Transmission electron microscopy investigations of ordered Zr3Al

Zr₃Al is an ordered fcc alloy of the L1₂ type. The ordered phase appears to be very stable thermally as it has not been possible to disorder Zr₃Al by quenching. It is possible, however, to disorder Zr₃Al by irradiation. In deformed Zr₃Al the superlattice dislocations were observed to be extended, i.e. they consisted of intrinsic stacking faults on {111} bounded by partial dislocations. _ The total Burgers vector is of the type <110> and the superlattice dislocations have dissociated as follows: $\text{«110}\text{a}\text{?}\text{> →}\text{1}\text{3}\text{«211}\text{a}\text{?}\text{> +}\text{1}\text{3}\text{«12}\text{1}\text{?}\text{a}\text{?}\text{>}$. During high-temperature annealing of the deformed material, dislocation networks were produced in which all of the dislocation nodes were extended; hence intrinsic and extrinsic stacking faults must alternate at the nodes. Weak beam images were obtained of long and relatively straight dislocation lines in annealed Zr₃Al in order to obtain information on the equilibrium width of the extended dislocations.     

A study of the irradiation behaviour of Zr3Al

Zr₃Al is an ordered f.c.c. alloy of the L1₂ type. In this investigation, the stability of the ordered phase when subjected to Ar⁺ ion bombardment was explored using transmission electron microscopy. At low ion fluences (up to 10¹² ions/cm²) individual damaged regions were observed. Imaging with fundamental reflections revealed those regions having a spherically symmetrical strain field whereas imaging with superlattice reflections also revealed disordered regions. At ion fluences above 10¹² ions/cm² overlap of the damage regions occurred thus resulting in a complex damage configuration. In the fluence regime 5 × 10¹⁴ to 1 × 10¹⁶ ions/cm², complete disordering of Zr₃Al initially occurred and this was followed by complete transformation to the amorphous state. The fluence required to reach a particular disordered state and degree of amorphicity was dependent upon the amount of annealing which occurred within the defect cascade at the temperature of the bombardment.     

The notch-sensitivity of ordered Zr3Al

Experiments using notched tensile specimens have established that ordered Zr₃Al is inherently notch sensitive. The notchsensitivity ratio, NSR, increases from ?0.7 at temperatures ?435 K to ～-0.9 at temperatures ?575 K. Grain size and trace alloying with boron have negligible effects on the results. Neutron irradiation, on the other hand, suppresses notch-sensitivity and causes notch-strengthening. The NSR data are correlated with fracture mechanisms.     

Irradiation swelling of Zr3Al

Heavy ion (0.5–2 MeV Ar⁺) and 1 MeV electron irradiation of Zr₃Al have established that the lattice parameter is increased by ~0.5% upon irradiation disordering and that the specific volume is increased by ($\text{5 ± 1}$) % following an irradiation-induced crystalline to amorphous transformation. These effects have been incorporated into a quantitative model of irradiation swelling which is shown to be in reasonable qualitative and quantitative agreement with fast-neutron induced dimensional changes in Zr₃Al. The model predicts that swelling will saturate and that the largest changes will occur at low temperatures.     

Plastic flow of ordered Zr3Al

Room-temperature tensile experiments established that ordered Zr₃Al of the Ll₂ type obeys the relationship $\text{σ}{}_{\mathrm{?}}\text{= σ}{}_{\mathrm{0,?}}\text{+ kd}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ where σ_? is the flow stress at a given strain ?, σ_0,? is a strain-dependent frictional stress, $\text{d}$ is the average grain diameter, and $\text{k}$ is a strain-independent constant of magnitude $\text{(2.8 ± 0.3) kg/mm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$. Zr₃Al flows by fine, planar slip, and is susceptible to intergranular cracking.     

Characteristics of the electron-emission defects introduced in Si-SiO2 structures by MeV electron irradiation

Defects induced by high-energy electrons in Si-SiO₂ structure have been studied by the optically stimulated electron emission (OSEE) method. Si-SiO₂ structures with oxide thickness of 100 nm are irradiated with 23 MeV electrons for different durations. It is shown that most of the defects created by electron irradiation at the interface and in the oxide bulk are vacancies like E′-centers. Most of the photoemission activity changes are observed during low doses electron irradiation. Some uncharged defects like diamagnetic oxygen-deficient centers are also observed, together with E′-centers.     

Channeling simulation in Ni3Al

Measurements using ion channeling and Rutherford backscattering have indicated that Hf and Ta dopants in ordered Ni₃Al alloys are located predominately on the Ni sites. Because other experiments have indicated the dopants to be on the Al sites, computer simulations of the ion channeling and scattering processes have been performed to see whether some unusual factor could lead to erroneous conclusions when the standard methods to interpret channeling results are used. Consideration has been given to the effects of a higher average charge on the Al sites if high Z dopants are located there, to the effects of displacement amplitudes for the dopants that differ from those of the host atoms, and to the effects of mosaic spread in the crystal. It is concluded that the most straightforward way to interpret the ion scattering results is that the Hf and Ta are mostly on the Ni sites in the alloys. However, it appears that the impurities could be mostly on the Al sites if the impurity atoms have a substantially smaller displacement amplitude than do the host atoms in the alloys.     

Atomic structure and disordering induced by 350 MeV Au ions in MgAl2O4

Microstructure change and atomic disordering in MgO · nAl₂O₃ (n = 1.1) irradiated with 350 MeV Au ions (S_e = 35 keV/nm) were investigated through transmission electron microscopy (TEM) and high angular resolution electron channeling X-ray spectroscopy (HARECXS) techniques. High resolution TEM revealed that each ion track maintains crystalline structure. The core region of ion track is found to reveal a lattice fringe with a half period of spinel matrix, suggesting the phase transformation from spinel to rock-salt structure. HARECXS analysis clearly showed progress of cation disorder at a significantly large region of 10 nm in diameter. These results are compared with the previous results of 200 MeV Xe ion irradiated spinel (S_e = 25 keV/nm). The structure of ion tracks is found to consist of three concentric circle structures: the defective core region (2 nm in diameter), strained region (5 nm) and cation disordered region (10–12 nm).     

Oxidation of stoichiometric Zr3Al-based alloy

Stoichiometric Zr₃ Al-based alloy consisting of α-Zr(Al) and Zr₃Al phases has been exposed isothermally to dry oxygen at temperatures of 701–828 K. Cubic ZrO₂ was formed below 750 K, above that temperature monoclinic ZrO₂ appeared beside the cubic phase. The α-Zr(Al) phase was found to be more reactive than Zr₃Al. Oxidation obeys a parabolic rate law, with an activation energy of 161.95 kJ.     

The tensile and corrosion behaviour of ordered Zr3Al-based alloys

Polyphase alloys based on ordered Zr₃Al (Ll₂ type) have been deformed in tension at 20 to 600°C and exposed to moist air (300°C), pressurized water (300°C) and atmospheric pressure steam (400°C). Certain alloys display a uniform elongation of 25 to 30% before failure, an ultimate tensile strength at 300°C of 1120 MN/m² (160 000 psi), and an oxidation rate of 1.2 mg/dm² d day in atmospheric steam at 400°C. For good ductility a requirement is the absence (or at least a fine distribution) of Zr₂Al, an intermetallic phase which may remain following the transformation $\text{Zr + Zr}{}_2\text{Al → Zr}{}_3\text{Al}$. Similarly, a requirement for corrosion resistance is the absence (or at least a fine distribution) of the highly corrodible α-Zr(Al) phase. At low temperatures yield appears to be controlled by long-range, internal stresses. Failure occurs suddenly, suggesting that a critical fracture stress exists.     

Ion irradiation induced nanocrystal formation in amorphous Zr55Cu30Al10Ni5 alloy

Ion irradiation can be used to induce partial crystallization in metallic glasses to improve their surface properties. We investigated the microstructural changes in ribbon Zr₅₅Cu₃₀Al₁₀Ni₅ metallic glass after 1 MeV Cu-ion irradiation at room temperature, to a fluence of 1.0 × 10¹⁶ cm⁻². In contrast to a recent report by others that there was no irradiation induced crystallization in the same alloy [S. Nagata, S. Higashi, B. Tsuchiya, K. Toh, T. Shikama, K. Takahiro, K. Ozaki, K. Kawatusra, S. Yamamoto, A. Inouye, Nucl. Instr. and Meth. B 257 (2007) 420], we have observed nanocrystals in the as-irradiated samples. Two groups of nanocrystals, one with diameters of 5–10 nm and another with diameters of 50–100 nm are observed by using high resolution transmission electron microscopy. Experimentally measured planar spacings (d-values) agree with the expectations for Cu₁₀Zr₇, NiZr₂ and CuZr₂ phases. We further discussed the possibility to form a substitutional intermetallic (Ni_xCu_1−x)Zr₂ phase.     

6 MeV electron irradiation effects on electrical properties of Al/TiO2/n-Si MOS capacitors

The irradiation effects of 6 MeV electrons on the electrical properties of Al/TiO₂/n-Si metal-oxide-semiconductor capacitors have been investigated. Nine Al/TiO₂/n-Si capacitors were fabricated using radio frequency magnetron sputtering and divided into three groups. Groups were irradiated with 6 MeV electrons at 10, 20, and 30 kGy doses, respectively, keeping the dose rate ∼1 kGy/min. The variations in the capacitance-voltage and leakage current-voltage characteristics, in addition to the electrical parameters, such as conductance (G/ω), flat-band voltage, interface trap density and the surface charge density with electron dose were studied. The Poole-Frenkel coefficient of the MOS capacitors was determined from current-voltage characteristics. Possible mechanisms for the enhanced leakage current in the electron irradiated MOS capacitors are discussed.     

Effect of 4MeV electron beam irradiation on carbon films

Pulsed KrF excimer laser is used to deposit tetrahedral amorphous carbon (ta-C) thin films on Si (1 1 1) single crystal substrates at room temperature under vacuum ∼10⁻⁶ mbars. The pristine deposited films are then irradiated by 4 MeV electron beam at doses varying from 1000 to 4000 cGy. Analysis through AFM illustrates that the irradiation of electron has induced cluster formation on the film surface and increased the surface roughness. Optical properties (n, α and Tauc optical band gap) measured by spectroscopic ellipsometry and electrical resistivity measured by four probe technique are found to depend strongly on electron dose. High electron doses cause significant alteration in order/disorder or sp² states in the film which is the main cause of modifying band gap in the carbon films. The electrical conductivity of the films also increases by increasing electron dose which is due to tunneling of charge carriers through neighbouring conductive chains. The present electron irradiation process at varying electron doses proved to be successful to modulate the optical and electrical properties of carbon films.     

Formation of planar waveguide in BiB3O6 crystal by MeV carbon implantation

Non-leaky planar waveguide structure has been fabricated in x-cut BiB₃O₆ crystal by 6 MeV C³⁺ ion implantation at a dose of 1 × 10¹⁴ ions/cm². The effective refractive indices of the waveguide are measured at a wavelength of 632.8 nm. We perform a computer code based on the finite difference method to reconstruct the refractive index profiles of n_x and n_y of this waveguide. The beam propagation method is used to calculate the electric and magnetic field profiles in the waveguide region from the reconstructed refractive index profiles. Our simulated data show that the refractive index increased waveguide layer can confine the mode completely.     

氦-3对Zr0.85Ti0.15Co合金吸氚特性影响研究

通过铀床向Zr_0.85Ti_0.15Co床转移氚过程中,研究氦-3对Zr_0.85Ti_0.15Co合金吸氚特性的影响,并结合Ortman模型分析氦-3影响机理。结果表明：氦-3对床体的屏蔽效应明显影响粉末的吸附性能,但屏蔽效应并不能完全抑制Zr_0.85Ti_0.15Co的吸氚反应,覆盖现象严重时其仍能在较低的速率持续吸氚直至吸附完全;氦-3浓度较低时,吸氚完成时间主要由氦-3浓度影响,而氦-3浓度较高时,主要由初始氚分压影响;氦-3对Zr_0.85Ti_0.15Co吸氚的屏蔽过程分为整体流阶段和扩散散流阶段,Ortman模型可较好的预测整体流阶段的氦-3屏蔽压强。     

8 MeV electron irradiation effects in silicon photo-detectors

Results of investigations on the electrical properties of n⁺-p-p⁺ silicon (Si) photo-detectors irradiated with 8 MeV electrons are presented. The photo-detectors were irradiated with electrons of doses up to 100 kGy. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics under dark conditions were measured as a function of dose. A significant change in the diffusion component of the saturation current is observed after irradiation, while the generation-recombination component of the saturation current remains almost unchanged. The series resistance is found to increase with increasing dose while the shunt resistance and carrier concentration decrease with dose. Optoelectronic properties, namely short circuit current I_sc, open circuit voltage V_oc under air mass zero illumination and spectral response, were measured at various doses. From the spectral responses of the devices, the minority carrier diffusion length was estimated.     

Dislocation loop nucleation and growth in zirconium-2.5 wt% niobium alloy during 1 MeV electron irradiation

A high voltage electron microscope has been used to study loop formation in thin foils of Zr, Zircaloy and two Zr-Nb alloys. The effects of varying irradiation temperature and displacement dose were examined in the light of nucleation and growth theories. It was found that Nb solute enhanced loop densities by up to more than an order of magnitude but loop growth at 773 K was more than proportionately retarded so that total point defect precipitation is diminished. The temperature dependence of loop density corresponds to an activation energy 0.36 eV with <0.1 eV solute binding.     

The 3 MeV/6 MeV Electron Linac Embraces First Export

正A 3 MeV/6 MeV Electron Linear Accelerator(Linac)developed independently by CIAE was exported overseas on 14 May,2018.The Linac used for Non Destructive Testing(NDT)is a dual energy(3 MeV/6 MeV)accelerator which can switch between 3 MeV and6 MeV in milliseconds.With widest energy band,it has been one of the most advanced accelerators