Establishing Microstructure - Electron Work Function - Property Relationships towards a New Design Methodology for Structural Materials

• Author / Creator

  Luo, Yuzhuo

• Conventional metallurgy has been widely used in material design for centuries, which however does not always effectively guide material design and modification. A large number of trial-and-error tests are often needed in material development. Material developers have been making considerable efforts in developing complementary or alternative approaches to guide material design. Attributed to the intrinsic correlation between electron work function (EWF) and the atomic bond strength and stability, which govern mechanical and electrochemical properties of materials, EWF has been demonstrated to be a promising guiding parameter for material analysis and design. Many intrinsic properties of metals such as Young’s modulus, thermal expansion coefficient, and electrochemical activity, etc., can be well correlated with EWF theoretically, confirmed by experimental studies. For pure metals and single-phase solid solutions, the higher the EWF of a material, the higher atomic bond strength with higher mechanical stability. However, engineering materials are generally multi-phase materials. It is unclear whether or not the overall EWF of multiphase materials with specific microstructure features can still reflect the material properties. In this study, two-phase high-Cr cast irons were used to investigate microstructure-EWF-property relationships. A charge-compensation model was established to elucidate the mechanism responsible for such relationships. It turned out that fine and densely distributed second phase, i.e. the carbide in the ferrous matrix, contributed to higher interfacial/volume ratio, leading to charge redistribution at interface. Such charge redistribution at interface results in increased overall EWF, corresponding to elevated Young’s modulus. For further information and verification, low carbon steels with two-level microstructural complexity were used to verify the microstructure-EWF-property relationships and the charge-compensation model. Various experimental tools, including Scanning Kelvin Probe, Atomic Force Microscope, Scanning Electron Microscope, Transmission Electron Microscope and acoustic instrument etc., were used to investigate the effect of microstructure on overall EWF and corresponding properties of the steels. It was demonstrated that the properties of steel samples, including Young’s modulus, hardness and corrosion resistance, can be well reflected by their overall EWFs and explained based on the charge-compensation model. The calculated theoretical EWF was in consistent with experimental results. This study is of significance to the extension of utilizing EWF in structural materials design from single-phase materials to multi-phase ones.

• Subjects / Keywords

  • Microstructure
  • Mechanical Property
  • Electron Work Function

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-cx1r-5a57

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.