Year

2019

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

Many engineering components fail due to wear, corrosion and poor strength in extreme operating conditions. Designing a component being able to survive in such environment with longer durability is a practical challenge. Functionally graded materials (FGM) can be very useful in such cases where two materials with desired properties can be combined together. Cemented tungsten carbide (WC-Co), offers attractive properties such as high hardness, excellent wear and corrosion resistance, and exhibits a wide range of applications in various industries including wear and hard metal industries, cutting tools, micro drills, and microelectro mechanical system (MEMS). Consequently, high strength steel (HSS) has the advantages of high strength and toughness to provide structural support to improve the longevity of the components. A bilayered composite of WC-Co and HSS, therefore, can provide high hardness, wear and corrosion resistance in one side, and high strength and toughness on the other side. Thus making a bilayered composite of ceramic and steel materials is of practical significance with numerous potential applications.

However, bonding between ceramic and steel materials is a challenging task due to their large difference of physical and thermal properties. These differences create thermally induced residual stresses entrapped at the joining interface during cooling period of the composite. The residual stresses result in generation of microcracks and delamination at their bonding interface and ultimately produce weak bonds. Such composite with poor bonds and mechanical properties are not suitable for practical applications. The prime objective of this study, therefore, is to analyse the bonding phenomena between ceramic and steel materials and fabricate a successful bilayered FGM of ceramic and steel materials.

In this study, a powder-solid diffusion bonding mechanism was employed for analysing the sintering and bonding process of cemented tungsten carbide powder and solid high strength steel. Two combinations of the materials were used. Firstly, ultrafine WC (with 8% Co added as a binder) powder and solid stainless steel (SS 304). Secondly, nanocrystalline WC (with 10% Co added as binder) powder and solid HSS (AISI 4340). A novel manufacturing method, namely ‘hot compaction diffusion bonding (HCDB)’ was developed and implemented to fabricate a bilayered composite of ceramic and steel materials. For comparison, a series of experiments was also conducted in spark plasma sintering (SPS) machine. The influences of key experimental parameters such as sintering time, compression pressure and sintering temperature on the sintering properties of cemented carbides and their bonding phenomena with steel, were investigated.

FoR codes (2008)

0910 MANUFACTURING ENGINEERING, 0912 MATERIALS ENGINEERING, 0913 MECHANICAL ENGINEERING

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.