Formation of the gamma phase by a peritectoid reaction in the zirconium-hydrogen system

Studies on the zirconium-hydrogen system have indicated that a peritectoid reaction occurs at about 255 °C between the α and δ phases to give the γ phase. This reaction is dependent upon the interfacial contact and hence is sluggish if the two phases are in massive form. The γ is a stable phase of composition ZrH below 255 °C and decomposes rapidly if heated above this temperature to give α and δ phases. Quenched α with saturated hydrogen, or δ of hightemperature composition, precipitate the γ phase at room temperature and require a long time for completion of the process. Non-equilibrium δ phase in a 49 at% hydrogen alloy, on β quenching and roomtemperature ageing, may transform fully to γ phase by a shear type of mechanism quite similar to the δ to ε transformation.     

The strain induced martensitic transformation in zirconium/3 wt% molybdenum/1 wt% aluminum

A study has been made of certain morphological and crystallographic changes associated with the strain induced transformation of retained β to martensitic α' in Zr/3 wt% Mo/1 wt% Al alloy. It has been found that the c/a ratio for the hep α' phase increases with increasing transformation (deformation). On the basis of a decreasing a parameter of the α' phase with increasing deformation it has been deduced that the regions of the β phase that are deficient in the β stabilizer (Mo) transform first of all to α'. Resistivity measurements and metallography have shown that the transformation occurred at the early stages of deformation. The platelets of α' nucleated at twin, deformation and grain boundaries and propagated in definite crystallographic directions. Varying the deformation temperature produced a change in both the amount and the morphology of the transformation. An increase in hardness was noted during the course of the transformation which could provide the basis for a high-strength alloy.     

Etude de la forgeabilite et de la resistance a la deformation de l'alliage U-0,2% V par essais de torsion entre 400 et 800°C

We have measured by hot torsion the resistance to deformation and the ductility of U/0.2wt% V alloy between 400 and 800°C for strain rates in the range 10^?2 ?3.6 sec^?1. In this temperature range, the alloy shows three successive distinct phases — orthorhombic α, tetragonal β, cubic γ — which behave differently. We found two useful ranges for hot-working of this alloy: in the α range below 600°C and in the γ range. By means of plasticity theory we have established the equivalence of hot torsion and hot tension and simulated a first rolling pass. Some tensile tests between 600 and 800°C and a rolling test at 600°C have shown good justification for the transition from torsion to other modes of deformation. A metallographic study after fracture showed the existence of recrystallisation in the α phase above 600°C and also in the γ phase, which explains the good hot workability.     

Effects of Temperature,Strain Rate,and Specimen Orientation on Localized Plastic Deformation of Irradiated Zircaloy-2

Both transverse and longitudinal Zircaloy-2 specimens irradiated up to 1.2 × 10²⁰ n/cm² (E> 1 MeV) were tested in tension with strain rates ranging 1.1 × 10^-4~1.1 × 10^-2 s^-1 in the temperature range 200~400°C. Detailed observations of the specimen wall surface and microstructure were also made on samples deformed to various amounts of plastic strain, with a projector and an optical microscope.

It was found that localized plastic deformation bands occurred in the temperature range approximately 280~330°C during straining to the ultimate tensile stress. Results also showed that the strain rate dependence of tensile properties, particularly the strain to the ultimate tensile stress, was associated with changes in the number and width of the localized deformation band with strain rates at a temperature of 300°C at which localized bands occurred. From a break of the straight line tracing the true stress-true plastic strain relationship, it was established that the onset stress and strain of the localized deformation band could be estimated.

The effect of specimen orientation on localized deformation band was also discussed on the basis of differences in the onset stress and strain between the transverse and longitudinal specimens.     

Material Properties of a Natural UF6 Transport Cylinder Vessel at High Temperature

Abstract

The IAEA Regulations for the Safe Transport of Radioactive Material are to be revised in 1996 and the fire test (800°C for 30 min) could become a requirement for the natural UF₆ transport cylinder. ASME SA 516 carbon steel is used as the structural material for this type of cylinder. It is very important to obtain high temperature data for SA 516 steel to be able to evaluate the integrity of the UF₆ transport cylinder vessel in the fire test. CRIEPI has therefore conducted material tests on SA 516 at high temperatures. The AC₁ and AC₃ transformation points of actual SA 516 steels have been measured. Tensile tests up to 900°C were conducted using USA, French and Japanese manufactured materials and the influence of phase transformation assessed. Preliminary creep tests show that assessment by creep strength can give a more conservative estimation than using the tensile strength. Creep deformation equations have been obtained using uniaxial creep tests and internal pressure creep tests. In addition, by the use of internal pressure creep rupture tests, the relation between the circumferential stress, the test temperature and the rupture time has been obtained.     

The effects of silicon and titanium on void swelling and phase stability in 12Cr-15Ni austenitic alloys irradiated with 46 MeV nickel ions

The structure of 20% cold-worked 12 wt%Cr-15 wt%Ni austenitic alloys with Si and Ti contents in the ranges 0.14-1.42 and <0.02-0.27 wt%, respectively, has been investigated by TEM following irradiation with 46 MeV Ni⁶⁺ ions to 60 dpa at 525, 575 or 625° C in the Harwell VEC. Increasing the Si content progressively reduced the void concentrations and swelling to zero at all three temperatures and the addition of Ti further reduced the void concentration and swelling. The higher Si alloys were structurally unstable during irradiations at 525 and 575°C, when γ'(Ni₃Si) particles, M₂₃X₆ type precipitates and grains of a bcc phase were formed. Small amounts of the γ' and bcc phases were observed following irradiation at 625° C, the principal precipitates being of the M₂₃X₆ type. Voids were present in both austenite and bcc phases in the lower Si alloys and segregation of an unidentified fcc phase was observed around voids. It was concluded that all the void nucleation occurred in the austenite phase and that the bcc phase resulted from the partial transformation of the austenite to α'-martensite during cooling from the irradiation temperatures. This occurred as a consequence of the M_s(α') transformation temperature being raised to well above ambient owing to elemental depletions of the alloy matrices resulting from precipitation and segregation.     

Microstructure and kinetics of the plutonium β → α transformation at subzero temperatures

The relationship between β-Pu grain size and the grain size of the α-Pu formed by the $\text{β → α}$ transformation at subzero temperatures (?60°C to ?100°C) was investigated using retained β prepared from high-purity, α-phase extruded Pu. Recently developed high-rate quenching techniques for Pu were used to retain coarse-grained β-Pu. The grain size of the a formed by the rapid $\text{β → α}$ transformation of coarse-grained β was substantially larger than the grain size of the a produced at the same subzero temperature by the comparatively sluggish transformation of fine-grained β. Conversely, the α formed from fine-grained β at a high a-phase transformation temperature (+ 78°C) had coarse grains. These microstructural observations represent the first direct evidence of a correlation between β and α grain size for the $\text{β → α}$ tranformation at subzero temperatures. They also support previous observations of an apparent correlation between β grain size and $\text{β → α}$ transformation rates. These results further demonstrate that the subzerotemperature grain-size relationship does not extend to high a-phase transformation temperatures. An activation energy of 10 kcal/mol was derived from the kinetic data for the $\text{β → α}$ transformation of retained, fine-grained β at temperatures below ?80°C.     

Stress Intensity Factor at the Tip of Cladding Incipient Crack in RIA-Simulating Experiments for High-Burnup PWR Fuels

RIA-simulating experiments for high-burnup PWR fuels have been performed in the NSRR, and the stress intensity factor K _I at the tip of cladding incipient crack has been evaluated in order to investigate its validity as a PCMI failure threshold under RIA conditions. An incipient crack depth was determined by observation of metallographs. The maximum hydride-rim thickness in the cladding of the test fuel rod was regarded as the incipient crack depth in each test case. Hoop stress in the cladding periphery during the pulse power transient was calculated by the RANNS code. K _I was calculated based on crack depth and hoop stress. According to the RANNS calculation, PCMI failure cases can be divided into two groups: failure in the elastic phase and failure in the plastic phase. In the former case, elastic deformation was predominant around the incipient crack at failure time. K _I is available onlyin this case. In the latter, plastic deformation was predominant around the incipient crack at failure time. Failure in the elastic phase never occurred when K _I was less than 17 MPam1^/2. For failure in the plastic phase, the plastic hoop strain of the cladding periphery at failure time clearly showed a tendency to decrease with incipient crack depth. The combination of K _I, for failure in theelastic phase, and plastic hoop strain at failure, for failure in the plastic phase, can be an effective index of PCMI failure under RIA conditions.     

Ferrite formation in neutron-irradiated type 304L stainless steel

Austenitic (γ) to ferrite (α) transformation was observed using transmission electron microscopy in type 304L stainless steel that had been irradiated at ~500°C to fast-neutron (E > 0.1 MeV) fluences greater than ~ 3 × 10²²n/cm². Previous studies on similar unirradiated stainless steels found no such transformation, indicating that the γ → αtransformation was irradiation-induced. The α phase appeared to nucleate on stacking faults, indicating that the presence of large Frank loops was the critical step in the transformation. After an entire grain of austenite had transformed, the only remaining γ phase existed as shells around voids. Coincidence of rapid swelling behavior with γ → α transformation indicated that the two were related, perhaps by reaction of both phenomena to the effects of irradiation and temperature on microchemical segregation. A volume expansion of about 2.5% was found to be associated with the transformation. Inferences are drawn relating this behavior in type 304L steel to the effects of radiation on other reactor structural materials such as type 316 stainless steel, which is also a metastable austenitic composition.     

Untersuchungen im system Gd-C-N

An isothermal section at 1200°C of the system Gd-C-N was examined by X-ray techniques. The results give evidence of complete miscibility of the phases GdC_x (x = 0.35–0.65) and GdN. No appreciable miscibility of GdN with Gd₂C₃ or GdC₂ at 1200°C could be found. The reaction of nitrogen with GdC₂ under pressure of 30 bar at 1200°C does not lead to a ternary carbonitride phase as it does in the case of LaC₂.     

Some Generalised Characteristics of the Electro-dynamics of the Plasma Focus in Its Axial Phase: Illustrated by an Application to Independantly Determine the Drive Current Fraction and the Mass Swept-Up Fraction

We describe the axial phase of the Mather plasma focus by two coupled equations of motion and circuit. We non-dimensionalised these equations resulting in two coupled equations which are characterised by only three scaling parameters α, β and δ which are ratios of electrical to transit times, inductances and impedances respectively. The normalised current waveform, trajectory and speed profile are unique for each combination of α, β, δ which are the ratios of characteristic times (electrical discharge vs. axial transit), inductances (tube inductance vs. static inductance) and impedances (stray resistance vs. electrical surge impedance). This leads to important information and insight into various aspects of the axial phase. In the present work we show that in a time-matched plasma focus shot we deduce the value of axial phase current fraction f_c simply by measuring the calibrated voltage waveform and the uncalibrated current waveform. The scaling parameters β and δ are fixed; and by form-fitting the measured current waveform to the normalised current waveform using the value of α of the shot is determined uniquely; from which the peak current and the ratio of peak to average speed [the speed form factor (SFF)] are obtained. The average transit speed is measured by time-of-flight using the voltage upturn as indicator of end of axial phase. Then the SFF yields the peak speed. The measured voltage (back EMF), peak current and peak axial speed (all at the end of axial phase) allows the unambiguous measurement of f_c. The value of the mass swept-up fraction f_m is deduced from α which is the ratio of the characteristic discharge and the characteristic transit times, both deduced during the non-dimensionalisation of the equations. Analysis of a time-matched shot in the INTI PF at 15 kV, 3 Torr D₂ gave f_c = 0.68 and f_m = 0.05.     

Gas Chromatography of Uranium Hexafluoride at Low Temperatures

Gas chromatography of UF₆ at low temperature was studied with the use of columns of polytrifluoromonochloroethylene oils as liquid phase. The dependence of retention time and HETP of UF₆ on (1) degree of polymerization of oils, (2) liquid phase loading, and (3) kinds of solid support were studied in the temperature range between ?10° and 40°C, and the most favorable conditions for quantitative analysis of UF₆ are discussed.

The relation between the gas chromatographic characteristics of the columns and the B.E.T. surface area of the solid support has been briefly examined.     

Heteroepitaxial Er0.49Gd0.51Si1.7 layers formed by channeled ion beam synthesis

Epitaxial ternary silicide Er_0.49Gd_0.51Si_1.7 layers with a good crystalline quality (χ_min of Er and Gd is 3.7%) have been formed by 60 keV Er and Gd ion implantation into Si(1 1 1) substrates to a total dose of 1.0 × 10¹⁷/cm² at 450°C using channeled ion beam synthesis (CIBS). The composition, the structure, the strain and the thermal stability of these layers have been studied using energy dispersive spectroscopy (EDS), Rutherford backscattering (RBS)/channeling and X-ray diffraction (XRD). It is shown that the perpendicular and parallel elastic strains of the Er_0.49Gd_0.51Si_1.7 epilayer are e^⊥=−0.46% ± 0.02% and e⁶=+0.73% ± 0.19%. The layer is stable up to 900°C. Annealing at 950°C results in a phase transformation.     

Phase equilibria in the Li4SiO4Li2SiO3 region of the pseudobinary Li2OSiO2 system

The constitution of the Li₄SiO₄Li₂SiO₃ region of the pseudobinary L₂OSiO₂ system was investigated between 1000 and 1300°C by isothermal heat treatment, differential thermal analysis, ceramography and X-ray diffraction. The two boundary phases of the sub-system, Li₄SiO₄ and Li₂SiO₃, melt congruently at 1258°C and 1209°C, resp. An intermediate high-temperature phase, Li₆Si₂O₇, forms peritectically at 1030°C and decomposes eutectoidally at 1020°C. A eutectic sub-system exists between Li₄SiO₄ and Li₆Si₂O₇ with the eutectic temperature and composition of 1025°C and 38.3 mol% SiO₂, resp. Li₆Si₂O₇ can be quenched to room temperature in a metastable state and crystallizes in a tetragonal system with the lattice parameters a = 770.9 pm and c = 486.0 pm.     

In-reactor deformation of solution annealed type 304L stainless steel

Over the past six years at EBR-II, a great deal of information has been obtained on the in-reactor behaviour of solution annealed-Type 304L stainless steel. This information consists of the following: (1) Irradiation induced swelling results in the form of immersion density and transmission electron microscope (TEM) measurements on unstressed material that extends over a temperature range of 395° to 530°C and a neutron fluence range of 1.8 to 9.3 × 10²² n/cm² (E > 0.1 MeV). (2) Irradiation induced creep results from helium pressurized capsules irradiated at a temperature of 415°C. The hoop stress range covered in the experiment was 0 to 27.3 ksi, and the peak neutron fluence obtained to date is 7 × 10²² n/cm² (E > 0.1 MeV). (3) Residual stress measurements (slit tube technique) with complementary TEM gradient studies on stressed and unstressed capsules. (4) Comparative swelling studies of stressed cladding material and unstressed capsule material from encapsulated EBR-II driver fuel experiments over wide ranges of temperature and neutron fluences. The deformation information derived from the four above studies represent an extensive data base from which to obtain an understanding of the in-reactor deformation of austenitic stainless steel. It is the purpose of this paper to review our information on the in-reactor deformation of solution annealed Type 304L stainless steel.     

Microstructure of Ti5Al2.5Sn and Ti6Al4V deformed in tensile and fatigue tests

The microstructural characterization of two titanium alloys, Ti5Al2.5Sn and Ti6Al4V, was performed. These alloys were selected as representatives of the α and α+β titanium families, to investigate their possible application as structural materials in fusion reactor technology. Scanning and transmission electron microscopy have been used to obtain the relevant features of the microstructure in the as-received state and after mechanical deformation in tensile and fatigue experiments. Deformation modes and defects resulting from the deformation process were analyzed. Deformation occurred in the α phase of both alloys mainly through slip of the basal dislocations in basal, prismatic and pyramidal planes, together with slip in the 〈c+a〉 direction. A layered structure of dislocation loops developed in the α phase after cyclic fatigue tests. Deformation induced a phase transformation, namely a martensitic phase transition, that occurred solely in the β phase present in the Ti6Al4V alloy.     

Deformation of polycrystalline Li2O

Constant-crosshead-speed compression of Li₂O polycrystals has been performed at temperatures of 700–950°C with strain rates ranging from about 10⁻⁶-10⁻⁴s⁻¹. For temperatures greater than 850°C, data suggest deformation rates are controlled by recovery via dislocation climb. For lower temperatures, impurity effects may alter the deformation mechanism. At 950°C, viscous creep occurs at low strain rates. For porosities ranging from about 7 to 21%, deformation is strongly dependent on porosity, but is virtually independent of grain size.     

Mechanical properties of molybdenum neutron-irradiated at a high temperature

Molybdenum specimens prepared by two processes, powder-metallurgy (PM) and electron-beam melting (EB), were irradiated to a fast neutron fluence of 2.74 × 10²⁴n/m² (E_n? 1 MeV) at about 600°C (873 K), and their mechanical properties were studied in detail. It was shown that the degree of irradiation embrittlement in EB-Mo was smaller than that in PM-Mo, which might be caused by stronger grain-boundaries and probably smaller irradiation-hardening in the former. From the relation between the recovery of ductility and microstructural changes in post-irradiation annealed PM-Mo at 800 (1073 K), 1000 (1273 K) and 1200°C (1473 K), it was concluded that the recovery resulted from a decrease of irradiation hardening due to a rearrangement and a disappearance of depleted-zones, dislocation-loops and voids in order with increasing annealing temperature. An anomalous mode of fracture was observed in as-irradiated specimens, which consisted of inhomogeneous deformation, then brittle fracture not at the center but at the root of the deformation neck. This mode was observed in a narrow temperature range near the DBTT. A possible mechanism is discussed.     

Residual stress behavior in fast neutron irradiated SA AISI 304l stainless steel cylindrical tubing

Residual stress measurements were made on solution-annealed (SA) AISI 304L stainless steel (SS) irradiated in EBR-II over a temperature range from 402 to 524°C by axially slitting short sections of tubing. The data were analyzed by using SA AISI 304 SS physical properties and SA AISI 304L SS swelling and irradiation creep empirical equations to calculate the slit width change (δ) versus fluence (φt) curve. At temperatures equal to and above 445°C, δ versus φt calculations indicate that the stress effect on swelling is sufficiently large to reduce the swelling rate temperature gradient, and consequently the on-power stress gradient, to zero. This behavior is confirmed by void volume gradient measurements. At lower temperatures, δ versus φt calculations indicate that stress affected swelling is smaller and does not relax the swelling rate temperature gradient. Void volume gradient measurements confirm the presence of a swelling gradient. Calculations of the δ versus φt curve were made with four different empirical swelling equation fluence dependencies, and the best agreement with the δ versus φt data was obtained with a power form type swelling equation. The equations fit the immersion density data ($\text{ΔV}\text{V}{}_0\text{versus}\text{φt}$) within experimental scatter, but predict significantly different δ versus φt behavior. These results show that the slit tube results are very sensitive to the empirical swelling equation form.     

High-temperature oxidation of zircaloy-2 and zircaloy-4 in steam

At temperatures above the $\text{(α + β)}\text{β}$ transformation temperature for zirconium alloys, steam reacts with β-Zr to form a superficial layer of zirconium oxide (ZrO₂) and an intermediate layer of oxygen-stabilized α-Zr. Reaction kinetics and the rate of growth of the combined (ZrO₂ + α-Zr) layer for Zircaloy-2 and Zircaloy-4 oxidation in steam were measured over the temperature range 1050–1850°C. The reaction rates for both alloys were similar, obeyed parabolic kinetics and were not limited by gas phase diffusion. The parabolic rate constants were consistently less than those given by the Baker and Just correlation for zirconium oxidation in steam. A discontinuity was found in the temperature dependence of both the reaction rate and the rate of growth of the combined (ZrO₂ + α-Zr) layer. The discontinuity is attributed to a change in the oxide microstructure at the discontinuity temperature, an observation which is consistent with the zirconium-oxygen phase diagram.