| Zirconium nitride and zirconium carbide have excellent physical and chemicalproperties suggesting a potential use in extreme environments, e.g. as-hightemperature aerospace material or as coating for fuel particles in high temperaturenuclear reactors. In addition, zirconium nitride and zirconium carbide can be used as aprotective film in cutting tools because of their high hardness and wear resistance.Furthermore, the high electrical conductivity combined with a good chemicalinertness suggest a potential use in sliding electrical contacts, such as brushes,microelectromechanical devices, circuit breakers and motor vehicle starters.Zirconium nitride and zirconium carbide films can be deposited by many techniquesand the most widely used techniques is sputter.Based on these issues, we start to deposite polycrystalline ZrN films, andinvestigate the relationship among preferred orientation, phase structure, stress andhardness.In Chapter2, the stress of zirconium nitride films is controlled by changing theenergy of sputtered atoms. The influence of stress on the evolution of microstructure,such as prefer orientation and phase transition, has been studied. Thethermodynamic calculations are used to understand the evolution of the preferredorientation. Also the mechanism of a phase transition from substoichiometric tooverstoichiometric films is revealed. According to the thermodynamic calculations,with increasing strain energy, induced by an increase in Vb, the preferred orientationchanges from ZrN(200) to ZrN(111). Being high enough, the strain energy becomes adriving force for a phase transition of the film.The residual stresses are often unintentionally introduced into films during thedeposition process. Therefore, the influence of the residual stress on deformationbehavior (pile-up) around the indent on the surface of zirconium nitride film has beeninvestigated in Chapter3. Atomic force microscopy (AFM) is performed to reveal thebehavior of deformation (e.g. pile-up) around the indent on the surface of the film. The pile-up occurs for the film under a compressive stress, and is enlarged withincreasing the compressive stress, which leads to that the actual contact area byindenter significantly deviates to the one calculated by Oliver–Pharr method. Aftercorrecting the contact area contributed by pile-up via AFM experiments, the residualstress does not affect the nanoindentation measured hardness and modulus.In Chapter4, the hardness enhancement mechanism for ZrN/SiNx multi-layershas been studied. First, ZrN/SiNx double-layers with different density of SiNx layers,which is controlled by applying different substrate bias for depositing SiNx layers, aresynthesized for investigating the interfacial electronic structure. Results indicated thatthe interfacial electrostatic polarization existed as the ZrN and SiNx bond with eachother to form a heterojunction, since the electrons donated from ZrN layer to SiNxlayer. Moreover, the degree of polarization is affected by the density of SiNx layer.The corresponding ZrN/SiNx multi-layers are deposited for studying the correlationbetween interfacial electronic structure and mechanical properties. The results ofhardness test imply that the interfacial electrostatic polarization would enhance thehardness to a certain extent.The working life of film on practical application is depanded on the tribologicalproperties. ZrN film has an excellent hardness, but does not have good tribologicalproperties. Comparing to ZrN, ZrC film shows an outstanding tribological properties.Therefore, in the following chapters we have deposited ZrC and ZrSiC films, andinvestigeted the relationship among microsturcture, chemical bonding state, stress,hardness, tribological properties and electrical properties.In Chapter5, Zirconium carbide films have been deposited on silicon (100)substrates using CH4as a carbon source. The films exhibit a typical nanocompositestructure consisting of nanocrystalline ZrCx(nc-ZrC) grains embedded in a matrix ofamorphous carbon (a-C) at low carbon content. Almost no crystalline phase can befound for carbon contents above86at.%. The mechanical, tribological and electricalproperties of the films showed a significant dependency on the amount of the a-C inthe nanocomposite structure. A larger amount of a-C gives rise to reduced hardnessand higher resistivity of the film. However, both friction coefficient and wear resistance are improved by increasing the content of the surplus a-C. The influence ofbinding state of excess a-C phase on the properties has also been investigated. Alarger sp2/sp3ratio was beneficial to relax the stress and improve the electricalproperties. The Zr-based films exhibited lower friction coefficients thannanocomposites films based on e.g. Ti suggesting a potential application for thismaterial in sliding contacts.In Chapter6, ZrSiC films with different Zr content and Si/C atomic radio havebeen deposited by magnetron co-sputtering. The relationship between composition,microstructure, chemical bond state, hardness, friction, and resistivity has beenstudied. Also, the results for ZrSiC films have been compared with those for ZrCfilms in Chapter5. The resistivity for ZrSiC films is similar to that for ZrC films. Themain difference is the influence of a-C content on hardness and friction. The affectionof a-C content on hardness for ZrSiC films is not obviously, because themicrostructure is XRD amorphous. The hardness of ZrSiC films depends on the Si-Cbond fraction in the films. The wear chemical reactive has been found during the weartest, and the a-C fraction in the transfer layer is also contributed to improve thefriction for ZrSiC films. However, the friction of some films with higher zirconiumcontent or silicon content shows an abnormal increase with the increase in a-C content,which is attributed to the existence of delamination. In summary, not only the a-Ccontent in transfer layer but also the level of delamination controls the friction ofZrSiC films. |
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