Abstract Work is underway at Los Alamos National Laboratory to fabricate machined-and-bonded target capsules of Be-6 wt% Cu for the National Ignition Facility. Significant progress has been made in producing material with the desired composition, purity, and homogeneity of composition, by arc melting. This material is thermomechanically processed by equal channel angular extrusion, to break down the coarse ascast structure and refine the grain size, to about 20 μm. Machining with diamond tooling results in a significant improvement of the as-machined roughness, that also results in improved bond strengths. Bonding with a sputtered layer of Al can achieve high strengths with a bond 1.2 μm thick, and thinner bonds are being investigated. Laser-drilled holes and fill-tube counterbores produced by electrodischarge machining appear to be feasible, but will require improvements in specimen positioning.

Phonon densities of states were measured on pure uranium and solutions U-0.4% C, U-1.5% Si, and U-0.91% Fe (atomic) using inelastic neutron scattering. The solute atoms stiffened the phonons, resulting in large decreases in vibrational entropy. The vibrational entropy decrease for carbon was four times the configurational entropy increase, showing that the mixing entropy is not only negative but is dominated by vibrations. Comparison with single-crystal dispersion curves indicates that the phonon stiffening for all solutes involved the transverse optic branch propagating along (001) and displacing atoms along (010). The magnitudes of the changes were too large to be explained in terms of short-range force constant models but may originate with impurity pinning of collective modes associated with alpha-U's charge density wave transitions.

UPt3 exhibits anomalous, possibly time-fluctuating antiferromagnetic (AFM) order below 6K. Th substitution induces conventional AFM order with the same magnetic structure. Recent μSR studies on U1−xThxPt3 for 0⩽x⩽0.05 showed that the transition into the conventional AFM state was sharp for x=0.05, but broadened for x⩽0.02 (Phys. Rev. B 84 (2003) 224421), indicative of a crossover behavior. We present X-ray diffraction and transmission electron microscopy (TEM) results that show no significant material inhomogeneity in those samples. However, specific heat measurements corroborate the μSR measurements and show signs of an increase near 7K for x>0.01. This supports the conjecture that Th impurities slow down the fluctuating AFM, rendering them observable on the timescale of thermodynamic measurements.

A thermodynamically complete equation of state for the compression and heating of near-equiatomic Ni–Ti alloy in the CsCl (B2) structure was predicted, based on quantum-mechanical calculations of the electron ground states and a Grüneisen lattice-thermal model. The quantum-mechanical calculations used ab initio pseudopotentials and the local-density approximation; the accuracy of the calculations was investigated for elemental Ni and Ti. These calculations demonstrated that simple averaging techniques do not provide an accurate prediction of the properties of metal alloys, and rigorous treatment of the electron wave functions is needed. Predictions were also made of the behavior of NiTi under uniaxial loading. The pressure-density relation obtained from isotropic compression did not match the mean pressure calculated from uniaxial compression, demonstrating that it is not generally accurate to split the stress response of a material into a scalar equation of state and a stress deviator according to the usual prescription. Polycrystalline NiTi samples were prepared with a range of compositions, in the form of disks from 100 to 400μm thick and 5mm in diameter. Flyer impact experiments were performed using a long-pulse laser drive at the TRIDENT facility to obtain shock wave data on the response of NiTi to around 15GPa; the new data were consistent with the published results from gas gun experiments. The theoretical equation of state was consistent with the shock wave data.

The isothermal growth of partitioned pearlite in a series of high purity Fe–C–Mn alloys over the temperature range 575–650 °C has been investigated. Two types of behavior were observed. For those alloys transformed within the (α+M3C) two phase field of the respective Fe–C–Mn isothermal section, growth occurred under steady-state conditions, with constant rate and interlamellar spacing. Those compositions transformed within the (γ+α+M3C) three phase field invariably transformed under non-steady-state conditions with a growth rate which decreased and an interlamellar spacing that increased (divergent) in time. Detailed analytical transmission electron microscropy (ATEM) measurements of the Mn concentration profiles across the γ/α and γ/M3C growth interfaces were made as a function of time for two alloys transformed at 625 °C. For the alloy transformed within the (α+M3C) two phase field, the Mn contents inherited by the growing α and M3C were remarkably constant for much of the reaction and are well approximated by the local equilibrium values. In the case of the alloy transformed within the (γ+α+M3C) three phase field, the Mn contents inherited by the growing α and M3C both increased with time. The Mn contents of the growing M3C were at all times observed to fall within the bounds expected by the local equilibrium (LE) model, whereas a Mn enrichment over and above the LE values was observed for the growing ferrite. The effect of this enrichment on the expected pearlite growth rate is shown to be very small and it is concluded that the LE approximation for the interfacial conditions during pearlite growth under the conditions studied is a good approximation.

Several authors in the 1960 Decomposition of Austenite by Diffusional Processes Proceedings remarked about the thermodynamic possibility of austenite decomposition to non-equilibriunt products. These concepts are generalized in terms of the total reaction path traversed during the diffusional decomposition of single phase supercooled austenite from start to finish during its approach toward an equilibrium microstructure. A set of equilibrium reaction path characteristics are proposed. Non-equilibrium reaction paths followed during decomposition of austenite to pearlitic and bainitic products in ternary Fe-C-M steels are evaluated in light of these criteria. Specific examples include divergent pearlite and bay-region bainite formed above and below the TTT diagram start-curve bay. The roles of diffusion, crystallography and carbides are given specific attention.

A microanalysis study of the eutectoid decomposition of austenite to ferrite and M2C (bainite) at the bay in Fe-0.24C-4Mo is reported. The carbon remaining in the austenite showed little variation with position at any given reaction time, which ruled out carbon diffusion as a rate-limiting process. Fine-probe EDS at bainite-austenite growth fronts revealed Mo enrichment in the interface and up to 15 nm in the austenite. EDS of extracted M2C carbides always revealed Mo enrichment, but with a non-equilibrium Fe/Mo ratio at early reaction times. It was concluded that alloy element partition between ferrite and alloy carbides at the reaction front is largely responsible for the slow kinetics in this and related alloys. A thermodynamic analysis showed that ferrite-carbide interfacial energy and non-equilibrium carbide compositions reduce the thermodynamic driving force for diffusive processes (Mo partition) by up to 20%, further slowing the kinetics.

A comprehensive theory concerning the shapes and temporal locations of TTT start curves ill a wide spectrum of low-to-medium carbon tertiary Fe-C-M steels is presented. The most critical factor is the temperature-deperldent tendency of the substitutional alloying element M to partition between ferrite and partitioned carbides or between ferrite and austenite. The diffusion length (and path) for the partitioning process determines the temporal locations of these start curves ill the partitioning regime at higher temperatures. The intersection of these higher-temperature partitioning C-curves with lower-temperature non-partitioning C-curves then determines the overall (composite) start curve shape. This view accounts for the finding that bays are observed only ill the TTT diagrams of alloys that exhibit partitioned carbides. predictions based oil these concepts are made for low-carbon quaternary steels.

The thermodynamics of the Al–Ni–Gd system in its Al-rich corner were assessed using the calculation of phase diagrams (CALPHAD) approach. Parameters describing the Gibbs free energy of various phases of the Al–Ni–Gd systems were manually optimized in this study. Differential thermal analysis (DTA) of 46 alloys yielded critical temperatures pertaining to the solid–liquid equilibria. Model-calculated phase equilibria and phase boundaries gave good agreement with DTA data from this study. Calculations of phase fraction vs. temperature agreed closely with the microstructure of alloys cooled after isothermal holding at intermediate temperatures.

This paper reports the results of a fine-probe EDS microanalytical study of cellular precipitation in a Cu-Ti binary alloy. Compositional profiles across the solute depleted Cu-rich FCC lamellae and the Cu4Ti lamellae within isothermally formed cellular colonies were measured in a FEG-TEM from thin-foil specimens prepared by conventional electropolishing and by a technique using a Ga+ focused ion-beam (FIB). The Cliff-Lorimer ratio method, with an absorption correction, was employed to quantify the compositions. Two FIB samples were prepared with different orientations of the lamellae with respect to the ion-milling direction. The compositional profiles across the Cu-rich FCC lamellae and the Cu4Ti compound lamellae in both the FIB-prepared samples and the electropolished sample were, within experimental error, numerically equivalent. The composition of the Cu4Ti compound phase lamellae was very close to the ideal stoichiometric composition of 20 at % Ti. It is concluded that for this system, and for the specimen preparation procedures used in this study, the Ga+ ion-milling process has had no detectable effect on the chemistry changes across the interlamellar interface at the scale studied. These results indicate that the possible sources of chemical artifacts which include redeposition, preferential sputtering and ion-induced atomic migration can be minimized if several precautions are taken during milling in the FIB. Consistent with previous investigators, it was also found that the ion-milling process does introduce significant structural artifacts (e.g., dislocations) into the softer FCC Cu-rich phase compared with a specimen produced by conventional electropolishing.

Owing to its importance as a metallic glass-forming system, the ternary Al–Fe–Gd system in its Al-rich corner was examined experimentally to assist in a thermodynamic assessment of this system. X-ray diffraction and TEM–EDS results from annealed specimens confirmed the solid-state equilibria reported previously. Differential thermal analysis of 24 alloys yielded critical temperatures pertaining to the solid–liquid equilibria. A self-consistent thermodynamic database for the Al–Fe–Gd system was developed using the CALPHAD approach. Parameters describing the Gibbs free energy of various phases of the Al–Gd and Al–Fe–Gd systems were manually optimized in this study. Phase equilibria calculations carried out with these parameters showed good agreement with DTA data from this and other studies, as well as thermochemical data reported previously. Several critical issues surrounding metallic glass formation and its subsequent micro-structural evolution upon heating are discussed in light of these results.

Degenerate ferrite grown below the bay in an Fe–C–W alloy was serially sectioned and reconstructed in a computer to examine its 3D structure. The 3D reconstruction revealed the true shape, orientation and connectivity of ferrite subunits, highlighting the misleading appearance that 2D sections can sometimes give.

Bending and uniaxial tensile tests for Al-base amorphous ribbons were performed at room temperature for a number of compositions, Al-nanocrystal precipitation was observed within vein protrusions on fracture surfaces and along crack propagation paths. as well as within shear bands resulting from bending. A composition dependence of crystallization upon bending was also observed. Effects of local adiabatic heating was observed on fracture surface.

A sol-gel process employing silicon alkoxide, chelated aluminum sec-butoxide, and magnesium acetate as starting precursors, was used to synthesize cordierite xerogels, aerogels and thin films. The xerogels were prepared using normal drying conditions, while supercritical drying conditions were employed to synthesize the aerogels. Thin films were grown by spin coating polymerized sols on (100) silicon substrates. The aerogel and xerogel powders as well as thin films were studied for phase evolution and phase stability using X-ray diffraction. All three forms indicated the formation of the μ-cordierite phase at 900°C. In addition, the aerogels and thin films showed evolution of other phases. The initiation of the μ → α cordierite transformation was observed in the temperature range 1000–1100°C for both the xerogels and thin films, while μ-cordierite obtained from the aerogels showed a much higher stability and transformed to α-cordierite only at 1200°C.