α+β两相区热处理对Zr-Sn-Nb合金微观组织和腐蚀性能的影响

对Zr-Sn-Nb合金在α+β两相区温度下不同工艺热处理后所得样品,在360 ℃/18.6 MPa纯水环境中进行均匀腐蚀试验,并采用扫描电子显微镜（SEM）观察样品微观形貌、聚焦离子束（FIB）和原子力显微镜（AFM）分析腐蚀后样品表面氧化膜。结果表明,Zr-Sn-Nb合金在α+β两相区温度下热处理时,锆合金中会形成条带状β-Zr第二相,再经过α相区温度最终退火后,β-Zr区域会分解为α-Zr和第二相粒子;经α相区最终退火的样品,在360 ℃/18.6 MPa纯水中的耐腐蚀性能优于未经最终退火的样品;未退火样品中条带状β-Zr第二相区域的氧化膜较α-Zr基体的氧化膜厚,而经过α相区温度退火后β-Zr发生分解,该区域的腐蚀氧化膜出现凹陷。     

用正电子湮没技术研究新锆合金包壳的离子辐照效应

国产Zr-Sn-Nb系新锆合金SZA-4和SZA-6是CAP1400大型先进压水堆包壳材料的主要候选材料,对其辐照性能的研究可为制备工艺改进提供科学依据。在中国原子能科学研究院HI-13串列加速器辐照终端,在300 ℃温度下,用100 MeV的Fe束流对两种新锆合金包壳管材进行5 dpa剂量辐照。辐照前后的正电子湮没寿命测量表明：两种样品辐照前湮没寿命为Zr中单空位寿命,表明管材制备过程中最后的退火温度和时间尚未完全消除加工引入的缺陷;两种样品辐照后的正电子湮没寿命减小,分析表明这是由于辐照导致Fe在锆合金中重新分布,主要分布在bcc结构的β-Nb沉淀相颗粒与hcp结构的α-Zr基体之间具有开空间的相界,正电子被相界捕获,与周围Fe原子电子湮没,造成湮没寿命减小。     

Zr-0.2Cu-xNb合金的显微组织及腐蚀行为

对Zr-0.2Cu-x Nb(质量分数x=0.2,0.5,1.0,2.5)合金进行真空β相油淬、冷轧及退火处理,并在静态高压釜中进行过热蒸汽腐蚀试验,最后采用扫描电镜和透射电镜研究了合金及其腐蚀生成的氧化膜的显微组织。结果表明,随着Nb含量的增加,Zr-0.2Cu-x Nb合金中Zr2Cu第二相的数量逐渐减少,而β-Zr第二相数量逐渐增加;合金中尺寸较小的Zr2Cu第二相对耐腐蚀性能有利;β-Zr第二相在氧化过程中会促进氧化膜微裂纹的产生,降低合金的耐腐蚀性能。Zr-0.2Cu-x Nb合金中Nb含量接近其在α-Zr中最大固溶度时,合金具有最优的耐腐蚀性能。     

热处理对U3Si—Al燃料板包壳显微组织及其厚度测量的影响

研究了ＬＴ２４铝合金的显微组织与热处理制度间的关系，模拟燃料板轧制加工时的热处理条件，研究了合金元素固溶或以第二相析出后对燃料板包壳的涡流测厚的影响，证明燃料板的最终退火温度波动或沿燃料板长度方向温度不均匀是造成燃料板包壳测厚误差的主要原因。建议燃料板最终退火的温度为３８０℃。     

最终退火温度对N36合金管材微观结构和性能的影响

为了对N36合金管材的微观结构和应用性能进行优化和调控,通过分析不同最终退火温度（520～560℃）下N36合金管材的性能数据,研究了最终退火温度对N36合金管材微观结构和性能的影响。经过研究发现,不同最终退火温度对于N36合金管材中的第二相粒子影响不大,主要影响N36合金管材的再结晶程度和晶粒尺寸,最终退火温度越高,则N36合金管材的再结晶程度越高,晶粒尺寸越大。随着最终退火温度升高,N36合金管材的室温和高温轴向和环向的强度明显降低,同时延伸率明显升高,主要是最终退火工艺对N36合金管材再结晶程度和晶粒尺寸的影响所造成的。随着最终退火温度升高,N36合金管材耐腐蚀性能提高,560℃最终退火温度的N36合金管材耐腐蚀性能明显优于其他管材,主要是560℃最终退火温度的N36合金管材再结晶程度最高所造成的。     

热处理对U_3Si_2－Al燃料板包壳显微组织及其厚度测量的影响

研究了ＬＴ２４铝合金的显微组织与热处理制度间的关系。模拟燃料板轧制加工时的热处理条件，研究了合金元素固溶或以第二相析出后对燃料板包壳的涡流测厚的影响。证明燃料板的最终退火温度波动或沿燃料板长度方向温度不均匀是造成燃料板包天测厚误差的主要原因。建议燃料板最终退火的温度为３８０℃。     

加工工艺对Zr-4合金管材氢化物取向的影响

着重研究了热加工制度,冷轧工艺,成品退火制度对Zr-4合金管材氢化物取向的影响。结果表明,再结晶退火的成品管材,铸锭经过淬火后,氢化物取向因子低于铸锭直接挤压的氢化物取向因子。本试验进行的四种冷轧工艺对氢化物取向因子影响不大。在合适的冷轧工艺条件下,清除应力退火的管材,氢化物取向因子非常少。氢化物几乎都沿着圆周方向分布。在现有的工艺条件下,成品管靠外壁的氢化物取向因子高于内壁的氢化物取向因子。     

加工工艺对Zr-4合金管材氢化物取向的影响

着重研究了热加工制度,冷轧工艺,成品退火制度对Zr-4合金管材氢化物取向的影响。结果表明,再结晶退火的成品管材,铸锭经过淬火后,氢化物取向因子低于铸锭直接挤压的氢化物取向因子。本试验进行的四种冷轧工艺对氢化物取向因子影响不大。在合适的冷轧工艺条件下,清除应力退火的管材,氢化物取向因子非常少。氢化物几乎都沿着圆周方向分布。在现有的工艺条件下,成品管靠外壁的氢化物取向因子高于内壁的氢化物取向因子。     

再加工对改进型N18板材第二相的影响

采用差热分析(DSC)、扫描电镜(SEM)和透射电镜(TEM)等多种研究手段系统地研究了改进型N18板材再加工(在750℃、780℃和800℃热轧3或4道次后再冷轧,冷轧后在540~600℃退火1.5~50 h)对第二相的影响。结果表明:热轧进入了双相区。在冷轧和随后的退火过程中,热轧过程中形成的β-Zr发生分解,析出细小的第二相,导致团簇状分布的细小第二相的形成;第二相为密排六方(HCP)的Zr(Fe,Cr,Nb)_2相。原板材中大部分第二相的合金元素原子百分比n(Fe)/[n(Cr)+n(Nb)]在5/3附近。再加工之后,n(Fe)/[n(Cr)+n(Nb)]呈现下降的趋势。团簇析出的细小第二相中Nb含量更高,n(Fe)/[n(Cr)+n(Nb)]接近1。     

N36锆合金管棒材第二相研究

利用扫描电子显微镜(SEM)和透射电子显微镜(TEM)及其能谱仪(EDS)附件,研究了N36锆合金成品管棒材中的第二相粒度、分布、成分及结构。结果表明,N36合金管材和棒材中的第二相平均尺寸差别不大,但二者的形貌及分布有较明显的差别。衍射及能谱分析表明,N36管棒材中的第二相主要为六方相的C14型Zr(Nb,Fe)_2 Laves相及少量的β-Nb,与文献报道的基本一致,但棒材中Laves相的Nb含量较低,晶格常数也较小。研究还表明,管材α-Zr基体中Nb含量与其固溶度较接近,质量百分数约为0.3%~0.4%,低于一般认为的0.6%。     

Effect of Heat Treatment in α+β Phase Field on Microstructure and Corrosion Property of Zr-Sn-Nb Alloy

Uniform corrosion tests were carried out with the specimens prepared by different heat treatments at the temperature in α+β phase field. The surface microstructure of specimens was observed by scanning electron microscope, the corrosion behavior was analyzed by autoclaves, and the oxide layer on the surface after the corrosion test was analyzed by focused ion beam (FIB) and atomic force microscope (AFM). The results show that after the heat treatment in α+β phase field, lamellar β-Zr phase appeares in the Zr matrix, and after the subsequent α phase final heat treatment, the β-Zr phase will be decomposed to α-Zr and discontinuous second phase particles. For the specimens heat treated in α+β phase field, after the α phase final heat treatment, the corrosion resistance under 360 ℃/18.6 MPa pure water condition is better than that of specimens without final heat treatment. The oxide film formed on the β-Zr protrudes on the oxide surface, on the contrary, after α phase final heat treatment, β-Zr decomposes, and the oxide layer is sunken in this area.     

Effect of low-temperature pre-deformation on precipitation behavior and microstructure of a Zr-Sn-Nb-Fe-Cu-O alloy during fabrication

The effect of low-temperature pre-deformation on the microstructural evolution of a Zr–Sn–Nb–Fe–Cu–O alloy was investigated by optical metallography, scanning electron microscope, transmission electron microscope, and electron backscattering diffraction (EBSD). It is found that a reasonably homogeneous and fine equiaxed grain structure with uniformly distributed second-phase particles (SPPs) can be obtained in 40% pre-deformed samples (Group A) but not in directly hot-rolled ones (Group B) after hot rolling. The initial SPPs diameter in Group A is also reduced. Noticeable differences in microstructural evolutions including the distribution and size of SPPs, grain size of matrix, and texture are observed between both groups. Reasons for such discrepancies are attributed to the defects (such as dislocations and interfaces) introduced during the pre-deformation and more preferred precipitation sites formed in Group A. The aging after the pre-deformation results in new slip systems activated during hot rolling, leading to more thorough refinement of grains. In addition, the growth of SPPs is interpreted by the Lifshitz–Slyozov–Wagner model.     

Evolution of microstructure and second-phase particles in Zr–Sn–Nb–Fe alloy tube during Pilger processing

Evolution of microstructure and second-phase particles (SPPs) in Zr–Sn–Nb–Fe alloy tube were investigated during Pilger process using electron backscatter diffraction, secondary electron and transmission electron microscopy imaging techniques. Results show that the Pilger rolled tubes present heterogeneous structures with the C axes of less deformed grains mostly concentrated in the axial direction. During the Pilger rolling, the increase of deformation caused weakening of linear distribution of second-phase particles. The mean diameters of the precipitates are in the range of 70–100 nm in all specimens, and the growth mechanism of SPPs follows second-order kinetics. The grain growth is controlled by Zener pinning in the Pilger rolling–annealing specimens. Clusters containing the Zr(Nb,Fe)₂ and β_Nb precipitates formed in the Zr–1.0Sn–1.0Nb–0.12Fe alloy. Most of the particles located in grain boundaries are the Zr(Nb,Fe)₂ Laves phase with hexagonal structure, and stacking faults have been found in the Zr(Nb,Fe)₂ precipitates. The types, morphology and distribution of precipitates depend on the constituent and structural fluctuations of the nucleation area.     

Towards a more comprehensive microstructural analysis of Zr-2.5Nb pressure tubing using image analysis and electron backscattered diffraction (EBSD)

Zr-2.5Nb pressure tubes used in CANDU (CANada Deuterium Uranium) reactors have a very complex microstructure, with two major crystallographic phases, α and β. These phases include a fair amount of deformation from the extrusion process and the cold working (∼25%) performed at the end of the manufacturing process. This microstructure (texture, grain aspect ratio, etc.) changes along the tube’s length and differs from tube to tube. In order to better understand the deformation mechanisms, these microstructural differences must be statistically characterized. Scanning electron microscopy combined with direct image analysis or with electron backscattered diffraction (EBSD) are good techniques for carrying out such a measurement. However it is not possible, using specimen preparation methods specific for each of these techniques, to reveal all of the grain and phase boundaries. We have thus developed post-treatment algorithms to be able to partially analyze the revealed Zr-2.5Nb microstructure. The first algorithm was used for image analysis treatments of micrographs taken at 5 kV on the radial-tangential plane of etched samples using a reactive ion etch (RIE, CF₄ + O₂). The second was developed for EBSD grain mapping and can be used to characterize α-Zr grain shape and orientation. The two techniques are complementary: EBSD gives information about the micro-texture and the relationship between the microstructure and micro-texture while image analyses of SEM micrographs reveal the direction and distribution of the α-Zr lamellae more easily and over a greater sample area than EBSD. However, the SEM micrographs that were used did not reveal any grain boundary (only phase boundary). An analysis of EBSD grain maps reveals that the average α-Zr grain size, mainly in the elongated direction (tangential), is smaller than what is normally obtained from an image analysis of SEM micrographs. The grain size distribution of type I α-Zr grains (deformed original (prior) α-Zr) and type II (stress-induced β-Zr → α-Zr phase transformation) is also shown to be different for sizes greater than 0.4 μm².     

The effect of alloying modifications on hydrogen uptake of zirconium-alloy welding specimens during corrosion tests

The hydrogen uptake behavior during corrosion tests for electron beam welding specimens made out of Zircaloy-4 and zirconium alloys with different compositions was investigated. Results showed that the hydrogen uptake in the specimens after corrosion tests increased with increasing Cr content in the molten zone. This indicated that Cr element significantly affected the hydrogen uptake behavior. Fe and Cr have a low solubility in α-Zr and exist mainly in the form of Zr(Fe,Cr)₂ precipitates, which is extremely reactive with hydrogen in its metallic state. It is concluded that the presence of Zr(Fe,Cr)₂ second phase particles (SPPs) is responsible for the increase in the amount of hydrogen uptake in the molten zone of the welding samples after corrosion, as Zr(Fe,Cr)₂ SPPs embedded in α-Zr matrix and exposed at the metal/oxide interface could act as a preferred path for hydrogen uptake.     

The dissolution of oxide on α-Zr(1%Nb) and β-Zr(20%Nb) alloys

The oxide dissolution rates on β-Zr(20%Nb) and α-Zr(1%Nb) alloys have been measured by AES at various temperatures. The results indicated that oxide films on the β-Zr(20%Nb) alloy dissolve much more rapidly into the bulk alloy than is the case for the α-Zr(1%Nb) alloy. The oxygen diffusion coefficients in both the β-Zr(20%Nb) and α-Zr(1%Nb) alloys were deduced from the oxide dissolution kinetics, which are 0.172 exp(−187.47 kJ/RT) and 0.69 exp(−149.45 kJ/RT) for the α-Zr(1%Nb) alloy and β-Zr(20%Nb) alloy, respectively.