This study was carried out in 3 series experiments. In the first series, thick 4-layered ZrB2/TiB2 multilayer was deposited on Si substrate by sputtering TiB2 and ZrB2 ceramic targets in different bias so as to choose a suitable bias voltage for rest of the experiments. Results from this series experiment showed at -90 V substrate bias, both TiB2 and ZrB2 layers gained preferred orientation with highly crystalline diffraction peaks. Ion bombardment as a result of -90 volt substrate bias induced appropriate amount of defects and increased the compressive stress of the film which resulted in hardness enhancement and shorter crack length upon indentation fracture.

In the second series, using the -90V substrate bias as seen best from 1st series, multilayers of ZrB2/TiB2 with bilayer thickness varying from 200 nm to 25 nm were synthesized. Results from this series experiment showed hardness increment, as the bilayer thickness decreased the crystallinity of individual layers decreased due to insufficient crystal growth time in thinner layers. The hardness increased from 31 GPa to 36.6 GPa as the bilayer thickness varied from 200 nm to 25 nm. All the films showed enhanced toughness when compared to similar thickness single layer TiB2 or ZrB2. As long as the films were crystalline, increase in number of bilayers caused increase in residual stress most probably due to interface induced stress. Cross sectional FESEM images reveals clear intact layers. However, by this deposition technique, bilayer thickness lower than 25 nm was not possible to synthesize.

Finally, third series refers to deposition of ZrB2/TiB2 multilayers with bilayer thickness varying from 19 nm to 1 nm. Films with bilayer thickness 19 nm to 7 nm were very less crystalline or amorphous. However, for samples with bilayer thickness 4 nm to 2 nm, the crystallinity enhanced with the peaks lying between TiB2 001 and ZrB2 001. These samples also possess additional unique peaks at angles lower than ZrB2 001 peak. The diffraction peak of sample at 1 nm bilayer thickness corresponds to ZrB2 001. Samples from this series were the toughest with the highest Kc value of 2.6 MPa m½ for 2 nm bilayer sample. The maximum hardness reached upto 44 GPa for this same sample which was harder than single layer ZrB2 or TiB2.

Table of Contents
Acknowledgement i
Summary iii
Abstract vii
1.Preface 1
1.1Foreword 1
1.2 Research motivation 2
2. Introduction and Literature Review 3
2.1 Properties and preparation of TiB2 and ZrB2 3
2.2 TiB2 literature review 6
2.3 Limitations of hard ceramic diboride coatings 8
2.4 Multilayer coatings 9
(a) Coatings with a limited number of single layers 9
(b) Coatings with a high number of non isostructural single layers 9
(c) Superlattice coatings 9
i. Single crystal Superlattice coatings 10
ii. Polycrystal superlattice coatings with Superlattice hardening 10
iii. Polycrystal superlattice coatings without Superlattice hardening 11
2.5 Multilayer thin film strengthening mechanism 13
2.5.1 Interface hardening 13
2.5.2 Interface toughening 13
2.5.3 Fine Grain Hardening Hall-Petch Mode 15
2.6 TiB2 and ZrB2 as a multilayer combination 16
3. Experimental method and Instruments 17
3.1 Sputtering system 17
3.2 Preparation of sample 20
3.2.1 Substrate used 20
3.2.3 Substrate preparation 21
3.3 Experimental process planning 22
3.2 Thin film analysis 24
3.2.1 X-Ray Diffraction (XRD) 24
3.2.3 Three-dimensional surface profiler 26
3.2.4 Field emission scanning electron microscope (FESEM) 28
3.2.5 Nanoindentor 29
3.2.6 Toughness measurement by Vickers indentation fracture 30
4. Results and Discussion 31
4.1 4-layered ZrB2/TiB2 multilayer in different bias 31
4.1.1 Preparation of films in different bias 31
4.1.2 Thickness and crystal structure of the films in different bias 33
4.1.3 Composition and Morphology of the films in different bias 35
4.1.4 Hardness, Elastic modulus and Residual stress of ZrB2/TiB2 multilayer 38
4.1.5 Toughness measurement by Vickers Indentation 44
4.1.6 Discussion 46
4.2 ZrB2/TiB2 multilayer with different bilayer thicknesses (200 nm-25 nm) 49
4.2.1 Preparation of films 49
4.2.2 Crystal structure of the films in different bilayer thickness 51
4.2.3 Hardness, Elastic modulus and Residual stress of ZrB2/TiB2 multilayers 56
4.2.4 Composition and Morphology of the films of ZrB2/TiB2 multilayer 61
4.2.5 Toughness measurement by Vickers Indentation 64
4.2.6 Discussion 64
4.3 ZrB2/TiB2 multilayer with bilayer thickness ranging 19 nm-3 nm 67
4.3.1 Preparation of films 67
4.3.2 Crystal structure of the films in different bilayer thickness 69
4.3.3 Hardness, Elastic Modulus and Residual stress of ZrB2/TiB2 multilayer 74
4.3.4 Composition and Morphology of the films of ZrB2/TiB2 multilayer 81
4.3.5 Toughness measurement by Vickers Indentation 85
4.3.6 Discussion 85
5. Conclusion 93
6. References 97

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