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<p>Controlling stray corrosion through stable passivation is critical for the high-precision electrochemical machining (ECM) of advanced TiAl alloys. However, a fundamental understanding of the film’s dynamic evolution under applied potential is lacking, which hinders the rational design of films with optimal protective properties. Here, we establish a new framework by treating passivation as a complete nonlinear dynamic system, revealing for the first time the entire lifecycle of film formation on a Ti-48Al-2Cr-2Nb alloy from atomic-scale nucleation to steady-state growth. This process, characterized by fractional Brownian motion, involves a potential-dependent transition from 2D instantaneous to 3D progressive nucleation, resulting in a protective n-type semiconductor bilayer with an Al₂O₃-rich outer layer. Critically, increasing the applied potential to 1.6&#xa0;V exponentially decreases the density of oxygen vacancies, enhancing the film’s corrosion resistance by over 27-fold. These insights, integrated into a comprehensive Point Defect Model (PDM-III), provide a new theoretical basis for designing passive films based on nonlinear dynamic principles to improve ECM quality and efficiency.</p>

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Nonlinear dynamics and mechanistic insights into the formation and evolution of passive films on Ti-48Al-2Cr-2Nb alloy in NaNO₃ solution

  • 期刊论文

  • 发表日期：

    2025年12月29日

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  • Cuijiao Liao,
  • Xin Wang,
  • Hanjie Hu,
  • Zeliang Ding,
  • Wen Yuan Li

摘要

Controlling stray corrosion through stable passivation is critical for the high-precision electrochemical machining (ECM) of advanced TiAl alloys. However, a fundamental understanding of the film’s dynamic evolution under applied potential is lacking, which hinders the rational design of films with optimal protective properties. Here, we establish a new framework by treating passivation as a complete nonlinear dynamic system, revealing for the first time the entire lifecycle of film formation on a Ti-48Al-2Cr-2Nb alloy from atomic-scale nucleation to steady-state growth. This process, characterized by fractional Brownian motion, involves a potential-dependent transition from 2D instantaneous to 3D progressive nucleation, resulting in a protective n-type semiconductor bilayer with an Al₂O₃-rich outer layer. Critically, increasing the applied potential to 1.6 V exponentially decreases the density of oxygen vacancies, enhancing the film’s corrosion resistance by over 27-fold. These insights, integrated into a comprehensive Point Defect Model (PDM-III), provide a new theoretical basis for designing passive films based on nonlinear dynamic principles to improve ECM quality and efficiency.