Browsing by Author "Chao, CG"

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A novel method for net-shape forming of hypereutectic Al-Si alloys by thixocasting with powder preforms
(2005-08-25)
Chen, CM
;
Yang, CC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
This work presents a novel and feasible method for net-shape forming of hypereutectic A1-Si alloy parts. This method, briefly termed as powder thixocasting in this paper, combines the techniques of thixocasting and conventional powder metallurgy. Consolidated preforms made of gas-atomized and pre-alloyed A1-25Si-2.5Cu-1Mg-0.5Mn powder were used as the feedstock for thixocasting. The alloy powder was preheated under protection of argon atmosphere and then was compacted to form powder preforms. The powder preforms were quickly heated into semi-solid state by induction coils and were immediately thixocast using a die-casting machine. A die with a center gate, a long runner and plate-shaped cavities was designed to examine the feasibility of this process. Results demonstrated that the powder preforms exhibits very good formability by this unique process. The powder thixocast products have satisfied strength and substantial structure with uniform distribution of fine Si particles, while the processing temperature is suitably controlled. This novel process was also successfully used to fabricate compressor scrolls for demonstration. (c) 2004 Elsevier B.V. All rights reserved.
A novel technique for manufacturing metal-bonded Nd-Fe-B magnets by squeeze casting
(2002-03-01)
Ji, JF
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A new method was developed for forming Nd-Fe-B rapidly quenched ribbon to metal-bonded magnets. The process was carried out by a squeeze casting technique. The A356 aluminum alloy and zinc alloy (ZAS) were used as metal binders. The energy product (BH) of A356-bonded magnet was 62.2 k J/m(3) and that of ZAS-bonded magnet was 61.2 k J/m(3). The maximum bending strength of ZAS-bonded magnets (259 MPa) was greater than that of A356-bonded magnets (148 MPa). The corrosion behavior of both magnets was studied in the salt spray test and the magnetization flux loss was measured. The magnetization flux loss of ZAS-bonded magnets is less than that of A356-bonded magnets due to Zn as a sacrificial anode to protect MQ powders.
Aging kinetics of heat-treated Zn-4Al-3Cu alloy
(1999-06-18)
Li, BJ
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Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Analysis of instability in a critical dimension bar due to focus and exposure
(2005-08-01)
Kuo, YK
;
Chao, CG
;
Lin, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
in the photolithography processing of semiconductor, the line width becomes smaller and smaller. Therefore, the requirements of process window are stricter than before. Among them, the control of focus and exposure dose is one of the most important factors that may affect the line width. Bad control of focus and exposure may not only affect line width. but also cause the increment of rejects of products. The research mainly explored the effects of focus and exposure dose on line widths of different photo resists. The research obtained related coefficients of exposure dose line width and focus line width by coating photo resist of different components on the surface of the silica wafer. The results of research found that focus may not only change line width but also had a positive-negative symmetric relationship with line width. It also found that there was linear relationship between exposure dose and line width. (c) 2004 Elsevier Ltd. All rights reserved.
Analysis of instability line width and white wall created by the photolithography process
(2004-11-01)
Kuo, YK
;
Chao, CG
;
Lin, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In the photolithography processing of semiconductor, line width is smaller and smaller. Therefore, the requirements of process window are stricter than before. In the small line width, the formation of serious white wall will affect line width and cause rejects in following process. The study conducted research on the control of best focus in which particularly explored the relationship between exposure dose and line width and the phenomenon of white wall generated by focus. The research obtained related coefficients of exposure dose-line width and exposure dose-white wall by coating photo resist of different components with the same thickness on the surface of fused silica wafer. The results of research found that exposure dose might not only change line width but also had important effects on white wall. Among others, the most important factor for exposure dose is the component of sensitivity of photo resist. (C) 2004 Elsevier Ltd. All rights reserved.
Analysis of the effects of reflectance and refraction generated by wafers made from fused silica, ALOxNy and TiSixNy under different light sources on pattern length and best focus
(2005-01-01)
Kuo, YK
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In semi-conductor photo-lithography processing, line-width is constantly shrinking. That is why process window requirements are becoming stricter. Under these strict conditions, the influences of focus and pattern length are more important. This investigation tries to explore the deviation of best focus and the variation in pattern length resulting from the reflectance and refraction of fused silica, ALOxNy and TiSixNy wafers are coated with the same thickness of SEPR 432 PR (Photo Resist). Experimental results indicate that after excluding the influence of photo resist impacts, the refraction generated by the auto focus light source(halogens lamp) causes deviation of the best focus, and the extent of deviation has a directly proportion relationship with refraction, and no direct relationship exists between exposure light source (laser) and the deviation of best focus. The reflectance generated by exposure light source only changes the measures of pattern length, and an inverse relationship exists between reflectance and pattern length; that is, received pattern length reduces with increasing wafer reflectance. (C) 2004 Elsevier Ltd. All rights reserved.
Characterization of lead-bismuth eutectic nanowires
(2005-04-01)
Kuo, CG
;
Hsu, YY
;
Wu, MK
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Chao, CG
;
材料科學與工程學系
In this work, lead-bismuth eutectic alloy nanowires were fabricated by a novel vacuum melting method and centrifugal process. An anodic aluminum oxide (AAO) template was used to produce an array of ordered, dense, and continuous Pb-Bi nanowires. Scanning electron microscopy and transmission electron microscopy investigations reveal that nanowires with a diameter of 80 nm are composed of Pb7Bi3 and Bi phases, and have a single orientation of growth. Magnetic susceptibility and hysteresis measurements have been used to characterize the superconductive and magnetic properties of the nanowires. The results show that Pb-Bi nanowires have a slightly lower superconducting transition temperature than Pb-Bi eutectic alloy bulk, and only about 1% superconductivity volume fraction in magnetic fields both perpendicular and parallel to the plate. In magnetization curves, a fairly large hysteresis is observed for both field orientations.
Deformation and fracture of Al2O3/Al-Zn-Mg-Cu metal matrix composites at room and elevated temperatures
(2000-04-30)
Wu, YL
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Al2O3/Al-Zn-Mg-Cu metal matrix composites containing 2.22 similar to 3.08 wt.% Mg in the matrix alloys have been fabricated by squeeze casting. The aim of the present study is to investigate the deformation and fracture behavior of the composites at RT (room temperature) and elevated temperature. Optical microscopy, scanning electron microscopy and image analysis were used to examine and to analyze the details of the microstructure and the fracture surface. Tensile tests were utilized to evaluate the mechanical properties from 25 to 400 degrees C. The yield stress (YS) values and UTS values for all the composites were larger than those of monolithic alloys. The UTS values for composites and monolithic alloys increased with increasing Mg content. Elevated temperature tests indicated a good strength retention for the composites; especially, UTS values of the composites showed an improvement of 18% exceeds that of the monolithic alloys from 200 to 300 degrees C. Significant dynamic strain aging occurred for composites; however, recovery and softening remained the dominant process for monolithic alloys in the range 25-300 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.
Dry sliding wear behaviors of Al-25Si-2.5Cu-1Mg alloys prepared by powder thixocasting
(2005-04-25)
Chen, CM
;
Yang, CC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The wear performance of an Al-25Si-2.5Cu-1Mg alloy prepared by powder thixocasting was studied using a pin-on-disc machine. LM13 and an Al-25Si-2.5Cu-lMg alloy prepared by conventional ingot metallurgy were also investigated for comparison. The sliding tests were performed under ambient conditions and without lubricant. During the tests, the applied load was increased stepwise until wear seizure occurred. Experimental data reveal that the powder thixocast alloys exhibit better wear performance than that of conventional alloys, especially under heavy load conditions and following T6 treatment. This work demonstrates the potential of the new method, powder thixocasting, for fabricating hypereutectic Al-Si-X alloys with a high wear resistance. Moreover, the variation in the wear rate with the applied load for the alloy can be divided into three regions. The mechanisms associated with these wear regions were discussed based on the investigations of the worn subsurface and the wear debris. (c) 2005 Elsevier B.V. All rights reserved.
Effect of heat treatments on in-situ Al2O3/TiAl3 composites produced from squeeze casting of TiO2/A356 composites
(2002-02-01)
Hsu, CW
;
Chao, CG
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材料科學與工程學系
;
Department of Materials Science and Engineering
In-situ Al2O3/TiAl3 intermetallic matrix composites were fabricated via squeeze casting of TiO2/A356 composites heated in the temperature range from 700 degreesC to 780 degreesC for 2 hours. The phase transformation in TiO2/A356 composites employing various heat-treatment temperatures (700 degreesC to 780 degreesC) was studied by means of differential thermal analysis (DTA), microhardness, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). From DTA, two exothermic peaks from 600 degreesC to 750 degreesC were found in the TiO2/A356 composites. The XRD showed that Al2O3 and TiAl3 were the primary products after heat treatment of the TiO2/A356 composite. The fabrication of in-situ Al2O3/TiAl3 Composites required 33 vol pet TiO2 in Al and heat treatment in the range from 750 degreesC to 780 degreesC. The hardness (HV) of the in-situ Al2O3/TiAl3 composites (1000 HV) was superior to that of nonreacted TiO2/A356 composites (200 HV). However, the bending strength decreased from 685 MPa for TiO2/A356 composites to 250 MPa for Al2O3/TiAl3 composites. It decreased rapidly because pores occurred during the formation of Al2O3 and TiAl3. The activation energy of the formation of Al2O3 and TiAl3 frorn TiO2 and A356 was determined to be about 286 kJ/mole.
Effect of magnesium on mechanical properties of Al2O3/Al-Zn-Mg-Cu metal matrix composites formed by squeeze casting
(1996-07-15)
Hsieh, JH
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Al2O3Al-Zn-Mg-Cu composites containing 2.0-3.0wt% Mg in the matrix alloy have been fabricated by squeeze casting. Light microscopy, scanning electron microscopy and image analysis were used to examine and analyze the details of the microstructure and the fracture surface. Tensile tests were used to evaluate the mechanical properties. The aging behavior of the composites was studied using differential scanning calorimetry (DSC) techniques and microhardness tests. The microhardness and ultimate tensile strength (UTS) of the composites increase with increasing Mg content, The maximum microhardness and UTS of the composites occur after aging for 24 h at 120 degrees C.
Effect of magnesium on mechanical properties of Al2O3/Al-Zn-Mg-Cu metal matrix composites formed by squeeze casting
(1996-07-15)
Hsieh, JH
;
Chao, CG
;
交大名義發表
;
材料科學與工程學系
;
National Chiao Tung University
Al2O3Al-Zn-Mg-Cu composites containing 2.0-3.0wt% Mg in the matrix alloy have been fabricated by squeeze casting. Light microscopy, scanning electron microscopy and image analysis were used to examine and analyze the details of the microstructure and the fracture surface. Tensile tests were used to evaluate the mechanical properties. The aging behavior of the composites was studied using differential scanning calorimetry (DSC) techniques and microhardness tests. The microhardness and ultimate tensile strength (UTS) of the composites increase with increasing Mg content, The maximum microhardness and UTS of the composites occur after aging for 24 h at 120 degrees C.
Effect of magnesium on mechanical properties of Al2O3/Al-Zn-Mg-Cu metal matrix composites formed by squeeze casting
(1996-08-30)
Hsieh, JH
;
Chao, CG
;
交大名義發表
;
材料科學與工程學系
;
National Chiao Tung University
Al2O3/Al-Zn-Mg-Cu composites containing 2.0 similar to 3.0 wt.% Mg in the matrix alloy have been fabricated by squeeze casting. Light microscopy, scanning electron microscopy and image analysis were used to examine and analyze the details of microstructure and the fracture surface. Tensile tests were utilized to evaluate the mechanical properties. The aging behavior of the composites was studied by using differential scanning calorimetry technique and microhardness tests. The microhardness and ultimate tensile strength (UTS) of the composites increase with increasing Mg content. The maximum microhardness and UTS of the composites occur at 120 degrees C aging for 24 h.
Effect of magnesium on the aging behavior of Al-Zn-Mg-Cu/Al2O3 metal matrix composites
(1996-07-01)
Chou, MC
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The effect of magnesium content on the aging behavior of Al-Zn-Mg-Cu alloy reinforced with alumina (Al2O3) was studied by using the differential scanning calorimetry (DSC) technique and hardness measurement. The magnesium contents were studied in the range from 1.23 to 2.97 wt pct. The addition of magnesium was found to increase the coherent Guinier-Preston (GP) zones in composites. The apparent formation enthalpy of GP zones of composites (0.1 V-f) was 0.932 cal/g for 1.23 wt pct magnesium content and 1.375 cal/g for 2.97 wt pct magnesium content. The precipitation time to achieve the maximum hardness in the composites depends on the magnesium content. The time changed from 12 to 48 hours as the magnesium content increased from 1.23 to 2.97 wt pct. Both Vickers microhardness and Rockwell hardness increased with increasing magnesium content. The maximum hardness occurred in the composites that contained maximum amounts of GP zones and eta' precipitates. However, the microhardness of the composites was always lower than that of monolithic alloys due to the alumina fibers which caused the suppression of GP zones and eta' formation in the composites.
Effect of magnesium on the aging behavior of Al-Zn-Mg-Cu/Al2O3 metal matrix composites
(1996-07-01)
Chou, MC
;
Chao, CG
;
交大名義發表
;
材料科學與工程學系
;
National Chiao Tung University
The effect of magnesium content on the aging behavior of Al-Zn-Mg-Cu alloy reinforced with alumina (Al2O3) was studied by using the differential scanning calorimetry (DSC) technique and hardness measurement. The magnesium contents were studied in the range from 1.23 to 2.97 wt pct. The addition of magnesium was found to increase the coherent Guinier-Preston (GP) zones in composites. The apparent formation enthalpy of GP zones of composites (0.1 V-f) was 0.932 cal/g for 1.23 wt pct magnesium content and 1.375 cal/g for 2.97 wt pct magnesium content. The precipitation time to achieve the maximum hardness in the composites depends on the magnesium content. The time changed from 12 to 48 hours as the magnesium content increased from 1.23 to 2.97 wt pct. Both Vickers microhardness and Rockwell hardness increased with increasing magnesium content. The maximum hardness occurred in the composites that contained maximum amounts of GP zones and eta' precipitates. However, the microhardness of the composites was always lower than that of monolithic alloys due to the alumina fibers which caused the suppression of GP zones and eta' formation in the composites.
Effect of particle-size distribution on the properties of high-volume-fraction SiCP-Al-based composites
(2000-09-01)
Chen, CY
;
Chao, CG
;
材料科學與工程學系
;
Department of Materials Science and Engineering
High-volume-fraction SiC-Al-based composites have been fabricated by squeeze casting. The effect of particle-size distribution and squeeze-cast parameters on the metal-matrix composites (MMCs) was investigated. The results showed that bulk density of the composites was 2.855 to 3.067 g/cm(3) with the various component mixtures of SiC particulates, i.e., the SiC volume fraction was 51.6 to 74.4 pet. The young's modulus of the composites was between 220 and 226 GPa. The maximum four-point bending strength and fracture toughness reached 478 MPa and 9.42 MPa(m)(-1/2), respectively. The coefficient of thermal expansion (CTE) of the composites was from 5 to 8 x 10(-6)/K, depending on the volume fraction of SIG.
Effect of substrate on the step coverage of plasma-enhanced chemical-vapor deposited tetraethylorthosilicate films
(2003-07-01)
Lan, JK
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Wang, YL
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Chao, CG
;
Lo, K
;
Cheng, YL
Plasma-enhanced chemical-vapor deposition tetraethylorthosilicate (TEOS) films are extensively used as the interlayer dielectric films in multilevel interconnection processes. When TEOS oxide films were deposited on metal patterns three different substrates, titanium nitride (TiN), aluminum (Al), and oxide (SiO2), were used. This study examines the dependence of these substrates on TEOS step coverage. The deposition rates of TEOS oxide revealed that the SiO2 substrate lead to highest TEOS deposition rate during the initial deposition period of 5 s. Then, the TEOS deposition rate of the substrates was nearly the same. The TiN substrate exhibited the highest sidewall step coverage but the sidewall step coverage of the Al substrate deteriorated due to its granular surface. Additionally, different substrates exhibited different coverage of the bottom step. Moreover, the bottom step coverage exceeded the sidewall coverage for all substrates. (C) 2003 American Vacuum Society.
Effects of carbon fiber/Al interface on mechanical properties of carbon-fiber-reinforced aluminum-matrix composites
(2004-07-01)
Li, SH
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Chao, CG
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材料科學與工程學系
;
Department of Materials Science and Engineering
Carbon-fiber (CF)-reinforced aluminum-matrix composites were prepared by spreading fibers and squeeze casting. The interface structure of CF/Al composites was examined using high-resolution transmission electron microscopy (HRTEM) and electron spectroscopy for chemical analysis (ESCA). Aluminum carbide (Al4C3) interfacial reaction products were observed to nucleate heterogeneously from carbon fibers and to grow toward the aluminum matrix in the form of lath-like crystals after heat treatment. The growth of aluminum carbide was anisotropic, since it was faster along the a- and b-axes of the basal plane than along the c-axis. Both the tensile strength and the elongation of composites decline with an increased duration of heat treatment. The results of ESCA revealed that approximately 1 pct of carbide enhanced interface bonding. However, increasing the content of brittle carbides to over 3 pct after heat treatment degraded the mechanical properties of composites.
Effects of TMT on reinforcement characteristics of combustion-assisted in-situ titanium matrix composite
(1997)
Tsang, HT
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Chao, CG
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Ma, CY
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材料科學與工程學系
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Department of Materials Science and Engineering
The effects of thermomechanical processing (TMP) on the reinforcement characteristics and mechanical properties at ambient temperature of an in-situ 10 vol.% TiC/Ti MMC produced by combustion synthesis were studied in this work. With increasingly imposed TMP, the morphology, size and distribution TiC reinforcement can be changed, refined and successfully controlled. According to the image analysis results, a linear relationship between interparticle distance and reduction of TMP can be established. Due to the refinement of TiC and the decrease of interparticle distance during TMP, both the strength and elongation are clearly enhanced. From a linear plot of strength against inverse interparticle distance, the Orowan mechanism is mainly responsible for the strengthening in this system.
Effects of volume fraction of reinforcement on tensile and creep properties of in-situ TiB/Ti MMC
(1997-11-01)
Tsang, HT
;
Chao, CG
;
Ma, CY
;
材料科學與工程學系
;
Department of Materials Science and Engineering