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

技术综述：本研究的最终目的是更全面地了解三重结的特性，以及三重结的几何特性与观察到的微观结构的性质和局部特性之间的关系。建立了一个三结点分布函数(3DF)，它刻画了三结点的完整空间，而不假设某种类型的边界或结点是特殊的。3df测量将使用晶界工程铜和Inconel合金600和617。3df将包括晶格错位、晶格三线取向和晶界面取向的函数依赖关系。完整的功能位于一个非常大的空间中，因此很难获得统计上可靠的测量结果。这个问题将通过关注与孪生边界相关联的三重结点来克服，从而降低函数的维度。建议的分析特别适用于晶界工程合金，这些合金以共格孪晶为主，但该技术可以很容易地扩展到包括所有三重结。微观结构表征在这一程度上尚未用于晶界工程的研究，这为更全面地了解形成三重结的机制提供了一个真正的机会。最后，将使用3DF.NON-技术摘要来表征617合金中的碳化物和空洞的分布：多晶材料在高温长时间的应力作用下，往往在某些最容易受到这种微结构损伤的区域发展脆性相，甚至空洞和裂纹。例如，这种材料用于传统的化石燃料和核电站，而这些合金是这个项目的主要重点。为了能够预测这种材料的寿命，应该量化最有可能发生损伤的晶界及其交叉点(三重结)的分布。为此，测量三结点分布的困难阻碍了在真实材料中对这些特征的可靠表征。目前的工作集中在开发一个三结点分布函数，该函数将使研究人员能够正确地描述最容易受到损伤的区域，并将它们与最不容易受到损伤的区域区分开来。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制造出最具抗损伤能力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其中。

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.