Mechanical Properties and Characterization of Nanocrystalline Ni and Ni Solid Solutions

• Main Author: Schwacke, Miranda Lee
• Format: Others
• Language: en
• Published: 2020
• Online Access: https://thesis.library.caltech.edu/13819/1/schwacke_miranda_2020_thesis.pdf; Schwacke, Miranda Lee (2020) Mechanical Properties and Characterization of Nanocrystalline Ni and Ni Solid Solutions. Senior thesis (Major), California Institute of Technology. doi:10.7907/j8rq-5c26. https://resolver.caltech.edu/CaltechTHESIS:06122020-164731280 <https://resolver.caltech.edu/CaltechTHESIS:06122020-164731280>

In this work we investigate the mechanical properties of nanocrystalline Ni and Ni solid solutions made by both traditional fabrication methods (through a literature review) and by a newly developed chemical-derivation method (through experimental characterization and nanoindentaiton testing). Chapter 1 consists of a review of the current literature on nanocrystalline Ni. It focuses specifically on how the grain size of these materials is related to hardness through the Hall-Petch relationship and at grain sizes past the Hall-Petch breakdown. Given the number of apparent deviations from the Hall-Petch relationship found in the literature, in Chapter 2 we consider factors other than grain size which can impact hardness, including additives, annealing, and texture. Chapter 3 provides a description of our own experimental methods and results, including sample fabrication, grain size measurement, and nanoindentation. The hardness and reduced modulus of our nanocrystalline Ni samples are calculated to be 56 MPa and 1.76 GPa, respectively. These values are very low compared to what is described in the literature. Chapter 4 presents models for the hardness and Young’s modulus of nanocrystalline materials as functions of porosity, impurity content, and other factors which might cause anomalously low values. However, we find that these models are unable to account for the values we have observed. Chapter 5 includes a discussion of future work which should be done in order to better understand the deformation occurring in chemically-derived nanocrystalline Ni and how it differs from what is described in the literature.