Microstructure and Mechanical Properties of AlN/Cu Brazed Joints

In this study, the AlN/Cu bonding was explored using the brazing technique. During AlN/Cu brazing, the temperature was set at 800, 850, and 900 °C for 10, 20, 30, and 60 min, respectively. We studied the bonding mechanism, microstructure formation, and the mechanical characteristics of the bond. The reaction layer developed at the interface of AlN/Cu is observed to be TiN. The activation energy of TiN is about 149.91 kJ/mol. The reaction layer thickness is linearly dependent on the temperature and duration at 800 and 850 °C for 60 min and 900 °C for 30 min. However, the growth of the reactive layers decreases gradually at 900 °C when the duration changed from 30 to 60 min. The strength of the specimens with thickness ranging between 1 and 1.5 μm is 40-51 MPa.     

Overview of SIMS-Based Experimental Studies of Tracer Diffusion in Solids and Application to Mg Self-Diffusion

Tracer diffusivities provide the most fundamental information on diffusion in materials, and are the foundation of robust diffusion databases that enable the use of the Onsager phenomenological formalism with no major assumptions. Compared to traditional radiotracer techniques that utilize radioactive isotopes, the secondary ion mass spectrometry (SIMS)-based thin-film technique for tracer diffusion is based on the use of enriched stable isotopes that can be accurately profiled using SIMS. An overview of the thin-film method for tracer diffusion studies using stable isotopes is provided. Experimental procedures and techniques for the measurement of tracer diffusion coefficients are presented for pure magnesium, which presents some unique challenges due to the ease of oxidation. The development of a modified Shewmon-Rhines diffusion capsule for annealing Mg and an ultra-high vacuum system for sputter deposition of Mg isotopes are discussed. Optimized conditions for accurate SIMS depth profiling in polycrystalline Mg are provided. An automated procedure for correction of heat-up and cool-down times during tracer diffusion annealing is discussed. The non-linear fitting of a SIMS depth profile data using the thin-film Gaussian solution to obtain the tracer diffusivity along with the background tracer concentration and tracer film thickness is demonstrated. An Arrhenius fit of the Mg self-diffusion data obtained using the low-temperature SIMS measurements from this study and the high-temperature radiotracer measurements of Shewmon and Rhines (Trans. AIME 250:1021-1025, 1954) was found to be a good representation of both types of diffusion data over a broad range of temperatures between 250 and 627 °C (523 and 900 K).     

Ferrochromium from Domestic Lateritic Chromites

As part of its effort to devise suitable technology for processing low-grade domestic materials and recycling wastes, the U.S. Bureau of Mines has evaluated the feasibility of smelting a chromite concentrate derived from residues generated by the processing of nickel and cobalt from domestic later-ites. The product sought was a high-carbon ferrochromium suitable for stainless- and alloy-steel production. The concentrate was blended with re-ductants and fluxing constituents and was smelted under submerged arc conditions in a laboratory-scale, single-phase ac electric arc furnace. The results revealed that metallurgical-grade coke provides the best quality product. High-carbon ferrochromium, which met ASTM specifications except for phosphorus and sulfur, was obtained. Agglomeration of the charge materials was not required.     

Energy and Resource Saving of Steelmaking Process: Utilization of Innovative Multi-phase Flux During Dephosphorization Process

An increase in the utilization efficiency of CaO, one of the major fluxing agents used in various steelmaking processes, is required to reduce the amount of discharged slag and energy consumption of the process. The authors have intensively focused on the development of innovative dephosphorization process by using so called “multi-phase flux” composed of solid and liquid phases. This article summarizes the research on the above topic done by the authors, in which the formation mechanisms of P₂O₅-containing phase during CaO or 2CaO·SiO₂ dissolution into molten slag, the phase relationship between solid and liquid phases at equilibrium, and thermodynamic properties of P₂O₅-containing phase have been clarified. The reactions between solid CaO or 2CaO·SiO₂ and molten CaO-FeO _x -SiO₂-P₂O₅ slag were observed by dipping solid specimen in the synthesized slag at 1573 K or 1673 K. The formation of the CaO-FeO layer and dual-phase layer of solid 2CaO·SiO₂ and FeO _x -rich liquid phase was observed around the interface from the solid CaO side toward the bulk slag phase side. Condensation of P₂O₅ into 2CaO·SiO₂ phase as 2CaO·SiO₂-3CaO·P₂O₅ solid solution was observed in both cases of CaO and 2CaO·SiO₂ as solid specimens. Measurement of the phase relationship for the CaO-FeO _x -SiO₂-P₂O₅ system confirmed the condensation of P₂O₅ in solid phase at low oxygen partial pressure. The thermodynamics of 2CaO·SiO₂-3CaO·P₂O₅ solid solution are to be clarified to quantitatively simulate the dephosphorization process, and the current results are also introduced. Based on the above results, the reduction of CaO consumption, the discharged slag curtailment, and energy-saving effects have been discussed.     

Macrosegregation in ESR and VAR Processes

The method of heat generation, heat transfer characteristics, and ingot structure are very different in the VAR and ESR processes, which result in different tendencies and mechanisms for macrosegregation formation in forged IN-718. Freckles are niobium rich and can be generated in both ESR and VAR, with higher incidence in ESR than VAR. White spots are niobium lean and can only be found in VAR-processed materials. Freckles are indige-nous in nature, and result from the flow of solute-rich interdendritic liquid in the mushy zone during solidification. The most plausible cause for white spots is exogenous material, which remains unmelted, falling into the molten pool. The best way to minimize the formation of freckles is to improve the ingot heat transfer rate, a more difficult task in ESR than in VAR.     

The Center for Microanalysis of Materials

“Excuse me,” said a graduate student that I’ve not seen before, “I’d like to get some time on the Auger.” “Fine” I reply, “If you are going to need a lot of time, Nancy will train you so that you can use the machine yourself. If it’s only a small project, she’ll work with you. In either case, see Nancy to get a session scheduled.” Shaking off the last remnants of sleep, I realize that I’ve forgotten the most important question, “Oh, just a minute …. Why? … I mean, what do you want to find out?” And so begins a discussion which leads to the recommendation that, instead of Auger spectroscopy, the student use a combination of SIMS and STEM. We schedule time appropriately.     

Laboratory Produced P/M Aluminum 2XXX + Zr Sheet

Laboratory procedures were established to produce advanced aluminum 2XXX+ Zr alloy powder metallurgy sheet in the T8X temper. The sheet was tested for tensile and Kahn Tear properties in the longitudinal and long transverse directions. The results from the laboratory-produced sheet were compared to the results of a pilot-scale NASA contractual study which used the same alloy powders, leading to the conclusion that laboratory-scale sheet properties are good to excellent predictors of the pilot-scale tensile properties and tear notch toughness values. Tear resistance toughness at pilot scale was not satisfactorily predicted by the laboratory results.     

Fibers for Structurally Reliable Metal and Ceramic Composites

NASA Lewis Research Center is presently involved in developing structurally reliable metal and ceramic matrix composites for application in advanced gas turbine engines. This paper examines the general property requirements for the high performance fibers of these composites. Also presented are examples of how these fiber property guidelines are influencing current fiber improvement and evaluation studies, with specific emphasis on commercially available boron and SiC fibers.     

A Combined Thermodynamic/Kinetic Modeling Approach to Predict SiC Recession Due to SiO2 Scale Volatility Under Combustion Environments

A computational approach, which targets on the prediction of SiC recession caused by SiO₂ scale volatility under combustion environments, was developed in this study. In this approach, thermodynamic calculation was integrated with a gaseous-diffusion model to calculate the fluxes of volatile species, such as SiO(g), Si(OH)₄(g), SiO(OH)₂(g), and SiO(OH)(g), produced by the reaction of SiO₂ scale with the combustion air. The resulted weight loss of SiC was then calculated under a variety of combustion environments. The benefit of using environmental barrier coating (EBC) in the protection of SiC from recession was demonstrated by the calculation. It is shown that the weight loss of SiC-based ceramics could be significantly reduced when EBCs, such as mullite (Al₆Si₂O₁₃ or written as 3Al₂O₃·2SiO₂) or SrAS₂ (SrO·Al₂O₃·2SiO₂), are used. The effects of combustion conditions, such as temperature and total pressure, on the volatility of SiO₂ scale were also discussed.     

An Efficient Reactor for High-Lead Slag Reduction Process: Oxygen-Rich Side Blow Furnace

This work reports an efficient reactor, i.e., oxygen-rich side blow furnace (OSBF), for high-lead slag reduction. An OSBF with a cross-sectional area of 8.4 m² was applied in an industrial-scale test and the results were compared with those from a traditional high-lead slag reduction reactor, i.e., blast furnace (BF), with which an additional electric heating fore well (EHFW) was connected for slag cleaning. By using the OSBF, Pb and Cu recoveries were raised by 1.07% and 7.99% compared with those from the traditional BF+EHFW, respectively. The optimal slag type for recovering metal values in the OSBF was also analyzed. Within the range of Fe/SiO₂ = 1.56–1.87 and CaO/SiO₂ = 0.8–1.05, lower Pb and Cu contents of the slag can be achieved with Fe/SiO₂ = 1.65–1.75 and CaO/SiO₂ = 1.0.     

Metal Corrosion Screening in a Nitrogen-Based Fuel at High Temperature and Pressure

We report here for the first time on a metal corrosion screening study of a novel nitrogen-based fuel under high temperature and pressure continuous combustion. The fuel consists of an aqueous urea and ammonium nitrate solution. Three austenitic stainless steels (SS) 316L, 310S, 330 were tested for 200 h under 20 MPa. One coupon set was positioned in the hot reactor zone, while a second set was placed in a colder zone. The temperatures in the hot and cooler zones were 745 ± 5 and 545 ± 5 °C, respectively. Microstructure, chemical composition, depth profile, and oxide scale thickness were studied by SEM/EDS and TOF-SIMS analyses. The heaviest corrosion was observed in the hot reaction zone for 316L SS. No protective Cr-rich oxide films were found in the scales formed on all tested SS.     

Synthesis and characterization of iron oxide nanoparticles by solvothermal method

In the present work iron oxide nanoparticles have been synthesized by alkaline solvo thermal method using anhydrous ferric chloride, sodium hydroxide, polyethylene glycol and cetyl trimethyl ammonium bromide and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermal Gravimetric Analysis (TGA). XRD indicated that the product is a mixture of different phases of iron oxide viz. gamma-Fe₂O₃ (maghemite, tetragonal), Fe₂O₃ (maghemite, cubic), Fe₃O₄ (magnetite, cubic) and ?-Fe₂O₃(epsilon iron oxide). FESEM studies indicated that size of the particles is observed in the range of about 19.8 nm to 48 nm. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR spectra indicated absorption bands due to O-H stretching, C-O bending, N-H stretching and bending, C-H stretching and Fe-O stretching vibrations. TGA curve represented weight loss of around 3.0446 % in the sample at temperature of about 180°C due to the elimination of the water molecules absorbed by the nanoparticles from the atmosphere.     

Processing and designing parts using structural reaction injection molding

A new process called structural reaction injection molding (SRIM) has been developed to combine the high strength and modulus properties of fiber reinforced composites with the advantages of the reaction injection molding process. Along with the process, a new reactive resin has been developed expressly for the structural RIM process. With the new resin and SRIM process conventional design methods can be used, but the designer must also consider several facets of the structural RIM process.     

Corrosion Resistance Enhancement of AZ91D Magnesium Alloy by Electroless Ni-Co-P Coating and Ni-Co-P-SiO2 Nanocomposite

Electroless Ni-Co-P coating and Ni-Co-P-SiO₂ nanocomposites were successfully applied on AZ91D magnesium alloy via environmentally friendly cerium-lanthanum-permanganate treatment and their properties were compared with traditionally binary Ni-P coating. The prepared coatings were analyzed using scanning electron microscopy, x-ray diffraction, and energy dispersive x-ray spectroscopy. Moreover, the corrosion behavior of the coatings in 3.5 wt.% NaCl was evaluated by two electrochemical methods. It is found that the Ni-Co-P coating possesses more uniform and compact structure and better corrosion protection characteristics in comparison with the Ni-P coating. The plating rate of Ni-Co-P bath is relatively lower than the Ni-P bath, but it significantly increases after addition of SiO₂ nanoparticles more probably due to adsorption of silica nanoparticles on alloy surface. The corrosion resistance of Ni-Co-P-SiO₂ composite coatings was superior with respect to Ni-P and Ni-Co-P coatings due to formation of thick and compact coating with tortuous grain boundaries.     

Polyolefin Nanocomposites with Enhanced Photostability Weathering Effect on Morphology and Mechanical Properties

This research aims to study the effect of accelerated weathering conditions on the photodegradation characteristics for fibrillar silicate clay-filled Polypropylene (PP) nanocomposites in the presence of metallocene linear low density polyethylene (m-LLDPE). Silane-treated attapulgite (ATP) clay along with ethylene octene elastomer-grafted maleic anhydride (POE-g-MAH) was used to compatibilize both blend and nanocomposite system. The result showed that developed PP/m-LLDPE nanocomposites displayed good UV resistance with little change in retained stress-at-break and elongation-at-break values. Balanced loss of toughness values noted maintaining higher fracture toughness values for nanocomposites containing 5 phr ATP clay. Infrared analysis was used to detect progress of degradation followed by change in carbonyl index revealed predominated chain scission in late irradiation, while crosslinking was dominant for initial irradiation period. An increase in crystallinity during UV exposure (chemi-crystallization) was detected with exposure time for all compositions and virtually independent of initial structure of the polymer. The highest value of crystallization observed for PP and the lowest one for nanocomposites containing 5 phr of ATP clay revealed good oxidation stability. Surface morphology revealed induced degradation throughout cross-section of PP, while severity of the surface degradation was significantly reduced for developed nanocomposites.     

Effect of applied potential on fatigue crack propagation behavior of API X80 steel in seawater

In the present study, the fatigue crack propagation (FCP) tests were conducted on X80 steel in air and artificial seawater (ASW) under various applied potentials to establish optimum and safe working limits of cathodic protection (CP). The slow strain rate test (SSRT) was also conducted on the X80 BM specimens in ASW under CP potential to identify the susceptibility of hydrogen affecting the FCP behavior. The CP potential of ?850 and ?1,050 mV_SCE suppressed the environmental effect of seawater on the FCP behavior of X80 BM and WM specimens, showing almost identical da/dN-ΔK curves for both air and ASW environments. The SSRT in ASW under CP potential of ?1,050 mV_SCE suggested that the X80 BM specimen steel is susceptible to hydrogen embrittlement, but the effect of hydrogen was believed to be marginal in affecting the FCP behavior of the X80 specimens at a loading frequency of 10 Hz. The FCP behavior of high strength X80 steel is discussed based on the fractographic observation to understand the FCP mechanism in seawater under various CP potentials.     

面向敏捷生产调度与控制的基于MAS的制造系统

面对动态制造环境中制造系统必须面对的时间不确定性、设备可靠性/可用性、订单变化、人力资源变化等问题,提出一种面向敏捷生产调度与控制的基于MAS的制造系统组织框架以支持进行有效的生产调度和控制.引入招投标方法实现任务的分解与分配,通过制造任务的分解与分配建立各层Agent之间的协调工作及协同决策机制;采用能力匹配与动态调度相结合的方法实现任务分配与调度控制的有效集成;面向生产任务需求动态确定Agent粒度、组建MAS模型;为了便于构造各种Agent,提出一种Agent的多层混合结构.从而制造系统中的各种制造资源被重组成为Agent网络,使其能够利用各种Agent的自治和合作特性适应制造环境的变化,实现动态调度与控制.     

Spectroscopic and microscopic evaluation of immobilized cytochrome c interaction with cyanide/arsenic ligands in quantitative analysis

The electrochemical, spectroscopic and microscopic analyses of cytochrome c and its immobilization on bare glassy carbon (GC) and platinum (Pt) electrodes were performed. Cytochrome c interaction was examined by studying cyanide and arsenic as model compounds for these types of behavior. Subtractively normalized interfacial Fourier transform infrared (SNIFTIR) spectroscopy, fluorescence and electrochemical methods, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to characterize the protein in the immobilized state and to confirm that the protein was not denatured upon binding to the pre-treated bare GC and Pt electrodes. The spherical morphology of the immobilized protein, which is typical of native cytochrome c, was observed using AFM. The protein binding was monitored as a decrease in peak currents (by CV) for the immobilized protein. Under analysis was also a decrease in emission intensities by fluorescence in solution, by the FTIR and SNIFTIR spectroscopies. Fluorescence and AFM proved the existence of the binding process between the protein and the analytes. This behavior was confirmed by the FTIR and SNIFTIR spectroscopies, which gave evidence that the binding event took place at the amino acids side chain of the protein.     

Extracting Regularities in Space and Time Through a Cascade of Prediction Networks: The Case of a Mobile Robot Navigating in a Structured Environment

We propose that the ability to extract regularities from time series through prediction learning can be enhanced if we use a hierarchical architecture in which higher layers are trained to predict the internal state of lower layers when such states change significantly. This hierarchical organization has two functions: (a) it forces the system to recode sensory information progressively so as to enhance useful regularities and filter out useless information; and (b) it progressively reduces the length of the sequences which should be predicted going from lower to higher layers. This, in turn, allows higher levels to extract higher-level regularities which are hidden at the sensory level. By training an architecture of this type to predict the next sensory state of a robot navigating in an environment divided into two rooms, we show how the first-level prediction layer extracts low-level regularities such as 'walls', 'corners' and 'corridors', while the second-level prediction layer extracts higher-level regularities such as 'the left side wall of the large room'. The extraction of these regularities allows the robot to localize its position in the environment and to detect changes in the environment (e.g. the presence of a new object or the fact that a door has been closed).     

多智能体系统在焊接柔性制造系统中的应用

焊接柔性制造系统 (WFMS)已经成为焊接自动化生产的一个重要的发展趋势。面对这样高度集成 ,高度复杂的自动化生产系统 ,采用单一的基于定量数学模型的传统控制理论和技术的控制系统已经不能对其实施有效的控制了。分布式人工智能 (DAI)领域中的多智能体系统 (MAS)的理论和技术已经应用于柔性制造系统。由于WFMS内在的分散性 (时间、空间和功能上的分散性 )以及它与MAS的内在联系和相似性 ,使得MAS成为WFMS的最佳控制策略之一。文章介绍了DAI中的MAS的概念和特点 ,讨论了MAS的网络结构及组织结构。针对WFMS的结构特点和焊接生产工艺特点 ,详细讨论了MAS系统和WFMS系统之间的内在联系以及MAS应用于WFMS的可行性。