UNIVERSITI TEKNOLOGI MARA
SYNTHESISE AND CHARACTERISATION OF
PULVERIZED TITANIUM NIOBIUM ALLOY FOR POTENTIAL
BIOMEDICAL APPLICATION
MAZYAN YAHAYA
Thesis submitted in fulfilment of the requirements for the degree of
Doctor of Philosophy (Mechanical Engineering)
College of Engineering
January 2022
ABSTRACT
Biomaterials is a rising field of research that focuses on introducing bioinert materials as a substitution or an aid in the human bone healing process. Ongoing investigation in finding suitable materials for implant application is endless. Among the types of biomaterials, metal-based were favoured due to their excellent strength and being biocompatible with human body fluids. Metal-based materials such as stainless steel, Ti, and cobalt chrome have been used extensively in biomedical applications owing to their unique properties, such as high strength and corrosion resistance. Some do not produce toxic substances that may be harmful to the human body. In recent advancements, Ti alloys have become the primary candidate for bone replacement due to their ability to closely mimic the human bone requirement. Ti6Al4V has been used considerably in biomedical applications, but the toxicity of vanadium is always a serious concern. One of the alloying elements of Ti that have been researched extensively is Nb. Nb has been introduced as a non-toxic element that creates the beta phases and potentially to lower Young's modulus of Ti metal. However, the beta phase in Ti alloys is metastable, which strongly influence the mechanical properties. Even though it is an excellent strategy to reduce Young's modulus, the fundamental question on these metastable phases is unknown theoretically and experimentally. Hence the objectives of this study are to simulate the concentration Nb elements for Ti-Nb alloys, synthesise and prepare the Ti-Nb alloys, determine Young's modulus of Ti-Nb alloys, and characterise the Ti-Nb alloys of Y-shaped bio-plate. The methods of achieving the objectives are to use the first principle study with density functional theory (DFT) via CASTEP© computer code with pseudopotential calculations, and to synthesize all Ti- Nb alloys via conventional powder metallurgy method with elemental powder metals as the primary materials. The process consisted of mixing, compacting, and sintering, and preparing alloys into bars for the compressive test to determine Young's modulus of alloys. Finally, the preparing the alloys into Y-shaped plates. The results show that the optimisation of the Ti-Nb crystal structure using DFT calculation provided an atomic bonding analysis and predicted Young's modulus of Ti-Nb alloys. Alloying with Nb showed random and disordered atomic arrangements and a strong d-d hybridization, which provided phase stability to the Ti alloys. The Young's modulus at the fully beta phase was approximately 82 GPa. The as-sintered sample showed reducing volume shrinkage from 28% to 17%, an average relative density of 90.7% relative density, and 9.3% mean porosity. At 40 wt% Nb, the alpha phase dissipated, and only the beta phase existed. The impurities level for all as-sintered samples was sufficiently low due to mixing without the PCA or binders, although the initial powders exhibit slightly higher oxygen (O) levels. The hardness value obtained for 40 wt% Nb in this research study is lower than other literature but still higher than bone hardness with HV=143.6±19. The value obtained from the compression test is yield strength, s0.2=413.99 MPa, Young's modulus, E=18.09±1.39 GPa and compressive strain, e=25.23±5.17% for 40 wt% Nb composition. Preparing the exact composition of Nb (40 wt%) into a Y-shaped fracture plate revealed that the major fraction beta phase was observed with a slightly higher hardness value HV=195.57±11.87. The hardness value may be due to the higher compaction pressure during the powder pressing process. This finding is beneficial for the potential alloy as bone replacement with a very stable beta phase of Ti-Nb alloys.
ACKNOWLEDGEMENT
Thank you to Almight ALLAH for giving me strength and ability to understand, learn and complete this thesis.
I would like to express my sincere gratitude to my supervisor Assoc. Prof. Dr.
Muhammad Hussain bin Ismail for the continuous support of my PhD study and research, for his patience, motivation, enthusiasm, and immense knowledge. His guidance helped me in all the time of research and writing of this thesis.
Besides my supervisor, I would like to thank co-supervisors Prof. Ir. Dr. Jamaluddin Mahmud and Dr. Mohamad Fariz bin Mohamad Taib for their encouragement, insightful comments and hard questions. Thank you for the financial support from KPT (HLP) and other research grants from KPT. I would like to recognise the important roles of Maheran Sulaiman, Salhana Sahidin and Nurul Ain Haris.
These acknowledgements would not be complete without mentioning my research lab colleagues: Nur Hidayatul Nadhirah, Siti Mariana Hosnie, Nur Aisyah Abd. Malik Marwan and Dr. Hazrie Samat. It was a great pleasure working with them and I appreciate their ideas, help and good humour.
My deepest appreciation belongs to my husband Oskar Hasdinor and my family for their prayer, support, patience and understanding throughout my research study.
TABLE OF CONTENT
Page CONFIRMATION BY PANEL OF EXAMINERS ii
AUTHOR’S DECLARATION iii
ABSTRACT iv
ACKNOWLEDGEMENT iv
TABLE OF CONTENT vi
LIST OF TABLES x
LIST OF FIGURES xii
LIST OF SYMBOLS xviii
LIST OF ABBREVIATIONS xx
CHAPTER ONE INTRODUCTION 1
1.1 Research Background 1
1.2 Aim and Motivation 4
1.3 Problem Statement 4
1.4 Objectives 6
1.5 Scope 7
1.6 Thesis Outlines 7
CHAPTER TWO : LITERATURE REVIEW 9
2.1 Introduction 9
2.2 Biomaterials and Implant Devices 9
2.2.1 Biomedical Implant and Devices 11
2.2.2 Plates for Bone Fracture 16
2.2.3 Biomaterials 18
2.2.4 Titanium and its Alloy 24
2.2.4.1 Alpha Type Titanium 30
2.2.4.2 Alpha-Beta Titanium Alloy 31
2.2.4.3 Beta Titanium 32
2.3 Titanium Niobium Alloy 33
2.4 Computational Material Science 36
2.4.1 The Theory of Quantum Mechanics 36
2.4.2 The First Principles 39
2.4.3 The Density Functional Theory (DFT) 41
2.4.4 Orbital Hybridization: Density of States (DOS) 48 2.4.5 Material Properties Calculation: Mechanical Properties 50
2.5 Processing of Titanium Alloy 54
2.5.1 Powder Metallurgy Routes 54
2.5.1.1 Compaction 56
2.5.1.2 Hot Isostatic Press (HIP) 58
2.5.1.3 Metal Injection Moulding (MIM) 59
2.5.1.4 Additive Manufacturing (AM): 3D Printing 61
2.5.2 Casting 64
2.5.3 Sintering Fundamental of Titanium Alloy 66
2.5.4 Elemental Powder Sintering 70
2.6 Summary of the Literature Study 74
CHAPTER THREE : RESEARCH METHODOLOGY 75
3.1 Overview 75
3.2 Computational Method using CASTEP© 76
3.2.1 Modelling Ti Structure 78
3.2.2 Model Refinement 81
3.2.3 Properties Calculation 81
3.3 Powders Characterisation 82
3.3.1 Particle Size and Shape Analysis 83
3.3.2 Powder Mixing 84
3.3.2.1 Density by Pycnometer 84
3.3.3 Compaction and Sintering 85
3.4 Characterisation of As-sintered Ti-Nb Alloy 87
3.4.1 Physical Properties 87
3.4.1.1 Dimensional Measurement 88
3.4.1.2 Density Determinations 88
3.4.2 Phases and Microstructural Analysis 89
3.4.2.1 XRD Analysis 89
3.4.2.2 SEM-Secondary/Backscattered and EDX 90
