23 Jun 2021 (Wed)

3:30 – 4:30 pm (HK Time)

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Speaker: Prof. San-Qiang Shi

Head and Chair Professor of Mechanical Engineering
Department of Mechanical Engineering
The Hong Kong Polytechnic University

Prof. Shi obtained his BSc and MSc in Physics from University of Science and Technology Beijing in 1982 and 1984, respectively, and Ph.D. and postdoctoral fellowship in Materials Science from McMaster University, Canada in 1991. He then spent seven years at Atomic Energy of Canada Limited (AECL) as a research scientist and project leader. He joined the Department of Mechanical Engineering of PolyU in 1998. Prof. Shi’s current research and consultancy interests are focused on environmental degradation of materials and protection, computational materials modeling and advanced materials.

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Modeling of morphology evolution of metallic materials under environmental attack

Abstract:

A computational framework based on the multi-phase-field method was developed to study the complex microstructure and morphology evolution of metallic materials under the influence of chemical reaction, bulk and surface diffusion, surface passivation, sensitization, applied electrical and/or mechanical loading in aqueous or gas environment. The proposed framework makes use of Allen-Cahn equations for long rang order parameters (phase-field variables), Cahn-Hilliard equations for conserved variables, Nernst-Planck equations for ion transport, and Poisson’s equation for electrostatic condition, together with mechanical equilibrium equations. When chemical reactions were involved, the reaction rate was expressed as a function of the chemical (or electrochemical) potentials of reactants and products based on a detailed balance of the reactions. The framework was applied to study pitting corrosion of steels with or without the formation of insoluble corrosion products (passive film), stress corrosion cracking, corrosion of metal matrix composite under mechanical loading, intergranular corrosion of sensitized aluminium alloys, high-temperature metal oxide formation in gas phase under the influence of high Pilling-Bedworth ratio, nano-porous structure evolution during chemical dealloying of binary alloys. The characteristics of the model predictions agree well qualitatively, in many cases also quantitatively, with the experimental observations. Future perspectives of the developed framework in studying anisotropic growth and self-assembly of nanostructure and nanomaterials are discussed. This work was supported by grants from Hong Kong RGC (PolyU 152140/14E and PolyU 152174/17E).