Plastic Deformation of <111> Oriented Aluminum Single Crystals

It is known that an aluminum single crystal having tensile orientation shows an initial rapid hardening, and that its flow stress increases gradually until failure. However, many problems pertaining to the deformation mechanism of the oriented single crystal remain unsolved. In the present study, to clarify the deformation mode of aluminum single crystals having multiple slip orientations, tensile test were performed at various temperatures on oriented single crystals. At room temperature, the oriented single crystal deformed only by fine multiple slips, and the flow stress increased with an increase of strain until failure. On the other hand, the coarse wavy slips composed of {111} and {100} slips occurred at high temperatures, such as 473K. In the single crystal having a tensile orientation deviated from by a few degrees, the clustered slips were observed in addition to the fine multiple slips. It is concluded that the deformation mode and flow stress of the single crystal are very sensitive to the tensile oriention in the vicinity of

Effect of Deformation Temperature on the Stage IV Deformation in <100> Oriented Aluminum Single Crystal

It is known that at room temperature the tensile stress-strain curve of an aluminum single having tensile orientation becomes flat after about a two percent elongation. (This flat region of the stress-strain curve is named Stage IV). In the previous paper, the propagation of a clustered slip accompanied by a prominent cross slip was observed in the Stage IV region of curve. In the present study, oriented aluminum single crystals were tested in tension at various temperatures so as to clarify the influence of temperature on the deformation mechanisms in Stage IV. At 203K, a few clustered slip lines accompanied by a prominent cross slip occurred, but they did not propagate in the entire region of the specimen. The stress-strain curve became flat only from about a ten percent elongation. In the crystal stretched at 77K, the cluster did not propagate at all from either end of the specimen, and so the stress-strain curve did not become flat. On the other hand, a wavy coarse slip was observed and the curve became flat from about a 0.5 percent elongation at 473K. It was suggested that these wavy slip lines were produced by a frequent repetition of the cross slip on two {111} planes and also possidly on a {110} plane having the same slip direction. It was confirmed that the occurrence of Stage IV is caused by the of the clustered slip accompanied by a prominent cross slip, and is much influenced by the temperature of deformation due to the easiness of the cross slip

Pneumatic direct-drive stepping motor for robots

A new type of pneumatic stepping motor, named pneumatic nutation motor, was developed. This motor achieves stepping positioning of 720 steps/rotation without any electrical devices or sensors mounted on the servo mechanisms. This makes the motor possible to be used under hazardous conditions such as in water and in strong magnetic fields where conventional electromagnetic motors cannot be used. The motor torque is so big that the motor can be used as a direct motor. In this report, the driving principle and design of this motor are presented. Its characteristics are analyzed experimentally and theoretically. The motors were applied to a parallel linkage mechanism with six degrees of freedom. The mechanism shows that the pneumatic nutation motors can be used as a direct servo motor for robot mechanisms.</p

Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars

Extensive statistical-equilibrium calculations on neutral sulfur and zinc were carried out, in order to investigate how the non-LTE effect plays a role in the determination of S and Zn abundances in F, G, and K stars. Having checked on the spectra of representative F-type stars (Polaris, Procyon, and alpha Per) and the Sun that our non-LTE corrections yield a reasonable consistency between the abundances derived from different lines, we tried an extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I lines for metal-poor halo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTE corrections amounting to <~ 0.2--0.3 dex, while LTE is practically valid for S I 8683/8694 lines. Embarrassingly, as far as the very metal-poor regime is concerned, a marked discordance is observed between the [S/Fe] values from these two abundance indicators, in the sense that the former attains a nearly flat plateau (or even a slight downward bending) while the latter shows an ever-increasing trend with a further lowering of metallicity. The reason for this discrepancy is yet to be clarified. Regarding Zn, we almost confirmed the characteristic tendencies of [Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars), since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive and gradually increasing towards lower [Fe/H]) are quantitatively of less significance (<~ 0.1 dex).Comment: 33 pages, 7 figures, PASJ, Vol. 57, No. 5 (2005) in pres

Effect of Grain Boundary on Pseudo-elastic Deformation of Cu-Zn-Si Bicrystal of Shape Memory Alloy

Two sorts of Cu-Zn-Si pseudo-elastic bicrystals of shape memory alloy were tested in tension to know the effects of the grain boundary. The remaining martensites were observed in the vicinity of the grain boundary, and the propriety of analyses through use of m/m。 and Nᵢj values and of the compatibility of the plastic strain were studied. The variant of martensite occurring primarily in each grain during deformation, can be predicted with use of them value (shear factor of the variant) in general. The analyses through use of m/mᵢ and Nᵢj values and the equations of the plastic strain compatibility are sufficiently useful to know the variant of martensite nucleated additionally in the vicinity of the grain boundary. However, the possibility of activation of slip must be considered in this case. The reversible strain of the isoaxial bicrystal is larger than that of the non-isoaxial bicrystal. However, the relation between the reversible strain and the misorientation of bicrystal is not yet sufficiently known

Corrosion Behavior of Amorphous Nickel-Valve Metal Alloys in Boiling Concentrated Nitric and Hydrochloric Acids

The corrosion behavior of amorphous nickel-base alloys containing titanium, zirconium, niobium, tantalum and/or phosphorus in boiling 9 N HNO_3 solutions with and without Cr^ ion and in a boiling 6 N HCl solution was investigated. In boiling 9 N HNO_3 solutions alloys containing 20 at% or more tantalum were immune to corrosion, maintaining the metallic luster, and Ni-40～60Nb alloys showed low corrosion rates of the order of μm/year. In the boiling 6 N HCl solution only tantalum-containing alloys were immune to corrosion although a higher tantalum content was required in the 6 N HCl solution in comparison with 9 N HNO_3 solutions. Protective surface films on the Ni-Nb and Ni-Ta-(P) alloys were composed exclusively of NbO_2(OH) and TaO_2(OH). Consequently, the corrosion resistance is not provided unless alloys contain elements, the passive film of which is highly stable in these aggressive boiling acids, such as tantalum

Studies on the Flow Patterns of Liquids in a Cylindrical Mixing Vessel, Over a Wide Range of Reynolds Number

The flow patterns of liquids agitated in a cylindrical mixing vessel without baffles were measured by a photographic method, ranging from laminar to so-called transitional flow. The authors are now able to discuss the flow pattern of the liquid and the discharge performance of the impellers over a wide range of Reynolds number, combined with the previous results published for the turbulent flow range. Some of the experimental results are shown in Figs. 6, 7, 8 and 10. The authors discovered the following results on the velocity distribution of the liquid : In the range of very small Reynolds number, the liquid velocity is considerably high only in the neighbourhood of the impeller and decreases abruptly with the distance from the impeller. On the other hand, in the range of high Reynolds number, secondary circulation flow occurs as shown in Fig. 9 and also the flow becomes turbulent, so that the liquid attains considerable velocity even at a distance from the impeller by the transmission of momentum, and the velocity distribution is considerably unified throughout the vessel. Concerning the discharge flow from the tip of the impeller blades which causes the secondary circulation, the non-dimensional quantities, Nq₁, and Nᴘ/Nq₁, are defined, as in the previous report. These values were calculated and the characteristic curves of discharge performance were obtained for various types of impellers (refer to Table 1), as shown in Fig. 12. Furthermore, the relations between flow pattern, discharge performance and power consumption (Nᴘ-Rₑ relation) were discussed

Flow Patterns of Liquids in a Cylindrical Mixing Vessel with Baffles

The velocity distribution of a liquid in a cylindrical mixing vessel with flatplate-baffles was measured by a method similar to that adopted in the case without baffles. Some of the experimental results are shown in Figs. 3, 4, 5, 6, 7, 8 and 9. Variations of the liquid velocity distribution caused by inserting baffle-plates are shown in Fig. 10. Obviously, the insertion of baffle-plates reduces the circulation flow around the impeller axis (the tangential component vₜ of liquid velocity) and increases the circulation flow in the vertical direction. The discharging performance of various impellers is represented by the ratio NₚB/Nq₁, which is the dimensionless factor corresponding to the relative power required for the unit quantity of discharge. The comparisons of these ratios for various impellers are shown in Table 3, together with those for the non-baffled condition. It is to be noted that, in spite of a considerable increase in Nq₁ the circulation efficiency of the agitators is eventually lowered by inserting baffle-plates. Furthermore, the power consumption in the neighbourhood of the impeller (Nᴘᵢₚₘ) was calculated and compared with that consumed in the outer region of the vessel (ΔNₚ) as shown in Table 4, It may be considered that the improvement in the circulating capacity is accomplished by the proper design of the baffle-plates