Browsing by Author "Liu, Tzeng-Feng"

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A facile cosolvent/chelation method for the preparation of semi-crystalline CuCl2(ethylene glycol)/poly(3-hexylthiophene) complexes displaying specific luminescence properties
(2015-01-01)
Lu, Fang-Hsien
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Mohamed, Mohamed Gamal
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Liu, Tzeng-Feng
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Chao, Chuen-Guang
;
Kuo, Shiao-Wei
Semi-crystalline CuCl2(ethylene glycol)/poly(3-hexylthiophene) complexes (CE-P3HT) with specific textures and self-assembled structures can be fabricated using a facile co-solvent/chelation method. The morphologies and self-assembled structures of these CE-P3HT complexes were dependent on the concentration of CuCl2(ethylene glycol) (CuCl(2)EG) in solution. Transmission electron microscopy (TEM) revealed the CE-P3HT sample comprising EG and numerous CuCl2/P3HT dots (C-P3HT dots) that originated from the P3HT main chains interacting with CuCl2 crystals; the average size of this C-P3HT dots was ca. 20 nm. Prior to formation of the solid state of CE-P3HT structures, the CE-P3HT complex in solution displayed a novel phenomenon: a specific luminescence property with an absorption energy gap of 3.71-4.46 eV. This quantum effect resulted from the chelates formed between the Cu2+ ions and the thioether units of the conjugated P3HT polymer.
A novel high-strength, high-ductility and high-corrosion-resistance FeAlMnC low-density alloy
(2013-03-01)
Chen, Po-Chih
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
;
Department of Materials Science and Engineering
The as-quenched Fe-8.68 wt.% Al-30.5 wt.% Mn-1.85 wt.% C alloy is plasma-nitrided at 500 degrees C for 8 h. The nitrided layer obtained is 40 mu m thick and composed predominantly of AlN, with a small amount of Fe4N. The resultant surface hardness (1860 Hv), substrate hardness (550 Hv), ductility (33.6%) and corrosion resistance in 3.5% NaCl solution in the present nitrided alloy are far superior to those obtained previously in optimally nitrided high-strength alloy steels, as well as martensitic and precipitation-hardening stainless steels. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
A quenching method for the preparation of metal oxide-polythiophene composites having fiber structures
(2014-01-01)
Lu, Fang-Hsien
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Mohamed, Mohamed-Gamal
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Liu, Tzeng-Feng
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Chao, Chuen-Guang
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Dai, Lizong
In this study we developed a simple quenching method to fabricate metal oxide (CuO, ZnO, TiO2, Fe(OH) 3)polythiophene (PT) composites. By varying the metal oxide, PT, and rate of crystallization, we could control the fiber morphology in these composites. Four-probe-station analyses revealed that the conductivities of these metal oxide-PT composites ranged from 10(-5) to 10(-3) S cm(-1), higher than that of any species of metal oxide alone (from 10(-10) to 10(-7) S cm(-1)), because the fiber morphology behaved as an exceptional transmission factor for electrons. Moreover, these metal oxide-PT composites exhibited the characteristics of colloids, as well as high viscosity, suggesting that they could also be applied as coatings on silicon and glass substrates, and could provide the opportunity to form useful materials for large-scale gas sensors due to good flexibility and porosity. UV-vis spectroscopic analyses revealed variations in the energy level (>3.37 eV for ZnO) and confirmed the mechanism of the morphology change of the composite.
A study of weldability and fracture modes in electron beam weldments of AZ series magnesium alloys
(2006-11-05)
Chi, Chao-Ting
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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Wang, Che-Chung
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材料科學與工程學系
Given the growing need for environmental protection and lightweight construction, electron beam welding (EBW) is becoming the most important welding technology because it can compensate for the poor formability of magnesium alloys. This paper examines interactions between the properties of three AZ series magnesium alloys and welding conditions. The EBW process can yield four kinds of defect in a weld: cavities, the heat-affected zone (HAZ), undercuts, and root concavities. These defects obviously induce stress concentrations in the weld, and may seriously damage its strength. Additionally, the distribution of precipitates (gamma phase, Mg17Al12) in the fusion zone (FZ) changes from a relatively small number of scattered particles to a dense population of dendrites as the Al content of the magnesium alloy increases. Under excessive tensile stress, alloy weldments break in one of two fracture modes: an irregular FZ fracture, or a regular HAZ fracture. AZ31B usually exhibits the former mode and AZ91D the latter, while AZ61A exhibits each mode half the time. The overall weldability, which depends on the random distribution of these precipitates and defects, is found to be greatest for the AZ61A alloy. The best process window, on the other hand, is found for the AZ91D alloy. Finally, we obtain optimum parameters for the EBW process and empirical formulae for the weldment strength as a function of these parameters. These results are closely related to each other. (c) 2006 Elsevier B.V. All rights reserved.
A study on fabrication, morphological and optical properties of lead sulfide nanocrystals
(2008-02-01)
Chen, Jung-Hsuan
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Lo, Shen-Chuan
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
To investigate the properties of lead sulfide (PbS) nanocrystals, we have prepared PbS nanocrystals on/in the porous alumina membrane with a pore diameter 20 nm. Utilizing the reaction of Pb wires and the hydrogen sulfide (H2S) gas, PbS nanocrystals produced and grew as the reaction time increased. The composition identification of the nanocrystals was performed by the XPS and EDS analyses. More structure characteristics of the PbS nanocrystals obtained from the TEM analysis. As indicated in the PL spectra, an orange-red emission band appeared and the emission intensities were obviously related to the defects in the nanocrytals. A significant quantum confinement effect made the energy gap of PbS nanocrystals produce a blue shift from 0.41 eV to 1.89 eV. Furthermore, the growth mechanism of the PbS nanocrystals was also discussed.
Aluminum element effect for electron beam welding of similar and dissimilar magnesium-aluminum-zinc alloys
(2007-05-01)
Chi, Chao-Ting
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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Lee, Chuan-Hua
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材料科學與工程學系
Defects causing stress concentration from electron beam welding are related to the Al content of the Mg-AI-Zn weldment and its effect will be most conspicuous for the welding of dissimilar metals. Precipitates which are gamma phase (Mg-17(Al,Zn)(12)) also influence the formative mechanism of pores, the heat-affected zone and the fracture mode of the weld. More noteworthy is that the Al content of 6.0 wt.% is a very important delimitation for these mechanisms. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Conducting Ag/oligothiophene complex pastes through a simple quenching/chelation method
(2014-08-14)
Lu, Fang-Hsien
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Chang, Feng-Chih
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Mohamed, Mohamed-Gamal
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Liu, Tzeng-Feng
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Chao, Chuen-Guang
This paper describes a simple and environmentally friendly approach-a facile, one-pot, quenching/ chelation method-for the fabrication of a silver paste in the form of Ag/oligothiophene complex composites. These Ag/oligothiophene complex composites possess excellent conductivities of 1.8 x 10(4) S cm(-1) in the bulk state and 6.08 x 10(2) S cm(-1) in the form of thin films. We have used X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to characterize the microstructures of these novel Ag/oligothiophene complex composites.
Conducting Ag/oligothiophene complex pastes through a simple quenching/chelation method
(2014-08-14)
Lu, Fang-Hsien
;
Chang, Feng-Chih
;
Mohamed, Mohamed-Gamal
;
Liu, Tzeng-Feng
;
Chao, Chuen-Guang
This paper describes a simple and environmentally friendly approach-a facile, one-pot, quenching/ chelation method-for the fabrication of a silver paste in the form of Ag/oligothiophene complex composites. These Ag/oligothiophene complex composites possess excellent conductivities of 1.8 x 10(4) S cm(-1) in the bulk state and 6.08 x 10(2) S cm(-1) in the form of thin films. We have used X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) to characterize the microstructures of these novel Ag/oligothiophene complex composites.
Deformation mechanisms in ultrahigh-strength and high-ductility nanostructured FeMnAlC alloy
(2014-02-15)
Lin, Chih-Lung
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Chao, Chuen-Guang
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Juang, Jenh-Yih
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Yang, Jenn-Ming
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Liu, Tzeng-Feng
The deformation mechanisms of a bulk nanostructured Fe-30Mn-9.5Al-2.0C (in wt.%) alloy were investigated. After aging at 450 degrees C for 9-12 h, the alloy exhibits an exceptional strength-ductility combination (e. g. yield strength similar to 1406 MPa with elongation similar to 32%). The aged alloy exhibits a novel microstructure with isolated austenite nano-channels bounded by an extremely high volume fraction of directional nano-sized (Fe,Mn)(3)AlC carbides (kappa'-carbides). The plastic deformation was found to be dominated by bursting dislocation nucleation within the isolated austenite nano-channels. (C) 2013 Elsevier B. V. All rights reserved.
DNA Mismatch Detection by Metal Ion Enhanced Impedance Analysis
(2009-10-01)
Jangjian, Peng-Chung
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Liu, Tzeng-Feng
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Tsai, Chuan-Mei
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Li, Mei-Yi
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Tsai, Ming-Shih
Conventional diagnoses of genetic mutation and disease depend on the analysis of DNA sequences. However, mismatches in the DNA sequences are difficult to detect using traditional sequencing. Doping metal ions, such as nickel, into the short DNA (28 mer similar to 30 mer), markedly reduces its electrical resistance, which is measured by electrical impedance analysis. The change in resistance that is caused by a mismatched base-pair in short DNA can also be monitored by this approach. In this study, the resistance increased exponentially with the number of mismatched base-pairs. Accordingly, an intuitive and direct method for evaluating the number of DNA mismatches can possibly be developed.
Effect of ECAE on Microstructures and Mechanical Properties of Solution Heat Treated Mg-5(mass%) Sn Alloy
(2013-08-01)
Tsai, Hao-Jan
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Kuo, Chin-Guo
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
The microstructures and mechanical properties of the Mg-5(mass%) Sn alloy subjected to a solution heat treatment (SHT) were investigated by using equal channel angular extrusion (ECAE). The average grain size was significantly refined from 147 mu m (as-cast) to 16 mu m by ECAE four passes. Further, the fine Mg2Sn particles were uniformly distributed in the matrix by dynamic precipitation after ECAE four passes. The yield strength (YS), ultimate tensile strength (UTS) and elongations also showed notable improvements at room temperature and high temperatures (100 and 200 degrees C) on account of the ECAE process. Further, the tensile strength and elongations were better than those of the ECAE without SHT alloy. Those results show that SHT is a useful way to enhance the effect of ECAE on the mechanical properties of Mg-5 (mass%) Sn alloy.
Effect of phosphate surface pretreatment on corrosion resistance and adhesion of PI coating on Mg-5 wt.% Sn alloy
(2015-06-18)
Lee, Hsiao-Chien
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Huang, Yi-Chia
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Liu, Tzeng-Feng
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Whang, Wha-Tzong
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Chao, Chuen-Guang
In this study, phosphate surface pretreatment (PSPT) and poly[pyromellitic dianhydride-co-4,4MODIFIER LETTER PRIME-oxydianiline] polyimide (PMDA-ODA PI) coating were used to provide corrosion protection for Mg-5 wt.% Sn alloy. PSPT enhanced the adhesion of PI coating by mechanical interlocking and chemical anchoring. Surface roughness was increased and provided stronger mechanical interlocking. Phosphates were formed on the alloy surface to act as anchor groups. Energy dispersive X-rayspectrometer and X-ray photoelectron spectroscopy results indicated that bonds formed between anchor groups and PI coating. The bonds provided chemical anchoring and enhanced the adhesion of PI coating. The increase of corrosion resistance of PI coating on Mg-5 wt.% Sn alloy (E-corr = -0.86V/SCE, [GRAPHICS] mu A cm(-2) and corrosion rate far less than [GRAPHICS] showed the bonds were stable enough to stand the attack of electrolyte and inhibit the electrochemical reaction at the interface.
Effect of polyimide baking on bump resistance in flip-chip solder joints
(2014-03-01)
Cheng, Hsi-Kuei
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Feng, Shien-Ping
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Lai, Yi-Jen
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Liu, Kuo-Chio
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Wang, Ying-Lang
The effect of polyimide (PI) thermal process on the bump resistance of flip-chip solder joint is investigated for 28 nm technology device with aggressive extreme low-k (ELK) dielectric film scheme and lead-free solder. Kelvin structure is designed in the bump array to measure the resistance of single solder bump. An additional low-temperature pre-baking before standard PI curing increases the bump resistance from 9.3 m Omega to 225 m Omega. The bump resistance increment is well explained by a PI outgassing model established based on the results of Gas Chromatography-Mass Spectrophotometer (GC-MS) analysis. The PI outgassing substances re-deposit on the Al bump pad, increasing the resistance of interface between under-bump metallurgy (UBM) and underneath Al pad. The resistance of interface is twenty-times higher than pure solder bump, which dominates the measured value of bump resistance. Low-temperature plasma etching prior to UBM deposition is proposed to retard the PI outgassing, and it effectively reduces the bump resistance from 225 m Omega to 10.8 m Omega. (C) 2013 Published by Elsevier Ltd.
Effect of Temperature and Extrusion Pass on the Consolidation of Magnesium Powders Using Equal Channel Angular Extrusion
(2013-05-01)
Lee, Hsiao-Chien
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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Lin, Che-Yi
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Wang, Hsiao-Chung
The microstructure and characteristics of bulk magnesium consolidated from Mg powder by equal channel angular extrusion (ECAE) were investigated. Cu cans filled with Mg powder, of about 74 mu m in diameter, were ECAE processed for one, two and four passes via the Bc route at 473, 523 and 573 K. The microstructure of ECAE-processed samples was observed by OM and SEM. The density of each sample was determined using Archimedes' principle. Microhardness and compression tests were conducted to investigate the mechanical properties of each ECAE-processed sample. The best consolidated condition between powders was achieved after four passes of ECAE at 573 K. Density at 98.4% of the ideal density of bulk Mg was achieved, microhardness was about 49 Hv, and compressive yield stress was about 100 MPa.
Effects of direct current and pulse-reverse copper plating incubation behavior of self-annealing
(2010-10-01)
Cheng, Min-Yuan
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Chen, Kei-Wei
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Liu, Tzeng-Feng
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Wang, Ying-Lang
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Feng, Hsien-Ping
This study investigates spontaneous microstructural evolution in electroplated Cu films with various plating current densities involving direct current and pulse-reverse waveforms and various possible driving forces. Studies have explained the grain growth and resistivity decrease during the self-annealing of as-deposited Cu film, but the incubation behavior of self-annealing under various direct current and pulse-reverse current waveforms at a certain film thickness is unknown. In this study, it was found that pulse-reverse current retards the incubation behavior more significantly than does direct current. According to the measurements of resistivity, stress, and secondary ion mass spectrometer, the large stress difference between the initial and critical values and the low impurity content of pulse-reverse current postponed the incubation, and led to a slow self-annealing rate. The combination of the stress difference and the impurity effect explains the incubation behavior of self-annealing under various plating current densities. The resistivity and X-ray diffraction results suggest that stress is the primary driving force that dramatically speeds up grain growth above the critical stress, and that high current density with a rapid grain growth rate enhances the (200) texture for strain energy minimization in electroplated Cu film. (C) 2010 Published by Elsevier B.V.
Effects of direct current and pulse-reverse copper plating incubation behavior of self-annealing
(2010-10-01)
Cheng, Min-Yuan
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Chen, Kei-Wei
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Liu, Tzeng-Feng
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Wang, Ying-Lang
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Feng, Hsien-Ping
This study investigates spontaneous microstructural evolution in electroplated Cu films with various plating current densities involving direct current and pulse-reverse waveforms and various possible driving forces. Studies have explained the grain growth and resistivity decrease during the self-annealing of as-deposited Cu film, but the incubation behavior of self-annealing under various direct current and pulse-reverse current waveforms at a certain film thickness is unknown. In this study, it was found that pulse-reverse current retards the incubation behavior more significantly than does direct current. According to the measurements of resistivity, stress, and secondary ion mass spectrometer, the large stress difference between the initial and critical values and the low impurity content of pulse-reverse current postponed the incubation, and led to a slow self-annealing rate. The combination of the stress difference and the impurity effect explains the incubation behavior of self-annealing under various plating current densities. The resistivity and X-ray diffraction results suggest that stress is the primary driving force that dramatically speeds up grain growth above the critical stress, and that high current density with a rapid grain growth rate enhances the (200) texture for strain energy minimization in electroplated Cu film. (C) 2010 Published by Elsevier B.V.
Effects of equal channel angular extrusion on the microstructure and high-temperature mechanical properties of ZA85 magnesium alloy
(2012-07-01)
Lin, Che-Yi
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Tsai, Hao-Jan
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
This study examined the microstructure and high-temperature tensile properties of the Mg-8wt.%Zn-5 wt.%Al (ZA85) alloy that was subjected to equal channel angular extrusion (ECAE) with various passes at 180-250 degrees C. The original grain size and precipitate size of the as-cast specimen were 150 and 100 mu m, respectively. The average grain size was reduced to 4 mu m by dynamic recrystallization and the precipitate size was reduced to 1 mu m after six ECAE passes at 180 degrees C. However, the average grain size of the ECAE-processed specimens at 250 degrees C increased from 14 mu m after two passes to 20 mu m after four passes owing to the grain growth effect. In tensile tests at 200 degrees C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimens processed with six ECAE passes at 180 degrees C improved to 249 MPa and 162 MPa, respectively, compared with 105 MPa (UTS) and 74 MPa (YS) for the as-cast specimens. Furthermore, elongation increased from 5.1% to 28.5%. This significant improvement in the high-temperature tensile properties of the ZA85 alloy was attributed to the refined grains and the well-distributed fine Mg-32(Al, Zn)(49) (tau-phase) precipitates. (C) 2012 Elsevier B.V. All rights reserved.
Effects of Rhenium on Microstructure and Phase Stability of MAR-M247 Ni-Base Fine-Grain Superalloy
(2010-04-01)
Liao, Jian-Hong
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Bor, Hui-Yun
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
The effects of Re additions on the microstructure and phase stability of the cast fine-grain Mar-M247 superalloy were investigated in this study. The results showed that the grain sizes of the alloys with 0, 3, and 4.5 mass% Re content were 90, 60, and 50 mu m, respectively. The primary gamma' phase became finer and more cuboidal as Re content increased. The addition of 3 mass% Re caused strip-like MC carbides within the grain to degenerate into discontinuous M(23)C(6) carbides and initiated the formation of a deleterious topological closed-packed (TCP) phase within the grain interior. The addition of 4.5 mass% Re promoted phase instabilities that led to the precipitation of large amounts of needle-like P phase in the grain interior, attributable to Re and W segregation. This study found that 3 mass% Re was a critical addition to maintain optimal microstructure and phase stability, and improved the ultimate tensile strength and the yield strength at room temperature and 760 degrees C. However, the addition of 4.5 mass% Re obviously resulted in a decrease in tensile properties at room temperature and 760 degrees C. [doi:10.2320/matertrans.M2009331]
Enhanced ductility of the ZA85 magnesium alloy fabricated by equal-channel angular pressing
(2013-04-15)
Lin, Che-Yi
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Bor, Hui-Yum
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
Equal-channel angular pressing (ECAP) was applied to the as-cast Mg-8 wt.% Zn-5 wt.% Al (ZA85) alloy to produce a fine-grained structure with fine and uniformly distributed Mg-32 (Al, Zn)(49) (tau-phase) particles. Experiments showed that the ZA85 alloy had an initial grain size of similar to 150 mu m after casting and was significantly reduced to 4 mu m after six ECAP passes at 180 degrees C. After annealing at 300 degrees C for 1 h, the average grain size merely increased to 7.1 mu m. This thermal stability of the fine-grained structure at temperatures at or below 325 degrees C is attributed to the presence of the fine and well distributed tau-phase. It was demonstrated that ECAP processing greatly enhances ductility of the experimental alloy. By testing over a range of temperatures and strain rates, a maximum elongation to failure of 400% was obtained in the ECAP ZA85 alloy tested at 300 degrees C (0.53 T-m) with the initial strain rate of 1.0 x 10 (4) s (1). The dominant deformation mechanism for the specimens tested at 300 and 350 degrees C with the initial strain rates ranging from 1.0 x 10 (4) s (1) to 1.0 x 10 (3) s (1) is GBS controlled by grain boundary diffusion. At the higher testing temperature of 400 degrees C, the deformation mechanism for the experimental alloy is dislocation creep. (C) 2012 Elsevier B. V. All rights reserved.
Excellent enhancement of corrosion properties of Fe-9Al-30Mn-1.8C alloy in 3.5% NaCl and 10% HCl aqueous solutions using gas nitriding treatment
(2015-06-05)
Chen, Yung-Chang
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Lin, Chih-Lung
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Chao, Chuen-Guang
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Liu, Tzeng-Feng
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材料科學與工程學系
The as-quenched Fe-9.0Al-30Mn-1.8C (in wt.%) alloy gas nitrided at 550 degrees C for 4 h show excellent corrosion resistance investigated in 3.5% NaCl and 10% HCl solutions. Owing to the high corrosion resistance components, the gas-nitrided layer consists mainly of AlN with a slight amount of Fe3N and Fe4N identified by grazing incidence X-ray diffraction technique. Therefore, the pitting potential and corrosion potential of the nitrided sample are + 1860 mV and + 30 mV, respectively. Surprisingly, it is worthy to be pointed out that the nitrided and then tensile-tested alloy reveals very shallow in fracture depth and the excellent lattice coherence is shown between the nitrided layer and the substrate. Moreover, due to the extremely high nitrogen concentration (about 17-18 wt.%) at stretched surface, the corrosion resistance of present gas-nitrided and then tensile-tested alloy is superior to those optimally gas-nitrided or plasma-nitrided high-strength alloy steels, as well as martensitic stainless steels. The nitrided and then stretched alloy still retains a satisfactory corrosion resistance (E-pit = + 890 mV; E-corr = + 10 mV). Furthermore, only nanoscale-size pits were observed on the corroded surface after being immersed in 10% HCl for 24 h. (C) 2015 Elsevier B.V. All rights reserved.