Investigation On The Microstructure And Mechanical Properties Of WC_xN_y,NbC_xN_y And TiC/α-C:H Nanocomposite Thin Films

During the last decades, much interest has been paid to the investigation the nanocomposite thin films (typical: Me-X-N, Me stands for transition metal and X = Si, B, C, etc.) because of their much better mechanical properties than that of unitary or binary coating. Many studies have been performed to control the mictostructure and improve the mechanical properties of thin films. Base on the previous work in literatures, we focused on the texture, phase transition and mechanical properties of nanocomposite thin films in this thesis.. The main works of this thesis are summarized as follows:In chapter 1, we give a brief introduction to the mechanism of film growth, texture behavior, phase transition and mechanical properties. Furthermore, some unresolved issues in the study of structure and properties for nanocomposites and the objective of this dissertation are given.In chapter 2, we introduce the basic concepts and progress of the experimental method used in this work in detail.In chapter 3, we have successfully synthesizedα-WC at a relatively low temperature using direct current reactive magnetron sputtering, and observe a phase transition fromβ-WC toα-WC in the film by increasing N dopant concentration. We find that N content has a significant influence on the intrinsic stress, preferred orientation, phase structure, and hardness for films.In chapter 4, We deposit ternary WCxNy thin films on Si(100) substrates at 500℃using direct current (DC) reactive magnetron sputtering in a mixture of CH4/N2/Ar discharge, and the effects of both bias voltage and annealing on the intrinsic stress, preferred orientation and phase transition for the obtained films have been explored. From the experimentally results, we have found that the substrate voltage bias and annealing have a significant influence on the structure and mechanical properties of the obtained films.In chapter 5, size-effect on the texture behavior has been demonstrated and discussed for TiC/α-C:H nanocomposite films. The texture of film is found to be significantly affected by the grain size, and the size-dependence correlation of texture behavior is discussed by thermodynamic calculations. The results show that the size-dependent Gibbs free energies are likely to be a key factor that controls the texture development in thin films if the grain sizes of films are sufficient small.In chapter 6, the microstructure behavior and texture evolution of nanocomposite films have been explored for NbCxNy films. The relationship between microstructure change and texture evolution have been built in this thesis. Furthermore, the mechanical properties of NbCxNy films including stress and hardness have also been discussed.In conclusion, the microstructure and mechanical properties have been systemically investigated by means for W-C-N, Nb-C-N and Ti-C-H system of films. The results of this thesis can be used for reference to designing and synthesizing of high performance nanocomposite films.