Dissertation > Industrial Technology > General industrial technology > Materials science and engineering > Special structural materials

Microstructure and Superhardness Effect in VC-based Nanomultilayers

Author LiGuanQun
Tutor LiGeYang
School Shanghai Jiaotong University
Course Materials Science
Keywords Nanomultilayers Superhard effect Vanadium carbide Modulation structure Coherent interface Strengthening mechanisms
CLC TB383.2
Type PhD thesis
Year 2011
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Hard films are a class in modern industry has important application of surface coating materials. NANOMULTILAYERS superhard material combination effects and the diversity and performance can be cut, it has a broad application prospects. The design of such materials by hand to obtain high hardness, microstructure strengthening mechanism is has a more important theoretical research value. After twenty years of research, the multilayer films with high hardness characteristics and microstructure development and other aspects of material systems have made significant progress. However, strengthening mechanisms and design criteria such as basic research lag become obstacles to the further development of such materials. In this thesis the VC, HfC monolayer and VC / TiC, VC / TiN, VC / TiB 2 , VC / SiC, VC / AlN, VC / Si 3 N 4 and HfC / Si 3 N 4 and other carbide-based multilayers. The main contents include: carbide-based nano-multilayer film structure and growth of superhard effect; cubic carbides on the crystallization of amorphous materials template effects; reactive sputtering method to obtain high hardness carbide based nano and more layer membrane preparation techniques; discussed nanomultilayers strengthening mechanism and modulation of structural parameters on the performance of multilayer films. Thesis nanomultilayers new material system development, design criteria and preparation of new technologies complement three new approach has made some innovative results, the main conclusions are as follows: 1. Single-phase VC film in Ar gas ceramic target was prepared by magnetron sputtering VC obtained. Sputtering pressure on the film's chemical composition, phase composition, microstructure, deposition rate and the corresponding mechanical properties have a greater impact, by adjusting the VC target stoichiometry can significantly alter the growth of the resulting film structure and mechanical properties. Other than the VC stoichiometric target degree of crystallinity of the obtained film is poor, the maximum hardness of 28.0GPa; the metal element of the VC-rich target resulting film at a low sputtering gas pressure to achieve a good crystallinity and high mechanical properties, the maximum hardness up 31.5GPa. 2. VC / TiC multilayer films obtained in a small modulation cycle was significantly higher hardness. In which the metal-rich element consisting of VC and TiC multilayer films formed a good epitaxial growth structure, and access to the hardness of superhard incremental effect of 40%, the highest hardness 41.9GPa; while the other stoichiometric than the VC and TiC multilayer films consisting of the formation of coherent interface structure is relatively poor, increase the hardness of multilayers is only about 19%, the highest hardness 31.0GPa. 3 Different VC, TiN layer thickness VC / TiN multilayer films were prepared in a small period of time can be obtained epitaxial growth structure and hardness increased significantly superhardness effect. Among them, the fixed modulation ratio VC / TiN multilayers obtained hardness increase up to 62% of superhard effect, the maximum hardness reaches 45.8GPa; fixed VC thick TiN layer thickness and a fixed VC / TiN multilayers films were also achieved 41% and 42% of the hardness increase. Modulation cycle or variable modulation layer thickness increases, the multilayer structure destroyed coherent interface, the hardness gradually decreases. 4. VC / TiB 2 multilayers can also be obtained under the appropriate modulation structure significantly increased the hardness of superhard effect. VC cubic and hexagonal structures TiB 2 in a small modulation cycle or variable modulation layer thickness is very small structures forming a coherent interface, and its coherent relationship: {111} VC / / {0001} TiB lt; 110 gt; VC / / lt; 1120 gt; TiB. Structural parameters at different modulation VC / TiB 2 nanomultilayers fixed modulation multilayer film obtained in increments of 26% of the hardness of superhard effect, the maximum hardness 38.3GPa; VC fixed thickness and fixed TiB 2 thick multilayer film were achieved by 39% and 41% of the hardness increase. Modulation cycle or variable modulation layer thickness increases, the multilayer film is gradual destruction of cell growth, the hardness is gradually decreased. 5 by the cubic crystal VC and amorphous SiC or AlN multilayer films composed of superhard effect can be obtained. VC templates in the template layer under the action of the deposited amorphous SiC and AlN are less than about 0.7nm in thickness is forced into NaCl crystal structure of metastable crystal epitaxial multilayers showing the growth of structure and obtain hardness The significantly increased. Which VC / SiC nano-multilayers highest attainable hardness 36.0GPa; VC / AlN nano-multilayers highest attainable hardness up 40.1GPa. SiC or AlN layer with thickness increases again after changed to amorphous growth of multilayers coherent interface quickly destroyed, immediately reduce its hardness. 6 In Ar-C 2 H 2 gas mixture, the use of sputtered metal V and Hf reactive sputtering target material can be efficiently synthesized carbide and vanadium carbide Hf film. Film chemical composition, phase composition, microstructure and mechanical properties of the C 2 H 2 partial pressure is very sensitive. In C 2 H 2 of the total pressure of the mixed gas pressure of about 3% of high mechanical properties can be obtained when VC film cubic structure, its hardness up 35.5GPa; In C 2 H 2 partial pressure of the mixed gas total pressure of about 2.5 3 .0% range to qualify for a higher mechanical properties Single phase HfC film, the maximum hardness of 27.9GPa. 7 Since the Ar-C 2 H 2 mixed atmosphere, sputtered Si 3 N 4 particles are not associated with C 2 H 2 gas react, and thus by reactive magnetron sputtering technique can efficiently prepare VC / Si 3 N < sub> 4 and HfC / Si 3 N 4 multilayers. In VC or HfC templates role, originally amorphous Si 3 N 4 in thickness less than 1nm is forced crystallization and the formation of the template layer epitaxial growth structure, the corresponding multilayers obtained significantly higher hardness of superhard effect. Which VC / Si 3 N 4 to get the highest hardness of 45.8GPa, while HfC / Si 3 N 4 The maximum hardness obtained was 38.2GPa. Si 3 N 4 layer thickness increases with more than 1nm and then converted to the amorphous growth of multilayers cell growth structure immediately destroyed, its hardness is also reduced accordingly. As reactive sputtering with a high deposition rate, which was prepared by reactive sputtering technique multilayer films with high hardness methods in industry has good prospects. 8 According to VC / TiN, VC / TiB 2 and VC / SiC nano-multilayers results summed up the cubic crystal / cubic crystals, cubic crystal / hexagonal crystals, cubic crystal / amorphous three typical structure combinations nanomultilayers modulation structure parameters and film hardness of the specific relationship diagram. Since these three structure types portfolio covers most ceramic nano-multilayers structure type, the parameter map in nanomultilayers modulation structural design has universal guiding value.

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