Synthesis, Microstructure And Properties Of Ti/ A-C Films

This thesis focuses on the microstructure and mechanical properties of a-C and Ti/a-C (multilayer) films, which are prepared by pulsed laser deposition (PLD), magnetron sputtering and unbalanced magnetron sputtering.1) Pure a-C and amorphous C/Ti multilayer films were prepared by pulsed laser deposition. The optimized process parameter for preparing a-C film was studied using orthogonally experimental design. Relationships between the microstructure and mechanical properties of a-C films were investigated. With increasing the laser fluence, the sp3 C bond ratio, internal stress and nanohardness of a-C films increase. Adhesion of film to the substrate is affected by the thickness and internal stress, whereas the buckling and delamination of thick films result in stress and microstructure relaxation, as well as the decrease of sp3 C bond ratio and nanohardness. Higher laser fluence results in more relaxation of the films with poor adhesion.The microstructure and mechanical properties of amorphous C/Ti multilayer films were investigated. The multilayered structure results in lower stress and better adhesion. The amorphous C/Ti multilayer films combine the constituent bilayers both in amorphous structure, where the sp3 C bond ratio and hardness of the multilayer films are higher than the buckled pure a-C film deposited at the same fluence. Adhesion strength of the films to the substrate is enhanced by depositing the Ti-C transition layer. The amorphous C/Ti multilayer films with lTi=2.1～4.1 nm provide reduced friction and good wear resistance.2) a-C/TiN multilayer films were deposited by magnetron sputtering. The hardness of a-C/TiN multilayer films deceases with decreasing the bilayer period (or increasing the number of interface). The specific wear rates of a-C/TiN multilayer films are higher than that of the TiN monolayer, and even increases with the increase of bilayer period. The analogical behavior of W/NbN superlattice films was introduced, which possessed higher hardness but lower wear resistance than monolayer NbN film. It is deduced that low wear resistance of a-C/TiN multilayer films results mainly from the weak shear resistance of the interfaces between a-C and TiN.Amorphous C/Ti multilayer films with lC= 10 nm,lTi= 0.6-10 nm and lTi=lC= 20 nm were designed, in which Ti bilayer appeared when lTi was more than 3 nm. The microstructure of Ti incorporating into a-C matrix results in the formation of nanoclusters, as well as the declination of sp3 C bond ratio and hardness of the films. The internal stress of the amorphous C/Ti multilayer films decreases with the increase of lTi and reaches its lowest at lTi= 10 nm, while the adhesion strength of films shows the reverse trend. The film with designed lTi= 1.5 nm (showing nanocomposite structure) possesses better wear resistance under variant loads and sliding speeds.3) Ti/a-C films containing 0～15.2 at.% Ti were deposited by unbalanced magnetron sputtering to 1.5μm in thickness. The pure a-C film shows the nanohardness 50.2 GPa, sp3 C bond ratio 35.1% and internal stress -3.4 GPa. The microstructure of Ti/a-C films evolves with Ti incorporation. The nanohardness, sp3 C bond ratio and internal stress decrease continuously with increasing the Ti content in the a-C films.In Hanks'solution, the Ti/a-C films containing 0～3.1 at.% Ti possess good resistance to the electrochemical corrosion, while the film with 15.2 at.% Ti is susceptible to crevice corrosion. The friction coefficient of Ti/a-C films under dry sliding and the lubrication of Hanks'solution is among 0.11～0.14 and 0.04～0.078, respectively, which rises with the increase of Ti content in both situation. Low friction coefficient of the Ti/a-C films in the Hanks'solution results from the combining effect of self lubrication of a-C and boundary lubrication of the Hanks'solution. The Ti/a-C film with 3.1 at.% Ti exhibits the best wear resistance among the studied films both in the dry sliding and the Hanks'solution.