Design And Mechanical Properties Of Nanostructured CN_x-based Films

This thesis focuses on the construction of two-phase nanocrystalline/amorphous CNx,FL-CNx,CNx based multilayer and Ti/a-CNx films which are prepared by direct current magnetron sputtering. Meanwhile, the microstucture, surface morphology and the internal mechanism between microstructure and mechanical properties of the films were discussed and investigated.1) Two-phase nanocrystalline/amorphous CNx films have been successfully prepared on the Si substrate by two step method, combine direct current magnetron sputtering and the following thermal annealing at 1000 K. The films contain a very dense and homogenous distribution of nanocrystalline grains with size of 2-10 nm, and the lattice parameters of these crystalline phases are in good agreement with thetheoretically predicted P-C3N4 lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the hardness is not varied with the annealing time.2) Carbon nitride films were deposited by direct current magnetron sputtering at different N2 fractions and a substrate temperature of 450℃. The microstructure of CNx films change from amorphous to fullerene like nanostructure as the N2 fraction is ranged from 0.05 to 0.1, and then to nitridized graphite nanocrystals in amorphous matrix at pure N2, and the curvature of the basal planes decreases with the increase of N content in CNx films. Combine with the structural analysis provides by the high resolution transmission electron microscopy, X-ray absorption near-edge spectroscopy and Raman spectroscopy. The formation of C-sp3 sites has been generally considered as the cross-linking path in FL-CNx. As compared with the amorphous CNx film, FL-CNx film with respect to its high hardness and elastic recovery, and the fricition and wear behavior are also less dependence on the test enviorment. FL-CNx film exhibits the lower fricition coefficient under both humidity and oxygen enviorment.3) TiN/CNx multilayer films with bilayer periods of 4.5 nm-40.3 nm were deposited by direct-current magnetron sputtering. The films with A= 4.5 nm exhibited the lowest friction coefficient (0.18), the wear rate (8.5×10-17 m3 N-1 m-1) and highest hardness 32 GPa, while the friction coefficient, wear rate and hardness of film with A = 40.3 nm is 0.32,5.2×10-16 m3 N-1m-1 and 24 GPa, respectively. The films with larger modulation period possess excellent wear resistant and high hardness. Meanwhile, one series of films with A=16.5 nm were deposited at the substrate temperature of 100℃,300℃and 500℃repectively. The films deposited at the 300℃exhibited coherent epitaxial growth due to the mutual growth-promoting effect, produced the thickest interlayer (about 2.5 nm), and the interlayer disappears at 500℃. The growth of interlayer mainly depends on the deposition temperature. The film with a maximum interlayer thickness of 2.5 nm exhibits superhardness up to 40 GPa. Based on the experimental results and therticl analysis, it is suggested that the interfacial intermixing and the crystal quality of TiN are the main reasons for the superhardness effect in TiN/CNx multilayers.4) Amorphous carbon nitride films with functional gradient Ti-TiN/CNx underlayer were deposited on Ti6A14V by direct current magnetron sputtering. The a-CNx-based films suffer a graphitization process with the increasing deposition temperature, the hardness and elastic modulus decrease. With the design of the Ti-TiN/CNx gradient underlayers, some important advantages of relatively thick CNx films can be achieved, such as increased hardness, improved adhesion strength, and the wear resistance of the films can be also improved significantly.5) Design and prepared the CNx/CNx multilayers with sequential sp3-rich and sp2-rich layers with A= 2 nm,4nm,20 nm and 60 nm. In these films, the sp3 CN rich and the sp2 CN rich layers exhibit amorphous feature and graphite-like structure, respectively. The multilayer films showed lower compressive stress and higher hardness than their monolayer components. Meanwhile, the a-CNx multilayer film with a bilayer period of 60 nm exhibited the improved mechanical properties, and the lowest friction coefficient and the highest wear resistance.6) About 1.5μm thickness a-CNx films with 2.7-12.3 at.% Ti was deposited on Ti6Al4V by direct current magnetron sputtering. The film with 2.7 at.% Ti is amorphous structure while the films with 12.3 at.% Ti is nanocomposite structure. With the Ti content increase, Ti formed the bonds with C or N elment and replaced the sp3 bond, the content of sp3 bond increased. The titanium incorporation increases the corrosion resistance of a-CNx films. Meanwhile, the hardness and adhesion strength of films increased with the Ti content, the films with 12.3 at.% Ti possess high hardness up to 28.4 GPa,and the satured adhesion strength of 67 N. but the films with high Ti content possess the lower strain.Compared with the analysis result of electrochemical corrosion for Ti alloy in Troydes' simulate solution, the Ecorr of a-CNx film are higher and Icorr is lower than Ti alloy substrate. More obvious changes in Ecorr and Icorr can be observed for a-CNx:Ti films. The whole polarization curves of Ti/a-CNx films move to the region of higher potential and lower current density after the incorporation of Ti. The titanium incorporation increases the corrosion resistance of a-CNx films.