LiCl-KCl 용융염을 이용한 방사화 지르코늄-나이오븀 합금 전해제염 연구

김평화 서울대학교 대학원 2016 국내석사

The number of operational nuclear power plants over the world is 445 as of June 2016 and almost age of reactors is more than 30 years. In Korea, Kori unit #1 and Wolsung unit #1 are doing the long term operation after their design life (30years), and it is essential to replace obsolete equipment of Nuclear Power Plants (NPPs) to acquire the license renewal. For example, Wolsung unit #1 replaced Pressure Tubes (PTs). They are core components in a Pressurized Heavy Water Reactor (PHWR). Retired PTs were stored in radioactive waste storage facilities built newly in Wolsung unit #1. If the long term operation of Kori unit #1 finishes in June 2017, it will be decommissioned as related laws after sending a final decommissioning plan to an authority and receiving an approval of the decommissioning. KORAD had built the #1 underground repository cavern for low and intermediate level wastes (LILWs) and began operating the repository in 2015. But according to KHNP’s research, the LILW’s repository will be saturated in 2015 due to operational wastes and decommissioning wastes. Therefore, study on decommissioning should be continued the effectively operate the repository and to reduce disposal cost for LILWs. Zr, one of metals used in in NPPs, is so expensive metal, since a thermal neutron absorption cross section of zirconium is low and mechanical properties of zirconium are excellent, Zr based alloys are used variously in NPPs. If niobium is added to zirconium alloy, corrosion resistance of zirconium alloys is better. Zr-Nb alloys are used for structural components, claddings, pressure tubes in PWRs or PHWRs. And KAERI developed HANA claddings by adding niobium to zircaloy-4 and by modulating niobium. And have conducted verification tests in commercial reactors and research reactors. If HANA cladding is commercialized, it is expected that radioactive wastes of Zr-Nb will increase rapidly. ORIGEN-2 computational simulation results for PHWRs pressure tubes(Zr-2.5Nb) after 30 years of operation time and 10 years of cooling time showed that specific radioactivity of Nb94, Co60, Fe55, Ni63 is higher than other nuclides in the order named. In particular, Nb94 is critical for irradiated Zr-Nb alloys, because a half-life of Nb94 is 20,300 years and is longer than others. Irradiated PHWR pressure tubes by simulating ORIGEN-2 are intermediate level wastes and are need to dispose of in the cave repository as related laws. According to chapter 8.2 in the Safety Analysis Report (SAR) of #1 LILW repository, total radioactivity of Nb94 is 8.59×1010Bq in this repository. Based on this value, it is possible to dispose of about 10kg of irradiated pressure tubes for Nb94. Considering that mass of replaced Pressure Tubes for Wolsung #1 unit is 23 ton, waste to be possible to dispose of is almost nothing. And ILWs are impossible to be disposed of in the #1 LILWs repository, because KORAD’s acceptance criteria is equal to a low level waste standard, thus intermediate radioactive level of this waste should be lowered to LLWs or Very LLWs (VLLWs). If Nb94 is removed from irradiated pressure tubes, it will be possible to dispose of almost them. Therefore this study aims for assessment of electorefining steps to need to be exemption level wastes and decontamination effects by using electrorefining of Zr-Nb alloys. Electrorefining of zircaloy-4 and zirlo of main materials in nuclear fuel cladding was previously studied. Their results showed that purity of zirconium at the cathode increased and concentration of impurities at the cathode decreased. Like this, it is expected to reduce Nb94 from radioactive wastes by using electrorefining. Molten salts used in electrorefining are mainly fluorides or chlorides. In molten salts of fluorides, a high purity zirconium is acquired and the redox behavior of Zr is one-step reaction, but operating temperature is higher than chlorides due to melting point and there is a corrosion problem. In contrast, operating temperature of chloride is low and corrosion problem occurs less than the fluoride, but disproportion reaction like that, Zr(IV) + Zr ↔ 2Zr(II), occurs because zirconium is very unstable in chloride and ZrCl is electrodeposited at the cathode. This dissertation decided to use chloride molten salts due to operating temperature. Considering half-life and specific radioactivity of each nuclide, Nb, Co, Ni as impurities were selected to separate from PTs. After dissolving ZrCl4, NbCl5, CoCl2, NiCl2 in LiCl-KCl, cyclic voltammetry(CV) of each element is conducted at 500℃ to check the behaviors of redox for each element. Oxidation and reduction peaks were compared to previous studies and redox behaviors were checked. CV results of Zr have usually 3 reduction peaks. For low concentration (0.2wt.%, 0.5wt.%) of ZrCl4 in the molten salt, there is no reduction peak(ZrCl + e- → Zr) at -1.5V(vs. Ag/AgCl). Because reduction velocity from Zr(VI) to ZrCl is slower than that from ZrCl to Zr metal. Therefore, it is expected that ZrCl is electrodeposited at a cathode in LiCl-KCl will get solved for low concentration of ZrCl4. A reduction peak at -1.0V (vs. Ag/AgCl) is Zr(IV)↔Zr(II) and a reduction peak at -1.2V (vs. Ag/AgCl) is Zr(IV)↔ZrCl. Mainly Oxidation peak was at -0.9 ~ -0.7V (vs. Ag/AgCl). Disproportionate reaction of the niobium also occurs in LiCl-KCl, and redox behaviors of niobium are more complicated than Zr. Niobium chlorides are made up subchlorides due to nonstoichiometric reaction in LiCl-KCl. For niobium subchlorides(NbCly), the value of y is from 2.33 to 3.13. A dominant subchloride is Nb3Cl8. In contrast, cobalt and nickel ions are simply reduced to metals and are equal to previous studies. Since Zr is the most oxidizing among Nb, Co, Ni as results of CV, a applied potential at a anode electrode was decided -0.85V(vs. Ag/AgCl) to dissolve only Zr. No shielding facility is in our laboratory, so irradiated material should not be used. Because Zr-2.5Nb equal to PTs material for nuclear grade couldn’t be bought, HANA cladding scraps were used as surrogate materials at the anode. The lab-scale potentiostatic electrorefining experiments of unirradiated Zr-Nb alloys are conducted in LiCl-KCl-5wt% ZrCl4. ICP-MS result of Zr-Nb alloys used for experiments was not included Co, Ni, so these impurities are additionally inserted to an anode basket. First, the experiment was conducted at -0.85V(vs. Ag/AgCl) as the applied potential, but there was no electrodeposition at a cathode and black powders were sunken in molten salts. Thus after oxidizing anode for 15 hours, a working electrode was changed from the anode to the cathode and the applied potential was changed to reduction potential of Zr(-1.0V~-1.6V(vs. Ag/AgCl)). At reduction potential of Zr, electrodeposition was formed at cathode and was analyzed by ICP-MS and XRD to check compositions. Results of XRD showed that the electrodeposition was mainly ZrCl, because ZrCl4 concentration (5wt.%) in molten salts was higher than those of CV condition(0.1~2.0wt.%), and partailly ZrO2 was checked at the electrodeposition. It is expected that Zr was oxidized during XRD analysis, because oxygen concentration in the glovebox was lower than 0.1ppm. In the all of the experiment results, the purity of zirconium increased from 91~93% to 99% when anode composition before electrorefining was compare with the electrodepostion at cathde after electrorefining. A very small amount of Nb was measured, it is expect that impurities of anode for a counter electrode was chemically dissolved during electrorefining experiment and co-electrodeposit with molten salt at cathode. In all the experiment, Co was not discovered and Ni was only discovered within background concentration in LiCl-KCl. Therefore it was thought that Co and Ni would not be dissolved during electrorefining experiment. Decontamination factors were evaluated by using results of electrorefining. And the number of electrorefining steps needed to be exemption level wastes is three. Because recovered zirconium from irradiated wastes is included Zr93, one of the radioactive nuclides, it can be not recycled for general industry, but can be reused for storage drums of radioactive wastes or shielding materials in nuclear industry. Considering only one replacement of PTs for domestic four PHWRs, it is assessed that about 500 waste-drums will be reduced and economic effect is about 19 billion won. If nuclides (Nb94, Co60, Ni63) separated by electrorefining in molten salts or anodes are conducted nuclear transmutation to nuclides which have low radioactivity and short half-life through fast reactors or accelerators or dispose of in High Level wastes disposal repository which will be built, it is expected to solve disposal problem of radioactive wastes. Existing surface decontamination or melting decontamination can’t remove selectively activated products as this study. Therefore it is certainly necessary that volume reduction of radioactive wastes and limited recycling of valuable radioactive metals by developing electrochemical decontamination for electrorefining continuously to improve public acceptance for nuclear power as well as to reduce disposal cost and to effectively operate the repository.

Surface Stability, Phonon Band Structure, and Vibrational Dynamics of the Nb(100) Surface Oxide Reconstruction

McMillan, Alison Ann ProQuest Dissertations & Theses The University of 2022 해외박사(DDOD)

Niobium is the current industry standard for modern superconducting radiofrequency cavities in particle accelerators, but technology has pushed these cavities to niobium’s fundamental limits. Future progress rests on improved growth procedures for existing materials and the development of new materials, and a complete, detailed, atomic-scale characterization of the niobium surfaces used in accelerators is a prerequisite for this progress. Towards this end, this thesis contains a set of experiments that employ helium atom scattering to describe the (3 x 1)-O reconstruction of the Nb(100) surface. Elastic helium diffraction from the (3 x 1)-O Nb(100) surface is used to characterize the structure of the surface over a wide range of high temperatures. High-resolution helium diffraction and line-shape analysis, confirmed by Auger electron spectroscopy, reveal that the (3 x 1)-O reconstruction is stable up to at least 1130 K. The atomic-scale surface structure, composition, and coherence do not change up to this temperature, which exceeds the temperature at which niobium is held during typical tin nucleation procedures. Inelastic helium time-of-flight measurements are used to map out the phonon band structure of the Nb(100) oxide and determine the nature of the surface’s vibrational dynamics and force constants. Density-functional theory calculations correspond with measured phonon dispersions and elucidate the atomic displacement patterns for each measured phonon resonance. The difference between the calculated bare and oxidized Nb(100) surfaces show that the oxide disperses electron-phonon coupling strengths to higher energies and significantly increases force constants at the surface, potentially affecting surface superconductivity and superconducting radiofrequency cavity behavior.

Advancing the Maximum Accelerating Gradient of Niobium-3 Tin Superconducting Radiofrequency Accelerator Cavities: RF Measurements, Dynamic Temperature Mapping, and Material Growth

Porter, Ryan Douglas ProQuest Dissertations & Theses Cornell University 2021 해외박사(DDOD)

Niobium-3 Tin (Nb3Sn) is the most promising alternative material for Superconducting Radiofrequency (SRF) particle accelerator cavities. Current SRF accelerators use superconducting niobium accelerator cavities, which are nearing their theoretical limits of performance. Nb3Sn promises increased quality factors, twice the operational temperature (4.2 K instead of 2K), and almost twice the theoretical accelerating gradient--96 MV/m in a TESLA elliptical style cavity. These advances can reduce the size and complexity of particle accelerators while simultaneously making them more efficient. The capability of operating at 4.2 K enables the creation of small-scale superconducting accelerators that are run off cryocoolers and could be used in research and industrial applications. Current Nb3Sn cavities achieve quality factors of 2·1010 at 4.2 K. The accelerating gradient, however, is limited far below the theoretical potential of this material, with the best recorded reaching 24 MV/m. In this work we present studies on what is limiting the maximum accelerating gradients in these cavities. We study cavity performance under RF testing, make dynamic measurements of cavity heating during operation, study samples with microscopy, and develop models of Nb3Sn material growth. In the process we develop new diagnostic tools for SRF development: a dynamic/high speed temperature mapping system that measures the spatial heat distribution on a cavity at 50 ksps, and high-power test system for measuring the ultimate critical fields (theoretical limit of the accelerating gradient) of new materials. We explore models of cavity losses/heating that limit the accelerating gradient and propose modifications to the material growth process to create Nb3Sn cavities with higher accelerating gradients and quality factors. We conclude with results from a new cavity coating wherein we have suppressed multi-gap superconductivity that has been seen in these cavities and was a limitation to the quality factor.

Atomic Scale Characterization of Engineered Interfaces in Superconducting Qubits

Garcia-Wetten, David Andres Northwestern University ProQuest Dissertations & T 2025 해외박사(DDOD)

Superconducting microwave circuits are a promising physical implementation of quantum computing. A significant challenge with the development of superconducting qubits is the materials source of loss leading to qubit decoherence. Much of this loss is dielectric loss or quasiparticle dissipation at superconductor surfaces and interfaces. In order to understand the loss mechanisms microscopically, it is necessary to have an accurate picture of the atomic structure and microstructure. In this work, we explore the structure of three interfaces. First, we present nondestructive X-ray characterization of the NbH surface precipitation in Nb thin films. Unwanted hydride precipitation in niobium-based superconducting circuits is a side effect of hydrofluoric acid etching of the Nb surface oxide. The precipitate microstructure is challenging to probe because of the high mobility of hydrogen in niobium. Using X-rays diffraction, we show evidence supporting phase-field simulations that the nucleation of NbH occurs at free surfaces. Using darkfield X-ray nanoprobe microscopy, we identify a complex microstructure suggesting a martensitic nucleation that transitions to a dendritic growth. Next, we present X-ray standing wave excited X-ray photoelectron spectroscopy of the annealed, Nb(110) ordered oxide surface layer. We discover the existence of an oxygen interstitial rich subsurface layer and identify the origin of two distinct oxygen chemical states at the surface: one coming from this subsurface layer, and the other from the surface NbO termination. Last, we present the heteroepitaxy of single crystal Al2O3 with a TiN. We identify TiN as an ideal substrate for the epitaxial growth of Al2O3 in a capacitor geometry based on the high degree of crystallinity and sharp interfaces with minimal diffusion and we measure the two-level-state loss of the Al2O3 junction dielectric layer. We present this interface as an alternative to the commonly used amorphous alumina in Josephson Junctions.

Properties of Nb-modified Pd/Sio_(2) catalyst for selective hydrogenation of acetylene : Niobium으로 변형된 아세틸렌의 선택적 수소화 반응용 Pd/SiO_(2) 촉매의 특성

김정환 서울대학교 대학원 2003 국내박사

Synthesis of niobium compounds by CVD and epitaxial growth

김관우 성균관대학교 일반대학원 2019 국내석사

Chemical Vapor Deposition (CVD) method is widely used for high quality synthesis of nanomaterials such as graphene, CNT, and MoS2. However, CVD synthesis for Niobium compounds (Niobium oxide, Niobium carbide, Niobium selenide), especially Niobium selenides, has not been studied much. Niobium oxide (Nb2O5) can be used for various applications including gas sensors, photo-catalysts, photo-detectors, batteries, and solar cell. Also, Niobium carbide (NbC) is promising for various applications such as a reinforced phase in an iron matrix, hard coating, and wear protection. In case of Niobium selenides, NbSe2 and NbSe3 are well known materials because they exhibit interesting physical properties like the presence of both superconductivity (SC) and charge density waves (CDW) and the competition between SC and CDW. In this study, we aimed to study on CVD synthesis of Niobium compounds Furthermore, all three compounds have grown epitaxially on c-plane sapphire substrates, and the mechanism for the epitaxial growth will also be discussed.

양극산화를 통한 니오븀 산화물 나노구조체 제조 및 에너지 저장 장치에서의 응용

김연진 인하대학교 대학원 2025 국내석사

본 연구에서는 리튬 이온 배터리(LIB)의 음극 소재로 고용량과 고안정성을 제공하는 Nb2O5 와 NbO 로 구성된 다중상 나노채널 니오븀 산화물(NONC) 구조를 제작하였다. 전기화학적 양극산화를 통해 기판에 직접 성장한 다중상 NONC 는 바인더가 필요 없는 음극으로 기능한다. 100 회 사이클 동안 전극은 0.4 A g-1 에서 440 mAh g-1 의 가역 용량을 나타내며, 700 회 사이클 후에도 236 mAh g-1 의 용량을 유지하여 이론 용량을 초과한다. 또한, 4 A g-1 의 고속 사이클링에서도 1000 회 사이클 후 최소한의 용량 감소를 보여 안정적인 전기화학적 거동을 입증한다. 이러한 뛰어난 성능은 다중상 NONC 구조에 기인하며, NbO 는 전기 전도성을 향상시키고 Nb2O5 는 결정질에서 비정질 상으로 변형된다. 또한, 사이클링 중에 안정적인 고체 전해질 계면(SEI) 층이 형성되고 분해되어 셀의 수명을 연장하고 안정적인 나노채널 구조를 유지하는 데 기여한다. 본 연구는 이러한 현상이 고성능 금속 산화물 전극 재료 개발에 유망하다는 것을 시사한다. 추가적인 응용으로, LIB 로서 사용된 니오븀 산화물 전극을 슈퍼커패시터 전극으로 재사용할 가능성을 논의한다. 합성된 나노구조체의 구조적 및 결정학적 특성은 양극산화 매개변수를 고려하여 분석한다. 또한, 정전용량을 평가하고, 전기화학적 성능의 동역학 분석은 정전 및 확산 제어 충전 저장 과정의 해석을 통해 설명한다. LIB 에서 사용된 니오븀 산화물 전극을 슈퍼커패시터 응용에 사용할 가능성은 리튬이 함유된 니오븀 산화물을 중심으로 평가하며, 이는 형성된 전극과 비교하여 정전용량의 향상과 충전 저장 메커니즘의 변화를 보여준다. 이러한 개선은 나노채널 형태와 니오븀 산화물 층의 활성 영역에서의 변화를 통해 설명된다. 이 연구는 에너지 저장 장치를 위한 고성능 금속 산화물 전극 재료 개발에 통찰력을 제공하고자 하며, 나노구조 니오븀 산화물의 다양한 에너지 저장 응용에서 향상된 전기화학적 특성을 입증함으로써 지속 가능하고 효율적인 에너지 저장 솔루션의 발전에 기여하고자 한다. In this study, a multiphased niobium oxide nanochannel (NONC) structure comprising Nb2O5 and NbO is fabricated as an anode material for LIBs, offering high capacity and stability. The multiphased NONC, directly grown on the substrate through electrochemical anodization, functions as a binder-free anode. During 100 cycles, the electrode exhibits a reversible specific capacity of 440 mAh g-1 at 0.4 A g-1, maintaining a capacity of 236 mAh g-1 after 700 cycles, exceeding the theoretical capacity. Even under high-rate cycling at 4 A g-1, the electrode exhibits minimal capacity degradation after 1000 cycles, demonstrating stable electrochemical behavior. This exceptional performance is attributed to the multiphased NONC structure, with NbO enhancing electrical conductivity and Nb2O5 undergoing a crystalline- to-amorphous phase transformation. Additionally, a stable solid electrolyte interface (SEI) layer forms and decomposes during cycling, contributing to the prolonged lifespan of the cell and maintaining a stable nanochannel structure. This study suggests that these phenomena are promising for developing high-performance metal oxide electrode materials. As a further application, we discuss the potential of reusing spent niobium oxide electrodes, utilized in LIBs, as electrodes for supercapacitors. The morphology and crystallographic characteristics of the synthesized nanostructures are analyzed, considering the anodization parameters. In addition, the specific capacitances are evaluated, and the kinetic analysis of the electrochemical performance are further elucidated through the interpretation of the capacitive and diffusion- controlled charge storage processes. The feasibility of utilizing niobium oxide electrodes from spent LIBs for supercapacitor applications is assessed, focusing on lithium-incorporated niobium oxide. This approach demonstrates an enhancement in specific capacitance and alterations in the charge storage mechanisms compared to the as-formed electrodes. These improvements are attributed to the changes in the nanochannel morphology and active area of the niobium oxide layer. We hope that this study provides valuable insights into the development of high-performance metal oxide electrode materials for energy storage devices. By demonstrating the enhanced electrochemical properties of nanostructured niobium oxide across different energy storage applications, we aim to contribute to the advancement of sustainable and efficient energy storage solutions. Keywords: Niobium oxide, Anodization, Nanochannels, Lithium ion battery, supercapacitor

Surface and interface effects in epitaxially grown niobium and iron pnictide superconductors

김성민 서울대학교 대학원 2015 국내박사

Superconductivity has been one of the most actively studied field in physics since it was discovered. In BCS superconductor, it is well explained microscopic phenomena by BCS theory, yet some BCS superconductor studies such as low dimensional superconductor or superconductor junction behaviors are still performed. For high TC superconductor such as iron pnictide compound, more phenological studies are needed since theory that fully describe the mechanism is not established. During my Ph.D course, I have performed the scanning tunneling microscopy and spectroscopy (STM/STS) studies for niobium and iron pnictide superconductors to extend the understanding of superconductivity. For this study, I constructed a cryogenic STM system and an STM combined molecular beam epitaxy (MBE) / pulsed deposition (PLD) growth system. I observed that the superconducting gap of niobium appears when film thickness is over 40 Å, and investigated the suppression of superconductivity in disordered niobium film correspond to Finkel’stein’s model. In epitaxially grown niobium film on W(110) substrate, I observed the oscillation of electron density around superconducting gap, which is analyzed to be an interface effect of superconducting and normal junction ? Tomasch effect. I synthesized Co doped BaFe2As2 film by PLD, and measured with STM/STS. I observed surface state effect by electronic screening of barium atoms on the surface, which made the superconducting gap be distorted. And I found some features which has not been reported with cleaved surface. For another iron pnictide superconductor, LiFeAs, I performed the STM measurement of epitaxially grown film by PLD.

Physical Separation of Tantalum and Niobium from an Artificial Mineral : 물리적 선별에 의한 인공광물로부터 Nb 및 Ta의 회수에 관한 연구

Bat-Erdene Davaadorj 강원대학교 대학원 2012 국내석사

본 연구에서는 희유금속에 속하는 네오븀 (Nb)과 탄탈륨(Ta)에 대한 회수 연구를 진행하였다. 네오븀과 탄탈륨은 고온안정성(melting point, Nb : 2477 oC, Ta : 2996 oC) 및 강한 내화학성을 특징으로 거의 녹지 않는 물질로 알려져 있다. 네오븀과 탄탈륨은 첨단 전자산업에 널리 쓰이고 있으며, 철강 산업에서 첨가물질로 활용되고 있다. 하지만 지각 중에 존재하는 네오븀과 탄탈륨의 존재가 매우 적을 뿐만 아니라 (네오븀은 약 20 ppm, 탄탈륨은 약 1.7 ppm정도) 주로 저품위 광석으로 존재하고 있다. 따라서, 저품위 Ta-Nb의 광석으로부터 맥석을 제거하고 광석품위를 높이기 위한 전처리 공정에 관한 연구가 절실히 필요하다. 따라서, 본 연구에서는 인공광물을 제조하여, 다음과 같이 Nb 및 Ta의 물리적 선별에 관한 3가지 실험을 진행하였다. (1) Nb 및 Ta의 침강속도 실험; (2) 인공광물로부터 Nb 및 Ta의 중액선별 실험, (3) Nb 및 Ta를 이용한 합성광물 제조 실험. 실험물질로는 시약급 분말시료인 Ta2O5, Nb2O5, SiO2을 이용하였다. Niobium and tantalum, with high melting points, have been utilized widely in the steel, electronic and other high-tech industries. However, the overall abundances of niobium and tantalum in the average continental crust are relatively low and most of them are low-grade. Therefore, the pre-treatment process is important part of the separation of niobium and tantalum from ore. Because of aforementioned reasons, the pre-treatment method to separate niobium and tantalum from an artificiality mineral was studied in this thesis. Three kind of experiments were performed that including the settling test of Nb2O5 and Ta2O5, heavy medium separation and mechanochemical synthesis of an artificiality mineral of niobium and tantalum. 腦粧贍脹 蓀 杖翟拗? 贓 ө庄ө? 鎭逸儼城債? 鎚雨菴?, 侁陰 緝竣嬉緝? 靭診應寨? ??. 枇晞үү 鋪掌 妬壯終? 贓 星嵬乙? 侁帳惚 ү雨壓嬉衣?, 凞焉疾佺 灑依? 修焌? ө庄ө? 鎭蹴鏑謫僥? ү雨壓嬉衣陰 ө造ө?өө? 星嵬乙焌燮 蓀勖?. 攣怏? 震雩 ? 診粧贍脹-杖翟拗荏? 腋椅僥? ?ө猝ө庄 說寨乙宸性 ?өө打勖 膵靷羲 鎚綜稱帳猖 蓀侁 蓀 撓噫? 贓 蓀侁 汚造僥? 說寨蔭城纖 蓀藕說. 多押羲鳥勖 說寨蔭惑 腋熹?үү衣? 穽專嚴? ? 蓀?閱窓性 穽專嚴? 贓 診粧贍脹-杖翟拗荏? 蓀芋贍僥? ?ү崖羲? ?蔭陝 設性雪 茵造薛帳ү? 罷鎚? 穽專嚴證? 醬? ??. 漏雩羲? 噫晞үү 茵燼增終? 憎菴蔭薛裝 剡堯菴? 診粧贍脹-杖翟拗荏? 蓀侁 汚造僥? 說寨蔭城纖 ?ү崖僥? 歆心嬉 靭診應惚 淸預? 鋪掌 妬壯倧 ү庄希衣? 蓀?閱窓性 燮審? 診乙燮 憎菴蔭薛, 膣淙堯? 筑勖 ү? ?ү帳 醬訊心? 膣蠢葉陝 灑鷹?.

Hot Isostatic Pressing of Niobium-based Refractory Alloys

Mikler, Calvin Vijay The Ohio State University ProQuest Dissertations & 2021 해외박사(DDOD)

The period of niobium refractory alloy development in the 1950s-1970s was significant in metallurgical history because of its unique ability to operate at high temperatures (1200+°C). Marred by high costs and lack of processability through traditional industrial techniques, novel alloy development diminished, leaving behind a limited catalog of alloys and production methods. There is now a resurging interest in niobium alloys. However, the empirical metallurgy principles relied on for the development of the alloys in earlier research are no longer sufficient. Their exploration of alternative processing techniques such as metal powder consolidation was limited, at best.This work investigates hot isostatic pressing (HIP) of C103 (Nb-10Hf-1Ti wt%) and WC3009 (Nb-30Hf-9W wt%) powders into near net shapes. Subsequent isothermal heat treatments were conducted to better understand recrystallization behavior during HIP processing. This effort was performed to identify key alloy attributes that drive processability through HIP such that higher strength niobium alloys can be utilized. Dilute binary niobium alloys (Nb-1[Ti, Zr, Hf] at%) were fabricated and analyzed to elucidate variances in solute strengthening potency. Room-temperature mechanical tensile tests and nanoindentation were conducted to compare the relative strengths of alloys and to generate a deformed microstructure. Advanced SEM characterization of HIP-processed, pre-, and post-deformation structures was accomplished using electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI).The results shown in this study show that HIP processing of powder niobium alloys is a viable method to produce near-net shapes. Furthermore, the fact that alloys such as WC3009 can be consolidated indicates that this process is not limited to historically fabricable alloys like C103; It can also be applied to high-performance alloy systems that were previously thought impossible to use. The microstructures generated via HIP processing are heterogeneous compared with wrought material. Isothermal heat treatments of partially HIP processed materials revealed that recrystallization occurs heterogeneously throughout the microstructure where areas of comparatively high strain such as prior particle-particle interfaces are initially favored. The mechanical testing results for dilute binary niobium alloys confirm zirconium is the most potent and anomalous strengthener compared with titanium and hafnium.