Elastic and plastic properties of βZr at room temperature

Room temperature elastic and plastic properties of a single phase β_Zr have been studied by in-situ neutron diffraction compression testing. The measured macroscopic Young’s modulus is ∼60 GPa and the yield strength is ∼500 MPa. Dislocation slip is the major mode of plastic deformation. An Elasto-Plastic Self-Consistent (EPSC) model was used to interpret the experimental results and was shown to be effective in extracting the single crystal properties from the polycrystalline data. The single crystal elastic constants of the β-phase are determined as: C₁₁ = 145.9 ± 2.6 GPa, C₁₂ = 117.4 ± 2.5 GPa and C₄₄ = 29.8 ± 0.2 GPa. The calculated elastic modulus of 〈1 0 0〉, 〈1 1 0〉, 〈1 1 1〉, 〈2 1 1〉 and 〈3 1 0〉 directions was ∼41.2, 66.2, 82.9, 66.2 and 47.7 GPa, respectively. Pencil glide on the {110}, {112} and {123} planes was used in the EPSC model and gave a good simulation to the early part of the plastic deformation. The average β-phase strain is best represented by the peak average method, while in cases where only a limited number of diffraction peaks are available, the {211} grain family is a good candidate for estimation of the average β-phase strain.     

Ideal mechanical properties of vanadium by a first-principles computational tensile test

We employ first-principles total energy method based on the density functional theory with the generalized gradient approximation to investigate the ideal tensile strengths of a bcc vanadium (V) single crystal systemically. The ideal tensile strengths are calculated to be 19.1, 32.8 and 31.0 GPa for bcc V in the [1 0 0], [1 1 0] and [1 1 1] directions, respectively. We show that the [0 0 1] direction is the weakest direction due to the occurrence of structure transition at the lower strain and the [1 1 0] direction is strongest because of the stronger interaction of atoms between the (1 1 0) planes in comparison with the (0 0 1) and (1 1 1) planes. We derive the Young’s modulus formula V single crystal in different tensile directions and give detailed analysis. According to the elastic constants of V single crystal, we have estimated some mechanical quantities of polycrystalline V, which are the bulk modulus of B, the shear modulus of G, Young’s modulus of E and the Poisson’s ratio of ν. The results might provide a useful reference for V as a candidate structural material in the fusion Tokamak.     

TRISO coated fuel particles with enhanced SiC properties

The silicon carbide (SiC) layer used for the formation of TRISO coated fuel particles is normally produced at 1500-1650 °C via fluidized bed chemical vapor deposition from methyltrichlorosilane in a hydrogen environment. In this work, we show the deposition of SiC coatings with uniform grain size throughout the coating thickness, as opposed to standard coatings which have larger grain sizes in the outer sections of the coating. Furthermore, the use of argon as the fluidizing gas and propylene as a carbon precursor, in addition to hydrogen and methyltrichlorosilane, allowed the deposition of stoichiometric SiC coatings with refined microstructure at 1400 and 1300 °C. The deposition of SiC at lower deposition temperatures was also advantageous since the reduced heat treatment was not detrimental to the properties of the inner pyrolytic carbon which generally occurs when SiC is deposited at 1500 °C. The use of a chemical vapor deposition coater with four spouts allowed the deposition of uniform and spherical coatings.     

Dynamic Young’s moduli of tungsten and tantalum at high temperature and stress

Recently reported results of the long lifetime of the tungsten samples under high temperature and high stress conditions expected in the Neutrino Factory target have strengthened the case for a solid target option for the Neutrino Factory. In order to study in more detail the behaviour of the material properties of tungsten, a dynamic method has been used for measurement of Young’s modulus at high stress, high-strain-rates (>1000 s⁻¹) and very high temperatures (up to 2650 °C). The method is based on measurements of the surface vibration of thin wires, stressed by a pulsed current, using a Laser Doppler Vibrometer. The measured characteristic frequencies under the thermal excitation have been used to obtain Young’s modulus as a function of applied stress and temperature. The same procedure has been used to measure Young’s modulus of tantalum up to 2500 °C.     

Fabrication and mechanical characterization of zirconium and gadolinium hydrides

We prepared three kinds of metal hydrides: Zr hydrides, Gd hydrides, and the hydrides of Zr-Gd alloys (Zr:Gd = 10:1, 8:1, 6:1), and characterized their mechanical properties. It was confirmed that the hydrides of Zr-Gd alloys were composed of Zr hydrides and Gd hydrides mixtures. We evaluated the Vickers hardness and the Young’s modulus of the hydrides. We succeeded in proposing empirical equations describing the density, Vickers hardness, and Young’s modulus of the hydrides of Zr-Gd alloys, as functions of the hydrogen content and the Gd content.     

Development of a high intensity Al beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of ^26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced ^26gAl beam intensities of 5.1 × 10¹⁰ s⁻¹.     

Experimental studies of mechanical properties of solid zirconium hydrides

Zirconium alloy Zr-2.5Nb has been hydrided to ZrH_x (x = 1.15-2.0), and studied using microhardness and unconfined and confined compression techniques. At room temperature, results on Young’s modulus and yield strength of solid hydrides show that these mechanical properties remain about the same as the original zirconium alloy for hydrogen compositions up to about ZrH_1.5. The levels of these properties start to drop when δ hydride becomes the major phase and reaches a minimum for the ε hydride phase. Between room temperature and 300 °C, Young’s modulus of solid hydrides decreases with temperature at about the same rate as it does for the original zirconium alloy.     

Thermophysical properties of (U,Y)O2

We prepared polycrystalline pellets of (U,Y)O₂, containing YO_1.5 up to 11 mol.%. We performed indentation tests on the pellets, and evaluated the Young’s modulus and hardness. We measured the heat capacity and the thermal diffusivity, and evaluated the thermal conductivity. We succeeded in evaluating the effect of Y content on the thermophysical properties of (U,Y)O₂. We revealed that the Young’s modulus, hardness, and thermal conductivity of (U,Y)O₂ decreased with increasing the Y content.     

Oil palm empty fruit bunch (OPEFB) fiber reinforced PVC/ENR blend-electron beam irradiation

The effect of irradiation on the tensile properties of oil palm empty fruit bunch (OPEFB) fiber reinforced poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) blends were studied. The composites were prepared by mixing the fiber and the PVC/ENR blend using HAAKE Rheomixer at 150 °C. The composites were then irradiated by using a 3.0 MeV electron beam machine at doses ranging from 0 to 100 kGy in air and room temperature. The tensile strength, Young’s modulus, elongation at break and gel fraction of the composites were measured. Comparative studies were also made by using poly(methyl acrylate) grafted OPEFB fiber in the similar blend system. An increase in tensile strength, Young’s modulus and gel fraction, with a concurrent reduction in the elongation at break (Eb) of the PVC/ENR/OPEFB composites were observed upon electron beam irradiation. Studies revealed that grafting of the OPEFB fiber with methyl acrylate did not cause appreciable effect to the tensile properties and gel fraction of the composites upon irradiation. The morphology of fractured surfaces of the composites, examined by a scanning electron microscope showed an improvement in the adhesion between the fiber and the matrix was achieved upon grafting of the fiber with methyl acrylate.     

Development of refractory armored silicon carbide by infrared transient liquid phase processing

Tungsten (W) and molybdenum (Mo) were coated on silicon carbide (SiC) for use as a refractory armor using a high power plasma arc lamp at powers up to 23.5 MW/m² in an argon flow environment. Both tungsten powder and molybdenum powder melted and formed coating layers on silicon carbide within a few seconds. The effect of substrate pre-treatment (vapor deposition of titanium (Ti) and tungsten, and annealing) and sample heating conditions on microstructure of the coating and coating/substrate interface were investigated. The microstructure was observed by scanning electron microscopy (SEM) and optical microscopy (OM). The mechanical properties of the coated materials were evaluated by four-point flexural tests. A strong tungsten coating was successfully applied to the silicon carbide substrate. Tungsten vapor deposition and pre-heating at 5.2 MW/m² made for a refractory layer containing no cracks propagating into the silicon carbide substrate. The tungsten coating was formed without the thick reaction layer. For this study, small tungsten carbide grains were observed adjacent to the interface in all conditions. In addition, relatively large, widely scattered tungsten carbide grains and a eutectic structure of tungsten and silicon were observed through the thickness in the coatings formed at lower powers and longer heating times. The strength of the silicon carbide substrate was somewhat decreased as a result of the processing. Vapor deposition of tungsten prior to powder coating helped prevent this degradation. In contrast, molybdenum coating was more challenging than tungsten coating due to the larger coefficient of thermal expansion (CTE) mismatch as compared to tungsten and silicon carbide. From this work it is concluded that refractory armoring of silicon carbide by Infrared Transient Liquid Phase Processing is possible. The tungsten armored silicon carbide samples proved uniform, strong, and capable of withstanding thermal fatigue testing.     

Deposition of zirconium carbonitride composite films using ion and electron beams emitted from plasma focus device

Nanocrystalline zirconium carbonitride (ZrCN) composite films were deposited on zirconium substrates for multiple (10, 20, 30, 40 and 50) focus shots. X-ray diffraction analysis shows diffraction peaks corresponding to nitrides (ZrN, Zr₂N and Zr₃N₄), carbide (ZrC) and carbonitride (Zr₂CN), confirming the formation of ZrCN composite films. The average crystallite size estimated for ZrN (2 0 0) and Zr₂CN (1 1 1) planes are found to vary from 10 to 20 nm. Maximum compressive stresses of ∼3.9 GPa in Zr₂N (0 0 2) plane for 30 focus shots and maximum tensile stresses of ∼6.5 GPa in ZrN (2 0 0) plane for 20 focus shots are observed. Tensile stresses observed in Zr₂CN (1 1 1) plane are transformed to compressive stresses for higher (40 and 50) focus shots. Raman analysis reveals the emergence of D and G bands related to carbide phases during the film deposition process. Scanning electron microscope analysis exhibits the nanocrystalline microstructure patterns of the composite films. Microstructure patterns showing agglomerates of 30-300 nm dimensions are also observed. Microhardness values of ZrCN composite films increases with increasing number of focus shots and is equal to 5.6 ± 0.45 GPa for 10 g imposed load, which is 4.5 times that of the virgin one.     

Molecular dynamics evaluation of the impact of Ga, He, and vacancy concentration on the mechanical properties of Ga-stabilized δ-Pu

The effects of self-irradiation on the mechanical properties of Ga-stabilized δ-Pu are investigated by means of classical molecular dynamics simulations using a modified embedded-atom method interatomic potential. The impact that variations in the concentration of Ga, He, and vacancies have on the elastic properties (Young’s modulus, Poisson’s ratio, shear modulus, and bulk modulus) of Ga-stabilized δ-Pu is determined through CMD simulation. The effect that variations in these concentrations have on plastic flow is assessed at strain rates of 10⁷-10¹⁰ s⁻¹. Comparison is made to experimental data.     

Formation of Si/SiC multilayers by low-energy ion implantation and thermal annealing

Si/SiC multilayer systems for XUV reflection optics with a periodicity of 10-20 nm were produced by sequential deposition of Si and implantation of 1 keV ions. Only about 3% of the implanted carbon was transferred into the SiC, with a thin, 0.5-1 nm, buried SiC layer being formed. We investigated the effect of thermal annealing on further completion of the carbide layer. For the annealing we used a vacuum furnace, a rapid thermal annealing system in argon atmosphere, and a scanning e-beam, for different temperatures, heating rates, and annealing durations. Annealing to a temperature as low as 600 °C resulted in the formation of a 4.5 nm smooth, amorphous carbide layer in the carbon-implanted region. However, annealing at a higher temperature, 1000 °C, lead to the formation of a rough poly-crystalline carbide layer. The multilayers were characterized by grazing incidence X-ray reflectometry and cross section TEM.     

Effects of gamma irradiation and post-irradiation annealing on carbon/epoxy UDC properties deduced by methods of local loading

Hardness and Young’s modulus of the matrix and fibers in carbon/epoxy gamma irradiated and annealed composites were investigated using nanoindentation technique. The Vickers microhardness of the tested composites after irradiation and annealing was studied, as well. Gamma irradiation to various doses (5-27 MGy) of UDC plates, were followed by thermal treatments of irradiated coupons at 180 and 250 °C, in vacuum. The measured changes of nano and micro properties were correlated to glass transition temperatures, as well as the delamination toughness changes, determined earlier on the same material. The established irradiation and annealing effects on nanoindentation properties and Vickers mocrohardness were analyzed as a function of the matrix plasticity change. An attempt was made to assess the contribution of chain scission mechanism and the change in plasticity mechanism on the property changes from irradiation and subsequent thermal treatments.     

Influence of ion irradiation on internal residual stress in DLC films

The dependence of internal residual stress in thin diamond-like carbon films grown on Si substrate by PECVD technique on most important growth parameters, namely RF-power, DC bias voltage and substrate temperature, is described. Results show that compressive stress reaches the highest value of 2.7 GPa at low RF-power and DC bias. Increase of substrate temperature from 250 to 350 °C leads to nonlinear increase of stress value. Inhomogeneity of residual stress along the film surface disappears when film is deposited at temperatures above 275 °C. Post-growth film irradiation by P⁺ and In⁺ ions cause decrease of compressive stress followed by its inversion to tensile. For all ion energy combinations used residual stress changes linearly with normalized fluence up to 0.2 DPA with slope (8.7 ± 1.3) GPa/DPA.     

Two-phase minor loss in horizontal bubbly flow with elbows: 45° and 90° elbows

The present study investigates the geometric effects of a 45° elbow on the pressure drop due to the minor loss in horizontal bubbly flow. A round glass tube with inner diameter of 50.3 mm is employed as a test section, along which a 45° elbow is installed at L/D = 353.5 from the two-phase mixture inlet. In total, 15 different flow conditions are examined. The local static pressures are measured at four axial locations at L/D = 197, 342, 363 and 419 from the two-phase mixture inlet. The effect of the elbow is clearly demonstrated in the pressure data along the axial direction. In the data analysis, the pressure data previously acquired with a 90° elbow is also utilized as well. The conventional Lockhart-Martinelli correlation with parameter C = 30 predicts the overall two-phase frictional pressure loss between the inlet and exit of the test section relatively well for both the 90° and 45° elbow experiments. However, it fails to predict the pressure loss across the elbows, because the existing model does not account for the additional loss due to the flow restrictions. In view of this, a new correlation analogous to Lockhart and Martinelli’s is developed for the two-phase frictional pressure loss across the elbows. The new correlation with the parameter C = 65 and the minor loss factors of k = 0.58 and k = 0.35 for the 90° and 45° elbows, respectively, yields the best fit to the data. The average percent differences between the predictions made by the new correlation and the data are ±2.1% and ±1.3% for 90° and 45° cases, respectively.     

High temperature surface effects of He implantation in ICF fusion first wall materials

The first wall armor of the inertial confinement fusion reactor chambers must withstand high temperatures and significant radiation damage from target debris and neutrons. The resilience of multiple materials to one component of the target debris has been investigated using energetic (20-40 keV) helium ions generated in the inertial electrostatic confinement device at the University of Wisconsin. The materials studied include: single-crystalline, and polycrystalline tungsten, tungsten-coated tantalum-carbide ‘foams’, tungsten-rhenium alloy, silicon carbide, carbon-carbon velvet, and tungsten-coated carbon-carbon velvet. Steady-state irradiation temperatures ranged from 750 to 1250 °C with helium fluences between 5 × 10¹⁷ and 1 × 10²⁰ He⁺/cm². The crystalline, rhenium alloyed, carbide foam, and powder metallurgical tungsten specimens each experienced extensive pore formation after He⁺ irradiation. Flaking and pore formation occurred on silicon carbide samples. Individual fibers of carbon-carbon velvet specimens sustained erosion and corrugation, in addition to the roughening and rupturing of tungsten coatings after helium ion implantation.     

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.     

Effect of microstructure on the corrosion of CVD-SiC exposed to supercritical water

Silicon carbide (SiC) is an important engineering material being studied for potential use in multiple nuclear energy systems including high-temperature gas-cooled reactors and water-cooled reactors. The corrosion behavior of SiC exposed to supercritical water (SCW) is critical for examining its applications in nuclear reactors. Although the hydrothermal corrosion of SiC has been the subject of many investigations, the study on the microstructural effects on the corrosion is limited. This paper presents the effect of residual strain, grain size, grain boundary types, and surface orientations on the corrosion of chemical vapor deposited (CVD) β-SiC exposed to SCW at 500 °C and 25 MPa. Weight loss occurred on all the samples due to localized corrosion. Residual strains associated with small grains showed the most significant effect on the corrosion compared to the other factors.     

Effect of coating temperature on properties of the SiC layer in TRISO-coated particles

The effect of coating temperature on properties of the SiC layer in TRISO-coated particles was investigated. An increase in coating temperature resulted in a significant coarsening of surface microstructures and an increase of the pore size and porosity of SiC layers. The SiC layers formed at 1400-1550 °C had nearly stoichiometric compositions whereas the SiC layer formed at 1600 °C contained a small amount of free carbon. The degradation of hardness and elastic modulus of the SiC layers coated at 1550 and 1600 °C was attributed to the increased porosity of the specimens and partly to the existence of free carbon. The fracture stress of the SiC layer measured by the crush test of hemispherical shell specimen did not correlate with the hardness and elastic modulus, and there was no clear dependence of the fracture stress on the coating temperature; this lack of correlation can be explained by the large roughness of the inner surface of the SiC layer.