The tribology of nano-crystalline diamond

Nano-crystalline diamond is the hardest diamond-Eke carbon (DLC) with prope rties very close to true diamond. Among such properties is the low friction al coefficient and high wear resistance. Cemented WC disks were coated by n ano-crystalline diamond deposited by cathodic are. These disks were rubbed cyclically by pins made of aluminum-silicon alloy (4032), carbon steel (521 00), and alumina ceramics (Al2O3). It was found that frictional coefficient , after the period of "break-in", was significantly reduced when compared w ith that of uncoated carbides. However, the frictional coefficient (0.2) wi th steel was more than twice that with Al alloy (0.09) and alumina (0.08). This abnormal high frictional coefficient is possibly due to the chemical i nteraction between surface atoms of iron and carbon. The wear mechanisms include mechanical attrition, chemical adhesion, and fa tigue. The wear loss was the highest for the softer Al alloy, and lowest fo r 52100 steel. However, the wear of nano-crystalline diamond was the highes t when it was rubbed against Al alloy. It was postulated that diamond was w orn down primarily by the hardened layers of Al alloy and oxygen formed in situ during the rubbing action. (C) 2001 Elsevier Science B.V. All rights r eserved.