Atmospheric effects of friction, friction noise and wear with silicon and diamond. part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen

摘要

In this part III of a multi-part paper series, the results of additional SEM tribometric experiments are described, performed with polished, mostly C(l00)-oriented polycrystalline CVD diamond film [PCD{sub}C(l00) vs. PCD{sub}c(100)] counterfacessliding in ~1 x l0{sup}-5 Torr and in 0.1-0.3 Torr partial pressures of pure hydrogen gas. These tests were completed under a 28 g (0.27 N) normal load, under standard and slow thermal ramping conditions at temperatures ranging from room temperature to1000°C. The friction data were examined per the computer logging and analysis techniques described in part I. The treatment of the data is similar to that of Si in part II: the maximum and the average coefficients of friction (MAX.COF and COF) and theirratios (the friction noise FN) are employed to measure possible lubricative interaction of the diamond surfaces with rarefied hydrogen. The results indicate that excited species of molecular hydrogen enter into tribothermally catalyzed reactions not onlywith Si but with PCD{sub}c(100) surfaces as well. Similar to the behavior of Si, the most beneficial friction-reducing regime occurs in a temperature range just before the thermal desorption of adsorbates. The general magnitudes of MAX.COF, COF and the FN are significantly lower than those of the Si crystallinities, in both vacuum and PH{sub}2. The wear rate of the PCD{sub}c(l00) film characteristic of the standard thermal ramping test procedure performed mostly in PH{sub}2 is around 4 x 10{sup}-16m{sup}3/(N m), in good agreement with the wear rate previously measured in vacuum for unpolished, fine-cauliflowered diamond films. The data indicate that smooth polycrystalline diamond is a significantly better bearing material for miniaturized movingmechanical assembly applications than Si.