Longzhou Ma

Identification of SAGBO-induced damage zone ahead of crack tip to characterize sustained loading crack growth in alloy 783

Sustained loading was applied to alloy 783 subjected to a non-standard heat treatment, annealing plus γ′ aging, at elevated temperature. The existence of damage zone ahead of the crack tip was identified and propagation rate of the damage zone was correlated to the sustained loading crack growth rate. The formation of damage zone was ascribed to stress accelerated grain boundary oxidation.

Effects of NiAl-β precipitates on fatigue crack propagation of INCONEL alloy 783 under time-dependent condition with various load ratios

Abstract Hold time fatigue crack growth with various load ratios and sustained loading crack growth tests were conducted on INCONEL ® alloy 783 for different microstructures at 650 °C in air. The results showed that the presence of intergranular NiAl-β precipitates significantly improves the resistance to fatigue crack propagation under time-dependent conditions. Crack growth retardation was observed as the cyclic loading approached the sustained loading status.

Dispersion of single-walled carbon nanotubes with poly(pyridinium salt)s

Dispersion of single-walled carbon nanotubes (SWNTs) with poly(pyridinium salt)s via non-covalent interactions in DMSO is demonstrated. The resulting composites display high quenching efficiency in the photoluminescent properties of this class of ionic polymers, and TEM study shows that SWNTs are wrapped by ionic polymers with thickness around 3 nm.

Effects of different metallurgical processing on microstructures and mechanical properties of inconel alloy 783

Different metallurgical processing, including the standard heat treatment, heat treatment without β aging, addition of high amount of Cr, and long-term isothermal exposure, was conducted on superalloy Inconel 783. For these processed materials, the tensile property and hardness at room temperature and stress relaxation behavior at 650 °C were examined. The testing results showed that isothermal exposure and heat treatment without β aging slightly enhanced the yield strength of alloy 783 at room temperature as well as all metallurgical processing in this study produced an identical stress relaxation behavior at 650 °C. The microstructure variation with different processing was analyzed using optical microscope, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Oxide-induced crack closure: an explanation for abnormal time-dependent fatigue crack propagation behavior in INCONEL alloy 783

Abstract INCONEL ® (trademark of Special Metals Corporation) alloy 783 was subjected to the fatigue crack growth under sinusoidal and hold-time waveform conditions at 650 °C in air. Interestingly, alloy 783 did not display full time-dependent fatigue crack propagation (FCP) with increase in the hold time. The oxide-induced crack closure is thought to be responsible for the abnormal time-dependent FCP behavior.

Application of electron microscopy in the observation of technetium and technetium dioxide nanostructures.

Transmission electron microscopy (TEM) was applied to characterize the microstructure of Tc metal and technetium dioxide synthesized by the decomposition of NH(4)TcO(4). The morphology of the Tc metal and well-resolved TcO(2) particles were characterized using bright-field TEM and scanning TEM modes. Structural characterization of these two samples using high-resolution (HR) TEM was successfully performed for the first time on the nanoscale. The morphology of Tc metal showed significant differences when compared to TcO(2). The crystal structure of Tc metal on the nanoscale was shown to contain well-resolved lattice fringes without any defects. Because of the deficiency in point resolution, however, the two-dimensional structure details of Tc metal could not be observed as expected. On the other hand, structural details of TcO(2) were prominent at high resolution. With a 2-fold multiplicity in both directions, TcO(2) showed a unique atomic distribution corresponding to a monoclinic unit cell. Furthermore, the lattice parameters of the samples were refined by the Rietveld analysis of the powder X-ray diffraction patterns and were estimated by HRTEM. In the case of technetium dioxide, the stoichiometry was approximated to be TcO(2.3) using quantitative analysis of X-ray energy dispersive spectrometry. Electron energy-loss spectrometry verified the chemical phase of the two samples by their different chemical environments based on an energy shift of 2.0 eV of the N(23) edge between TcO(2) and Tc metal.

Synthetic and coordination chemistry of the heavier trivalent technetium binary halides: uncovering technetium triiodide.

Technetium tribromide and triiodide were obtained from the reaction of the quadruply Tc-Tc-bonded dimer Tc2(O2CCH3)4Cl2 with flowing HX(g) (X = Br, I) at elevated temperatures. At 150 and 300 °C, the reaction with HBr(g) yields TcBr3 crystallizing with the TiI3 structure type. The analogous reactions with flowing HI(g) yield TcI3, the first technetium binary iodide to be reported. Powder X-ray diffraction (PXRD) measurements show the compound to be amorphous at 150 °C and semicrystalline at 300 °C. X-ray absorption fine structure spectroscopy indicates TcI3 to consist of face-sharing TcI6 octahedra. Reactions of technetium metal with elemental iodine in a sealed Pyrex ampules in the temperature range 250-400 °C were performed. At 250 °C, no reaction occurred, while the reaction at 400 °C yielded a product whose PXRD pattern matches the one of TcI3 obtained from the reaction of Tc2(O2CCH3)4Cl2 and flowing HI(g). The thermal stability of TcBr3 and TcI3 was investigated in Pyrex and/or quartz ampules at 450 °C under vacuum. Technetium tribromide decomposes to Na{[Tc6Br12]2Br} in a Pyrex ampule and to technetium metal in a quartz ampule; technetium triiodide decomposes to technetium metal in a Pyrex ampule.

Characterization of an Inorganic Cryptomelane Nanomaterial Synthesized by a Novel Process Using Transmission Electron Microscopy and X-Ray Diffraction

Layerand tunnel-structured manganese oxide nanomaterials are important because of their potential applications in industrial catalysis. A novel soft chemistry method was developed for the synthesis of inorganic cryptomelane nanomaterials with high surface area. Bright field transmission electron microscopy ~BF-TEM! and high-resolution transmission electron microscopy ~HRTEM! techniques were employed to characterize this nanomaterial. A nanosized material with fibrous texture comprised of 140–160 nm striations was identified by BF-TEM imaging. HRTEM images show multiple atomic morphologies such as “helix-type,” “doughnut-like,” and tunnel structures lying on different crystallographic planes. The crystallographic parameters of this material were analyzed and measured by X-ray powder diffraction ~XRD! showing that the synthesized nanomaterial is single phased and corresponds to cryptomelane with major diffraction peaks ~for 108 , 2u , 608! at d-spacing values of 6.99, 4.94, 3.13, 2.40, 2.16, 1.84, 1.65, and 1.54 Å. A “doughnut-like” crystal structure was confirmed based on the crystallographic data. Structure and lattice parameters refinement was performed by XRD/Rietveld analysis. Simple simulation of HRTEM images and selected area diffraction patterns were applied to interpret the HRTEM images as observed.