Development of Theory and Technique to Measure a Triple Junction Distribution Function (3DF)

技术总结：本研究的最终目的是对三重结的特征以及三重结的几何特征与观察到的微观结构的性质和局部特征之间的关系有一个更全面的了解。将开发一个三结分布函数（3DF），它可以表征三结的完整空间，而无需先验地假设某种类型的边界或结是特殊的。3DF测量将使用晶界工程Cu和Inconel合金600和617获得。3DF将包括对晶体晶格取向偏差的功能依赖，相对于晶格和晶界面取向的三重线取向。完整的函数位于一个非常大的空间，使得难以获得统计可靠的测量。这个问题将通过关注与孪生边界相关的三重结来克服，从而降低函数的维数。所提出的分析专门适用于具有相干孪晶优势的晶界工程合金，但该技术可以很容易地扩展到包括所有的三重结。这种程度的微观结构表征尚未用于晶界工程的研究，并提供了一个真正的机会，以获得对三重结形成机制的更完整的理解。最后，利用3DF对617合金中的碳化物和空穴分布进行表征。非技术概述：多晶材料在高温下长时间承受应力，往往会在某些区域形成脆性相甚至空洞和裂纹，这些区域最容易受到这种类型的微结构损伤。这些材料被用于传统的化石燃料和核电站，例如，这些合金是这个项目的主要焦点。为了能够预测这些材料的寿命，应该对最可能发生损伤的晶界及其交叉点（三重交叉点）的分布进行量化。为此，测量三结分布的困难阻碍了在实际材料中可靠地表征这些特征。目前的工作集中在三重结分布函数的发展，这将使研究人员能够适当地表征最容易受到损害的区域，并将它们与最不容易受到损害的区域区分开来。有了这些信息，就可以对工程材料的使用寿命做出更现实的预测，工艺工程师将能够设计出最耐损伤的微结构的制造程序。本科生和研究生将通过实验室经验和课程开发参与。

TECHNICAL SUMMARY: This research ultimately aims at developing a more complete understanding of triple junction character and how the geometric character of the triple junction relates to the observed properties and local character of the microstructure. A triple-junction distribution function (3DF) will be developed that characterizes the complete space of triple junctions without assuming a priori that a certain type of boundary or junction is special. 3DF measurements will be obtained using grain-boundary engineered Cu and the Inconel alloys 600 and 617. The 3DF will include the functional dependence on crystallite lattice misorientations, triple line orientations with respect to the lattice and grain-boundary plane orientations. The complete function lies in an extremely large space making statistically reliable measurements difficult to obtain. This problem will be overcome by focusing on triple junctions associated with twin boundaries, thereby reducing the dimensionality of the function. The proposed analysis applies specifically to grain-boundary engineered alloys that have a preponderance of coherent twins, but the technique can be easily extended to include all triple junctions. Microstructural characterization to this extent has yet to be employed in investigations of grain-boundary engineering and offers a real opportunity to gain a more complete understanding of the mechanisms involved in formation of triple junctions. Finally, carbide and void distributions in alloy 617 will be characterized using the 3DF.NON-TECHNICAL SUMMARY: Polycrystalline materials subjected to stress at high temperatures for long periods of time often develop brittle phases or even voids and cracks in certain regions that are most susceptible to this type of microstructural damage. Such materials are used in conventional fossil-fuel and nuclear power plants, for example, and these alloys are the primary focus of this project. To be able to predict the lifetime of such materials, the distribution of grain boundaries and their intersections (triple junctions), where damage is most likely to occur, should be quantified. To this end, the difficulty in measuring triple-junction distributions has prevented reliable characterization of these features in real materials. The present work focuses on the development of a triple junction distribution function that will enable researchers to properly characterize regions that are most susceptible to damage and distinguish them from those that are least susceptible. With this information, more realistic predictions of the useful life of engineering materials can be made, and process engineers will be able to design fabrication procedures that result in the most damage resistant microstructures. Undergraduate and graduate students will be involved through experience in the laboratory and development of curriculum.