| The thermal plasma chemical vapor deposition (TPCVD) process was used to synthesize nanostructured Si-C-N coatings for hard, wear-resistant applications. A series of depositions were produced in a triple torch thermal plasma reactor to investigate the influence of substrate temperature and reactant flow rates, including hexamethyldisilazane (HMDSN), hydrogen, and nitrogen on film morphology, composition, mechanical properties, and wear-resistance.; Films grown at substrate temperatures around 800°C were amorphous and included N-H, CHx, C≡C, and C≡N bonds. High hydrogen flows produced smooth, hard, and wear-resistant films. Replacing hydrogen with nitrogen gas, while maintaining the same HMDSN flow rate, produced columnar film structures. Low N:H ratios (0.0003-0.02) produced films with average hardness values between 19 and 24GPa, elastic modulus values between 177 and 225GPa, and wear volume losses around 0.0009mm3. While high film deposition rates can be achieved with the TPCVD process, smooth, hard, and wear-resistant films were obtained only under slow growth conditions.; Coatings deposited at substrate temperatures around 1000°C included nanocystallites within an amorphous matrix without N-H, CHx, C≡C, or C≡N bonding. Silicon carbide or silicon nitride nanocrystallites were produced with N:H ratios of 0.0003 or 0.02, respectively. Silicon carbide films approached superhard properties with average hardness and elastic modulus of 38 and 326GPa, respectively. With high hardness, wear-resistance declined sharply due to ball wear.; A chemical model simulating the reaction mechanisms occurring in the substrate boundary layer was constructed to include 140 gas-phase reactions and 57 surface reactions. Initial conditions entering the substrate boundary layer were determined from equilibrium calculations at the boundary layer edge. Kinetic gas-phase and surface reaction mechanisms occurring between the boundary layer edge and the substrate were verified by experimental film growth rates and relative elemental content obtained by Non-Rutherford Backscattering Spectrometry. The reaction model identified atomic silicon, carbon, nitrogen and hydrogen, along with molecular CH, CH2, CH3, C 2H2, CN, HCN, H2CN, NH, NH2, and N 2H2 as major species in the deposition process. Finally, the competition of each chemical reaction and species diffusion rates were investigated to determine their role in producing smooth film structures. |
