Microstructure and Mechanical Properties of (TiZrHf)50(NiCoCu)50 High Entropy Alloys

Chih‑Hsuan Chen,Yue‑Jin Chen,Jia‑Jyun Shen 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.5

The microstructure and mechanical properties of pseudo-binary (TiZrHf)50(NiCoCu)50 high entropy alloys(HEAs) with B2 matrix were investigated in this study. The studied HEAs includes Ti40Zr10Ni40Co5Cu5,Ti30Zr20Ni30Co10Cu10,Ti25Zr25Ni16.67Co16.67Cu16.67,Ti30Zr10Hf10Ni30Co10Cu10,Ti20Zr15Hf15Ni20Co15Cu15,andTi16.67Zr16.67Hf16.67Ni16.67Co16.67Cu16.67. XRD and SEM analyses revealed that all studied HEAs were a mixture of B2 andC15 intermetallic phases, instead of a single solid solution, due to their highly negative enthalpy of mixing and the relativelylarge difference in atomic radii. The B2 matrix was found capable of forming a solid solution of all six elements in a widecomposition range. The lattice constants of B2 and C15 phases increase linearly with increasing the difference in atomicradii. Additionally, the microhardness of these HEAs increases from 409 to 595 HV with the increasing difference in atomicradii as well. Compression tests demonstrated substitution of Zr with Hf can improve the ductility. In all studied HEAs, theTi30Zr10Hf10Ni30Co10Cu10HEA achieves a great balance between yield strength, ultimate compressive strength, and fracturestrain of 1574 MPa, 1933 MPa, and 6.5%, respectively.

Effects of Additives of CaO and Rare-Earth Oxides on the Sintering Behavior of AlN Ceramics

Chih-Hung Chu,Yun-Hwei Shen,Chih-Peng Lin,Shaw-Bing Wen 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5

The effect of additives of CaO plus three different rare-earth oxides (Y, Sm and Gd, separately) on the sintering behavior of AlN ceramics has been evaluated at 1700℃ by using a MoSi2 heater and ambient atmosphere. The results of density measurements show that the atomic weight of the rare-earth element may substantially affect the apparent density of the sintered AlN specimen due to the kinetics of atomic diffusion during sintering. The optimum results of this study show that these additives are effective in obtaining an apparent density of 3.26 g/cm3 (approaching a 100 % theoretical density of AlN). The Vicker's hardness of the sintered AlN can reach a high value of 1310 kg/mm2 and an apparent density of 3.34 g/cm3. A longer soaking time of between 3 and 5 h is necessary to practically eliminate the minor oxide phases. The effect of additives of CaO plus three different rare-earth oxides (Y, Sm and Gd, separately) on the sintering behavior of AlN ceramics has been evaluated at 1700℃ by using a MoSi2 heater and ambient atmosphere. The results of density measurements show that the atomic weight of the rare-earth element may substantially affect the apparent density of the sintered AlN specimen due to the kinetics of atomic diffusion during sintering. The optimum results of this study show that these additives are effective in obtaining an apparent density of 3.26 g/cm3 (approaching a 100 % theoretical density of AlN). The Vicker's hardness of the sintered AlN can reach a high value of 1310 kg/mm2 and an apparent density of 3.34 g/cm3. A longer soaking time of between 3 and 5 h is necessary to practically eliminate the minor oxide phases.

Thermal conductivity of micro hot-pressed AlN ceramics fabricated using a conventional MoSi2 heating element furnace

Chih-Peng Lin,Chih-Hung Chu,Shaw-Bing Wen,Yun-Hwei Shen 한양대학교 세라믹연구소 2011 Journal of Ceramic Processing Research Vol.12 No.5

AlN samples doped with sub-micron Y2O3 and CaO powders as sintering additives obtained using the micro hot-pressed (MHPed) sintering method in a MoSi2 heating element furnace were investigated. The minor amounts of secondary phases were identified as Al5Y3O12, CaYAl3O7, and CaAl4O7, which are related to the low sintering temperature as well as the removal of oxygen-related defects in the system. Relative densities of over 96% of the theoretical value were obtained after sintering at 1600 oC for 8 h, indicating that an adequate amount of additives and the use of the micro hot-pressed (MHPed) sintering process help improve the densification and thermal conductivity of AlN ceramics. The high thermal conductivity of 130Wm−1K−1was attributed to the purification of the AlN lattice, the elimination of some secondary phases, and the grain boundary phase distribution.

Dual-Output Single-Stage Bridgeless SEPIC with Power Factor Correction

Chih-Lung Shen,Shih-Hsueh Yang 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.2

This study proposes a dual-output single-stage bridgeless single-ended primary-inductor converter (DOSSBS) that can completely remove the front-end full-bridge alternating current?direct current rectifier to accomplish power factor correction for universal line input. Without the need for bridge diodes, the proposed converter has the advantages of low component count and simple structure, and can thus significantly reduce power loss. DOSSBS has two uncommon output ports to provide different voltage levels to loads, instead of using two separate power factor correctors or multi-stage configurations in a single stage. Therefore, this proposed converter is cost-effective and compact. A magnetically coupled inductor is introduced in DOSSBS to replace two separate inductors to decrease volume and cost. Energy stored in the leakage inductance of the coupled inductor can be completely recycled. In each line cycle, the two active switches in DOSSBS are operated in either high-frequency pulse-width modulation pattern or low-frequency rectifying mode for switching loss reduction. A prototype for dealing with an 85?265 Vrms universal line is designed, analyzed, and built. Practical measurements demonstrate the feasibility and functionality of the proposed converter.

Dual-Output Single-Stage Bridgeless SEPIC with Power Factor Correction

Shen, Chih-Lung,Yang, Shih-Hsueh The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.2

This study proposes a dual-output single-stage bridgeless single-ended primary-inductor converter (DOSSBS) that can completely remove the front-end full-bridge alternating current-direct current rectifier to accomplish power factor correction for universal line input. Without the need for bridge diodes, the proposed converter has the advantages of low component count and simple structure, and can thus significantly reduce power loss. DOSSBS has two uncommon output ports to provide different voltage levels to loads, instead of using two separate power factor correctors or multi-stage configurations in a single stage. Therefore, this proposed converter is cost-effective and compact. A magnetically coupled inductor is introduced in DOSSBS to replace two separate inductors to decrease volume and cost. Energy stored in the leakage inductance of the coupled inductor can be completely recycled. In each line cycle, the two active switches in DOSSBS are operated in either high-frequency pulse-width modulation pattern or low-frequency rectifying mode for switching loss reduction. A prototype for dealing with an $85-265V_{rms}$ universal line is designed, analyzed, and built. Practical measurements demonstrate the feasibility and functionality of the proposed converter.

THE PERFORMANCE OF CONDENSER UNDER DIFFERENT VEHICLE SPEEDS

CHIH-CHIU SHEN,JAU-HUAI LU 대한설비공학회 2013 International Journal Of Air-Conditioning and Refr Vol.21 No.2

Due to the concern in energy shortage and environmental protection, electric vehicle is considered to be a substitute for the conventional gasoline-powered vehicles due to its characteristics of high e±ciency and no emission. However, the load of air conditioning causes a serious problem for electric vehicles, especially in tropical and subtropical areas. The compressor of conventional air conditioning system is driven by engine and its speed is thus coupled to vehicle speed. In electric vehicles, the compressor is driven by electric motors and compressor speed could be decoupled to vehicle speed. This mechanism provides an opportunity to improve the energy e±ciency of electric vehicle since the operation of air conditioning system may be independent of vehicle speed. The purpose of this paper is to ¯nd out the electric fan operation model as vehicle speed is varied. This paper was to establish a theoretical model for the condenser of automotive air conditioner and to conduct simulation to evaluate the e®ect of vehicle speed on the cooling capacity and sub-cooling of condenser. Results of simulation demonstrated that vehicle with 6km h1 speed has the 5C of sub-cooling at 0:0266 kg s1 of refrigerant °ow rate and the cooling capacity was 4.93kW. In this study, an increase of 16.6% in cooling capacity can be reached as the speed of vehicle was raised from 6 to 110 km h1 and can promote the sub-cooling to 19:5C. It was also found that the cooling capacity of air conditioner is extremely sensitive to vehicle speed while the vehicle is running at low speed. Furthermore, increases in the vehicle speed resulted in reduction of the length of superheat region from 17.5 to 8.5 cm. Finally, a correlation among these variables and the simulated cooling capacity was obtained in this study, enabling the relevant researchers to evaluate automotive air conditioner performance under di®erent vehicle speeds more easily.

A Kinetic Study of Thermal Degradations of Chitosan/Polycaprolactam Blends

Shen Kun Liao,Chi Chih Hung,Ming Fung Lin 한국고분자학회 2004 Macromolecular Research Vol.12 No.5

키토산/카프로락탐 혼합체에 대한 수분의 영향

리아오셴쿤(Shen Kun Liao),훙치치(Chi Chih Hung),린망풍(Ming Fung Lin) 한국고분자학회 2004 폴리머 Vol.28 No.5

A Kinetic Study of Thermal Degradations of Chitosan/Polycaprolactam Blends

Liao, Shen-Kun,Hung, Chi-Chih,Lim, Ming-Fung The Polymer Society of Korea 2004 Macromolecular Research Vol.12 No.5

We have used FT-IR spectra to explain the effects of hydrogen bonding between chitosan and polycaprolactam (PA6). A dynamic mechanical analysis study suggested that the optimum chitosan and PA6 miscibility under the conditions of this experiment were obtained at a blending ratio of 40:60. We studied the thermal degradation of chitosan blended with PA6 (chitosan/PA6) by thermogravimetric analysis and kinetic analysis (by the Ozawa method). Dry chitosan and PA6 exhibited a single stage of thermal degradation and chitosan/PA6 blends having> 20 wt% PA6 exhibited at least two stages of degradation. In chitosan/PA6 blends, chitosan underwent the first stage of thermal degradation; the second stage proceeded at a temperature lower than that of PA6, because the decomposition product of chitosan accelerated the degradation of PA6. The activation energies of the blends were between 130 and 165 kJ/mol, which are also lower than that of PA6.

Magnetic Properties and Microscopic Structures of Ultrathin Co/p3 × p3 − R30˚-Ag/Si(111) Films

Jyh-Shen Tsay,Tsu-Yi Fu,Chih-Kuei Kao,Xiao-Lan Huang,Jyh-Ron Shue,Wei-Hsiang Chen,Yeong-Der Yao,구현주 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12

Combined scanning tunneling microscopy and surface magneto-optic Kerr effect studies were employedto study the relation between magnetic properties and the microscopic interfacial structuresof ultrathin Co/p3×p3−R30˚-Ag/Si(111) films. On the top of p3×p3−R30˚-Ag/Si(111), pureCo clusters formed without disrupting the p3 × p3 − R30˚ structure of the Ag buffer layer. Thegreat strain due to the large mismatch between Co and the substrate influenced the nucleation ofCo atoms to form large clusters. No magnetic hysteresis in the polar configuration was observed forfilms thinner than 10 monolayers. The easy axis of magnetization was in the surface plane. Cappingp3 × p3 − R30˚-Ag on top of the Si(111) surface before the deposition of the Co overlayerscan efficiently reduce the nonferromagnetic Co-Si compound to zero thickness. For Co coveragebetween 2.9 and 4.2 monolayers, a lower Curie temperature was observed in ultrathin films. Due tothe existence of a smooth interface between Co and the p3 × p3 − R30˚-Ag buffer, the coercivityfor Co/p3 × p3 − R30˚-Ag/Si(111) is smaller than that for Co/Si(111).