Dynamic Grain Growth in BCC Metals and Alloys

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1. Nontechnical AbstractMetals and their alloys are critically important to the production of structural components required in the complex machines supporting modern society. Examples of metallic structural components are readily evident in automobiles, aircraft, bridges and buildings. Less obvious are the microscopic features inside these materials that control their properties and enable them to effectively serve in the most demanding tasks, features that are collectively called the microstructure. The microstructure includes grains, small individual crystals of the metal, that determine strength, ductility and other material properties. The grain structure must be controlled during manufacturing of each component if it is to achieve the properties required for its technological application. This project seeks to build the science of how grains develop and grow while metals are deformed at elevated temperatures, an important processing step in a wide variety of metals manufacturing operations. The growth of grains under these conditions is called dynamic grain growth. The new understanding produced under this project is expected to positively impact future manufacturing practices for the forming of metals. Through participation in this scientific investigation, students at the graduate and undergraduate levels are trained. An integral aspect of this project is a partnership with ASM International on enhancing the open dissemination of research results so that valuable data can most positively impact the scientific and engineering communities, as well as broader society.2. Technical AbstractDynamic grain growth is a topic of great technological importance to the manufacture of wrought metal and alloy products. Yet, it is also a topic within metals science for which we have only a very limited understanding. This experimental research project seeks to produce new understanding for the mechanisms that cause dynamic grain growth, better establish why grain boundary migration behaviors are different between the dynamic and static cases, and organize these new understandings to positively impact manufacturing technologies. The mechanisms responsible for dynamic grain growth in body-centered-cubic metals are a primary focus. Both dynamic abnormal grain growth and dynamic normal grain growth are addressed. The materials studied include the refractory metals, molybdenum and tantalum, and iron-based alloys. The iron-based alloys include commercially important interstitial-free steels, which provide both a nearly ideal model material for scientific investigation and a material of technological relevance. Experiments are designed to test new hypotheses for the relationship between dynamic normal and dynamic abnormal grain growth; probe existing hypothesis for the mobility of grain boundaries under dynamic conditions; and explore questions for which no hypotheses currently exist. Experimental methods include unique mechanical testing, modern characterization techniques, advanced computerized data analysis techniques and interpretation through numerical models.