Nb涂层N36锆合金退火过程中缺陷演化行为的原位透射电镜研究

福岛核事故之后,为锆合金表面涂覆涂层是一种提高核燃料包壳事故容错能力的重要方式。含Nb涂层N36合金辐照后的透射电镜样品利用聚焦离子束进行制备,并通过原位透射电子显微镜研究了氪离子注入后,Nb涂层在退火过程中的气泡生长行为。原位加热结果表明,在退火过程中,界面对气泡的生长存在影响,界面在加热过程中通过对周围气泡的捕获与输送,导致界面附近气泡的生长速度低于远离界面的气泡生长速度。退火后的元素分析表明,辐照与加热均会导致涂层-基体元素扩散距离的增加,其中辐照过程中的元素扩散由热峰混合机制主导。元素的扩散有助于提高涂层的结合性能,并为N36合金提供一定的抗腐蚀能力。     

Impact of He and Cr on defect accumulation in ion-irradiated ultrahigh-purity Fe(Cr) alloys

The effect of He on the primary damage induced by irradiation in ultrahigh-purity (UHP) Fe and Fe(Cr) alloys was investigated by transmission electron microscopy (TEM). Materials were irradiated at room temperature in situ by TEM in a microscope coupled to two ion accelerators, simultaneously providing 500 keV Fe⁺ and 10 keV He⁺ ions. Single Fe ion and dual Fe and He ion beam experiments were performed up to a dose of 1 dpa and to a He content of up to 1000 appm. Defects appear in the form of nanometric black dots with sizes between 1 and 5 nm. Defocused images reveal a dense population of sub-nanometric cavities after both single-beam and dual-beam irradiation. In Fe(Cr) alloys, the number densities of visible black dot defects still resolved in TEM are significantly higher after single than after dual-beam irradiation. In UHP Fe, conversely, the presence of He strongly increases the defect number density. The presence of He changes a a₀〈1 0 0〉 dominated defect population to a 1/2a₀〈1 1 1〉 dominated one in all materials, and the more so in UHP Fe. It appears that Cr increases the number of visible defects relative to UHP Fe. The dependence with increasing Cr content is weak, however, showing only a slight decrease in the number densities. The decrease in the density of visible a₀〈1 0 0〉 loops and increase in the visible 1/2a₀〈1 1 1〉 loops in all materials when He is present supports the idea that visible a₀〈1 0 0〉 loops are formed by the interaction between mobile 1/2a₀〈1 1 1〉 loops, as the latter would be immobilized by He already at sub-microscopic sizes. It is concluded that the primary loop population is dominated by 1/2a₀〈1 1 1〉 loops.     

New orthorhombic phase in U-Fe-Al-Si system

A new quaternary phase with the approximate composition U-18.6 at%Fe-29.2 at%Al-32.6 at%Si was observed in U-Fe-Al-Si system. The crystal structure of this phase was investigated by electron diffraction and X-ray powder diffraction techniques. It has an orthorhombic unit cell with lattice parameters a = 12.241 Å, b = 18.362 Å and c = 4.066 Å and can be described by the Immm space group.     

TiC/A1-4.5Cu原位复合材料的相结构特征

采用熔体接触反应法制备了TiC/Al-4.5Cu复合材料,通过光学显微镜、透射电镜等,对TiC颗粒增强Al-4.5Cu原位复合材料的相结构进行分析。结果表明,5%TiC/Al-4.5Cu原位复合材料的主要增强相为TiC;TiC弥散分布在α-Al基体中,与基体结合良好且界面光滑。在5%TiC/Al-4.5Cu原位复合材料中TiC呈球形或近球形,颗粒细小,其尺寸约为0.1～0.5μm;而在5%TiC/Al-4.5Cu-ХMg原位复合材料中TiC呈规则六边形,颗粒较大,其尺寸约为0.5～0.8μm。     

In situ Observation of Thermal Behaviour of Implanted He in Ti by Means of Enhanced Proton Elastic Backscatt

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The interdependence of structural and electrical properties in TiO2/TiO/Ti periodic multilayers

Multilayered structures with 14–50 nm periods composed of titanium and two different titanium oxides, TiO and TiO₂, were accurately produced by DC magnetron sputtering using the reactive gas pulsing process. The structure and composition of these periodic TiO₂/TiO/Ti stacks were investigated by X-ray diffraction and transmission electronic microscopy techniques. Two crystalline phases, hexagonal close packed Ti and face centred cubic TiO, were identified in the metallic-rich sub-layers, whereas the oxygen-rich ones comprised a mixture of amorphous TiO₂ and rutile phase. DC electrical resistivity ρ measured for temperatures ranging from 300 to 500 K exhibited a metallic-like behaviour (ρ_473K = 1.05 × 10^?5 to 1.45 × 10^?6 Ω m) with a temperature coefficient of resistance ranging from 1.20 × 10^?3 K^?1 for the highest period (Λ = 50.0 nm) down to negative values close to ?4.97 × 10^?4 K^?1 for the smallest one (Λ = 14.0 nm). A relationship between the dimensions of periodic layers and their collective electrical resistivity is proposed where the resistivity does not solely depend on the total thickness of the film, but also depends on the chemical composition and thickness of each sub-layer. Charge carrier mobility and concentration measured by the Hall effect were both influenced by the dimension of TiO₂/TiO/Ti periods and the density of ionized scattering centres connected to the titanium concentration in the metallic sub-layers.     

In Situ Transmission Electron Microscopy Observations of the Growth Process of Fe_3O_4–Ag Nanoparticles

The properties of nanocrystals are highly dependent on their morphology, composition and structure. To obtain full control over their properties, the behavior of nanocrystals under external stimuli, such as heat treatment, needs to be understood. Herein, to in situ observe their microstructure and morphology changes, Fe_3O_4–Ag heterodimers were selected as a model system. Their structural changes after heat treatment were investigated by in situ transmission electron microscopy. A combination of real-time imaging with elemental analysis enabled observation of the transformation of Fe_3O_4–Ag heterodimers having a loose interface configuration to those with a Janus structure at the atomic scale after heating from room temperature to 600 °C. After incubation at 600 °C for 32 min, two kinds of Janus structures could be seen, including a clear linear interface in the Fe_3O_4–Ag heterodimers and a semi-crescent-shaped interface between the Ag and Fe_3O_4 nanoparticles(NPs). These dynamic observations provide unique insights into NP growth mechanisms, which are essential for understanding and controlling the structure and morphology of nanoparticles.     

In situ TEM observation of grain annihilation in tricrystalline aluminum films

Capillarity-driven grain boundary (GB) motion in Al tricrystalline thin films has been investigated by in situ transmission electron microscopy at intermediate temperatures. The GBs were observed to move erratically, with alternating periods of motion and stagnation, followed by rapid shrinkage of the grain and eventual annihilation accompanied by the emission of dislocations. The absence of measured deformation and grain rotation during the GB motion suggests that it is not associated with shear-migration coupling. This is in contrast to observations on the stress-driven motion of planar GBs. The present results can be interpreted by the absence of deformation associated with low internal applied stress or alternatively by a low shear-migration coupling factor. In both cases, a large amount of atomic shuffling is needed to account for the migration of grain boundaries.     

Intrinsic and extrinsic size effects in the deformation of metallic glass nanopillars

Nanosized pillars with diameters ranging from 90 to 600 nm of four amorphous alloys, Cu₄₇Ti₃₃Zr₁₁Ni₆Sn₂Si₁, Zr₅₀Ti_16.5Cu₁₅Ni_18.5, Zr_61.8Cu₁₈Ni_10.2Al₁₀ and Al₈₆Ni₉Y_5, were fabricated and tested in situ in a transmission electron microscope. The major consideration when varying the composition was the change in bulk modulus and Poisson’s ratio, which may affect the deformation mode and ductility of metallic glasses (MGs) at the nanoscale. Differences between the deformation behavior of tapered (1.5-3°) and taper-free systems were also investigated. The yield stress of all the MGs measured through the in situ experiments is found to be essentially size independent, irrespective of tapering. With increasing size, all the MGs examined show a ductile-to-brittle transition under compression; the transition point, however, depends on the chemical composition of the specific MG investigated. The lower the μ/B ratio, the larger the pillar diameter above which more brittle behavior occurs. Al₈₆Ni₉Y₅ taper-free MG showed a transition threshold to brittle behavior at the largest pillar diameter of 300 nm. A micromechanical model is presented to explain the various dependencies.     

Formation of Face-Centered Cubic Phase in Ti35 Alloy Under In Situ Heating Transmission Electron Microscopy

A thermally induced hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition was investigated in an α-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy (TEM) and ab initio calculations. TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at the twin boundaries in the thinner region of the TEM film, and the FCC-Ti precipitated as plates within the matrix/twin, while as equiaxed cells at twin boundaries. The crystallographic orientation relationship between HCP-Ti and FCC-Ti can be described as: $\left\{ {111} \right\}_{{{\text{FCC}}}} //\left\{ {0002} \right\}_{{{\text{HCP}}}} \;{\text{and}}\; < 110 >\,_{{{\text{FCC}}}} //\, <1\overline{2} 10>\,_{{{\text{HCP}}}}$. The HCP to FCC phase transition was accomplished by forming an intermediate state with a BB stacking sequence through the slip of partial dislocations. The formation of such FCC-Ti may be related to the thermal stress and temperature. Ab initio calculations showed that the formation of FCC-Ti may also be related to the contamination of interstitial atoms such as oxygen.     

Contribution of core-loss fine structures to the characterization of ion irradiation damages in the nanolaminated ceramic Ti3AlC2

The effect of low-energy ion irradiation on the nanolaminated Ti₃AlC₂ is investigated by means of X-ray diffraction, transmission electron microscopy, electron energy loss and X-ray absorption spectroscopy. The chemical sensitivity and local order probing from core-loss edges provide new insights into the structural modifications induced under irradiation. From the analysis of the C K energy loss near-edge structure and Al K X-ray absorption near-edge structure by ab initio calculations, the influence of the layered structure of this compound on the irradiation damage is demonstrated, and damage is found to be preferentially localized in the aluminum planes of the structure. On the basis of comparisons between calculations and experimental spectra, a structural model is proposed for the irradiated state. This study emphasizes the utility of core-loss fine structure analysis to enhance understanding of ion irradiation-induced damage in complex crystalline materials.     

Direct TEM Observation of Phase Separation and Crystallization in Cu_(45)Zr_(45)Ag_(10)Metallic Glass

The structural evolution of Cu_(45)Zr_(45)Ag_(10) metallic glass was investigated by in situ transmission electron microscopy heating experiments. The relationship between phase separation and crystallization was elucidated. Nucleation and growth-controlled nanoscale phase separation at early stage were seen to impede nanocrystallization, while a coarser phase separation via aggregation of Ag-rich nanospheres was found to promote the precipitation of Cu-rich nanocrystals.Coupling of composition and dynamics heterogeneities was supposed to play a key role during phase separation preceding crystallization.     

He ion irradiation induced nanocrystallization in Cu50Zr45Ti5 glassy alloy

Partial nanocrystallization induced by ion irradiation can be used to improve the surface properties in metallic glasses. We investigated the crystallization behavior and the structure of the formed nanocrystalline phases in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy irradiated with 140 keV He ions to a fluence of 1.7 × 10¹⁷/cm². Crystalline nanoparticles were precipitated by He ion irradiation. The nanocrystalline phases were identified as a mixture of the orthorhombic Cu₁₀Zr₇ phase, tetragonal CuZr₂ phase and monoclinic CuZr phase. Hardness enhancement was observed at a depth close to the projected range of the He ions, which was related to the formation of the crystalline nanoparticles.     

Structural stability of Nd2Zr2O7 pyrochlore ion-irradiated in a broad energy range

The phase transformations induced by electronic excitation (S_e) and ballistic processes (S_n) in Nd₂Zr₂O₇ pyrochlores irradiated with heavy ions in three domains of energy (～1 GeV, ～100 MeV and a few MeV) were investigated by X-ray diffraction, Raman spectroscopy and transmission electron microscopy. In the S_e regime at high energy, results show that: (i) ion tracks are formed above a S_e threshold of 12.5 keV nm^?1; (ii) both pyrochlore → anion-deficient fluorite phase transition and amorphization occur; (iii) total amorphization is always observed at the highest fluences; (iv) the internal structure (amount of amorphous phase vs. its anion-deficient fluorite counterpart) and the diameter of tracks depend on many parameters such as S_e, the deposited energy density and the recrystallization rate. For irradiations performed with low-energy ions in the S_n regime, only the anion-deficient fluorite phase is formed up to a dose of 40 dpa. Thus Nd₂Zr₂O₇ exhibits an unusual behaviour since this compound is amorphizable by S_e and non-amorphizable by S_n. Annealing of totally amorphized Nd₂Zr₂O₇ samples reveals strong differences in the recovery processes with other pyrochlore materials that are related to their different chemical compositions.     

Investigations of the redox process of conducting poly(2-methyl-5-amino-1,4-naphthoquinone) (PMANQ) film Interactions of quinone–amine in the polymer matrix

Poly(2-methyl-5-amino-1,4-naphthoquinone) (PMANQ) film is a new functionalized conducting polymer having two distinct redox systems. The polymer structure is of the polyaniline-type, bearing one methylquinone group per monomer unit. The redox mechanisms of PMANQ were investigated by in situ multiple internal reflection Fourier transform infrared spectroscopy (MIRFTIRS) and electrochemical quartz crystal microbalance (EQCM). It is shown that interactions occur between quinone and amine groups in the polymer chain.     

Synthesis, characterization, magnetic and electrical properties of the novel conductive and magnetic Polyaniline/MgFe2O4 nanocomposite having the core-shell structure

Conductive and magnetic Polyaniline/MgFe₂O₄ nanocomposite was successfully synthesized in the form of core-shell via in situ chemical polymerization of aniline in the presence of MgFe₂O₄ nano-particles. X-ray powder diffraction of ferrites indicated that the structure of the core material is having the spinel structure, and demonstrated the formation of PAni/MgFe₂O₄ nanocomposite. XRD and TEM photographs showed that the particle's size of the MgFe₂O₄ core-material were around 30-35 nm before coating with Polyaniline, and grown up to 45 nm in the core-shell nanocomposite after coating. Although PAni has a relatively smaller electrical field coefficient than the core-shell nanocomposite, the resistivity of the core-shell material decreased, and hence its conductivity increased after a certain threshold voltage of 0.98 V equivalent to threshold electric field value equals 5.5 V cm⁻¹. The magnetic hysteresis loops investigated with VSM indicated that coating MgFe₂O₄ with Polyaniline has an healing effect which covers the ferrite surface defects, thus decreasing the magnetic surface anisotropy of ferrite particles leading to a decrease of the saturated magnetization (Ms) from 21.33 emu/g to 5.905 emu/g and a decrease of the coercivity (Hc) from 88.66 Oe to 81.6 Oe for MgFe₂O₄ and the core-shell nanocomposite respectively due to the amount of Polyaniline added. TGA and DTA revealed improved thermal stability of the core-shell nanocomposite with respect to that of Polyaniline due to the incorporation of ferrites. Raman spectroscopy confirmed TGA, DTA and XRD studies, and revealed that pure PAni is less stable than the corresponding core-shell nanocomposite with respect to molecular changes which might occur during heating at elevated temperatures. Moreover, Raman study confirmed the interfacial interaction between the core and the shell materials, and lead to an assumption about the presence of different conjugation chain lengths and types, such as the presence of the semi-quinones aside the quinone rings in the polymer chain, which showed different response upon heating the sample.     

Stability evaluation of fluorite structure phases in ZrO2-MO2 (M=Th, U, Pu, Ce) systems by thermodynamic modelling

Thermodynamic modelling was demonstrated for ZrO₂-ThO₂ system based on the data for the ZrO₂-UO₂ and ZrO₂-CeO₂ systems in the literature. The calculated phase diagram for the ZrO₂-ThO₂ system showed a good agreement with the experimental data in the literature. Using the data obtained, together with the data for ZrO₂-UO₂, ZrO₂-PuO₂ and ZrO₂-CeO₂ systems, the stability of the fluorite structure phases in the ZrO₂-MO₂ (M=Th, U, Pu, Ce) systems was also studied with respect to the partial molar quantities. The effect of the ZrO₂ on the enthalpy in the MO₂ rich region increased as the cation size of the matrices decreased. The solubility limits of the ZrO₂ in the fluorite structure phase in this region also increased as the cation size of the matrix decreased. The effect of MO₂ on the partial molar Gibbs energy in the ZrO₂ rich region increased as the cation size of the MO₂ increased. It implies that the dissolution of the larger cation stabilises the fluorite structure of the ZrO₂ more.     

SiO_2与液态Al反应生成Al_2O_3/Al复合材料的研究

采用SiO2 粉与液态Al反应制备Al2 O3 /Al复合材料 ,讨论了SiO2 的加入量、反应温度、反应时间对反应速度的影响 ,分析了不同反应温度和保温时间下生成复合材料的微观结构。试验证明 :当SiO2 含量较低时 ,SiO2 与Al发生完全反应 ,形成均匀Al2 O3 /Al复合层 ;当w(SiO2 )达一定量时 ,反应速度反而降低 ;保温时间为 6～ 8h,反应速度最快 ,之后变慢