Silva F G, Neto M A, Fernandes A J S, Costa F M, Oliveira F J, Silva R F
Mechanical Engineering Department, Porto Superior Engineering Institute, ISEP 4200-072 Porto, Portugal.
J Nanosci Nanotechnol. 2009 Jun;9(6):3938-43. doi: 10.1166/jnn.2009.ns93.
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 H2-CH4 and H2-CH4-N2 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 microm. A micro-abrasion tribometer was used, with 3 microm 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) mm3 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.
纳米晶金刚石（NCD）涂层为摩擦学应用提供了一种极佳的替代方案，它保留了多晶化学气相沉积（CVD）金刚石的大部分固有机械性能，并在此基础上增加了极高的表面光滑度。据报道，氮化硅（Si3N4）陶瓷能确保与CVD微晶金刚石涂层具有高附着力，但NCD与Si3N4之间的附着力尚未得到充分研究。微磨损试验适用于评估给定表面的耐磨性能，但它也能提供有关薄膜/基体界面阻力（即薄膜附着力）的信息。在本研究中，对通过热丝化学气相沉积（HFCVD）和微波等离子体辅助化学气相沉积（MPCVD）技术沉积的NCD薄膜的性能进行了比较。选用氮化硅（Si3N4）陶瓷圆盘作为基体。分别使用H2-CH4和H2-CH4-N2气体混合物通过HFCVD和MPCVD进行NCD沉积。为每种CVD技术选择了一组合适的生长参数，得到的NCD薄膜最终厚度为5微米。使用微磨损摩擦计，以3微米金刚石磨粒作为磨料浆料元素。实验在恒定转速（80转/分钟）下进行，并在0.25-0.75 N范围内改变施加的载荷。MPCVD NCD的磨损率（3.7±0.8×10-5立方毫米/牛顿·米）与微晶CVD金刚石的报道值相符。HFCVD薄膜对Si3N4陶瓷基体的附着力比MPCVD薄膜差。然而，根据紫外拉曼数据，尽管HFCVD薄膜出现了过早的附着力失效，但由于其较高的结晶度，显示出更好的耐磨性能。
