Titanium-based Supra-nano Amorphous-crystalline Films: Processings and Mechanical Properties

鈦基超納雙相金屬薄膜的製備及力學性能

Student thesis: Doctoral Thesis

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Award date10 Sept 2020

Abstract

The familiar alloys or metals in ordinary items are mostly crystalline materials. Over the past few decades, amorphous metals or metallic glasses (MGs), as new kinds of advanced materials, have aroused tremendous research interests because of their distinct mechanical and functional properties such as high strength, superb catalytic properties, good friction resistance, and corrosion resistance. In this work, titanium (Ti) and Ti-based thin films were studied with the purpose of improving their mechanical properties for further biomedical and engineering applications.

Ti-niobium (Nb)-zirconium (Zr)-silicon (Si) thin film metallic glasses (TFMGs) have been successfully prepared by employing the magnetron sputtering method. They exhibited higher hardness and strength, prior to those of their crystalline counterparts. However, producing a large material that can reach the near-ideal strength is also challenging, especially for thin films, which significantly restricts their extensive applications under extreme mechanical conditions.

Great efforts have been dedicated to the exploration and development of new methods for the microstructure mediation of metallic materials, so as to improve their properties. By means of annealing on a prepared Ti-based TFMG, the sample became partially crystallized, forming a supra-nano amorphous-nanocrystalline alloy. This nanocomposite structural material exhibited a nearly ideal strength of 3.7 GPa, and a large elastic strain of 4%, which was far superior to the common amorphous alloys and nanocrystalline counterparts. The amorphous matrix, crystal-glass interface, and nanocrystals inside the composite resulted in preferable strength and elastic strain. Further study showed that partial crystallization allowed for the occurrence of chemical composition movement, facilitating the strength of the nanocomposite material system, also enhancing its glass-forming ability (GFA).

Ti-based thin films have a variety of potential applications such as being used to achieve functionalization in nano-devices and to offer surface protection. Here, the pure Ti was selected as a representative substrate candidate for mechanical properties research. The surface mechanical attrition treatment (SMAT) process was used to produce a gradient nanograined structure so as to enhance its mechanical performance, which could combine with film depositions for properties improvement on integrated materials systems.

With consideration for the actual use of materials in the human body, the wear/corrosion-resistance properties were also studied. The Ti-based TFMG and annealed Ti-based thin film exhibited much better performance in anti-wear properties, compared to those of the pure Ti and SMAT Ti counterparts. Interestingly, the annealed Ti-based thin film deposited on the pure Ti demonstrated a self-lubricating property, with the potential application of preventing injuries from bio-debris. Additionally, an electrochemical investigation was conducted for the pure Ti, and the results highlighted a positive influence of SMAT on its anti-corrosion performance.

By employing the magnetron sputtering technique or SMAT process, the film/substrate system could be suitable for more extreme conditions as mechanically required, or to meet specific functions desired for use, and also contribute to the fundamental research on materials engineering and the whole society.

    Research areas

  • Metallic glass, Thin film metallic glass, Surface mechanical attrition treatment, Mechanical properties, Near-ideal strength