1. Department of Mechanical Engineering, Huafan
University, Taipei, Taiwan, R.O.C.
2. Kinik Company, Taipei, Taiwan,
R.O.C.
3. Department of Mechanical Engineering, Tamkang University, Taipei, Taiwan, R.O.C.
Amorphous
diamond is the hardest diamond-like carbon (DLC) with properties very close to
true diamond. Among such properties is the low frictional coefficient and high
wear resistance. Cemented WC disks were coated by amorphous diamond deposited
by cathodic arc. These disks were rubbed cyclically by pins made of
aluminum-silicon alloy (4032), carbon steel (52100), and alumina ceramics (Al2O3).
It was found that frictional coefficient, after the period of “break-in,” was
significantly reduced when compared with that of uncoated carbides. However,
the frictional coefficient (0.2) with steel was more than twice that with Al
alloy (0.9) and alumina (0.8). This abnormal high frictional coefficient is
possibly due to the chemical interaction between surface atoms of iron and
carbon.
The
wear mechanisms include mechanical attrition, chemical adhesion, and fatigue.
The wear loss was the highest for the softer Al alloy, and lowest for 52100
steel. However, the wear of amorphous diamond was the highest when it was
rubbed against Al-alloy. It was
postulated that diamond was worn down primarily by the hardened layers of Al
alloy and oxygen formed in-situ during the rubbing action.