SGER: Thermal Modification of Alloy Composition Profile

SGER：合金成分概况的热改性

• 批准号: 0736640
• 负责人: Yong Kim
• 金额: --
• 依托单位: Lehigh University
• 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 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0736640&HistoricalAwards=false
• 关键词: SGER; Thermal; Modification; Alloy; Composition

TECHNICAL: A run of metal alloy of given bulk composition may be processed along any one of many pyrometallurgical pathways. Elemental composition may exhibit position dependence specific to the processing pathway; surface segregation by constituent elements is a long-standing example. Transport properties are sensitively affected by the structure of the elemental composition profile and therefore become dependent of processing history. The literature is filled with examples of widely varying numerical values for a given property, such as spectral emissivity and thermal diffusivity. This state of affair has persisted for two basic reasons: one, there has not been any robust development of a theoretical framework in mesoscopic scales that bridges the microscopic lattice-level analysis and the macroscopic thermo-chemical models; and two, there had not been any commensurate experimental methodologies for composition profile based characterization of thermophysical properties until now. The high-risk/high payoff and transformative project brings to the table a new measurement methodology and requisite instrumentation, which can provide measures of selected transport properties and local elemental composition simultaneously by time-resolved spectroscopy of laser-produced plasma (LPP) plume emissions. The project is supported by a body of evidence that the composition profiles of a given alloy specimen can be modified thermally in a reproducible manner; disparate thermal transport of constituent atoms can incur significant modifications of near-surface composition profiles. The goal of the project is to demonstrate that the modification is causal by characterizing the imposed thermal drive and examining the movement of the elemental composition profile by direct position-resolved measurement. Several different schedules of thermal cycling will be applied to the specimens and the composition profiles will be analyzed by the LPP methodology. The study will be focused initially on a nickel-chromium binary alloy. The project research has high risk in that the above-generalized picture of the ways an alloy responds to thermal cycling may not bear out over wider ranges of alloy systems. The primary system used in the study (low-melting point four-element Wood's alloy) as a model system could prove to be an exception, rather than a representative system for a wide class of alloys. We reason that use of simpler systems, such as two-element alloys, will be an effective approach to examine the potential uncertainty. NON-TECHNICAL: The phenomenon of near-surface composition anomaly suggests a potential for active modification of the alloy surface properties in a predictable manner by intentionally changing the alloy's near-surface composition. It may be to enhance material's corrosion resistance, scratch resistance or magnetic and electrical properties at material surfaces. Rigorous understanding of the relevant atom transport mechanisms will help formulate the predictive models to achieve these goals. The impact of such capability will provide a number of new development options to metals industries in the U.S. The broader impact will also be to help develop mesoscopic models of materials processing for functionality-specific alloys. The research once proven will have a transformative impact on the alloy design and processing fields; it will provide a basis for quantitative modeling. The investigation will also help produce a new generation of experts from the ranks of graduate students; during the one-year SGER project period a M.S. degree work will be completed. First-principle based understanding of the atom transport processes will be crucial to design of new materials and cost-effective management of materials utilization.

技术：一批给定的整体成分的金属合金可以沿着许多火法冶金途径中的任何一种进行加工。元素组成可能表现出特定于加工路径的位置依赖性；由组成元素引起的表面偏析是一个长期存在的例子。传输特性受到元素组成分布的结构的敏感影响，因此变得依赖于加工历史。文献中充满了给定属性（例如光谱发射率和热扩散率）的数值变化很大的示例。这种状况之所以持续存在，有两个基本原因：一是介观尺度的理论框架尚未得到强有力的发展，以连接微观晶格级分析和宏观热化学模型。第二，迄今为止还没有任何相称的基于成分分布的热物理性质表征的实验方法。这个高风险/高回报和变革性的项目带来了一种新的测量方法和必要的仪器，可以通过激光产生的等离子体（LPP）羽流发射的时间分辨光谱同时提供选定的传输特性和局部元素组成的测量。该项目得到大量证据的支持，表明给定合金样本的成分分布可以以可重复的方式进行热修改；组成原子的不同热传输会导致近表面成分分布的显着改变。该项目的目标是通过表征施加的热驱动并通过直接位置分辨测量检查元素成分轮廓的运动来证明这种修改是因果性的。几种不同的热循环方案将应用于样品，并通过 LPP 方法分析成分分布。该研究最初将集中在镍铬二元合金上。该项目研究具有很高的风险，因为上述合金对热循环响应方式的概括图可能不适用于更广泛的合金系统。研究中使用的主要系统（低熔点四元素伍德合金）作为模型系统可能被证明是一个例外，而不是多种合金的代表性系统。我们认为使用更简单的系统（例如二元合金）将是检查潜在不确定性的有效方法。非技术性：近表面成分异常现象表明，通过有意改变合金的近表面成分，可以以可预测的方式主动修改合金表面性能。它可能是为了增强材料的耐腐蚀性、耐刮擦性或材料表面的磁电性能。对相关原子传输机制的严格理解将有助于制定预测模型以实现这些目标。这种能力的影响将为美国金属行业提供许多新的发展选择。更广泛的影响还将有助于开发特定功能合金的材料加工介观模型。该研究一旦得到证实，将对合金设计和加工领域产生变革性影响；它将为定量建模提供基础。这项调查还将有助于从研究生队伍中培养新一代专家；在为期一年的 SGER 项目期间，获得硕士学位学位工作将完成。基于第一原理的对原子传输过程的理解对于新材料的设计和材料利用的成本效益管理至关重要。