Grain Size and Ductility of Nanocrystalline Intermetallics and Intermetallic Composites

DMR-9508797，Pi-Koch：这项拟议研究的科学目标是确定纳米晶材料中颗粒尺寸对本征延展性的影响，这将有助于阐明变形机制。本征延展性是指缺陷(裂纹、空洞等)、杂质或环境影响(例如氢脆)，它们可能掩盖基本的延展性行为。由于名义上易碎的金属间化合物的延展化(通过创造纳米晶微结构)将具有重大的科学和技术重要性，因此要强调的材料是金属间化合物和金属间化合物-基原位复合材料。为了消除由给定的加工路线引起的可能影响延展性的外部因素，至少选择了两种制备纳米晶材料的加工方法。它们是(1)粉末的机械磨损和压实，以及(2)快速凝固制备的非晶条带或薄片的晶化。机械测试包括用于筛选目的的压缩测试，但强调拉伸部件的测试，即小型化圆盘弯曲测试和拉伸测试。*金属间化合物和金属间化合物的本征延性随纳米晶尺寸变化的研究将有助于深入了解这类材料的变形机制，并确定延性和韧性的最佳晶粒度。该项目是北卡罗来纳州立大学和橡树岭国家实验室的合作成果。研究生在橡树岭度过暑假进行研究，为他们带来了特殊的教育利益。拟议的研究还将在普拉特&惠特尼及其纳米晶复合材料计划的指导和互动下进行。

DMR-9508797, PI-Koch: The scientific objective of the proposed research is to determine the influence of grain size on intrinsic ductility in nanocrystalline materials, which should help to elucidate the deformation mechanism. Intrinsic ductility means defects (cracks, voids, etc.), impurities, or environmental effects (e.g. hydrogen embrittlement) which may mask the fundamental ductility behavior. Since the ductilization of nominally brittle intermetallic compounds (by creating nanocrystalline microstructures) would be of significant scientific and technical importance, the materials to be emphasized are intermetallics and intermetallic-matrix in situ composites. In order to eliminated extrinsic factors which may influence the ductility that are induced by a given processing route, at least two processing methods for production of nanocrystalline materials are selected. These are (1) mechanical attrition and compaction of powders, and (2) crystallization of amorphous ribbons or foils prepared by rapid solidification. Mechanical testing includes compression tests for screening purposes, but emphasizes tests with tensile components, i.e., miniaturized disk-bend tests and tensile tests. ***This study of intrinsic ductility of intermetallics and intermetallic composites as a function of nanocrystalline grain size should provide insight into the deformation mechanism for such materials as well as determining the optimum grain size for ductility and toughness. This program is a collaborative effort between North Carolina State University and Oak Ridge National Laboratory. Special educational benefits to the graduate students result from spending the summers doing research at Oak Ridge. The proposed research will also be carried out under the guidance and interaction with Pratt & Whitney and its program on nanocrystalline composites.***