Oxidation behavior of TiAl coated with a fine-grain Co-30Cr-4Al film

The oxidation behavior of TiAl coupons coated with a fine-grain Co-30Cr-4Al (mass %) film of about 30-m thickness has been studied at 1100–1400 K in a flow of purified oxygen at atmospheric pressure for up to 500 ks. Three oxidation stages were recognized: initial transient, parabolic, and accelerated stages. However, at 1100 K a parabolic stage continues for more than 800 ks. The activation energy for parabolic oxidation agrees with reported values for the oxidation of alumina-former alloys, although the mass gains during the parabolic stages are relatively small at 1200 and 1300 K. Micropores developed mainly at the scale/coating and coating/substrate interfaces as oxidation proceeded. This is attributable to recrystallization of the coating during oxidation and a Kirkendall effect due to preferential diffusion of Co into the substrate. The accelerated oxidation can be explained in terms of the formation of rutile mounds on the scale.     

High-temperature oxidation of Al-deposited stainless-steel foils

The oxidation resistance of Al-deposited Fe–Cr–Al foils containing small amounts of La and Ce was assessed by a cyclic oxidation test with temperature varying between room temperature and 1323 K to 1423 K in static air. (1) The Al content of Fe–Cr–Al–La, Ce foils can be increased by depositing an Al layer from the vapor phase. The deposition of a 1-m-thick Al layer on both sides of the 50-m-thick foil is equivalent to a 1.5 mass% increase in the Al content. The deposited Al diffuses into the foil during heat treatment. The uniform distribution of Al is obtained by heating at 1273 K for 18 ks. (2) After the initial transition stage the oxidation follows the parabolic law until breakaway sets in. The scale consists mainly of -Al₂O₃ during the parabolic period. (3) The increase in the Al content by more than 5 mass% by the Al-deposition remarkably improves high-temperature oxidation resistance (smaller parabolic rate constant and longer protection time). (4) The Al-deposited foils have better oxidation resistance than the conventional foils with the same contents of Al and rare-earth elements. This is attributable to the different nature of the initially formed oxide on the Al-deposited foil. (5) The so-called rare-earth element effect was also observed for the Al-deposited foils. Predominant diffusion of oxygen through the Al₂O₃ scale and vacancy-sink mechanism are applicable to the present results.     

Quantum statistical foundation to the fermi liquid model and Ginzburg-Landau wave function

An energy eigenvalue equation for a quasi-particle is derived, starting with the Heisenberg equation of motion for an annihilation operator. An elementary derivation of the Fermi liquid model having a sharply defined Fermi surface in thek-space is given, starting with a realistic model of a metal including the Coulomb interaction amongand between electrons and lattice-ions. The Ginzburg-Landau wave function (r), where represents the superconducting pairon (Cooper-pair) state, is shown to be connected with the one-pairon density operatorn by (r) = r¦_n ^1/2¦. A close analogy between supercurrent and laser is indicated.On sabbatical leave from Department of Physics and Astronomy, State University of New York at Buffalo, Buffalo, New York.     

Real-time 3D microtubule gliding simulation accelerated by GPU computing

A microtubule gliding assay is a biological experiment observing the dynamics of microtubules driven by motor proteins fixed on a glass surface. When appropriate microtubule interactions are set up on gliding assay experiments, microtubules often organize and create higher-level dynamics such as ring and bundle structures. In order to reproduce such higher-level dynamics on computers, we have been focusing on making a real-time 3D microtubule simulation. This real-time 3D microtubule simulation enables us to gain more knowledge on microtubule dynamics and their swarm movements by means of adjusting simulation parameters in a real-time fashion. One of the technical challenges when creating a real-time 3D simulation is balancing the 3D rendering and the computing performance. Graphics processor unit (GPU) programming plays an essential role in balancing the millions of tasks, and makes this real-time 3D simulation possible. By the use of general-purpose computing on graphics processing units (GPGPU) programming we are able to run the simulation in a massively parallel fashion, even when dealing with more complex interactions between microtubules such as overriding and snuggling. Due to performance being an important factor, a performance model has also been constructed from the analysis of the microtubule simulation and it is consistent with the performance measurements on different GPGPU architectures with regards to the number of cores and clock cycles.     

TEM Observations of the Initial Oxidation Stages of Nb-Ion-Implanted TiAl

Coupon specimens of TiAl were implanted with Nb ions at an acceleration voltage of 50 kV with a dose of 10²¹ ions m.^–2 They were then slightly oxidized during heating to 900 or 1200 K, or at 1200 K for 3.6 ksec (1 hr) in a flow of purified oxygen under atmospheric pressure. The implanted specimens and oxidized specimens were characterized and observed by AES, X-ray diffractometry, SEM, TEM, EDS, and EPMA. Implantation improves the oxidation resistance significantly by forming virtually -Al₂O₃ scales. The implanted layer is about 75 nm thick; the outer part of 30-nm thickness is -Ti phase and the rest of 45-nm thickness is amorphous. Heating to 900 K in O₂ results in partial crystallization of the amorphous layer to Ti₅Al₃O₂ (Z-phase) and to 1200 K results in oxide scales of 270 to 400 nm thickness consisting mainly of Al₂O₃. The fraction of Al₂O₃ in the scale increases toward the substrate. Oxidation at 1200 K for 3.6 ksec results in Al₂O₃-rich scales of about 400-nm thickness. The oxide grain size is very fine, about 80 nm in size, and becomes smaller toward the outer scale surface. This implies that implantation enhanced the nucleation of Al₂O₃ grains relative to the growth of TiO₂ grains. This finding and the formation of -Ti phase are thought to be responsible for the excellent oxidation resistance obtained.     

Alkaline hydrolysis of alkylated acidic groups on carbon black

Potentiometric pH-stat titration was performed on alkylated carbon black dispersed in aqueous solution at pH 9.0, 10.0 and 11.0 and alkaline hydrolysis rate constant of the alkylated functional groups on the carbon black was obtained therefrom. Carbon black treated with C₁-C₈n-alcohols in vapor or liquid phase was used in this experiment. Hydrolysis proceeded more rapidly for carbon black treated with lower alcohols. For each alkylated carbon black, the hydrolysis rate constant decreased with time and, after the hydrolysis rate diminished, a hydrolysis resistant fraction of alkylated groups remained. For example, the hydrolysis rate constants at 25°C were 24.33, 17.50 and 4.501 · mol^?1 · sec^?1 at 15 min and 6.00, 6.00 and 3.671 · mol^?1 · sec^?1 at 45 min after the start of hydrolysis at pH 9.0 for carbon black treated with C₂, C₃ and C₄ alcohols respectively.     

Microstructure and analysis of oxide scales formed on Cr-Si-Ni compacts in air and H2O-containing atmosphere

The purpose of this study was to characterize the oxide scales formed on various Cr-Si-Ni compacts at 1273 K in air and H₂O-containing atmosphere by TEM. It was found that CrSi₂-(5-20)mass%Ni compacts form double layer scales, consisting of an outer Cr₂O₃ layer and an inner SiO₂ layer. The oxide scale changed from SiO₂- to Cr₂O₃-based scale with an increase in the Ni concentration. However, it was observed that the oxide scale formed in H₂O-containing atmospheres showed local SiO₂ growth into the substrate. This result suggests that the inward oxidant diffusion promotes the local growth of SiO₂ in the H₂O-containing atmospheres.     

Oxidation behavior of Ni2Al-0.1B containing 2Cr

Ni ₃ Al-0.1B containing 2% Cr was subjected to a thermal cycling oxidation test in pure flowing oxygen at atmospheric pressure at temperatures cycled between 400 and 1300 K. Scales formed on the alloy spalled repeatedly after several tens of cycles, resulting in a considerable mass loss of mass of the specimen. The isothermal oxidation behavior of the alloy was also studied at temperatures of 1300, 1400, and 1500 K in the same oxidizing atmosphere. Characteristic breakaway oxidation caused by extensive scale blistering was observed at 1300 and 1400 K after a protective period of about 50 ksec, whereas the oxidation at 1500 K followed a parabolic law without any significant blistering. Particularly at 1300 K, the alloy grain boundaries provided favorable sites for blistering. The influence of Cr may be explained by the modification of mechanical property of the scale.     

Improvement in the Oxidation Resistance of an Al-Deposited Fe–Cr–Al Foil by Preoxidation

The oxidation kinetics of conventional Fe–20Cr–5Al (in mass %) foil, Al-deposited foil and Al-deposited and preoxidized foil was studied at 1373 K in air. All the foils were 50-m thick and contained minor additions of rare-earth elements. The oxide scales were observed with SEM and TEM combined with EDS and were characterized with X-ray diffractometry and electron diffraction. The deposition of Al onto the foil from the vapor phase improves oxidation resistance. The details regarding this matter were reported elsewhere. The combination of the Al deposition and the subsequent preoxidation at 1173 K for 90 ks in air further increases the oxidation resistance, i.e., the smallest parabolic rate constant among the three kinds of foils, and excellent scale adherence. Preoxidation enhances the growth of -Al₂O₃, which transforms to -Al₂O₃ during subsequent oxidation. However, such -Al₂O₃ grains are much larger than those formed on the conventional foil of similar chemical composition. Small closed voids and small spinel-type, oxide particles appear in -Al₂O₃ grains with the progress of oxidation. The former is explained in terms of the volume decrease accompanying the phase transformation and the latter by the low solubility of Fe in -Al₂O₃.