Micro- and Macromechanical Properties of Fully Densified Nanocrystalline Metals

我们建议研究由惰性气体冷凝(IGC)和随后的严重塑性变形(SPD)或轧制致密化的创新和新组合制备的平均晶粒度在10-30 nm之间的全致密块体纳米晶(NC)金属的塑性变形的基本原理。被研究的模型体系是Pd(FCC)和几种单相Pd合金。实验将集中于使用新的测试设备对小型化试件进行力学测试，以应力状态条件、应变率和温度为变量。其目的是在这种非常小的晶粒度下获得一个显著改进的材料行为数据库，因为这之前只是零星地探索，并以以晶粒度、应变率和温度为参数的变形机制图的形式阐明和描述调节变形的微观机制。特别强调在纳米晶体材料塑性流动中的细观效应的现场研究，例如剪切带和/或协同晶界滑动的形成，以及定量和定性的断口研究。所获得的结果不仅对基础材料科学具有重要意义，还将有助于阐述技术上可行的纳米结构材料的开发原理，从而提供这些材料的最高水平的强度和延展性。

We propose to study the fundamentals of plastic deformation in fully dense bulk nanocrystalline (nc) metals with a mean grain size between 10 and 30 nm prepared by an innovative and new combination of Inert Gas Condensation (IGC) and subsequent densification by Severe Plastic Deformation (SPD) or rolling. The model system to be investigated is Pd (fcc) and several single-phase Pd alloys. The experiments will focus on mechanical tests using new testing equipment for miniaturized specimens with stress state conditions, strain rate and temperature as the variables. The aim is to obtain a significantly improved database of materials behaviour for these alloys at this very small grain size, since this has previously been explored only sporadically, and to elucidate and describe - in the form of a deformation mechanism map with the grain size, strain rate, and temperature as the parameters - the microscopic mechanisms that mediate the deformation. Special emphasis will be addressed to in situ investigation of mesoscopic effects in plastic flow of nanocrystalline materials, such as formation of shear bands and/or cooperative grain boundary sliding, and quantitative and qualitative fractography investigations. The obtained results will be important not only for fundamental material science, but also will allow to elaborate the principles of development of technically feasible nanostructured materials providing the highest level of strength and ductility of these materials.