Enhancement of Strength and Ductility of Al-Ag Alloys Processed by High-Pressure Torsion and Aging

This research was conducted by the application of high-pressure torsion (HPT) to Al-X wt pct Ag alloys (X = 5, 11, 20). Grain refinement was achieved to the size of ~300 nm after HPT processing at room temperature. The aging behavior of the alloys after HPT processing was investigated using Vickers microhardness measurement, tensile testing, scanning electron microscopy, and transmission electron microscopy. This study confirms the dual effect of grain refinement and fine precipitation on the enhancement of the strength. It is also shown that at peak-aged condition, the tensile strength is enhanced while maintaining considerable ductility.     

Thermal conductivity reduction of crystalline silicon by high-pressure torsion

We report a dramatic and irreversible reduction in the lattice thermal conductivity of bulk crystalline silicon when subjected to intense plastic strain under a pressure of 24 GPa using high-pressure torsion (HPT). Thermal conductivity of the HPT-processed samples were measured using picosecond time domain thermoreflectance. Thermal conductivity measurements show that the HPT-processed samples have a lattice thermal conductivity reduction by a factor of approximately 20 (from intrinsic single crystalline value of 142 Wm⁻¹ K⁻¹ to approximately 7.6 Wm⁻¹ K⁻¹). Thermal conductivity reduction in HPT-processed silicon is attributed to the formation of nanograin boundaries and metastable Si-III/XII phases which act as phonon scattering sites, and because of a large density of lattice defects introduced by HPT processing. Annealing the samples at 873 K increases the thermal conductivity due to the reduction in the density of secondary phases and lattice defects.     

Fabrication and Sintering of Fine Yttria-Doped Ceria Powder

Yttria–doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most–important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape–casting applications of the powder in particular, was more effective than wet milling. Tape–cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.     

Analysis of hair follicle penetration of lidocaine and fluorescein isothiocyanate-dextran 4 kDa using hair follicle-plugging method

Objective: Skin appendages including hair follicles (hfs) and the stratum corneum (sc) are beginning to be recognized as important permeation pathways for the skin permeation of drugs, but their detailed role is not yet clear. To investigate the contribution of hfs to drug permeation, we conducted skin permeation tests by controlling the hf contribution with a hf-plugging method.

Method: Lidocaine (LC) and fluorescein isothiocyanate-dextran 4?kDa (FD-4) were selected as model drugs and pig ear skin was used as model skin.

Results: Skin permeabilities of ionized LC and FD-4 decreased with hf-plugging, whereas no change was observed for the skin permeation of unionized LC. A fairly good correlation was found for ionized LC and FD-4 between skin permeability and the number of hfs plugged. Permeation parameters of model drugs for both skin pathways were calculated utilizing Fick's second law of diffusion. Consequently, the sc pathway could highly contribute to the permeation of unionized LC, since unionized LC shows markedly high partition to the sc. In contrast, the hf pathway could contribute to the permeation of ionized LC and FD-4, since these had high distributions to the hf pathway in spite of its very small surface area relative to whole skin surface area.

Conclusion: The hf pathway must be important for the skin permeation of ionized compounds and hydrophilic high molecular compounds. hf-plugging is also a useful method for assessing the skin permeability of compounds through the hf pathway.     

Effects of impurities on the degradation and long-term stability for solid oxide fuel cells

The effect of impurities on the degradation of performances was investigated for the flatten tube type SOFC stack. The durability tests of 20-cells stack were conducted at 750 °C (1023 K) with dry H₂ for more than 5000 h under a constant current density of 0.3 A cm⁻². The voltage loss showed a linear relationship between voltage loss and operation time (about 1.5%/1000 h). The ohmic resistance increased with operation time while the polarization resistance showed constant values. After the long-term operation test, the concentration levels of impurities were measured at cathode and interlayer by secondary ion mass spectrometry (SIMS). The concentrations of several elements were successfully determined in ppm levels. The concentrations of several elements increased with operation time (Na, Al, Si, and Cr), which suggested the transports and depositions on the cell component surface. The increase of resistance and impurity concentration at the interlayer were estimated from the literature data and SIMS impurity analysis.     

Using ring samples to evaluate the processing characteristics in high-pressure torsion

An Al–3% Mg–0.2% Sc alloy was processed by high-pressure torsion (HPT) using samples in the form of solid disks and rings. Following HPT, all values of the measured Vickers microhardness fall onto a single curve when plotted against the equivalent strain, such that there are increasing values of hardness at the lower strains and hardness saturation above equivalent strains of ～40. This saturation level is independent of the number of revolutions and the applied pressure. The grain size following HPT is ～220 nm, and tensile tests show that the material is superplastic at a testing temperature of 573 K.     

Long-term clinical course of Peyronie's disease treated conservatively

BACKGROUND: To evaluate the natural history of Peyronie's disease and to determine the suitable time for surgical treatment, we investigated changes of clinical findings of the disease over time. PATIENTS AND METHODS: We evaluated changes of plaque size, penile curvature and erectile dysfunction in 10 patients with Peyronie's disease. The mean follow-up period was 36.8 months. RESULTS: At the first examination, the mean plaque size of patients with erectile dysfunction was larger than that of those without erectile dysfunction, suggesting a positive association between size and erectile function. There was no significant relationship between plaque size and penile pain or penile curvature. The mean size of plaques decreased significantly compared with that at the first examination (p < 0.05). However, penile curvature, pain and erectile dysfunction persisted during the follow-up period in all but one patient, who showed improvement of penile curvature. CONCLUSION: These results suggest that we may recommend a shorter observation period until surgery that we have done for some patients who want to be surgically treated.     

Microhardness measurements and the Hall-Petch relationship in an Al---Mg alloy with submicrometer grain size

An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements.     

The age-hardening characteristics of an AI-6061/AI2O3 metal matrix composite

Experiments were conducted to determine the age-hardening behavior of an Al-6061 metal matrix composite reinforced with ∼20 vol pct of A1₂O₃ microspheres and prepared using liquid metallurgy processing. The presence of alumina microspheres increases the dislocation density in the matrix of the composite in the as-quenched state and, by comparison with the monolithic alloy, this leads to a significant increase in the yield stress in the as-quenched and unaged condition. From measurements of the 0.2 pct proof stress, there is no evidence for any significant acceleration in the aging process in the composite material: both materials attain similar peak-aged conditions after essentially the same aging times. The microstructures of the composite and the monolithic alloy are similar in the peak-aged condition, with a high density of fine needlelike β″ precipitates and, in the over-aged condition, with a reasonably homogeneous distribution of the rod-shaped β′ phase. It is proposed that the aging behavior is better quantified by determining the yield stress rather than by taking hardness measurements. Formerly Visiting Scholar, Kyushu University,