Date of Award

2013

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Engineering

Faculty

Computing, Health and Science

First Advisor

Associate Professor Laichang Zhang

Second Advisor

Dr Zonghan Xie

Abstract

This PhD research contributes to the part of advanced materials technology. The machining industry currently faces tremendous pressures with the need for durable cutting tools suitable for eco-friendly high speed machining operations becoming acute. In this thesis innovative design and synthesis strategies are explored to tailor the properties of nanocomposite coatings. Advanced characterisation techniques are applied to identify the mechanisms that control the mechanical, tribological, and corrosion behaviours of these coatings. Cutting tools protected by these coatings are anticipated to exhibit a unique combination of superior toughness and greater resistance to wear and corrosion, providing significant economic and environmental benefits. The thin ceramic coatings are commonly applied to various kinds of steel cutting and machining tools to enhance their mechanical and tribological properties. The most common ceramic coating is TiN. But the major issues that hamper the application of TiN are high friction co-efficient (typically~0.5), lower hardness, lower thermal stability (~5000 C) and lower corrosion resistance. To address some of these problems, TiSiN nanocomposite coatings are developed, which have super-hardness, better thermal stability (~10000C) and better corrosion resistance. But the as-deposited TiSiN coating still has high co-efficient of friction (~0.4) and high residual stress (~7-9 GPa) which consequently affect the adhesion and toughness of the coating. This project aims to address these problems by (a) the application of carbon implantation to modify the structure and chemistry of the surface layer of the nanocomposite coatings with reduced friction and residual stress; and (b) thermal annealing of the nanocomposite coating to reduce the residual stress with enhanced fracture toughness, better corrosion resistance and more thermal stability. In addition, the role of microstructure, residual stress and defects of these hard coating in corrosive environment will be studied. For this research, a combination of microstructural and mechanical properties characterization, corrosion analysis, tribological test and finite element modelling facilities will be used. The study includes focused ion beam (FIB) milling and transmission electron microscopy (TEM), Synchrotron X-Ray Diffraction (XRD), X-ray Photo Spectroscopy (XPS), Energy dispersive X-Ray (EDX), nanoindentation, nano-scratching, potentio-dynamic polarization cell and Atomic force microscopy(AFM).

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