Atmospheric effects of friction, friction noise and wear with silicon and diamond. Part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen
Mn. Gardos et Sa. Gabelich, Atmospheric effects of friction, friction noise and wear with silicon and diamond. Part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen, TRIBOL LETT, 6(2), 1999, pp. 103-112
In this part III of a multi-part paper series, the results of additional SE
M tribometric experiments are described, performed with polished, mostly C(
100)-oriented polycrystalline CVD diamond film [PCDC(100) vs. PCDC(100)] co
unterfaces sliding in similar to 1 x 10(-5) Torr and in 0.1-0.3 Torr partia
l 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 to 1000 degrees C. The friction
data were examined per the computer logging and analysis techniques describ
ed 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) an
d their ratios (the friction noise FN) are employed to measure possible lub
ricative interaction of the diamond surfaces with rarefied hydrogen. The re
sults indicate that excited species of molecular hydrogen enter into tribot
hermally catalyzed reactions not only with Si but with PCDC(100) surfaces a
s well. Similar to the behavior of Si, the most beneficial friction-reducin
g regime occurs in a temperature range just before the thermal desorption o
f adsorbates. The general magnitudes of MAX.COF, COF and the FN are signifi
cantly lower than those of the Si crystallinities, in both vacuum and P-H2.
The wear rate of the PCDC(100) film characteristic of the standard thermal
ramping test procedure performed mostly in P-H2 is around 4 x 10(-16) m(3)
/(N m), in good agreement with the wear rate previously measured in vacuum
for unpolished, fine-cauliflowered diamond films. The data indicate that sm
ooth polycrystalline diamond is a significantly better bearing material for
miniaturized moving mechanical assembly applications than Si.