope annular dark field images. Cu clusters, before transforming to 9R, are detected on the dislocation and have a periodical strain field. Ni enrichment is also observed in the vicinity of Cu clusters. Considering these enrichment phenomena of Cu and Ni, it is found that Cu diffuses rapidly through dislocation, while at the same time, Ni enrichment occurs by ejection from Cu clusters and forms a shell structure.     

Cu基钎料电弧钎焊接头强度及断口分析

研究用钨极氩弧焊作为热源,用Cu3Si1Mn钎料、56Cu8Mn26Zn钎料分别钎焊A3钢板及1Cr18Ni9Ti不锈钢板。试验结果表明,在钎料/母材界面分别存在Si、Mn富集带,经XRD分析表明,Si是以Fe2Si相形式存在,而Mn是以固溶体形式存在;用Cu3Si1Mn、56Cu8Mn26Zn钎料钎焊A3钢板接头抗拉强度试样均断在母材,抗拉强度为308.2～308.7MPa,钎焊1Cr18Ni9Ti不锈钢板,拉伸均断在钎缝,其抗拉强度分别是331.5 MPa、382.9 MPa;拉伸断口分析发现,断裂起裂点在搭接钎缝的根部,主要是母材成分与少量的钎料成分混合、溶解而成,是脆性断口;止裂点在钎缝金属中（Cu3Si1Mn钎料）或在近界面上（Cu3Si1Mn钎料）,是塑性断口。     

Characterisation of the early stages of solute clustering in 1Ni–1.3Mn welds containing Cu

Microstructural characterisation of neutron irradiated low alloy steels is important for developing mechanistic understanding of irradiation embrittlement. This work is focused on the early stages of irradiation-induced clustering in a low Cu (0.03 wt%), high Ni (∼1 wt%) weld. The weld was irradiated at a very high dose rate and then examined by atom probe (energy-compensated position-sensitive atom probe (ECOPoSAP) and local electrode atom probe (LEAP)) with supporting microstructural information obtained by small angle neutron scattering (SANS) and positron annihilation (PALA).     

低层错能FeMnSiCrCu形状记忆合金的空蚀

对低层措能Fe—26Mn—6Si—7Cr—lCu形状记忆合金和0Crl3Ni5Mo不锈钢进行了空蚀试验。结果表明，Fe—26Mn—6Si—7Cr—lCu形状记忆合金杭空蚀性能优于0Crl3Ni5Mo不锈钢。空蚀过程中应变诱发马氏体转变是该形状记忆合金具有良好杭空蚀性能的主要原因。     

Atom probe tomography of reactor pressure vessel steels: an analysis of data integrity

In this work, the importance of optimising experimental conditions for the analysis of reactor pressure vessel (RPV) steels using atom probe tomography is explored. The quality of the resultant atom probe data is assessed in terms of detection efficiency, noise levels and mass resolution. It is demonstrated that artefacts can exist even when experimental conditions have been optimised. In particular, it is shown that surface diffusion of some minority species, including P and Si, to major poles prior to field evaporation can be an issue. The effects were most noticeable during laser pulsing.The impact of surface migration on the characterisation of dislocations and grain boundaries is assessed. The importance of selecting appropriate regions of the reconstructed data for subsequent re-analysis is emphasised.     

奥氏体中锰钢的耐磨性与形变诱发马氏体及位错强化的关系

本文利用电镜和X射线等检验手段及磨损与现场运行实验,研究了非强烈冲击工况下奥氏体中锰钢的耐磨性与形变诱发马氏体和位错强化的关系。实验结果表明：奥氏体稳定性低的中锰钢,由于形变诱发马氏体的产生及其与位错交互作用促进了加工硬化能力和耐磨性的提高,而奥氏体稳定性高的中锰钢则是由于溶质原子和第二相粒子与位错产生的交互作用所致。因此降低碳、锰含量,大量形成第二相弥散硬粒子或增加溶质原子深度是提高奥氏体中锰钢加工硬化能力和耐磨性的有效途径。     

Fretting and fretting corrosion behavior of novel micro alloyed rail steels

The fretting behavior of two novel rail steels of composition Cu–Ni and Cr–Cu–Ni has been studied and compared with that of C–Mn and Cu–Mo rail steels. The rail steels were fretted in dry condition and in 3.5% NaCl solution. All the four rail steels exhibited similar fretting behavior in dry condition. The morphological features of the wear scar surface indicated delamination process as the main wear mechanism. The wear damage in 3.5% NaCl was lower compared to that in dry condition for all the rail steels due to lubricating effect of the solution. Fretting in presence of 3.5% NaCl resulted in lower wear volume for Cu–Ni and Cr–Cu–Ni rail steels. The friction coefficient for Cr–Cu–Ni rail steel was lower than that of C–Mn, Cu–Mo and Cu–Ni rail steels. Scanning electron microscopy (SEM) showed better adherence of tribo-electro-chemical layers formed on Cu–Ni and Cr–Cu–Ni rail steel than the C–Mn and Cu–Mo rail steels. This has been related to the improved fretting corrosion behavior of Cu–Ni and Cr–Cu–Ni rail steels.     

Atom probe characterization of precipitation in an aged Cu-Ni-P alloy

A temporal evolution of clusters associated with age hardening behavior in a Cu-Ni-P alloy during ageing at 250 °C for up to 100 ks after solution treatment has been carried out. A three-dimensional atom probe (3DAP) analysis has showed that Ni-P clusters are present in the as-quenched condition, and that the cluster density increases as the ageing time increases. The clusters have a wide range of Ni/P ratios when they are relatively small, whereas larger clusters exhibit a narrow distribution of the Ni/P ratio, approaching a ratio of approximately two. These results would indicate that the clusters with various Ni/P ratios form at the early stage of precipitation and the ratio approaches a value identical to that of the equilibrium phase at 250 °C as the clusters enlarge during ageing.     

承压热冲击瞬态下反应堆压力容器下降环腔内三维热工水力分析

以压水堆核电厂承压热冲击分析评定技术研究(PTS确定性分析方法研究项目)为背景,针对核电厂PTS瞬态下RPV下降环腔内热工水力分析问题,基于通用计算流体动力学软件Fluent,采用合适的对流换热分析和湍流模型,建立了RPV下降环腔内的三维热工流场分析模型,模拟分析RPV下降环腔内的三维流动与换热情况。重点模拟得到了RPV下降环腔内的三维流场分布和RPV内壁面的温度分布,并且在某些瞬态时刻得到了典型的热工水力现象即羽流(Plume)现象。得到的RPV下降环腔内详细的热工流场数据和羽流现象,为PTS下RPV应力分析和完整性提供了热工数据。     

Positive effect of natural pre-ageing on precipitation hardening in Al–0.44 at% Mg–0.38 at% Si alloy

Age hardening in a purely ternary Al-Mg0.4–Si0.4 (0.44 at% Mg, 0.38at%Si) alloy that is similar to AA6060 was investigated by hardness measurement, TEM and three-dimensional atom probe (3D-AP). In particular, the effect of natural pre-ageing before artificial ageing, which is known to have a positive effect in this alloy, was studied by comparing three different conditions: natural ageing only, artificial ageing for 1.5 h at 180 °C only and combined natural pre-ageing and subsequent artificial ageing for 1.5 h at 180 °C. Natural ageing influences the mechanical properties significantly. Naturally aged alloys exhibit a hardening response that is governed by the presence of small clusters. Subsequent artificial ageing of naturally aged specimens increases the value of peak hardness, which is attributed to the increase of the number density of needle-shaped precipitates as compared to the samples without natural ageing. It is assumed that besides these precipitates, the small Si clusters formed at room-temperature storage remain stable during artificial ageing.     

合金元素含量对耐候钢在模拟海洋大气环境下耐蚀性的影响

采用扫描电子显微镜和电化学交流阻抗谱研究了Q235B、SPA-H钢和2种不同镍、铬及铜含量的耐候钢在模拟海洋大气环境中的耐蚀性。结果表明:在有Cl-存在的环境中,当镍和铜含量都很低时,单独添加铬在腐蚀前期对减缓腐蚀有利,而在后期对腐蚀有促进作用;镍的质量分数小于0.25%时对耐蚀性的影响不起主导作用;电化学交流阻抗试验结果与腐蚀质量损失试验结果一致;4种钢周期浸润腐蚀48h后的锈蚀量都比较少,腐蚀192h后的锈蚀量明显增加。     

Irradiation tests of ITER candidate Hall sensors using two types of neutron spectra

We report on irradiation tests of InSb based Hall sensors at two irradiation facilities with two distinct types of neutron spectra. One was a fission reactor neutron spectrum with a significant presence of thermal neutrons, while another one was purely fast neutron field. Total neutron fluence of the order of 10(16)?cm(-2) was accumulated in both cases, leading to significant drop of Hall sensor sensitivity in case of fission reactor spectrum, while stable performance was observed at purely fast neutron spectrum. This finding suggests that performance of this particular type of Hall sensors is governed dominantly by transmutation. Additionally, it further stresses the need to test ITER candidate Hall sensors under neutron flux with ITER relevant spectrum.     

ODS钢液态重金属环境腐蚀研究进展

铅基快堆(Lead-cooled fast reactor,LFR)采用液态重金属(铅/铅铋合金)作为冷却剂,具有高安全性、高经济性等特点,并且在核能可持续发展方面具有一定的优势,目前被列为第四代核能系统六种参考堆型之一。液态金属冷却剂在服役过程中具有高温、高流速和高密度等特点,会对堆芯结构材料产生严重的腐蚀破坏。纳米氧化物弥散强化钢(Oxide dispersion strengthened steel,ODS)具有优异的抗辐照性能和优良的高温力学性能,目前已经成为先进快中子反应堆堆芯候选结构材料研究热点,其抗液态金属冷却剂腐蚀的能力是影响反应堆安全运行的关键性能之一。对目前有代表性的ODS钢在液态重金属环境中的腐蚀研究进展进行了综述,并结合ODS钢在氧化性气体环境和超临界水中的氧化腐蚀研究进展,对影响ODS钢液态金属腐蚀行为的因素进行了讨论。     

高强耐候钢在NaCl溶液中的腐蚀锈层特征和耐腐蚀性研究

为了研究高强耐候钢Q450NQR1和B2在2.0%NaCl溶液中的腐蚀锈层特征,获得其耐腐蚀性规律。采用交流阻抗谱（Electrochemical impedance spectroscopy,EIS）、X射线衍射仪（X-ray diffracmeter,XRD）、扫描电镜（Scanning electron microscope,SEM）和电感耦合等离子体（Inductively coupled plasma,ICP）手段分析它们的腐蚀行为和锈层特征,并讨论合金元素Cu、Ni、Cr、Mo等对耐腐蚀性的影响。结果表明：B2耐候钢的耐蚀性要优于Q450NQR1耐候钢的,其锈层表现出较高的电荷转移电阻（R_t）特征;两种耐候钢的非连续性（Non-adherent rusts,NAR）和连续性（Adherent rusts,AR）型锈层物相组成分别一致,但含量有差别;NAR型锈层主要由大量的γ-FeOOH和少量的Fe₃O₄、α-FeOOH组成,紧贴基体的AR型锈层几乎全为Fe₃O₄。Cu、Ni、Cr、Mo合金元素在两种锈层中的分布不同,影响着NAR型锈和AR型锈的协同保护作用,从而改变了基体表面的锈层特征,稳定锈层的存在可显著抑制Cl^-渗入,有助于改善材料耐腐蚀性。     

Segregation of solute elements at grain boundaries in an ultrafine grained Al-Zn-Mg-Cu alloy

The solute segregation at grain boundaries (GBs) of an ultrafine grained (UFG) Al-Zn-Mg-Cu alloy processed by equal-channel angular pressing (ECAP) at 200 °C was characterised using three-dimensional atom probe. Mg and Cu segregate strongly to the grain boundaries. In contrast, Zn does not always show clear segregation and may even show depletion near the grain boundaries. Trace element Si selectively segregates at some GBs. An increase in the number of ECAP passes leads to a decrease in the grain size but an increase in solute segregation at the boundaries. The significant segregation of alloying elements at the boundaries of ultrafine-grained alloys implies that less solutes will be available in the matrix for precipitation with a decrease in the average grain size.     

Effect of alloying additives on impact-abrasive wear of manual arc welded hadfield steel hardfacings

The results of studying the impact-abrasive wear of manual arc welded Hadfield steel hardfacings and this steel alloyed with Cr, Ni, Mo, B, Cu, and Si, both without and with coarse-grained tungsten carbide reinforcement, are presented. It has been found that under conditions of impactless wear the presence of the hardening phase in the Hadfield steel increases its wear by 40% on average compared to the wear of the base and alloyed Hadfield steels. With an increase in the impact energy from 2.8 to 5.6 J, the wear of the reinforced Hadfield steels decreases and becomes comparable with the wear of the base and alloyed Hadfield steels. Under the conditions of erosion by coarse particles, layers of the Hadfield steel reinforced by tungsten carbide have slightly lower wear rate than unreinforced ones.