resumo
Nanocrystalline diamond (NCD) coatings offer an excellent alternative for tribological applications, preserving most of the intrinsic mechanical properties of polycrystalline CVD diamond and adding to it an extreme surface smoothness. Silicon nitride (Si3N4) ceramics are reported to guarantee high adhesion levels to CVD microcrystalline diamond coatings, but the NCD adhesion to Si3N4 is not yet well established. Micro-abrasion tests are appropriate for evaluating the abrasive wear resistance of a given surface, but they also provide information on thin film/substrate interfacial resistance, i.e., film adhesion. In this study, a comparison is made between the behaviour of NCD films deposited by hot-filament chemical vapour deposition (HFCVD) and microwave plasma assisted chemical vapour deposition (MPCVD) techniques. Silicon nitride (Si3N4) ceramic discs were selected as substrates. The NCD depositions by HFCVD and MPCVD were carried out using H-2-CH4 and H-2-CH4-N-2 gas mixtures, respectively. An adequate set of growth parameters was chosen for each CVD technique, resulting in NCD films having a final thickness of 5 mu m. A micro-abrasion tribometer was used, with 3 mu m diamond grit as the abrasive slurry element. Experiments were carried out at a constant rotational speed (80 r.p.m.) and by varying the applied load in the range of 0.25-0.75 N. The wear rate for MPCVD NCD (3.7 +/- 0.8 x 10(-5) mm(3)N(-1) m(-1)) is compatible with those reported for microcrystalline CVD diamond. The HFCVD films displayed poorer adhesion to the Si3N4 ceramic substrates than the MPCVD ones. However, the HFCVD films show better wear resistance as a result of their higher crystallinity according to the UV Raman data, despite evidencing premature adhesion failure.
palavras-chave
3-BODY ABRASIVE WEAR; DIAMOND GROWTH; CVD DIAMOND; NANOCRYSTALLINE; FILMS; MPCVD; DEPOSITION
categoria
Chemistry; Science & Technology - Other Topics; Materials Science; Physics
autores
Silva, FG; Neto, MA; Fernandes, AJS; Costa, FM; Oliveira, FJ; Silva, RF
nossos autores
Filipe José Alves de Oliveira
Investigador Principal
Miguel Ângelo da Costa Neto
Investigador Principal
Rui Ramos Ferreira e Silva
Professor associadoagradecimentos
The authors whish to thank the financial Support by the two FCT Proiects: POCTI/CTM/45423/2002-