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runqi

应助: (幼儿园)
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虫号: 180128

[交流] PhD thesis

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Title:
Magnetron sputtered nc-TiN/a-SiNx nanocomposite thin films with high hardness and high toughness

Summary:
Nanocomposite thin films comprise at least two constituent phases, for example, a dispersed nanocrystalline phase and a matrix. The matrix phase can be either amorphous or nanocrystalline. Nanocomposite thin films represent a new class of materials which exhibit improved mechanical, electronic, magnetic and optical properties owing to the size effect. Of all the exotic properties of the nanocomposite thin films, hardness and toughness are the most important ones for the applications in manufacturing industry. So far, researchers are focusing more on hardness. Some even reach 105 GPa by forming nc-TiN/a-Si3N4 (where nanocrystalline titanium (nc-TiN) embedded in amorphous silicon nitride matrix (a-Si3N4)) nanocomposite thin films using chemical vapor deposition (CVD) method. However, in most wear related applications, hardness is only one of many important properties, such as high hardness, toughness, good oxidation resistance, and so on.

This project focuses on the study of hardening and toughening mechanisms for nanocomposite thin films. The aim of this project is to study the relationship between microstructure, hardness and toughness, therefore to obtain a thin film with high hardness and at the same time high toughness. Reactive magnetron sputtering was used to prepare hard and superhard nc-TiN/a-SiNx nanocomposite thin films by co-sputtering Ti and Si3N4 targets in a gas mixture (argon and nitrogen). In order to improve the toughness of the as-prepared nanocomposite thin films, nickel was doped into the nc-TiN/a-SiNx to obtain Ni-toughened nc-TiN/a-SiNx nanocomposite thin films by co-sputtering TiNi, Ti and Si3N4 targets. Co-sputtering of multi targets allows to tailor the microstructure by adjusting the deposition parameters, such as target power density, deposition temperature, substrate bias, and gas ratio. The as-deposited Ni-toughened nc-TiN/a-SiNx nanocomposite thin films possess high hardness and high toughness.

This project shows that superhard nc-TiN/a-SiNx nanocomposite thin films are obtainable by reactive magnetron sputtering. Silicon content has a significant effect on film topography, microstructure and mechanical properties. With 14.9 at.% Si, the nc-TiN/a-SiNx nanocomposite thin films possess an average hardness of 37 GPa. Refining grain size in the nanostructured thin films is the reason for the hardness increase. The toughness of the as-prepared nc-TiN/a-SiNx nanocomposite thin films is improved by doping nickel. Doping from 0 to 40 at.% Ni in nc-TiN/a-SiNx brings about an increase in toughness from 1.15 to 2.60 MPa m1/2 at an expense of hardness (dropped from 30 to 14 GPa). Ductile phase toughening through crack blunting and crack bridging is responsible for the toughness increase.

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