Microporosity Formation in Alloy Solidification

合金凝固过程中微孔的形成

• 批准号: 0132225
• 负责人: Christoph Beckermann
• 金额: $ 30.83万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0132225&HistoricalAwards=false
• 关键词: Microporosity; Formation; Alloy; Solidification

The objective of this research is to advance fundamental understanding of microporosity formation during solidification of alloys. The single most important feature of the research is that it focuses solely on the microscopic scale (on the order of microns) where nucleation, interfaces, growth morphologies, and micro-flows can be directly observed. Previous studies of microporosity formation have been concerned with larger length scales and have not resolved the actual solid and pore microstructures. The study will provide valuable knowledge of pore nucleation and growth rates, microscopic flow and solute fields in the solid-liquid-gas system present during pore formation, and the interactions between the pores and the evolving microstructure. The research will be accomplished through the combined use of novel modeling, numerical simulation, and experimental techniques. A phase-field method will be developed to model the complex phase transformation and transport phenomena present, including multi-component thermodynamics, curvature effects, and convection. Modern numerical techniques, such as deforming finite element meshes and highly efficient parallel solvers, will be employed to solve the model equations. The experiments will use transparent model alloys inside a Hele-Shaw cell under a high-resolution microscope. In the experiments, the initial gas content and the solidification conditions will be carefully controlled. The model predictions will be validated by the experimental measurements.The work finds application in nearly every metal casting process. The problem of microporosity is of renewed interest because of the dramatically increased use of castings in the automotive and aerospace industries. Only the detailed prediction of microporosity can aid in its prevention and in assessing its influence on the strength and fatigue life of cast components. The transfer of the knowledge obtained through the proposed project will take place through continued collaboration with the casting industry, the development of improved microporosity models for use in casting simulation software, and the education of students. From a more fundamental point of view, the project will advance a largely uncharted area of research that is concerned with micro-scale, multi-component, multi-phase systems with phase change. Such systems are important not only in metal casting, but also in other materials processing operations, in nature, and in living organisms.

本研究的目的是提高对合金凝固过程中微孔形成的基本认识。该研究的一个最重要的特点是，它只关注微观尺度（微米级），可以直接观察成核，界面，生长形态和微流。以前的研究微孔形成一直关注较大的长度尺度，并没有解决实际的固体和孔隙微观结构。这项研究将提供有价值的知识孔成核和生长速率，微观流动和溶质场的固-液-气系统中存在的孔隙形成过程中，和孔隙和不断变化的微观结构之间的相互作用。 这项研究将通过结合使用新的建模，数值模拟和实验技术来完成。相场方法将被开发来模拟复杂的相变和传输现象，包括多组分热力学，曲率效应和对流。现代数值技术，如变形有限元网格和高效的并行求解器，将被用来解决模型方程。实验将在高分辨率显微镜下使用Hele-Shaw细胞内的透明模型合金。在实验中，将仔细控制初始气体含量和凝固条件。模型的预测结果将通过实验测量得到验证。这项工作在几乎所有的金属铸造过程中得到应用。由于汽车和航空航天工业中铸件的使用急剧增加，微孔性问题重新引起人们的兴趣。只有详细预测微孔，才能帮助预防和评估其对铸件强度和疲劳寿命的影响。通过拟议项目获得的知识的转移将通过与铸造行业的持续合作，开发用于铸造模拟软件的改进的微孔模型以及对学生的教育来进行。从更基本的角度来看，该项目将推进一个很大程度上未知的研究领域，该领域涉及微尺度，多组分，多相系统的相变。此类系统不仅在金属铸造中很重要，而且在自然界和生物体中的其他材料加工操作中也很重要。