간행물
한국재료학회지 KCI 등재 SCOPUS Korean Journal of Materials Research
- 발행기관 한국재료학회
- 자료유형 학술지
- 간기 월간
- ISSN 2799-8525 (Print)2799-8681 (Online)
- 수록기간 1991 ~ 2024
- 주제분류 공학 > 재료공학 공학 분류의 다른 간행물
- 십진분류KDC 530DDC 620
권호리스트/논문검색
제21권 제7호 (2011년 7월) 9건
1.
2011.07
구독 인증기관 무료, 개인회원 유료
In this paper, high temperature oxidation behavior of newly developed alloys, Ti-6Al-4Fe and Ti-6Al-1Fe, is examined. To understand the effect of Fe on the air oxidation behavior of the Ti-Al-Fe alloy system, thermal oxidation tests are carried out at 700˚C and 800˚C for 96 hours. Ti-6Al-4V alloy is also prepared and tested under the same conditions for comparison with the developed alloys. The oxidation resistance of the Ti-Al-Fe alloy system is superior to that of Ti-6Al-4V alloy. Ti-6Al-4V shows the worst oxidation resistance for all test conditions. This is not a result of the addition of Fe, but rather it is due to the elimination of V, which has deleterious effects on high temperature oxidation. The oxidation of the Ti-Al-Fe alloy system follows the parabolic rate law. At 700˚C, Fe addition does not have a noticeable influence on the amount of weight gain of all specimens. However, at 800˚C, Ti-6Al-4Fe alloy shows remarkable degradation compared to Ti-6Al-1Fe and Ti-6Al. It is discovered that the formation of Al2O3, a diffusion resistance layer, is remarkably hindered by a relative decrease of the α volume fraction. This is because Fe addition increases the volume fraction of β phase within the Ti-6Al-xFe alloy system. Activities of Al, Ti, and Fe with respect to the formation of oxide layers are calculated and analyzed to explore the oxidation mechanism.
4,000원
2.
2011.07
구독 인증기관 무료, 개인회원 유료
Currently, there are two main issues regarding the development of core technologies in the automotive industry: the development of environmentally friendly vehicles and securing a high level of safety in the event of an accident. As part of the efforts to address these issues, research into alternative materials and new car body manufacturing and assembly technologies is necessary, and this has been carried out mainly by the automotive industries. Large press molds for producing car body parts are made of cast iron. With the increase of automobile production and various changes of design, the press forming process of car body parts has become more difficult. In the case of large press molds, high hardness and abrasive resistance are needed. To overcome these problems, we attempted to develop a combined heat treatment process consisting of local laser heat treatment followed by plasma nitriding, and evaluated the characteristics of the proposed heat treatment method. From the results of the experiments, it has been shown that the maximum surface hardness is 864 Hv by the laser heat treatment, 953 Hv by the plasma nitriding, and 1,094 Hv by the combined heat treatment. It is anticipated that the suggested combined heat treatment can be used to evaluate the durability of press mold.
4,000원
3.
2011.07
구독 인증기관 무료, 개인회원 유료
We report on the effects of TiO2 doping power on the characteristics of multicomponent TiO2-ITO (TITO) electrodes prepared by a multi-target sputtering system with tilted cathode guns. Both as-deposited and annealed TITO electrodes showed linearly increased sheet resistance and resistivity with increasing TiO2 doping power. However, the TITO electrodes exhibited a fairly high optical transmittance regardless of the TiO2 doping power due to the high transparency of the TiO2. Although the annealed TITO showed much lower sheet resistance and resistivity relative to the as-deposited samples, the electrical properties of the annealed samples exhibited similar dependence on the TiO2 power to the as-deposited samples. In addition, it was found that doping of an anatase TiO2 in the ITO electrode prevented the preferred (222) orientation of the TITO electrodes. Although the TITO electrode showed higher sheet resistance and resistivity than that of the pure ITO electrode, it offers a very smooth surface and usage of a low-cost Ti element. It is thus considered a promising multicomponent transparent conducting electrode for cost-efficient flat panel displays and photovoltatics.
4,000원
4.
2011.07
구독 인증기관 무료, 개인회원 유료
Thermoelectric power, dc conductivity, and the dielectric relaxation properties of La2NiO4.03 are reported in the temperature range of 77 K - 300 K and in a frequency range of 20 Hz - 1 MHz. Thermoelectric power was positive below 300K. The measured thermoelectric power of La2NiO4.03 decreased linearly with temperature. The dc conductivity showed a temperature variation consistent with the variable range hopping mechanism at low temperatures and the adiabatic polaron hopping mechanism at high temperatures. The low temperature dc conductivity mechanism in La2NiO4.03 was analyzed using Mott's approach. The temperature dependence of thermoelectric power and dc conductivity suggests that the charge carriers responsible for conduction are strongly localized. The relaxation mechanism has been discussed in the frame of the electric modulus and loss spectra. The scaling behavior of the modulus and loss tangent suggests that the relaxation describes the same mechanism at various temperatures. The logarithmic angular frequency dependence of the loss peak is found to obey the Arrhenius law with activation energy of ~ 0.106eV. At low temperature, variable range hopping and large dielectric relaxation behavior for La2NiO4.03 are consistent with the polaronic nature of the charge carriers.
4,000원
5.
2011.07
구독 인증기관 무료, 개인회원 유료
Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at 1000˚C under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. Ti2O, CaO, CaTiO3, and TixPy phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.
4,000원
6.
2011.07
구독 인증기관 무료, 개인회원 유료
Phase Transformation and Dielectric Properties of<001> 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 Single Crystals
The structure and dielectric properties of poled<001>-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) crystals have been investigated for orientations both parallel and perpendicular to the [001] poling direction. An electric field induced monoclinic phase was observed for the initial poled sample. The phase remained stable after the field was removed. A quite different temperature dependence of dielectric constant has been observed between heating and cooling due to an irreversible phase transformation. The results of mesh scans and temperature dependence of the dielectric constant demonstrate that the initial monoclinic phase changes to a single domain tetragonal phase at 370K and to a paraelectric cubic phase at 405K upon heating. However, upon subsequent cooling from the unpoled state, the cubic phase changes to a poly domain tetragonal phase and to a rhombohedral phase. In the ferroelectric tetragonal phase with a single domain state, the dielectric constant measured perpendicular to the poling direction was dramatically higher than that of the parallel direction. A large dielectric constant implies easier polarization rotation away from the polar axis. This enhancement is believed to be related to dielectric softening close to the morphotropic phase boundary and at the phase transition temperature.
4,000원
7.
2011.07
구독 인증기관 무료, 개인회원 유료
In this study, by using tin chloride solution as a raw material, a nano-sized tin oxide powder with an average particle size below 50 nm is generated by a spray pyrolysis process. The properties of the generated tin oxide powder depending on the inflow speed of the raw material solution are examined. When the inflow speed of the raw material solution is 2 ml/min, the majority of generated particles appear in the shape of independent polygons with average size above 80-100 nm, while droplet-shaped particles show an average size of approximately 30 nm. When the inflow speed is increased to 5 ml/min, the ratio of independent particles decreases, and the average particle size is approximately 80-100 nm. When the inflow speed is increased to 20 ml/min, the ratio of droplet-shaped particles increases, whereas the ratio of independent particles with average size of 80-100 nm decreases. When the inflow speed is increased to 100 ml/min, the average size of the generated particles is around 30-40 nm, and most of them maintain a droplet shape. With a rise of inflow speed from 2 ml/min to 5 ml/min, a slight increase of the XRD peak intensity and a minor decrease of specific surface area are observed. When the inflow speed is increased to 20 ml/min, the XRD peak intensity falls dramatically, although a significant rise of specific surface area is observed. When the inflow speed is increased to 100 ml/min, the XRD peak intensity further decreases, while the specific surface area increases.
4,000원
8.
2011.07
구독 인증기관 무료, 개인회원 유료
Micro speakers are used to reproduce sound in small electric and information and communications devices, such as cellular phones, PMPs, and MP3 players. The acoustical properties and sound quality, which are changed due to the decreased size of the speaker, are often adjusted varying the type and thickness of the diaphragm. The most widely used diaphragm material is thin polymer. It was previously reported by the author of this paper that the resonance frequency of a micro speaker is changed by the type and thickness of a polymer diaphragm. In this paper, the frequency response near the resonance frequency of a micro speaker was studied as functions of the type and thickness of the polymer diaphragm. While Rmax and RDC were affected by the type and thickness, an analysis of the electrical impedance curve revealed that Ro(= Rmax/RDC) and δf were not changed. Thus, QTS which was function of Ro, δf, and the resonance frequency, is only related to the resonance frequency. The increase of the resonance frequency led to a proportional rise of QTS. The change of the frequency response near the resonance frequency was not dependent on the type or thickness of the polymer diaphragm, but was affected by the resonance frequency.
4,000원
9.
2011.07
구독 인증기관 무료, 개인회원 유료
This study was carried out to evaluate the microstructures and mechanical properties of a friction stir welded Ni based alloy. Inconel 600 (single phase type) alloy was selected as an experimental material. For this material, friction stir welding (FSW) was performed at a constant tool rotation speed of 400 rpm and a welding speed of 150~200 mm/min by a FSW machine, and argon shielding gas was utilized to prevent surface oxidation of the weld material. At all conditions, sound friction stir welds without any weld defects were obtained. The electron back-scattered diffraction (EBSD) method was used to analyze the grain boundary character distributions (GBCDs) of the welds. As a result, dynamic recrystallization was observed at all conditions. In addition, grain refinement was achieved in the stir zone, gradually accelerating from 19 μm in average grain size of the base material to 5.5 μm (150 mm/min) and 4.1 μm (200 mm/min) in the stir zone with increasing welding speed. Grain refinement also led to enhancement of the mechanical properties: the 200 mm/min friction stir welded zone showed 25% higher microhardness and 15% higher tensile strength relative to the base material.
4,000원
