Microstructural Effects on Phase Transformations in Metals at High Pressures

高压下金属相变的微观结构效应

• 批准号: 0703891
• 负责人: Yogesh Vohra
• 金额: $ 22.52万
• 依托单位: University of Alabama at Birmingham
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0703891&HistoricalAwards=false
• 关键词: Microstructural; Effects; Phase; Transformations; Metals

TECHNICAL: This project is focused on the microstructural effects on phase transformations in transition and rare earth metals under high pressures. In semiconductors and transition metal oxides, an increase in transformation pressure with a decrease in crystalline grain size has been well documented. However, similar systematic studies on metallic systems under high pressures are lacking. In transition metals, PI will study the effect of varying grain size (50 nm to 1000 nm) on the hcp to omega and omega to bcc phase transitions in titanium, zirconium, and hafnium at high pressures. PI will also investigate additional orthorhombic and monoclinic phases that have been reported in pure titanium under high pressures. In rare earth metals, PI will investigate the effect of varying grain size on the regular rare earth structures and on the phase transformation to the alpha-U phase under high pressures. The focus will be on rare earth metals cerium and praseodymium that show "crystal grain growth" phenomenon under high pressures in the alpha-U phase and where the phase transformation sequence is strongly influenced by microstructural effects. PI will establish the microstructural effects on the equilibrium transformation pressure as well as transformation kinetics by performing time dependent x-ray diffraction and electrical resistance measurements under high pressures and high temperatures at a synchrotron source. All experimental studies will be carried out using high purity samples and under controlled shear stresses in a quasi-hydrostatic pressure medium. The phase transitions will be monitored by simultaneous image plate x-ray diffraction technique as well as four probe electrical resistance measurements under high pressures using designer diamond anvils. This research project is strongly complemented by the recent advances in the fabrication of designer diamonds and their applications in electrical measurements and ohmic heating at high pressures. NON-TECHNICAL: The experimental studies on the role of microstructure in controlling the equilibrium phase boundary and kinetics in high-pressure transformations will lead to fundamental understanding of high-pressure phase diagrams of transition and rare earth metals. This increased understanding of microstructural effects in high-pressure phase transformations is likely to yield novel metastable phases in pressure-temperature treated samples with enhanced physical properties. High pressure materials research facilities supported by this grant will be employed in the Research Experiences for Undergraduates (REU) projects during the summer period with active participation of underrepresented minority undergraduate students. In the last six years, five PhD graduate students trained in PI's high pressure research group have accepted positions at national laboratories, industry, and academic institutions. PI's research lab continues to serve as an important source of trained US workforce in high-pressure science and metals research. A special emphasis on recruiting students from underrepresented minority groups in the sciences and engineering has been highly successful as 41% of REU participants on UAB campus have been minorities. The undergraduate and graduate students in this project will publish their findings in peer-judged journals leading to a broad dissemination of new knowledge generated in this NSF supported research.

技术：该项目的重点是对高压下过渡和稀土金属相变的微结构影响。在半导体和过渡金属氧化物中，已充分记录了转化压力随着晶粒尺寸的减少而增加的。但是，缺乏对高压下金属系统的类似系统研究。在过渡金属中，PI将研究高压下钛，锆和Hafnium的HCP到Omega和Omega的晶粒尺寸（50 nm至1000 nm）的影响。 PI还将研究在高压下在纯钛中报道的其他原晶和单斜相。在稀土金属中，PI将研究不同晶粒大小对常规稀土结构的影响以及在高压下向α-U相变为α-U相的影响。重点将放在稀土金属葡萄和praseodymium上，在α-U相高压力下显示“晶粒生长”现象，而相变序列受微观结构效应的强烈影响。 PI将通过在高压和同步器源处进行高压和高温下的时间依赖性X射线衍射和电阻测量，对平衡转化压力以及转化动力学建立微观结构效应。所有实验研究将使用高纯度样品和在准静压培养基中的受控剪切应力下进行。相转换将通过同时使用Designer Diamond Anvils在高压下在高压下的同时图像板X射线衍射技术以及四个探针电阻测量进行监测。该研究项目的最新制造及其在高压下电气测量和欧姆加热中的应用中的最新进展得到了强烈的补充。非技术：关于微观结构在控制高压转化中平衡相边界和动力学在高压转化中的作用的实验研究将导致对过渡和稀土金属的高压相图的基本理解。对高压相变的微结构效应的这种增加的理解可能会在压力温度处理的样品中具有增强的物理特性中产生新的可稳态。该赠款支持的高压材料研究设施将在夏季的本科生（REU）项目的研究经验中采用，而代表性不足的少数群体本科生积极参与。在过去的六年中，在PI的高压研究小组中接受过培训的五位博士学位学生已经接受了国家实验室，工业和学术机构的职位。 PI的研究实验室继续成为高压科学和金属研究中训练的美国劳动力的重要来源。特别强调科学和工程中代表性不足的少数群体的招募学生已经取得了很大的成功，因为UAB校园中有41％的REU参与者是少数群体。该项目中的本科生和研究生将在同行判断的期刊上发布他们的发现，从而广泛传播NSF支持的研究中产生的新知识。