Both CrAlN and SiNx layers were deposited periodically by radio frequency reactive magnetron sputtering. In the multilayered CrAlN/SiNx coatings, the thickness of CrAlN layer was fixed to 4 nm, while that of SiNx layer was adjusted from 4 to 0.3 nm. The dependence of the thickness of SiNx layer on the preferred orientation, crystalline behavior, microstructure and mechanical properties of the multilayered coatings were discussed with the aid of XRD patterns, SEM and HRTEM. The corrosion resistance of the multilayered CrAlN/SiNx coatings in 3.5 wt.% NaCl solution was also investigated by the Tafel measurement and electrochemical impedance spectroscopy (EIS).
Amorphous SiNx layer was evidently transformed to a crystallized one, when its thickness was decreased from 1 to 0.3 nm. The crystalline SiNx layer grew epitaxially and formed the coherent interface with the CrAlN layer, enhancing the hardness of the multilayered CrAlN/SiNx coating to 33 GPa. In contrast, with further increasing the thickness of SiNx layer to 1 nm, the SiNx was transformed to an amorphous structure, destroying the coherent interfaces, and decreasing hardness of the multilayered CrAlN/SiNx coating.
It was also revealed that when the structure of SiNx layer was transformed from crystalline to amorphous, the multilayered films were changed from a columnar microstructure to a dense one. The denser microstructure exhibited a lower corrosion current density and a higher corrosion impedance, indicating that the obtained multilayered coatings had better corrosion protection. Additionally, the multilayered CrAlN/SiNx coating with the thickness ratio of lCrAlN to lSiNx = 13:1 was identified with similar composition but with a denser microstructure, as compared to the one with lCrAlN to lSiNx = 4:0.3. The former multilayer (lCrAlN to lSiNx = 13:1) showed better corrosion resistance than the later one (lCrAlN to lSiNx = 4:0.3), suggesting that the anti-corrosion properties was dominated by microstructure rather than by composition.

本研究採以兩種具高性能之氮化鉻鋁與氮化矽，以反應性磁控濺鍍系統沈積調變各層不同厚度的奈米多層氮化鉻鋁/氮化矽薄膜。實驗的結果顯示，多層膜中氮化矽層的厚度會影響氮化矽層的晶體結構以及多層膜的硬度。當氮化鉻鋁層厚度為4.0 nm、氮化矽層厚度為0.4 nm時，奈米多層膜中的氮化矽轉變成介穩態與氮化鉻鋁所形成的契合界面產生硬度提升高達33 GPa。隨著氮化矽層厚度的增加至0.7 nm，氮化矽層轉變成非晶結構並阻斷了多層膜的契合生長，使得多層膜的硬度迅速降低。實驗的結果也顯示，多層膜中氮化矽層的厚度控制氮化矽層的晶體結構從而改變多層膜的微結構並影響其抗腐蝕性質。當氮化矽為結晶態時會與氮化鉻鋁契合生長，晶粒穿過若干個週期厚度連續成長並形成柱狀晶結構。反之，當氮化矽為非晶態時會阻斷柱狀晶的成長，形成非常緻密的結構，同時，也阻擋了腐蝕性離子藉由晶界擴散至基材發生腐蝕的通道，進而提升抗腐蝕的效果。另外，本研究也藉由控制各層厚度達到控制成分，並控制氮化矽層的厚度控制多層膜微結構，從而設計兩組具有相同成分卻不同微結構的多層膜，排除成分的影響之後，實驗結果得知，使微結構緻密化的確對於抗腐蝕效果有明顯的提升。

List of Tables…………………………………………………III
Figures Caption………………………………………………IV
Abstract…………………………………………………………VII
Chapter 1 Introduction…………………………………………1
1.1 Background……………………………………………………1
1.2 Nanotechnology……………………………………………2
1.3 Nitride Based Hard Coatings………………………………2
1.4 Motivation and Objectives…………………………………3
Chapter 2 Literature Review……………………………………6
2.1 Concept of Surface Engineering……………………………6
2.2 Sputtering technique…………………………………………7
2.2.1 Sputtering………………………………………………7
2.2.2 Magnetron Sputtering………………………………………8
2.2.3 RF Sputtering…………………………………………9
2.3 Material Selections…………………………………………9
2.3.1 Hard Coating Materials……………………………9
2.3.2 Thin Film Structures………………………………10
2.3.3 Multilayered Coating………………………………………11
2.3.3.1 Strengthening Mechanism of Multilayer……12
2.3.3.1.1 Shear Modulus Difference Hardening…12
2.3.3.1.2 Strain Field Strengthening…………13
2.3.3.1.3 Expitaxial stabilization effect……14
2.4 Review of Nitride Based Hard Coating………………………15
2.4.1 Binary TiN and CrN coating……………………………15
2.4.2 Characteristics of CrAlN coating……………………16
2.5 Corrosion resistance of multilayered coatings…………18
2.6 Effects of thermodynamic and kinetic driving forces on the texture evolution………………………………………………20
2.6.1 Surface energy and strain energy models………………20
2.6.2 Surface diffusivities and adatom potential energies.21
2.7 Properties evaluation and characterizations……………23
2.7.1 Nanoindentation Method…………………………………23
2.7.2 Transmission Electron Microscopy……………………24
2.7.3 Application of electrochemical techniques on corrosion tests…25
2.7.3.1 Tafel measurement……………………………25
2.7.3.2 Electrochemical impedance spectroscopy…26
Chapter 3 Experimental Procedure……………...……………45
3.1 Sample preparations……………………………………45
3.2 RF sputtering fabrication……………………………45
3.3 Measurements and Analysis……………………………46
3.3.1 Composition analysis……………………………46
3.3.2 Phase indentifacation…………………………46
3.3.3 Nanohardness and elastic modulus evaluation.47
3.3.4 electrochemical corrosion testing…………47
3.3.5 Microstructure analysis………………………48
Chapter 4 Results and Discussion………………………………53
4.1 Microstructure and phase identification…………53
4.2 Preferred orientation evolution……………………56
4.3 Microstructure evolution and mechanism……………59
4.4 Hardness of multilayered CrAlN/SiNx coatings……60
4.5 Electrochemical properties of multilayered CrAlN/SiNx coatings…...62
4.6 Composition, microstructure and electrochemical properties of multilayered CrAlN/SiNx coating with the ratio of lCrAlN to lSiNx =13:1…………………………………65
Chapter 5 Conclusions………………………………………………93
References……………………………………………………………95

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