산소함량에 따른 Ti-AI-Fe-Si-O 합금의 미세조직 변화 및 기계적 특성

배진주 부산대학교 2017 국내석사

주사 가능한 상전이 칼슘포스페이트 골시멘트의 제조, 특성 평가 및 in-vitro 거동

정나현 부산대학교 대학원 2017 국내석사

Phase-transformed calcium phosphate (PTCP) bone cements including silanized-hydroxypropyl methylcellulose (Si-HPMC) were successfully prepared for application as novel injectable bone cements with enhanced biocompatibility. The crystal structure and chemical state of the synthesized PTCP and Si-HPMC powders as solid and liquid phase of the composite cements were measured via X-ray diffraction and Fourier transform infrared spectroscopy. The handling and mechanical properties of the Si-HPMC composite calcium phosphate cements were measured via viscometric analysis, injectability tests, and three-point bending tests using a universal testing machine. The cytotoxicity of the Si-HPMC composite calcium phosphate cements was evaluated. Analysis of the in-vitro performance such as mechanical properties, X-ray diffraction and SEM images of Si-HPMC composite calcium phosphate cements showed that hardening was an inherent function of the cements after immersion in Hanks` balanced salt solution. The Si-HPMC/A3P7 and Si-HPMC/A7P3 composite calcium phosphate cements showed better biocompatibility and injectability than Si-HPMC/A100 composite calcium phosphate cements. In addition, the Si-HPMC/A3P7 and Si-HPMC/A7P3 composite calcium phosphate cements have relatively higher mechanical properties than other Si-HPMC/P100 composite calcium phosphate cements. Therefore, these novel injectable cements can potentially be used as calcium phosphate cements for biomedical applications.

산소함량에 따른 Ti-Al-Fe-Si-O 합금의 미세조직 변화 및 기계적 특성

배진주 부산대학교 대학원 2017 국내석사

The effect of the oxygen content and the annealing temperature on the tensile behavior of the Ti-1.5Al-3Fe-0.25Si-(0.1~0.5)O alloy was investigated. The tensile properties were dependent on the volume fraction of the microstructure constituents, i.e. the equiaxed α, equiaxed β and lamellar α. The results showed that the O-partitioned equiaxed α had a much higher strength compared to the equiaxed β. The strength of the lamellar α increased with increasing the annealing temperature because the O content of the lamellar α increased. Ti-1.5Al-3Fe-0.25Si-0.3O alloy annealed to 900 °C where the volume fraction of lamellar α was the highest exhibited an excellent combination of the strength (1198.5 MPa) and ductility (27.5 %). The effect of the lamellar α on the ductility was discussed.

Ti-5Al-2.5Fe 합금의 연속 냉각 시 산소함량이 상변태 거동에 미치는 영향

김도헌 부산대학교 대학원 2017 국내석사

Ti alloys are emerging structural materials with high specific strength and stability at a wide range of temperatures and environments. Among these, Ti-6Al-4V alloy takes more than 60% of the Ti market share. But Vanadium is a strategic material and deteriorates corrosion resistance. Therefore, many researchers have focused on developing new Ti alloys with low material cost and high corrosion resistance at higher operating temperatures. Our previous study suggested Ti-Al-Fe alloy to increase operating temperature at a relatively low material cost. And this new alloy showed compatible with Ti-6Al-4V alloy in mechanical properties and high temperature formability. Recently, the effect of interstitial alloying elements such as oxygen or nitrogen on titanium alloy design become most attentive research area. Therefore, the present investigation focused about to understand the effect of oxygen content on Ti-Al-Fe alloy. The phase transformation behavior during continuous cooling was analyzed through microstructure observation. According to this result, continuous cooling curve was established. Continuous cooling curve was used to design of the thermo-mechanical process and to establish database on microstructure control prediction. β transus was increased 977℃ to 1045℃ with increasing oxygen content. In case of high oxygen contents coarse grains of α and β was observed. Phase transformation behavior was observed during continuous cooling and the nucleation rate for boundary α was faster for higher oxygen content compared to low oxygen content alloy. Thus, the formation of boundary α formation starts was possible with fast cooling rate. As the cooling rate slow down widmanstatten structure is formation and inner plate structure was growth was observed. The higher oxygen content, cooling from the higher temperature increases the driving force for microstructure formation, thereby promoting the growth of the inner microstructure. Highest Vickers hardness value was observed for high oxygen alloy. HV values change in correspondence with microstructure and increase with cooling rate. Acicular microstructure presented the highest hardness values. Slow cooling rate results in reduction in hardness. On the other hand, cooling rate of 0.05℃/s indicates increasing hardness. This is may be because of the precipitate phase formation. As the result of the construction of continuous cooling curve with increasing oxygen content, each phase formation areas moves in the left direction of the CCT curve. The α' area change to narrow while α + β area becomes wider. From this results of the phase transformation and mechanical properties, we can conclude that amount of oxygen is the main factor in alloy design in order to obtain desirable mechanical properties.

중속 디젤 엔진용 연료분사밸브 바디 파손거동에 관한 연구

김영록 부산대학교 대학원 2016 국내석사

Abstract High pressurization and atomization of fuel are methods to improve the efficiency of medium speed marine diesel engines. Failure of the fuel injection valve body occurred according to the increase of fuel pressure. In this study, component and slope inspection on failured fuel injection valve bodies, visual inspection, and observation tests were conducted by optical microscope and SEM to analyze the cause of fuel injection valve body failure of the marine 32/40 medium speed diesel engine. Also, maximum stress of the fuel injection valve was calculated by numerical analysis to see if it corresponded to the analyzed fatigue strength in the test. As a result of the test analysis, SCM440 which is machine structure-use alloy steel was shown to be the component from the component inspection of the valve body. Tensile strength of the damaged valve body was shown to be 788.3 MPa through the Rockwell harness test. Optical microscope analysis results showed that band structure existed in the material and this is judged to be the factor that lowers the strength. SEM analysis results showed that damaged parts were first shown in the edge of the intersecting points of holes. Primary cracks were shown in the corner part where the fuel hole and hemisphere meet and secondary cracks were shown after certain time passed. This is judged as a form of typical fatigue fracture. By numerical analysis, the fatigue strength of the valve body at 1,350 bar showed to correspond between the maximum stress of the valve body of 1,300 bar and 1,400 bar. Tensile strength of the damaged valve body was shown to be 788.3 MPa and it is judged that the cracks occurred because fatigue strength could not be tolerated when the internal pressure of the fuel hole was 1,350 bar or higher.

표면 증강 라만 산란을 기반으로 한 플라즈몬 금속 나노입자의 합성 및 라만 센서로의 응용에 관한 연구

최현지 부산대학교 대학원 2016 국내석사

In the first research, we synthesize Ag@SiO2@Au nanoparticles(Ag@SiO2@Au NPs) for the surface-enhanced Raman scattering (SERS) based sensing applications. They consist of gold nanoparticles (Au NPs) fixed on the silica shell, which sizes of Au NPs and thickness of silica shell can be controllable by varying the amount of reactants. Their surface plasmon resonance (SPR) properties were characterized using UV-vis spectroscopy, showing that the growth of Au NPs and thickness of silica shell exhibited the dramatic change in SERS activity due to the formation of hot spots. The optimized Ag@SiO2@Au NPs show a detection limit of rhodamine 6G (R6G) as low as 10-11M, which is about 105 times increase compared to R6G without any SERS probes. These findings suggest the importance of size control of Ag@SiO2@Au NPs and their SPR properties to develop highly efficient SERS sensor. In the second research, Metal-organic frameworks (MOFs), a type of porous hybrid organic-inorganic microporous materials, are typically characterized by high surface areas, uniform and nanostructured cavities and exceptional adsorptive capacities. These characteristics make them promising for application in catalysts and adsorbents materials. Especially, These materials, embedding metal nanoparticles, would be advantageous to develop a surface-enhanced raman scattering (SERS) detection element. In this study, we demonstrate the fabrication of a sensitive SERS-active materials by embedding metal nanoparticles within zeolitic imidazolate framework (ZIF-8) and control the dispersibility of included metal nanoparticles. In addition, the excellent preconcentrated SERS activity is confirmed by measuring the raman signals for organic pollutant in environmental water. 표면 증강 라만 산란 (surface-enhanced Raman scattering, SERS)은 단분자 수준의 물질까지 검출이 가능한 고감도 측정 기술로 최근 많은 각광을 받고 있다. 이 SERS 효과에 기초한 검출 기술은 감도가 뛰어나고 여러 개의 시료를 동시에 검출 할 수 있는 장점으로 차세대 분석법으로 많은 연구가 되고 있다. 기존의 라만 산란은 입사된 빛의 에너지가 변하는 비탄성 산란으로 빛을 특정 분자체에 가하면 분자체 고유의 진동전이에 의해 조사된 빛과는 파장이 약간 다른 빛이 발생하는 현상을 일컫는다. 이러한 라만 산란에 기초한 라만 분광학은 분자 고유의 진동 에너지 모드들을 보여줌으로써, 물질의 화학적 성분을 밝혀 낼 수 있다. 하지만 빛을 받아 실제적으로 산란 시키는 라만 산란 효율이 매우 작고 재현성이 낮기 때문에 라만 신호 자체를 검출하는데 큰 어려움이 있다는 단점이 있다. 이러한 문제를 극복할 수 있는 방법 중의 하나로 1974년 Fleishmann 등에 의해 앞서 말한 SERS기술이 보고되었다. 도체인 금속 나노입자에 존재하는 수많은 자유 전자들이 외부에서 빛 에너지를 받았을 때, 국부 표면 플라즈몬 공명 (localized surface plasmon resonance, LSPR) 특성이 나타나 독특한 광학적 성질을 가진다. LSPR은 금속 나노 입자 표면과 공기, 물 등의 유전체 사이에 빛이 입사되면 빛이 가지는 특정 에너지의 전자기장과의 공명으로 인하여 금속 표면의 자유 전자들이 집단적으로 진동하는 현상을 말한다. 입사되는 빛의 진동수와 표면 플라즈몬의 집단 운동의 진동수가 같을 경우, 이 표면 플라즈몬 공명으로 알려진 자유 전자의 집단적 진동을 유도하는 핫스팟 (hot-spot)에서의 강한 전자기장 증강 현상으로 인해 금속 나노입자 표면에 흡착된 분석 물질의 라만 신호를 증폭시킨다고 알려져 있다. 이러한 이유로 금속 나노입자는 높은 SERS 감도를 나타내지만 보통 기판에 부착 시 응집현상이 발생되어 감도가 떨어지거나 불균일한 신호를 얻을 수밖에 없다. 그러므로 기판에 부착된 입자의 응집현상을 제어하려면, 입자의 제조 외에도 추가적으로 나노입자의 고밀도 패킹 및 규칙적인 배열 공정이 필요하며, 이는 비용, 시간 및 노동력이 부가적으로 소요된다. 따라서 본 연구에서는, 효율적인 SERS 측정을 위해 추가공정이 필요하지 않은 센서 기판을 제조하여, 규칙적이고 감도가 높은 측정 성능 향상을 기대하였다.

자기냉매용 분말 합성 신공정 및 자기열량효과 연구

안종빈 부산대학교 대학원 2016 국내석사

Rare-earth (RE) compound are promising materials because they have a wide variety of excellent properties, such as high hardness, high melting point and large magnetization value. Especially, RE nitrides can be used magnetic refrigeration material for hydrogen liquefaction systems. The reason is RE nitrides exhibit ferromagnetism and have Curie temperature in the region of 6 to 70K [1]. In this study, microwave-assisted sol-gel method and plasma arc discharge technique, two methods were proposed to synthesize HoN particles. Firstly, microwave-assisted sol-gel method is using holmium chloride as precursor. Precursor and urea were dissolved in ethanol to form a coordination sphere around metal atom, sustain a stable reaction and decomposed at elevated temperature. Then microwave (MW) was irradiated for the simulation of chemical reaction. In this step polymerization and substitution reaction occurred from Holmium-urea chloride. The gel type reactant was loaded into the tube furnace for heat treatment in N2 atmosphere with step heat treatment. Finally, HoN were prepared without any impurities after heat treatment. Secondly plasma arc discharge technique was conducted in nitrogen gas, N2 was employed as an active element for arc discharge between two electrodes maintained at a constant current. Also it played an important role not only as a reducing agent but also as an inevitable source of excited nitrogen molecules and nitrogen ions for the formation of HoN phase. Partial pressure of N2 was systematically varied from 0 to 28,000 Pa in order to obtain single phase of HoN with minimal impurities. Fourier transform infrared spectroscopy (FTIR) was used to identify the structure of the solvents before and after MW irradiation. X-ray diffraction patterns of the synthesized products after heat treatment in N2atmosphereandplasmaarcdischargeprocessshowedtheseries of six sharp peaks exactly corresponded to each planes of crystallographic structure of HoN. Physical property measurement system (PPMS) was employed to measure the magnetic properties with temperatures and magnetocaloric effect of both method of HoN particles were evaluated by calculating the magnetic entropy changes () from the magnetization data sets. The synthesized HoN particles from microwave-assisted sol-gel method reveal a high magnetic entropy change () of 36.6 J/kgK in applied field of 5 T at 14 K which is comparable with those of rare earth mono-nitrides by carbothermic reduction method. Moreover, the synthesized HoN nanoparticles from plasma arc discharge technique was pronounced magnetic entropy change () of 27.5 J/kgK with a transition temperature at 14.2 K. Both of result indicate that the synthesized HoN particles from two method could be considered as the promising magnetic refrigerant materials for hydrogen liquefaction system.

석탄회로부터 다공질 알루미나/뮬라이트 층상복합체의 동결주조

김규헌 부산대학교 대학원 2016 국내석사

Rheological behavior of camphene-based coal fly ash, alumina and mixed powder suspension have been investigated in terms of solid loading and type of additives (dispersant, binder/dispersant, binder/dispersant/surfactant). A freeze casting technique was processed to fabricate porous mullite/alumina layered composite with a gradient in porosity and pore size. In this work, a camphene/coal fly ash slurry system with an appropriate addition of Al2O3 was used. In case of freeze casting method, Unidirectional aligned dendritic macropore channels were developed by controlling the solidification direction of the camphene solvent. The pore morphology was influenced by the starting solids loading and sintering temperature. After sintering at 1500oC, rod-shaped mullite crystals formed in the presence of relatively large amount of liquid phase. The compressive strength of monolithic specimen greatly decreased when the porosity increased. However, the layered composites with a graded porosity exhibited improved compressive strength with minor decrease in porosity, probably due to the formation of residual compressive stress and relatively dense glass phase in the outer layer.

선박용 밸브 디스크의 내마모 특성 연구

장승환 부산대학교 2015 국내석사

Welding was carried out with stellite 6 alloy welding rod on stainless 410 base metal by CO2 arc welding method. Microstructure, hardness, and wear resistance properties were examined according to the change of transfer current (90~150A) and preheat temperature (R.T.~400℃) in welding. And conclusions are as follows. The microstructure of weld-overlayer is hypoeutectic structure composed of dendritic primary crystal Co with structure where eutectic carbide of M7C3 type is surrounded in network shape. It was shown that, in case current increased, the amount of eutectic carbide decreased, and the size of dendrite tended to increase. It was shown that the hardness of weld-overlayer tended to decrease according to the increase of current. The hardness of weld-overlayer was affected by dilution effect produced in welding besides the size of dendrite and microstructure. It was shown that the wear volume of weld-overlayer tended to increase as current and preheat temperature increased.

Ti-Mo-Fe합금의 석출거동과 기계적 특성에 미치는 첨가원소의 영향

안정진 부산대학교 대학원 2015 국내석사

Beta titanium alloys are in general widely used for aerospace, transportation, and biological purpose, due to its high formability, good wear resistance, and excellent fatigue strength. However, the alloys contained high amounts of the expensive beta stabilizing alloys, such as V, Nb, Zr, and others. It hinders wide application due to the economical reasons. Recently the new beta alloys containing low cost alloys, such as Fe, Mo, and so on. In this experiments we designed low cost beta alloys, 1) Ti-12.1Mo-1Fe (hereafter, 0A1F), and 2) Ti-12.1Mo-1Fe-0.1B (hereafter, 0A1F-0.1B) for the low cost and high formability. Using those alloys were solution heat treatment and aging treated for the investigation on the phase transformation and on the mechanical properties variation by the alloying elements effects (Mo, Fe, B). The chemical composition of the manufactured alloys analyzed by the ICP have some different Mo and Fe. 0A1F alloy of [Mo]eq calculated 15.65 and 0A1F-0.1B alloy of [Mo]eq calculated 14.85. Also, 0A1F alloy of e/a ratio calculated 4.18 and 0A1F-0.1B alloy of e/a ration calculated 4.167. Due to the chemistry difference produce the different behavior on the alpha-beta transition temperature, and phase transformation and mechanical properties. After solution treatment, those alloys have remarkable different tensile behaviors. The deformation mode of 0A1F alloy have changed from twinning to a slip by difference in the Fe contents, which coincided with the prediction by the electron/atom (e/a) ratio. 0A1F-0.1B alloy showed the low tensile strength of 800 MPa with elongation of 40%. While 0A1F alloy showed the high tensile strength of 900 MPa with elongation of 15% due to the change in the deformation mode. When aged 550℃ 1hr, 0A1F alloy precipitated only α phase, but 0A1F-0.1B alloy precipitated α and ω phase. Because 0A1F and 0A1F-0.1B calculated different [Mo]eq. It makes different precipitation behavior which have different temperature and time to transform ω phase to α phase. Boron was α stabilizing elements, but 0A1F-0.1B alloy have lower boron compositions(0.1wt%) and when added boron at the ti alloy, TiB was made under the melting temperature. But boron was not solution at the titanium matrix. So it makes no difference beta transformation temperature, precipitation behaviors and mechanical properties. Consequently, alloying elements of Mo and Fe are effect on [Mo]eq and e/a ratio, it makes difference precipitation behaviors and mechanical properties. But Boron was not effect on the phase transformation and precipitation behaviors.