Browsing by Author "Kao, YL"

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A study on the hardness variation of alpha- and beta-pure titanium with different grain sizes
(2005-05-25)
Kao, YL
;
Tu, GC
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Huang, CA
;
Liu, TT
;
材料科學與工程學系
In this study, the hardness and the microstructure of alpha and beta-pure Ti treated with different grain sizes were investigated. The alpha-Ti specimens were obtained by heating pure Ti at 750 degrees C for various periods and then quenched in water, while the beta-Ti specimens by heating at 1000 degrees C for various periods and then quenched in water. Experimental results show that the hardness of a-Ti decreased with increasing the grain size; whereas, the hardness of beta-Ti tends to increase with increasing grain size. From the microstructures examined with transmission electron microscope, it can be realized that the strengthening mechanisms of alpha- and beta-Ti are quite different. Grain boundary could be the main strengthening microstructure of alpha-Ti and the smaller grain size the higher hardness. The major strengthening microstructure of beta-Ti was martensitic twin with a very high dislocation density. The amount of martensitic twin increased with increasing the grain size of beta-Ti and, therefore, the larger grain size the higher hardness. (c) 2005 Elsevier B.V. All rights reserved.
Hard chromium plating on cold swaged Cr-Mo steel using rotating cylinder electrode
(2000-08-01)
Huang, CA
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Tu, GC
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Liao, MC
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Kao, YL
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材料科學與工程學系
Microstructural study of the effect of chloride ion on electroplating of copper in cupric sulfate-sulfuric acid bath
(2005)
Kao, YL
;
Li, KC
;
Tu, GC
;
Huang, CA
;
材料科學與工程學系
The purpose of this work is to study the electrocrystallization behavior of the copper deposit on pure titanium substrate. The electroplating was conducted at 0.7 A/cm(2), 65 degrees C in cupric sulfate-sulfuric acid bath with various chloride additions (45-350 ppm). Initial growth morphology and microstructure of the deposit were examined with a field-emission scanning electron microscope (FESEM) and a high-resolution transmission electron microscope integrated with an energy-dispersive X-ray spectrometer. Results of cathodic polarization and galvanostatic plating experiments show that the increasing concentration of chloride ions in the plating bath would significantly increase the cathodic potential. This cathodic potential increase was found to be induced by the presence of CuCl precipitates on the cathodic surface as well as on the copper cluster formed during the electrocrystallization process. At the initial plating stage, both copper and hexagonal-shaped CuCl precipitates were produced simultaneously. Eventually, the pyramid-shaped CuCl precipitates were observed, which consisted of many parallel hexagonal planes stemming from a screw dislocation. The polarization effect of CuCl precipitate on the Ti substrate was further confirmed and clarified. Through measurement of the electrode response and investigation of the deposit using FESEM, it was observed that under identical electroplating conditions, much less CuCl forms on a copper substrate in the initial stages than on a titanium substrate, leading to lower polarization. (c) 2005 The Electrochemical Society.
The annealing behavior of copper deposit electroplated in sulfuric acid bath with various concentrations of thiourea
(2004-09-25)
Kao, YL
;
Tu, GC
;
Huang, CA
;
Chang, JH
;
材料科學與工程學系
The annealing behavior of electroplated copper deposits is reported in this study. The copper deposits were electroplated with a current density of 0.7 A/cm(2) at 53 degreesC in a sulfuric acid bath containing various concentrations of thiourea. The hardness values of the copper deposits were measured before and after annealing, and the differential scanning calorimetry (DSC) diagrams of the as-electroplated copper deposits were recorded. An improvement of the softening resistance of the copper deposits was observed when the bath contained thiourea greater than or equal to3 mg/L. By adding thiourea in the plating bath, smaller grain size of the copper deposits can be achieved. As thiourea content increased greater than or equal to3 mg/L, the twin boundary of the copper deposits was significantly increased, and many sulfur-rich particles were deposited along the grain boundaries and a few within the grains of the deposit. These sulfur-rich particles are capable of impeding migration of the grain boundaries and improving the softening resistance of the copper deposits during annealing. The aforementioned microstructures of the copper deposits were examined with transmission electron microscope (TEM) integrated with energy-dispersive X-ray spectrometer (EDX) for chemical composition analysis. (C) 2004 Elsevier B.V. All rights reserved.
The effect of 180 degrees C-annealing on the electrochemical behavior of nano-thick zinc-electroplated copper in aqueous solutions with different pH
(2006-02-01)
Kao, YL
;
Tu, GC
;
Huang, CA
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The anodic polarization and a.c. impedance measurements of 4 nm- and 25 nm-zinc-electroplated copper specimens were conducted in aqueous solutions with four different pH-values. The nano-thick zinc-electroplated copper was tested after electroplating and annealing at 180 degrees C for 1, 2 and 3 h, respectively. The results showed that the open-circuit potential (OCP) of 25 nm-zinc electroplated copper shifted toward noble potential after annealing. A more noble OCP of 25 nm zinc-electroplated copper could be achieved when zinc plated copper was annealed at 180 degrees C up to 1 h. Similar change was found for 4 nm-zinc electroplated copper only in neutral and alkaline solutions. The a.c. impedance response of all nano-thick zinc-electroplated copper corresponded to two Randle's circuits in series, in which the circuit measured in a high frequency region of their Nyquist diagrams revealed the electrochemical behavior of nano-thick zinc deposits. The charge transfer resistance of the nano-thick zinc electroplated copper was significantly raised after annealing at 180 degrees C when tested in pH 9.5 solution. Microstructures of the aforementioned nano-thick zinc electroplated copper were examined with cross-sectional TEM specimens. A distinct phase interface between zinc and copper was observed for as plated specimens, while alloying of zinc and copper at the interface was detected after annealing at 180 degrees C for 1 h. Electroplated zinc diffused into the copper foil during the 180 degrees C-annealing and the corrosion potential of the anodic polarization curve indicated the condition of the alloy surface. The annealing effect of 4 nm- and 25 nm-zinc eleetro-plated copper specimens could be related to the results of electrochemical measurement. (C) 2005 Elsevier Ltd. All rights reserved.