Grain Size and Ductility of Nanocrystalline Intermetallics and Intermetallic Composites

DMR-9508797， PI-Koch：提出的研究的科学目的是确定晶粒尺寸对纳米晶材料固有延性的影响，这将有助于阐明变形机制。内在延性是指可能掩盖基本延性行为的缺陷（裂纹、空洞等）、杂质或环境影响（如氢脆）。由于名义上脆性金属间化合物的延展性（通过产生纳米晶微观结构）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基质原位复合材料。为了消除由给定的加工路线引起的可能影响延性的外在因素，选择了至少两种纳米晶材料的加工方法。它们是(1)粉末的机械磨损和压实，(2)通过快速凝固制备的非晶带或箔的结晶。机械试验包括为筛分目的而进行的压缩试验，但强调使用拉伸元件的试验，即小型化的圆盘弯曲试验和拉伸试验。***研究金属间化合物和金属间复合材料的固有塑性随纳米晶粒尺寸的变化规律，有助于深入了解这类材料的变形机制，并确定具有最佳塑性和韧性的晶粒尺寸。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项目。研究生在夏季在橡树岭做研究，因此获得了特殊的教育好处。拟议的研究也将在普惠公司及其纳米晶体复合材料项目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.***