Duck-Gyu Lee

Deformation and annealing textures of silver wire

Abstract Silver is a rare material in which the major axial orientation component is 〈111〉 at low drawing reductions (less than about 90%) as other f.c.c. metals, but changes to 〈100〉 at high reductions (99%). Either orientation reduced to 〈100〉 after recrystallization. The further annealing gave rise to the 〈111〉 growth texture. The recrystallization texture could be explained based on the strain energy release maximization model, in which the absolute maximum internal stress direction determined by slip systems becomes parallel to the minimum Young’s modulus direction of recrystallized grains. The growth texture was discussed based on the mobility of the 〈100〉 and 〈111〉 tilt grain boundaries.

Deformation and recrystallization textures of surface layer of copper sheet

Abstract The texture of the surface layer of a 93% cold rolled copper sheet was approximated by {001}〈110〉, which changed to a new texture which may be approximated by {034}〈100〉 on recrystallization. The shear texture {001}〈110〉 was calculated to be stable at de12/de11 = √2 where subscripts 1 and 2 indicate the rolling direction and the sheet normal direction, respectively. The shear texture and related recrystallization texture did not have a common 〈111〉 relationship, which is usually regarded as a token of the oriented growth theory for recrystallization. The {034}〈100〉 orientation did not exist as a stable orientation under the condition of the shear texture being stable, which does not seem to support the oriented nucleation theory. The measured texture orientation, {034}〈100〉, is very close to the {01√2}〈100〉 orientation which is predicted by the maximum energy release theory in which the absolute maximum normal stress direction in the deformed matrix becomes parallel to the minimum elastic modulus direction of recrystallized grains.

The role of superhydrophobicity in the adhesion of a floating cylinder

Horizontal cylinders floating on liquid surfaces are mundanely observed, whose examples include the legs of aquatic arthropods and floating larvae, twigs and hairs. We study the force and energy required to lift the cylinder clear from the water surface, to evaluate the role of wettability, especially superhydrophobicity, in the adhesion of floating cylinders. We find that a drastic degree of energy saving is achieved when lifting a superhydrophobic cylinder as compared with a cylinder with moderate wettability. This can serve as a starting point to understand how the superhydrophobicity of the legs of water-walking insects help to propel them efficiently.

Sinking of small sphere at low Reynolds number through interface

A dense solid sphere gently released on an air-liquid interface slowly sinks into liquid due to gravity, while the motion is resisted by viscous and capillary forces. Here, we predict the sinking velocity of the interface-straddling sphere by a simplified model and experimentally corroborate the results. The viscous drag on the sphere is determined by integrating the surface stress, which is the solution of the Stokes equation, over the wetted area that changes with time. To compute the interfacial tension force that depends on the meniscus profile, we solve the dynamic boundary condition for the normal and tangential stresses at the air-liquid interface. The predicted sinking velocity, a function of the sphere density and radius, liquid density, viscosity and surface tension, and the dynamic contact angle, is in good agreement with the experimental measurements except for the late stages when meniscus snapping occurs. We also construct a scaling law for the steady velocity of a sinking sphere, which give...

A model of the development of recrystallization textures in body centered cubic metals

Abstract A model of the evolution of recrystallization textures for b.c.c. metals was suggested based on the texture change during annealing of cold rolled steel. The model relies on two principles: first, the maximum principal stress direction in the deformed grain becomes the minimum Youngs modulus direction in the recrystallized grain; second, a 110 plane, parallel to the maximum principal stress direction (and hence, minimum Youngs modulus direction), is taken as an invariant plane. The predictions obtained using the current model are compared with experimental results and discussed in cold rolled b.c.c. metals (steel, tantalum, molybdenum, tungsten, etc.).

The effect of rolling conditions on the strength and microstructure of dispersion strengthened copper strips

The effect of rolling conditions on the strength and microstructure of alumina dispersed copper strips was investigated. Commercial strips, Glidcop Al-25, were rolled to similar total reductions by one or multiple passes at room temperature or at 540°C. The specimens rolled at room temperature (cold rolled specimens) had higher strength and hardness than those rolled at 540°C (warm rolled specimen), when rolling schedules were the same. The strength and hardness of the cold rolled specimens were little influenced by the number of rolling passes, whereas the multi-pass warm rolled specimen had lower strength and hardness and higher elongation than the single-pass warm rolled specimen. The structure of specimens is characterized by banded substructures and their strength could be expressed as a function of the band size. In warm rolled strips, no dynamic recrystallization occurred, but the band growth was observed.

Evolution of {110}〈110〉 texture in silver sheets

Abstract Texture studies of silver have been motivated by its potential use for substrates of high temperature superconductors. The {110}〈110〉 texture is known to be the most desirable. In this study, a 99·9% silver sheet was rolled by 31–96% reductions in thickness and annealed. The textures of the rolled and annealed silver samples consisted of many components including the {110}〈110〉 and {110}〈112〉 components. The evolution of the rolling and annealing textures has been discussed based on crystal plasticity, recrystallisation and growth.

Enhanced Water Condensation Rate by the Mirco/nano Textured Surface

Extended Abstract Morphological studies on the surfaces of insects and plant leaves in arid and humid environments have led to the understanding of the role played by those surfaces for living in the harsh environments. Especially, the functional surface for the water condensation has been growing interest due to its relevance to the global issue of a water shortage. Motivated by the water harvest behaviour of beetles [1], we developed a high efficient surface for the water condensation. The functional surface was mimicked by the insect of which cuticles harvest water even in the water shortage region like a desert. It is well known that the surface of the insect is superhydrophilic so that the surface easily enables the humid air to be nucleated there. To make such a high energy surface, we treated a substrate using a metallizing method. The metallizing is a process for the metal coating onto the surface of objects. We used aluminium wire with 390 μm in diameter and fed into a hot nozzle at a rate of 110 mm/s to melt it. The air was blown into the nozzle and then the melted aluminium metal spreads to the substrate in the form of mico/nano powders. To deposit the metal uniformly onto the surface, we varied the angle of blowing and the number of coating. We experimentally found the optimized conditions for the uniform coating. During the water condensation, the surface wettability plays an important role as aforementioned. However, the persisting wettability is another critical parameter that affects the performance of water condensation. To sustain the wettable surface, we chemically oxidized the substrate with a surfactant. We first mixed the surfactant powder with distilled water in the ratio of 1 to 20 by weight. Then the aluminium metallized substrate was immersed into the surfactant liquid and sonicated for 15 min. The substrate was finally rinsed with distilled water for 15 min and dried by blowing nitrogen gas. To quantify the maintenance duration of the wettability, we measured the contact angle of the substrate with water every day. We observed that the surfactant treatment allows the wettability to last over 140 days. To verify the enhanced water condensation rate by the surface, the metallized substrate after the treatment of oxidation was exposed to the humid air. We performed the experiment in the constant temperature and humidity chamber