FeCr合金中Cr含量对微观结构影响的原子尺度模拟研究

低温辐照脆化是影响铁素体/马氏体（F/M）钢服役的主要问题之一。F/M钢低温辐照脆化的主要机理是辐照产生的纳米缺陷（如位错环、α′相(富Cr团簇)等）阻碍位错运动。本文利用分子动力学方法和迈氏蒙特卡罗方法对F/M钢模型材料--FeCr合金（Fe7%Cr、Fe9%Cr、Fe14%Cr）中Cr元素析出成团簇及在位错环上偏析的机理进行研究,并分析Cr团簇析出与合金成分的关系以及位错环尺寸、位错环类型和合金中Cr含量对位错环上Cr偏析量的影响。模拟结果表明：热力学模拟后,高Cr含量（>9%)的FeCr合金中会析出Cr团簇,且基体内Cr含量越高,析出的Cr团簇尺寸越大;在所研究的3种FeCr合金中,受位错环张应力场作用,合金元素Cr均会在位错环的外围偏析,且FeCr合金中Cr含量越高,Cr在位错环上偏析量越高。低Cr的FeCr合金中Cr对其辐照硬化的影响需考虑位错环上Cr偏析的影响,高Cr的FeCr合金中Cr元素对其辐照硬化的影响需综合考虑Cr团簇及位错环上Cr偏析。     

Mn对bcc Fe基中Cu析出物引起的辐照硬化的影响研究

正富Cu析出物引起的辐照硬化是导致反应堆压力容器出现辐照脆化现象的主要因素之一。随着研究的进一步深入,实验方面采用三维原子探针发现Cu析出物中存在溶质原子Mn和Ni。Mn和Ni原子的出现可以提高Cu析出物的数量和形核率。至于Ni对Cu析出物对位错阻碍作用的影响至今仍存在争议,而Mn对Cu析出物和位错相互作用的影响,目前未见相关报道。所以,开展Mn原子对富Cu析出物引起的辐照硬化的影响研究显得非常有价值。因此,本文采用分子动力学方法对bcc Fe基2、3和4nm Cu和Cu-Mn析     

核材料辐照损伤的并行空间分辨随机团簇动力学模拟

核反应堆中关键材料的辐照损伤演化对其性能有重要影响，且跨越多个量级的时空尺度。空间分辨随机团簇动力学是近年来发展的1种模拟核材料辐照损伤行为的有效方法，它避免了传统团簇动力学在缺陷种类和计算复杂性方面的限制，且能考虑缺陷的空间依赖性。在概述了空间分辨随机团簇动力学基本原理的基础上，论述了自主开发的大规模并行空间分辨随机团簇动力学程序MISA-SCD1.0的实现方式与关键技术，并将其应用于反应堆压力容器模型合金中富Cu团簇的析出模拟，验证了程序的正确性并测试了并行性能。结果表明，MISA-SCD1.0能获得与实验结果和类似模拟结果吻合的Cu析出过程，且具有较高的并行效率和良好的扩展性。     

非均匀形核对辐照诱导钨内微结构演化行为影响的团簇动力学模拟

金属钨(W)及其合金作为未来聚变堆最具应用前景的面向等离子体结构材料(PFMs),其服役性能直接影响聚变堆长期服役的安全性,辐照诱导W及其合金内微结构演化导致的辐照脆化现象始终是限制其工程应用的关键因素。本文基于分子动力学计算结果,进一步完善了辐照诱导材料微结构演化行为的团簇动力学模型,采用更加完备的物理模型描述材料内辐照缺陷的产生行为,并进一步探讨了W基体内辐照缺陷产生过程对微结构演化行为的影响。模拟结果表明,高能初始离位原子(PKA)诱发级联碰撞直接产生的缺陷团簇是W内位错环、空洞演化中最重要的形核机制;非均匀形核所产生的间隙团簇的扩散行为对位错环的长大行为有重要影响,会导致位错环尺寸分布中出现亚尖峰与台阶状形貌。     

反应堆压力容器钢中溶质元素空位型扩散机理研究

辐照或热老化导致元素偏析和沉淀析出是反应堆压力容器(reactor pressure vessel,RPV)钢性能退化的主要影响因素,点缺陷与合金/杂质元素结合与扩散是引起元素偏析和沉淀析出的主要原因。本文利用分子动力学方法研究了反应堆压力容器钢中几种主要合金/杂质元素(Cu、Ni、Mn、P)的空位型扩散机理。研究了空位与合金/杂质元素的结合性能;基于多频模型计算了合金/杂质元素的空位风参数和扩散系数。通过计算发现,Cu、P与第1近邻、第2近邻空位均具有较大的结合能,Ni与第2近邻空位具有较大的结合能;溶质元素的空位风均随着温度的升高而增大,表明在高温下合金/杂质元素均倾向通过与空位互换位置而扩散。     

双束同时辐照低活性Fe-Cr-Mn(W、V)合金微观组织损伤的影响

研究了时效热处理低活性Fe Cr Mn(W、V)钢双束同时辐照损伤行为 ,结果表明 :92 3K/ 3 0 0 0h时效合金 ,经单独电子辐照 (1 0a- 1)出现低密度空洞 ,而经双束同时辐照的时效合金 ,在辐照初期就形成间隙型位错环和微小空洞。与无时效合金相比 ,随时效温度增加 ,空洞尺寸、空洞密度和空洞肿胀量增大。随时效温度的提高碳化物析出数量增多 ,奥氏体中合金元素Cr、Mn、W、V降低 ,He的存在有效地促进空洞肿胀量增大。     

电子辐照条件下高纯铁中位错环演化的多尺度模拟

辐照诱导材料微观结构演化导致的材料力学性能降级或尺寸不稳定性是限制反应堆安全与经济性的关键因素之一。本文基于速率理论建立了辐照诱导材料微观结构演化的物理模型,并开发了模拟程序Radieff。采用分子动力学计算了高纯铁中缺陷的形成能、结合能、迁移能以及间隙原子位错环的构型,在此基础上模拟了电子辐照诱导高纯铁内位错环的演化过程,并与实验结果进行了对比。基于分子动力学的计算结果表明,当间隙原子团簇包含3个间隙原子时,团簇的排列方式为〈110〉构型,间隙原子团簇包含4个以上间隙原子时,团簇排列方式变为〈111〉构型。此外基于Radieff研究了400~600K温度范围内,损伤速率为1.5×10-4 dpa/s电子辐照条件下,位错密度对位错环演化的影响,位错密度对位错环数密度及其平均尺寸的影响取决于位错以及间隙原子团簇对间隙原子的阱强度;在464K和550K温度下辐照,位错环数密度及其平均尺寸分别在位错密度增加到1011 cm-2和1010 cm-2后急剧减小,这是由于此时位错对间隙原子的阱强度会大于间隙原子团簇对间隙原子的阱强度。     

反应堆压力容器模拟钢中富Cu原子团簇对材料力学性能的影响

采用淬火和时效处理方法诱发压力容器模拟钢中的微量杂质元素Cu以富铜原子团簇析出。力学性能试验结果表明,富铜原子团簇的出现导致压力容器模拟钢韧脆转变温度出现明显变化,而屈服强度和抗拉强度增长较小,塑性也只有较小程度下降。三维原子探针分析结果表明,富铜原子团簇的数密度为1023 m-3数量级,富铜原子团簇直径为1～3 nm。     

重金属团簇运移实验研究

设计一套可以观测重金属运移的装置,实验发现：当重金属中加入U、Th等α放射源后,放射源的α衰变能够使重金属产生明显的向上运移,这是因为重金属与He核形成团簇,当团簇的密度比空气小时,重金属团簇便可以向上运移。     

Zr-Cu-Cr合金的显微组织及腐蚀行为

以结晶锆为基材配制了7种Zr-Cu-Cr合金样品,经归一化加工及600 ℃/5 h退火处理,在不同水化学条件的静态高压釜中对所制得的Zr-Cu-Cr合金样品进行了腐蚀试验,并采用EBSD、SEM和TEM表征合金基体的显微组织,探究Cu和Cr交互作用对锆合金基体显微组织及耐腐蚀性能的影响。结果表明,添加Cu元素可细化合金再结晶晶粒,Cr含量为1.0%（质量分数）时,合金中出现40 μm以上的较大晶粒。Zr-Cu-Cr合金中存在2种第二相：100 nm以上的体心四方的Zr2Cu相和60 nm以下的密排六方的ZrCr₂相。Zr₂Cu相随Cu含量的增加而增多,ZrCr₂相随Cr含量的增加尺寸变化不明显,但数量及分布条带密度增加。在400 ℃/10.3 MPa过热蒸汽中,Zr-0.3Cu-0.2Cr和Zr-0.3Cu-0.5Cr合金耐腐蚀性能较差,其余合金腐蚀100 d后仍没有发生腐蚀转折,耐腐蚀性能较好,Zr-1.0Cr合金耐腐蚀性能最好。在360 ℃/18.6 MPa/0.01 mol/L LiOH水溶液中腐蚀42 d后,合金的耐腐蚀性能都很差,添加Cu元素会降低其耐腐蚀性能。     

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.     

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.     

Effect of an electron gas on a neutron-rich nuclear pasta

We studied the role that electron gas has on the formation of nuclear structures at subsaturation densities and low temperatures(T1 Me V).Using a classical molecular dynamics model we studied isospin symmetric and asymmetric matter at subsaturation densities and low temperatures varying the Coulomb interaction strength.The effect of such variation was quantified on the fragment size multiplicity,the inter-particle distance,the isospin content of the clusters,the nucleon mobility and cluster persistence,and on the nuclear structure shapes.We found that the presence of an electron gas distributes matter more evenly,disrupts the formation of larger objects,reduces the isospin content,and modifies the nucleon average displacement,but does not affect the inter-nucleon distance in clusters.The nuclear structures are also found to change shapes by different degrees depending on their isospin content,temperature and density.     

A kinetic Monte Carlo approach for the analysis of trapping effect on the defect accumulation in neutron-irradiated Fe

The trapping effect of self-interstitial atom (SIA) clusters in neuron-irradiated Fe was analyzed in terms of generic traps. The effect of the cut-off size between sessile and glissile SIA clusters was investigated. The accumulation of SIA clusters decreased drastically as the cut-off size increased, which originated from the elimination of the SIA clusters at a grain boundary through its one-dimensional motion. When the immobile generic traps were introduced to the kinetic Monte Carlo simulation model, the effect of trap parameters was assessed. An increase in the binding energy between the trap and SIA-species resulted in a decrease in the number of mono-SIAs that were dissociated from the trap and a corresponding delay in visible SIA clusters. The size-dependent prefactor for the dissociation rate of trapped SIA clusters was necessary for a realistic accumulation behavior of SIA clusters. The trap density affects the density and size of the accumulated SIA cluster density during irradiation. This parameterization of generic traps provided insight into the mechanism of accumulation of SIA and SIA cluster.     

Effects of dose rate change under irradiation on hardening and microstructural evolution in A533B steel

Iron-ion irradiations were carried out for 0.09wt%Cu A533B steel specimens at 290°C to investigate effects of dose rate change during irradiation; the irradiations consisted of the base irradiation (with an unchanged dose rate) and an additional one with changed dose rates from 1 to 50 times that of the base one. Nano-indentation hardness measurements showed that the increase in hardness was higher for lower dose rate of the base irradiation. A similar trend was identified during the additional irradiation. Transmission electron microscope (TEM) and three-dimensional atom probe (3DAP) analyses were carried out for the quantitative characterization of defect features. Mn/Ni/Si/Cu-enriched clusters and dislocation loops were observed in all specimens. The increase in hardness mainly depended on the formation of the solute atom clusters. The square root of the volume fraction of the solute atom clusters provided a good correlation with the increase in hardness. The effects of dose rate and dose rate change during irradiation were explained by the formation of solute atom clusters.     

Design considerations for palladium electrodes as suggested by a deuteron cluster model for cold nuclear fusion

According to our hypothetical model, the essential element for the occurrence of cold nuclear fusion within palladium is the formation of deuteron clusters within the palladium electrodes. There are several factors which can affect the size, density, and rate of cluster formation. These factors are (1) the presence of diffusion barriers at all upstream palladium surfaces that are not immersed in the electrolyte, and which also are not exposed to a sufficiently large electric field to prevent deuteron diffusion from the electrode, (2) the direction and magnitude of the electric field relative to the crystalline lattice, (3) local crystalline temperature excursions that are associated with the fusion events, and (4) the various deuterium diffusion mechanisms within the crystal which are associated with thermal gradients, deuterium concentration gradients, and externally-generated potential field gradients that can enhance interstitial quantum mechanical tunneling along the direction of the associated internal electric field.     

Ag-In-Cd合金辐照后的微观组织变化

Ag-In-Cd合金在核电站压水堆控制棒中广泛使用,其辐照肿胀行为是评价Ag-In-Cd控制棒使用寿命的关键因素。本文通过制备不同成分的模拟合金,来模拟Ag-In-Cd合金在堆内辐照后的成分变化,分析合金的密度及微观组织特点。结果发现,当Ag含量低至77.5%(质量分数)时,合金会分解为fcc和hcp两相,fcc相中贫Sn高Ag,hcp相中富Sn低Ag。当Ag含量在55%~61%之间时,合金以hcp单相存在。由实测的密度拟合出了合金密度随成分变化的关系式。此结果对于理解和掌握Ag-InCd合金的辐照肿胀行为有重要意义。