|M.Sc Student||Ilberg Liron|
|Subject||The Effect of Structure and Hydrogen Bonding of Amorphous|
Carbon Films on Their Tribological Properties
|Department||Department of Materials Science and Engineering||Supervisors||Professor Emeritus Yeshayahu Lifshitz|
|Assistant Professor Michael Varenberg|
The structure and properties of carbon based thin films produced by a variety of deposition systems were widely investigated. Many studies addressed the mechanical properties of carbon films in general and their tribological properties in particular. Most of the tribological studies were however focused on hydrogen containing carbon films while hydrogen free carbon films were less investigated.
The advantage of utilizing amorphous carbon (a-C) films for many applications stems from the possibility of tuning their properties over a large range by varying their local configuration between 100% sp2 bonding (obtaining properties similar to graphite) and 90% sp3 bonding (properties similar to diamond). Another parameter which modifies the characteristics of a-C films is the amount of hydrogen incorporated ranging from hydrogen free a-C films to hydrogenated (a-C:H) films with up to 50 at. % hydrogen. The present research studies the effect of the local carbon configuration and the hydrogen bonding on the friction and wear of a-C films.
Hydrogen free a-C films were produced using a filtered cathodic vacuum arc (FCVA) system under different conditions. The amorphous carbon hydrogenated (a-C:H) films were grown applying a CH4 fed plasma enhanced CVD system.
The friction and wear of a library of different a-C and a-C:H as well as reference films were studied applying a reciprocal sliding tribometer with Al2O3 balls pressed to the carbon films under normal loads of 2.5 and 5N. The tests were conducted under either humid (50% humidity) or dry (5% humidity) air. Optical and scanning electron microscopy as well as energy dispersive spectroscopy (EDS) were used to probe the pristine and the worn zones.
The friction and wear performance of the a-C films was found to depend on both their structure and the test ambient conditions. Hydrogen free a-C films have a friction coefficient of 0.1 for 90% sp3 bonded and 0.2 for 100% sp2 bonded films respectively under 50% humidity. The wear resistance of hydrogen free a-C films (much larger for sp3 bonded films, smaller for sp2 bonded films) significantly decreases under dry conditions. In contrast, a-C:H films show reduction in friction with decreasing humidity (0.2 and <0.1 in humid and dry conditions, respectively). Also in contrast to hydrogen free a-C films, the wear resistance of a-C:H films is larger for dry and smaller for humid environment. The above dependence of the tribological properties on the films structure and on the environmental conditions is discussed.