Amorphous alloy has the characteristics of uniform structure, high strength, high hardness, abrasion resistance, small coefficient of thermal expansion and nanoscale surface structure copy. In the supercooled liquid phase, it can quickly realize the multi-scale integration thermoplastic molding from macro to micro-nano, which is the ideal material for the preparation of high precision mold. However, the glass transition temperature of traditional amorphous alloy is low, and the high temperature strength and thermal stability are poor, so the service temperature is difficult to exceed 600 K, which cannot meet the requirements of the current optical glass molding temperature. The research and development of high temperature, high strength and high stability bulk amorphous alloy (high temperature amorphous alloy) is expected to transform the grinding process of optical glass mold is transformed into thermoplastic process, break through the inherent limitation that the grinding process cannot prepare micro-nano surface structures, and foster the transformative optical glass element" micro-nano molding "technology.
Based on this, with the support of the National Key Research and Development Program for Key Scientific Issues of Transformative Technologies, Ningbo Institute of Materials Sciences of Chinese Academy of Sciences, Institute of Physics of Chinese Academy of Sciences, Yanshan University, Shenzhen University and Beijing University of Aeronautics and Astronautics jointly carried out "New Materials and Application Basis of High temperature, high strength and high thermal stability bulk amorphous alloys" (Project No: 2018YFA0703600). Among them, the magnetoelectric functional characteristics team of amorphous alloys in Ningbo Institute of Materials Research of CAS is mainly responsible for project 4 "Oxidation and corrosion mechanism of high-temperature amorphous alloys". Recently, under the guidance of Junqiang Wang and Juntao Huo, Xiaodong Yang et al. have conducted an in-depth and systematic study on the corrosion behavior of Ir-Ni-Ta-(B) high temperature amorphous alloy [Nature 569 (2019) 99-103] developed by the previous project team. It is found that Ir-Ni-Ta-(B) high temperature amorphous alloy has better corrosion resistance than other alloy systems in acidic solution, because it can form relatively stable passive film composed of metal Ir and Ni and Ta oxides. This passive film has good protection, so it shows strong pitting corrosion resistance, so the corrosion occurs mostly in the defects. In addition, it is found that the corrosion resistance of Ir-Ni-Ta amorphous alloy can be significantly improved by adding metal-like element B, and the passivation current of Ir-Ni-Ta-B sample is one order of magnitude lower than that of Ir-Ni-Ta sample. The passive films formed on Ir-Ni-Ta and Ir-Ni-Ta-B amorphous alloys have almost the same composition, but have different thickness and pore density. These differences are caused by the addition of B, which promotes the rapid formation of the passive film while inhibiting the dissolution of the active metal. The surface enrichment of Ir and adsorption of [BO3]3- further improve the corrosion resistance of Ir-Ni-Ta-B amorphous alloys. The results show that protective passive films can be preferentially generated by electrochemical passive treatment to increase the corrosion resistance of Ir-based amorphous alloys as mold materials, which provides an important experimental basis and theoretical support for enhancing the service life of high temperature, high strength and high stability bulk amorphous alloys in harsh service environment. The results are published in Corrosion Science 200 (2022) 110227.
These achievements have been supported by the National Key Research and Development Program (2018YFA0703604, 2018YFA0703602), the National Natural Science Foundation of China (52001319, 52071327, 51922102, 52171148), Supported by the Youth Promotion Association of Chinese Academy of Sciences (2019296), Natural Science Foundation of Zhejiang Province (LR22E010004, LR18E010002), Ningbo 2025 Science and Technology Innovation Project (2019B10051) and Ningbo Natural Science Foundation (202003N4354), etc.
Fig.1 The figure on the left shows the comparison of crystallization and activation energy between Ir-Ni-Ta-(B) amorphous alloy and other alloy systems. The figure on the right shows the comparison of pitting potential and passivation current of different materials in sulfuric acid solution.
Fig.2 Schematic diagram of transport and passive film formation of various ions and electrons in sulfuric acid solution.