Experimental Investigation of Dynamic Abnormal Grain Growth

技术概要：动态反常晶粒长大（DAGG）是近年来发现的一种仅在高温塑性变形过程中发生的二次再结晶现象。DAGG可以在相对较低的同系温度（约0.65 Tm）下快速产生非常大的固态单晶，这是任何其他工艺都不可能实现的壮举。DAGG的动态性质是其最独特的特征，并提出了新的挑战，目前的理解异常晶粒生长和晶界迁移，在微观结构演化的金属科学的基础课题。迄今为止，DAGG仅在两种材料中观察到，Mo和Ta BCC难熔金属。拟议的研究将调查这些金属中产生DAGG的过程，然后开发对DAGG敏感的新金属系统。研究目标包括开发（1）预测何时以及在何种材料中发生DAGG的能力，以及（2）控制对异常晶粒生长敏感的材料中的DAGG的能力。动态反常晶粒生长（DAGG）是近年来在材料科学领域中发现的一种现象。在高温下使多晶材料变形时发生DAGG，并已用于在钼和钽中生长用于科学研究的大单晶。除了这一最初的实际应用，DAGG代表了一个机会，以获得新的基本见解材料微观结构的演变。控制材料微观结构对于许多行业，特别是运输行业的先进部件的制造至关重要。这项研究的潜在影响包括创造新材料和提高制造部件的质量。拟议的研究将加强与通用汽车和桑迪亚国家实验室的合作。研究生和本科生将通过研究活动以及学术研究期间的指导在材料和金属科学领域进行培训。将支持向当地社区推广科学和工程的外联活动。

TECHNICAL SUMMARY: Dynamic abnormal grain growth (DAGG) is a recently-discovered secondary recrystallization phenomenon that occurs only during plastic deformation at elevated temperature. DAGG can rapidly produce very large single crystals in the solid state at relatively low homologous temperatures, approximately 0.65 Tm, a feat not possible by any other process. The dynamic nature of DAGG is its most unique characteristic and poses new challenges to current understandings of abnormal grain growth and grain-boundary migration, foundational topics in the metals science of microstructure evolution. To date, DAGG has been observed in only two materials, Mo and Ta BCC refractory metals. The proposed research will investigate the processes which give rise to DAGG in these metals and then develop new metal systems susceptible to DAGG. Research goals include developing (1) a capability to predict when and in what materials DAGG will occur and (2) a capability to control DAGG in materials susceptible to abnormal grain growth. The resulting mechanistic understanding of DAGG will be used to predict the occurrence of DAGG under conditions of technological importance.NON-TECHNICAL SUMMARY: Dynamic abnormal grain growth (DAGG) is a recently-discovered phenomenon in the field of materials science. DAGG occurs while deforming polycrystalline material at elevated temperature and has been used to grow large single crystals in molybdenum and tantalum for scientific studies. Beyond this initial practical application, DAGG represents an opportunity to gain new fundamental insights into the evolution of material microstructure. Controlling material microstructure is critical to the manufacture of advanced components in many industries, particularly the transportation industries. Potential impacts of this research include creating new materials and improving the quality of manufactured components. The proposed research will enhance collaborations with General Motors and Sandia National Laboratory. Both graduate and undergraduate students will be trained in the fields of materials and metals science through research activities and as well as mentoring during academic studies. Outreach activities which promote science and engineering to the local community will be supported.