Browsing by Author "Chou, CP"

Now showing 1 - 20 of 34

A lab-scale digital acoustic emission system for source location
(1999-07-01)
Yang, MH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
Activated diffusion brazed repair for IN738 hot section components of gas turbines
(2001-09-24)
Su, CY
;
Lih, WC
;
Chou, CP
;
Tsai, HC
;
機械工程學系
The wide-clearance activated diffusion brazing (ADB) techniques with various brazing alloys, namely DF4B and Nicrobraz 150 were applied to restore worn areas of IN738 components. In this study, the microstructure of an ADB joint and the results of thermal cyclic tests as well as tensile tests within the temperature range of from 25 to 980 degreesC were investigated and discussed. The results of the tensile tests showed that ADB specimens brazed by 40 wt.% DF4B at 1190 degreesC exhibited 85% tensile strength of the IN738 base materials at room temperature and retained the same strength as that of the base material at 980 degreesC. However, the ductility of the ADB specimens with both brazing alloys was reduced. The results of cyclic-oxidation tests showed that ADB specimens with Nicrobraz 150 as the brazing alloy decayed after 150 cycles. However, the ADB specimens with DF4B had no obvious weight change until 205 cycles. (C) 2001 Elsevier Science B.V. All rights reserved.
An investigation of tank bottom leak detection using acoustic emission
(1998-07-01)
Yang, MH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
To investigate the acoustic emission (AE) bursts from leakage through a hole, experiments were conducted on a small test tank under different conditions. When neither backfill material nor air was involved, AE bursts were detected exactly at or very close to the hole. The instantaneous abrupt pressure change of fluid at the hole, frequently associated with the unsteady flow around the hole, is suggested as the origin of these AE bursts. On the other hand, the fluid-air or fluid-sand interaction can also produce AE bursts, but the occurrence sites and signal characteristics are different. Leakage at higher water level results in stronger AE bursts, and a larger leak hole produces move bursts. The leak rate alone is not a proper index as to whether AE bursts will occur or not. In many cases of the tests, the occurrence of AE bursts from leakage cannot be fully explained by the present knowledge of turbulence.
Carbon nanotubes grown using cobalt silicide as catalyst and hydrogen pretreatment
(2005-12-01)
Wen, HC
;
Yang, KH
;
Ou, KL
;
Wu, WF
;
Luo, RC
Cobalt catalytic-layers 25 mn were deposited by sputtering on silicon substrates. At the pretreatments, hydrogen plasma was conducted for 4-16 min at 600 degrees C in a MPCVD system. Pretreated samples were characterized using SEM and AFM. Surface morphologies of catalytic-layers were changed after hydrogen plasma pretreatments. The cobalt layers became discontinuous and some nanoparticles were formed. With pretreatments for a long time, nanoparticles tended to agglomerate to reduce surface energy and larger nanoparticles were observed. It is believed that the optimum pretreatment condition for the growth of carbon nanotubes could be achieved because relatively high growth failure and nanofibers (> 100 nm) was observed for shorter and longer than 12 min pretreatment, respectively. It is found that the hydrogen pretreatment is a crucial step for the making of nucleation sites in the synthesis of carbon nanotubes using cobalt silicide as catalyst on Si substrates. After the pretreatment, mixture gases of hydrogen and methane were then flowed into the chamber for 12 min, samples were characterized using SEM, TEM and Raman spectrum. Carbon atoms were adsorbed on the islands of catalysts, and then diffused into the edge of nanotubes. Cobalt silicides were formed due to high processing temperature, and cobalt atoms tended to diffuse and stay on the silicon substrates, which enhance carbon nanotubes to grow under the root growth mechanism. (c) 2005 Elsevier B.V. All rights reserved.
Corrosion behaviour of weld heat affected zone of aluminium alloy 7075
(1997)
Hwang, RY
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
The microstructure of the weld heat affected zone (HAZ) of alloy 7075 was simulated using a Gleeble system. The corrosion behaviour of several locations in the weld HAZ was investigated by means of differential scanning calorimetry, electrochemical measurement in 3.5 wt-%NaCl solution, and exfoliation corrosion tests. Different exfoliation corrosion morphologies for the base metal and weld HAZ were also observed. The corrosion morphology of the weld HAZ was mainly related to the degree of precipitation of eta' phase in the matrix. The HAZ in the region of the peak temperature 377 degrees C contained the most precipitation of eta phase, but no effect on corrosion morphology as a result of T6 post-weld heat treatment was observed. (C) 1997 The Institute of Materials.
Distortion analysis of single V-groove butt welding on heat treatable aluminum alloys
(2005-09-01)
Cheng, CM
;
Chou, CP
;
Lee, IK
;
Lin, HY
;
機械工程學系
In this study we conducted single V-groove butt welding (GTAW) on three types of heat treatable aluminum alloys 2024-T351, 6061-T6 and 7075-T6 and compared the angular distortion levels of the three aluminum alloys at different Vee preparation angles with or without restraint. Experimental results demonstrated that when the Vee preparation angle was 0 degrees (l-shaped groove), the angular distortion level of the restrained weldment can exceed that of the unrestrained weldments. Moreover, when. the Vee preparation angle was 45 degrees, 60 degrees or 90 degrees, the restrained weldment had lower angular distortion than the unrestrained weldments. The single Vee preparation angle (amount of filler metal) in butt welding affected the angular distortion of the weldment. Without restraint, the angular distortion tended to increase with the single Vee preparation angle. Meanwhile, the angular distortion tended to decrease when the single Vee preparation angle was 60 degrees. Additionally, a restrained weldment had high angular distortion when the single Vee preparation angle was 0 degrees. Notably, the angular distortion tended to reduce with increasing single Vee preparation angle. The angular distortion of the weldment was minimized at an angle of 60 degrees. However, the angular distortion increased when the Vee preparation angle exceeded 60 degrees. The high-temperature yield strength of a material also affected its angular distortion. Angular distortion increased with high-temperature yield strength. Experimental results also showed that, from the strongest to the weakest, the high-temperature yield strength of the three types of aluminum alloys followed the order 6061-T6 and 2024-T351 > 7075-T6.
Effect of aging treatment on the mechanical properties of C-250 maraging steel by flow forming
(2003-02-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long, thin walled tube made of C-250 maraging steel. The forward flow forming can save raw material, increase strength, and reduce the production process time. Because the work hardening effect on solution-treated C-250 using flow forming is minimal, the flow-formed tube requires an additional heat treatment to obtain higher hardness and strength. With the direct aging treatment, low elongation values are obtained, making this treatment unsuitable for the engineering design. It was found that the 540 degreesC/6 h/AC over-aging treatment results in better strength and elongation values. The strengthening phase of the flow-formed C-250 maraging steel was found to be the intermetallic compound of Fe3Mo.
Effect of heat treatment on microstructures of flow formed C-250 maraging steel
(2003-11-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long thin walled tube of C-250 maraging steel. Forward flow forming can conserve material, increase strength and reduce production process time. Since the hardness of solution treated C-250, using flow forming, can be increased by approximately 16.2%, flow formed tube must be given an additional aging treatment to increase hardness and strength. Direct aging treatment yields low elongation, which is not suited to design requirements. Using a homogenisation treatment, the microstructure of C-250 was of coarse grained lath type on aging and of needle type after solution treatment and aging. These treatments resulted in low tensile strength, and tensile fracture showed a tendency to brittleness. A 'solution + aging' treatment yielded greater strength and elongation.
Effect of mechanical properties using different filler metals on wide-clearance activated-diffusion-brazed Ni-based superalloy
(2000-12-01)
Su, CY
;
Chou, CP
;
Chang, WJ
;
Liu, MH
;
機械工程學系
The investigation of mechanical properties and failure mechanism of activated-diffusion-brazed (ADB) joints in IN-738 plate were conducted. Joints of this type, which had wide clearance, were formed using the brazing alloys Nicrobraz 150 and DF4B, The microstructural characterization showed that chromium borides with a blocky morphology were present in joints associated with the two brazing alloys. A major difference in matrix phase chemistry was observed, however, for the two brazing alloys, e.g., an Ni-B eutectic phase was observed in Nicrobraz 150, but DF4B exhibited a coarsened gamma prime (gamma) phase and an absence of a nickel boride matrix phase, Results of tensile test showed that ADB specimens using DF4B brazing alloy exhibited 95% nominal tensile strength of IN-738 base materials. Fracture cracks in the joint area mere initiated and confined to dispersed chromium boride sites. However, tensile test of ADB specimens using Nicrobraz 150 showed poor tensile properties at all testing temperatures, and their fractures were initiated at a brittle nickel boride site and propagated along the weak-bonded interface between the Ni-B eutectic phase and base materials.
Effect of nitrogen addition to shielding gas on residual stress of stainless steel weldments
(2002-02-01)
Tseng, KH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
The objective of the present study, was to investigate the effect of nitrogen additions to the shielding gels Oil the ferrite content and residual stress in austenitic stainless steels. Autogenous gas tungsten arc (GTA) welding was applied on austenitic stain less steels 304 and 310 to produce a bead on plate weld, The delta ferrite content of the weld metals was measured using a Ferritscope. The residual stress in the weldments was determined using the hole drilling strain gauge method. The present results indicated that the retained delta ferrite content in type 304 stainless steel weld metals decreased rapid v as nitrogen addition to the argon shielding gas was increased. The welding residual stress increased with increasing quantity, of added nitrogen in the shielding gas. It was also found that the tensile residual stress zone in austenitic stainless steel weldments was exteneded as the quantity of added nitrogen gas in the argon shielding gas was increased. (C) 2002 IoM Commuications Ltd.
Effect of pulsed gas tungsten arc welding on angular distortion in austenitic stainless steel weldments
(2001)
Tseng, KH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
The effect of the parameters of the pulsed gas tungsten arc welding (GTAW) process on the angular distortion in austenitic stainless steel weldments was investigated. Autogenous GTAW was conducted on types 304 and 310 stainless steels to produce a bead on plate weld. The weldment thermal cycle was recorded during pulsed GTAW to investigate the influence of thermal stress. Angular distortion was determined by using the mean vertical displacement method. The experimental results indicate that higher pulse frequency, smaller pulse spacing, greater amplitude ratio, and greater duration ratio can reduce the angular distortion. The angular distortion of type 310 stainless steel weldments was greater than that of type 304 weldments under the same welding conditions because of the lower thermal conductivity and thermal diffusivity of type 310. (C) 2001 IoM Communications Ltd.
Effect of stress relief on microstructure and mechanical properties of flow formed maraging steel weldment by electron beam welding
(2003-06-01)
Lee, IK
;
Chou, CP
;
Cheng, CM
;
Kuo, IC
;
機械工程學系
The technique of forward flow forming has been used to produce a long and thin wall tube of C-250 maraging steel. The work hardening effect of solution treated C-250 by flow forming is small. Therefore aging treatment after flow forming is required to increase hardness and strength. Final formed C-250 tubes are usually manufactured by combining aging treatment and electron beam welding (EBW). The hardness and tensile strength of aged C-250 maraging steel weldment decreased to the corresponding values obtained in the solution annealed state. Thus, the formed tube by EBW requires stress relieving treatment (and similarly for the aged condition) to increase hardness and strength and thus meet the required specification. The strength requirement was successfully achieved but the elongation of the aged, EBW, and stress relieved specimen was 88.5% lower than that of the unwelded specimen. (C) 2003 IoM Communications Ltd. Published by Maney for the Institute of Materials, Minerals and Mining.
Effect of thermal cycles on ferrite content of austenitic stainless steel
(1999)
Chen, MH
;
Chou, CP
;
機械工程學系
;
Department of Mechanical Engineering
The properties of austenitic stainless steel weld metals are strongly influenced by the duplex structure of austenite and ferrite. The objective of the present study was to investigate the effect of thermal cycles on the ferrite content in austenitic stainless steel weld metal, and to explore the ferrite-austenite solid state transformation of austenitic stainless steel weld metal. The results indicate that the peak temperature, cooling rate, and number of thermal cycles have a significant effect on ferrite content in the austenitic stainless steel weld. As the cooling rate increases, or the number of thermal cycles decreases, the amount of retained ferrite is increased at room temperature. New delta ferrite phase can be formed if the reheating peak temperature is above the optimum gamma solvus temperature of austenitic stainless steel, nod this new delta ferrite can be retained under rapid cooling conditions.
Effects of ammonia plasma treatment on the surface characteristics of carbon fibers
(2006-02-24)
Wen, HC
;
Yang, K
;
Ou, KL
;
Wu, WF
;
Chou, CP
Carbon fibers were grown from cobalt catalysts with larger size (> 100 nm), and the size distribution can be controlled by pretreatment. Pretreated cobalt catalytic-layers were observed as islands, which can enhance the growth of carbon fibers. The carbon fibers were treated by ammonia plasma in a PECVD system. High-energy ammonia plasma not only can cause damage but also adsorb on carbon fibers. The ammonia plasma treatment resulted in the etching effect. It is also observed that the more treatment time, the more disorder in structures of carbon fibers. The N-H functional groups were found on the surfaces of ammonia plasma treated carbon fibers and this observation can be further investigated to develop chemical sensor application. (c) 2005 Elsevier B.V. All rights reserved.
Effects of nitrogen plasma treatment on tantalum diffusion barriers in copper metallization
(2003-02-01)
Wu, WF
;
Ou, KL
;
Chou, CP
;
Wu, CC
;
機械工程學系
In this study, the barrier properties of ultrathin Ta, TaN, and nitrogen plasma-treated Ta films were investigated by Cu/Ta(N)/Si structure. The barrier properties were evaluated by sheet resistance, film stress, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Nitrogen plasma-treated Ta films possess better barrier performance than sputtered Ta and TaN films. The sheet resistance of Cu/Ta/Si and Cu/TaN/Si increases, apparently, after annealing at 600 and 625degreesC, respectively. The Cu/30 min plasma-treated Ta/Si is fairly stable up to annealing at 700degreesC for 1 h. Diffusion resistance of the plasma-treated Ta barrier is more effective. It is believed that a new amorphous layer forms on the surface of Ta film after plasma treatment. The new amorphous layer possesses some nanocrystalline Ta2N phases with lattice constant 0.305 nm. It is believed that the amorphous layer containing some nanocrystals can alleviate Cu diffusion into the Si substrate and, hence, improve barrier performance. (C) 2003 The Electrochemical Society.
Effects of the process parameters on austenitic stainless steel by TIG-flux welding
(2006-05-01)
Huang, HY
;
Shyu, SW
;
Tseng, KH
;
Chou, CP
;
機械工程學系
The effects of the process parameters of TIG (tungsten inset gas)-flux welding on the welds morphology, angular distortion, ferrite content and hot cracking in austenitic stainless steel were investigated. Autogenous TIG welding process was applied to the type 304 stainless steel through a thin layer of activating flux to produce a bead on plate welded joint. TiO2, SiO2, Fe2O3, Cr2O3, ZnO and MnO2 were used as the activating fluxes. The experimental results indicated that the TIG-flux welding can increase the weld depth/width ratio and reduce the HAZ (heat affected zone) range, and therefore the angular distortion of the weldment can be reduced. It was also found that the retained ferrite content within the TIG-flux welds is increased, and has a beneficial effect in reducing hot cracking tendency for stainless steels of the austenitic type weld metals. A plasma column constriction increases the current density at the anode spot and then a substantial increase in penetration of the TIG-flux welds can be obtained.
Evaluation of hot workability of H13 through processing map
(1999)
Wang, SC
;
Chou, CP
;
Lin, CH
;
Chang, CC
;
機械工程學系
Evaluation of TIG flux welding on the characteristics of stainless steel
(2005-09-01)
Huang, HY
;
Shyu, SW
;
Tseng, KH
;
Chou, CP
;
機械工程學系
The aim of the present study was to investigate the effect of specific oxide fluxes on the surface appearance, weld morphology, retained delta ferrite content, hot cracking susceptibility, angular distortion and mechanical properties obtained with the tungsten inert gas (TIG) process applied to the welding of 5 mm thick austenitic stainless steel plates. An autogenous gas tungsten arc welding process was applied to stainless steels through a thin layer of activating flux to produce a bead on plate welded joint. The MnO2 and ZnO fluxes used were packed in powdered form. The experimental results indicated that the 80% MnO2 - 20% ZnO mixture can give full penetration and also a satisfactory surface appearance for type 304 stainless steel TIG flux welds. TIG welding with MnO2 and/or ZnO can increase the measured ferrite number in welds, and tends to reduce hot cracking susceptibility in as welded structures. It was also found that TIG flux welding can significantly reduce the angular distortion of stainless steel weldments.
High resolution x-ray micromachining using SU-8 resist
(2003-09-01)
Shew, BY
;
Hung, JT
;
Huang, TY
;
Liu, KP
;
Chou, CP
This paper investigates the feasibility of using SU-8 as a high contrast x-ray resist. The SU-8 resist was irradiated with various x-ray doses and then developed for a fixed time. The developing rate was then measured and plotted versus absorbed x-ray dosage. The results revealed that SU-8 exhibited very high lithographic contrast other than elevated sensitivity. Therefore, a very thin mask absorber is required to switch the negative resist 'ON' or 'OFF'. Preliminary results showed that 1 mum wide, 17 mum thick SU-8 resists could be successfully patterned using an absorber of submicron thickness. Once the absorber thickness is effectively reduced to less than 1 mum, a high-resolution x-ray mask can be patterned simply by conventional UV lithography. An extra soft x-ray beamline was not required to increase the absorber's thickness in certain cases. The process of fabricating the membrane x-ray mask could thus be considerably simplified. X-ray micromachining may be an easy way to pattern high-resolution and high-aspect-ratio microstructures for optical and photonic applications.
Hot cracking of welds on heat treatable aluminium alloys
(2005-06-01)
Cheng, CM
;
Chou, CP
;
Lee, IK
;
Lin, HY
;
機械工程學系
The Spot Varestraint test was used to evaluate the hot cracking susceptibility of several aluminium alloys namely 6061-T6, 6061-T6 ( H), 7075-T6, 7075-T6 ( H). The effects of augment strain, the number of thermal cycles and cold working ( rolling) on the cracking susceptibility were investigated, and the total crack length was used to evaluate the hot cracking susceptibility. The results indicate that the number of thermal cycles is irrelevant to the hot cracking susceptibility in the weld fusion zone, but does affect this susceptibility in the heat affected zone (HAZ). More thermal cycles correspond to larger hot cracks in the HAZ, especially in the weld metal HAZ. The hot cracking susceptibility of materials increased with augment strain in both the fusion zone and the HAZ. Cold working of the materials can reduce their hot cracking susceptibility. The hot cracking susceptibility of 7075-T6 aluminium alloys is higher than that of 6061-T6. There was significant Cu segregation in the HAZ of 7075-T6 aluminium alloy, resulting in a higher susceptibility to hot cracking in this zone.