Behavior of a submicrocrystalline aluminum alloy 1570 under conditions of cyclic loading

A study of the resistance to fatigue-crack growth in a submicrocrystalline alloy Al-6% Mg-0.3% Sc-0.4% Mn in combination with a precision analysis of the fracture surface of the samples has been performed. A comparison of crack resistance between coarse-grained and submicrocrystalline states of this alloy showed that only at the stage of near-threshold crack growth the velocity of fatigue-crack propagation in the submicrocrystalline state proves to be higher than that in the coarse-grained state. At the stage of linear crack growth, the fatigue-crack propagation becomes insensitive to the grain size. Upon transition to the stage of accelerated crack growth, the velocity of crack propagation in the submicrocrystalline alloy is retarded. A fractographic analysis of the fracture surface of the samples indicates that the retardation of the fatigue-crack growth in the submicrocrystalline alloy is connected with a gradual transition from the intercrystalline to the transcrystalline mechanism of fatigue fracture of the material.     

Rapid amorphization of molecular crystals by absorption of solvent molecules in the presence of hydrophilic matrices

Two organic molecular crystalline species, ibuprophen (IB) and indomethacine (IM) were subjected to methanol absorption in the presence of hydrophilic organic matrix, hydroxypropyl methylcellulose (HPMC). While spraying of 8–10% methanol or water on the drug–matrix mixture decreased the subsequent milling time for amorphization, absorption of methanol in a closed container caused spontaneous amorphization of IB was observed to give a nanocomposites with macroscopic agglomerates up to 250 μm after methanol absorption for overnight. Gentle mechanical homogenization under saturated methanol vapor with a newly developed apparatus, a tandem rotation mill (TRM), brought about homogeneous grains of IB-HPMC nanocomposites with the average particle size, 30 μm. We observed amorphous particles of IB in 60 nm regime dispersed in HPMC matrix under a transmission electron microscope (TEM). In the case of IM, mechanical homogenization with TRM was indispensable to obtain similar nanocomposites with HPMC.     

Thermophysical Property Measurements of Liquid Gadolinium by Containerless Methods

Thermophysical properties of liquid gadolinium were measured using non-contact diagnostic techniques with an electrostatic levitator. Over the 1585 K to 1920 K temperature range, the density can be expressed as ρ(T) = 7.41 × 10³ − 0.46 (T − T _m) (kg · m⁻³) where T _m = 1585 K, yielding a volume expansion coefficient of 6.2 × 10⁻⁵ K⁻¹. In addition, the surface tension data can be fitted as γ(T) = 8.22 × 10² − 0.097(T − T _m)(10⁻³ N · m⁻¹) over the 1613 K to 1803 K span and the viscosity as η(T) = 1.7exp[1.4 × 10⁴/(RT)](10⁻³ Pa · s) over the same temperature range.     

Generation control circuit for photovoltaic modules

Photovoltaic modules must generally be connected in series in order to produce the voltage required to efficiently drive an inverter. However, if even a very small part of photovoltaic module (PV module) is prevented from receiving light, the generation power of the PV module is decreased disproportionately. This greater than expected decrease occurs because PV modules which do not receive adequate light cannot operate on the normal operating point, but rather operate as loads. As a result, the total power from the PV modules is decreased if even only a small part of the PV modules are shaded. In the present paper, a novel circuit, referred to as the generation control circuit (GCC), which enables maximum power to be obtained from all of the PV modules even if some of the modules are prevented from receiving light. The proposed circuit enables the individual PV modules to operate effectively at the maximum power point tracking, irrespective of the series connected PV module system. In addition, the total generated power is shown experimentally to increase for the experimental set-up used in the present study     

Microstructural factors affecting superplastic properties in magnesium-based composites

Effect of microstructural factors on superplastic behavior in magnesium-based composites was reviewed in order to obtain insights on ways to enhance the superplastic properties, such as highstrain-rate superplasticity, low-temperature superplasticity, and high ductility. The review shows that the reduction in grain size of the matrix directly increases the strain rate and/or decreases the temperature for optimum superplastic flow. The effect of reinforcement addition is shown to reduce the superplastic elongation, but enhance the superplastic strain rate, presumably owing to grain size stability of composites at high temperatures. Ductility enhancement is not necessarily attained by refining initial grain size. It is suggested that it is necessary to disperse the reinforcement uniformly in order to obtain higher ductility.     

Effect of Moisture on the High-Temperature Stability of Unidirectionally Solidified Al2O3/YAG Eutectic Composites

The corrosion resistance of a unidirectionally solidified alumina/yttrium aluminum garnet (Al₂O₃/YAG) eutectic mixture was investigated at high temperature. Samples were exposed to high temperature (1200°–1800°C) in different atmospheres, which included argon, argon/water vapor, air, and air/water vapor. The most important microstructural changes occurred at the interface between the YAG and the Al₂O₃. Those changes consisted of localized thermal grooving, especially when the corrosive atmosphere contained water vapor. The samples exhibited significant weight loss at high temperature (1800°C) after 20 h of exposure. The calculated volume gain that was induced by the increased surface relief was low and limited, except when the corrosive atmosphere contained air, which indicated that the presence of air (particularly oxygen) induced a more-active corrosion process. On the other hand, no change in the flexural strength was observed, even after 100 h at 1800°C in a humid atmosphere, because of the cross-linked structure of the composite, which limited propagation of the groove.     

New Sol–Gel Route for the Preparation of Pure α-Alumina at 950°C

An anhydrous alumina (Al₂O₃) sol was prepared from aluminum isopropoxide and an organic solvent, using an acetic acid stabilizer. The complete conversion of the dried sol to α-Al₂O₃ was accomplished at a temperature of 950°C by a single transition via γ-Al₂O₃. Al₂O₃ that was deposited via dip coating resulted in amorphous films, even after annealing at 1100°C, because of the silicon diffusion from the substrate. This phenomenon was avoided using a rapid thermal treatment in a flame after dip coating, which resulted in uniform thin films that are converted to α-Al₂O₃ via heat treatment.     

A channel-erasing 1.8-V-only 32-Mb NOR flash EEPROM with a bitlinedirect sensing scheme

A 1.8-V-only 32-Mb NOR flash EEPROM has been developed based on the 0.25-μm triple-well double-metal CMOS process. A channel-erasing scheme has been implemented to realize a cell size of 0.49 μm² , the smallest yet reported for 0.25-μm CMOS technology. A block decoder circuit with a novel erase-reset sequence has been designed for the channel-erasing operation. A bitline direct sensing scheme and a wordline boosted voltage pooling method have been developed to obtain high-speed reading operation at low voltage. An access time of 90 ns at 1.8 V has been realized     

A mechanical sensorless control system for salient-pole brushlessDC motor with autocalibration of estimated position angles

In this paper, a mechanical sensorless control system is reported for salient-pole brushless DC motor drives. Here, two new methods are proposed for obtaining the position angle, the accuracy of which affects the operation of the switching devices of the inverter that drives the motor. First, the method for estimating the position angle is proposed. Secondly, the correcting method for reducing the errors involved in the estimation of position angle is given. The experimental results show that the estimated position angles are calibrated automatically, and then the proposed sensorless control system can control the speed and the position angles of the motor precisely