Deformation and Failure of Nanocrystalline Metals

9980213 Ebrahimi该项目的目的是通过实验评估FCC和BCC纳米晶金属的机械行为，并开发各种晶粒尺寸制度的机械变形模型。 通过表征纯Ni、Ni-Cu和Fe-Ni合金的屈服、应变硬化、塑性失稳和断裂随温度和应变速率的变化规律，研究了纯Ni、Ni-Cu和Fe-Ni合金的变形和失效机制。 结合详细的微观结构分析，这样的结果分析应导致系统的理解的运作机制。 一些合金的变化进行了检查。 当铜被添加到镍中时，堆垛层错能显著降低，从而影响位错的产生和积累。 在Fe-Ni合金中，镍的浓度稍有增加，就会导致晶体结构由BCC转变为FCC。 以这种方式，晶体结构的影响可以在相当的组成进行研究。 %尽管过去十年对纳米结构金属合金的研究有所扩展，但很少有实验研究来研究这些材料的机械性能。 微晶尺寸小于约100 nm的金属固体被称为纳米晶金属。 这些材料具有吸引人的特性，包括非常高的强度水平。 这项研究的成果将有助于开发与硬化钢（700 - 1800 MPa）一样坚固的金属结构，但具有更好的物理性能（例如磁性）和上级耐腐蚀性。

9980213EbrahimiThe aims of this project are to evaluate experimentally the mechanical behavior of FCC and BCC nanocrystalline metals and to develop mechanistic deformation models for various grain size regimes. The deformation and failure mechanisms of pure Ni, Ni-Cu and Fe-Ni alloys are studied by characterizing yielding, strain hardening, plastic instability, and fracture as functions of temperature and strain rate. Analysis of such results in conjunction with detailed microstructural analyses should lead to a systematic understanding of the operating mechanisms. Some alloy variations are examined. When copper is added to nickel the stacking fault energy is reduced significantly, thereby affecting the generation and accumulation of dislocations. A small increase in the concentration of nickel in Fe-Ni alloys results in a change of crystal structure from BCC to FCC. In this way, the effect of crystal structure can be investigated at comparable compositions. %%%Despite an expansion of research in the past decade on nanostructured metallic alloys, there have been few experimental studies that investigate the mechanical properties of these materials. Metallic solids with crystallite sizes less than approximately 100nm are referred to as nanocrystalline metals. These materials have attractive properties, including very high strength levels. The outcome of this research will contribute to the development of metallic structures that are as strong as hardened steels (700 - 1800 MPa) but have better physical properties (e.g. magnetic properties) and superior corrosion resistance.***