纳米晶切屑微结构表征及热稳定性研究

This research mainly aimed at the microstructure characterization and thermal stability of nanocrystalline machined chip. The characterization and mechanism of grain shape, grain size and its distribution, grain width and aspect ratio, grain boundary, etc should be further studied. And the lattice distortion and defects in nanocrystalline machined chip should also be discovered. After heat treatment, the grain shape, grain size and its distribution, defects should be characterized. The critical temperature of grain growth and the effect of defects on the thermal stability should be determined and the correlation would be made between the critical temperature and the defects. The hybrid model for the thermal stability of nanocrystalline materials and grain growth should be established and the method to preserving the thermal stability should be analyzed. If successful, the complementing of this research may lead to advance fundamental knowledge of the mechanism of nanostructure fabrication via machining. Another important benefit will be providing the possibility of improving the material properties, designing and developing novel bulk nanomaterials.

本项目以纳米晶切屑的微观结构表征和热稳定性为研究对象。分析纳米晶切屑材料的晶粒形状、晶粒尺寸及其分布、晶粒的纵横比、晶粒间的位向差、以及晶界等特征及其形成机理。分析纳米晶切屑材料的各种晶格畸变和缺陷的形成机理。并研究晶粒尺寸、晶粒取向、晶粒分布、缺陷等微结构在热作用下变化规律。探明晶粒明显长大的临界温度以及晶体缺陷对热稳定性的影响机理，并建立临界温度与晶体缺陷之间的关系模型。最终建立纳米晶组织的热稳定性及纳米晶粒长大行为的热力学模型，探明纳米晶切屑晶粒热稳定机制以及抑制晶粒长大的方法和手段。本课题的立项和完成，在学术上可以丰富和完善纳米晶切屑材料的制备理论，对于预测和改善纳米材料性能、设计和开发大尺寸纳米晶块体材料具有重要的科学意义和实用价值。

本项目以大应变挤出切削法制备的超细晶/纳米晶切屑的微观结构表征和热稳定性为研究对象。课题组分析了关键加工参数对超细晶材料的显微织构与力学性能的影响。研究了不同切屑材料的热力学行为，分析不同材料晶体结构与晶粒明显长大的临界温度关系。探明了刀具前角、切屑厚度压缩比等挤削参数对超细晶纯铜带材性能的热力学行为的影响规律。在此基础上，最终探明超细晶/纳米晶切屑带材的晶粒热稳定机制，得出了抑制晶粒长大的方法和手段。