1. Tribology of Carbide Derived Carbon Coatings Grown on Tungsten Carbide M. Tlustochowicz 1, M. McNallan 1, A. Erdemir 2, S. Sudarshan 3, and R. Radhakrishnan 3 1.University of Illinois, Chicago, IL 2.Argonne National Laboratory, Argonne, IL 3.Materials Modification, Inc., Fairfax, VA

2. Etching in Halogens metal carbide carbon metal carbide carbon metal carbide carbon metal carbide carbon metal carbide carbon Etching in halogens The surface of the metal carbide converts into carbon. Deposition process of CVD or PVD leads to growth of carbon on the metal carbide surface. Other Methods Me = W, Si, Ti, Zr, B, Nb, etc. Carbide Derived Carbon (CDC) MeC+ xCl 2 (g)MeCl 2x (g)+ C H 2 Ar MeC 2 (g)MeCl H 2 Ar H 2 Schematic showing how our CDC process differs from other coating techniques, such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), that are currently used to produce carbon coatings.

3. Properties of Carbide Derived Carbon Structure resembling partially graphite and partially diamond Diamond structures are found only close to the interface; graphite and carbon onions are more common further away Nanoporous structure Residual chlorine present

4. Challenges Posed by Conventional Microcrystalline Tungsten Carbide (WC) Cermets Most commercial WC products are cermets containing typically ~6% Co or Ni as binder Chlorination causes selective attack of the metal binding phase before carbide is etched Samples may experience significant weight loss or complete disintegration

5. Nanocrystalline WC – a Novel Material When the nc-WC is densified with minimal or no binder, appropriate selection of CDC processing conditions can produce coatings with tribological characteristics comparable to those of CDC on SiC. Nanoindentation results: Modulus [GPa]Hardness [GPa] CDC on nano-WC (900 C for 3 hrs) 15.3±2.81.05±0.25 CDC on SiC (1000 C for 1 hr) 15.3±3.71.00±0.37

6. Typical Microcrystalline Cermet-WC Tribological Results

7. Nanocrystalline WC Tribological Results Friction coefficient versus time in pin-on-disk test on nanocrystalline WC before and after chlorination treatment at 900 C. After Treatment at 900 C

8. Silicon Carbide Tribological Results

10. Conclusions Carbide derived carbon (CDC) can be produced on nanocrystalline tungsten carbide by selective reaction of tungsten with chlorine When created in appropriate processing conditions, CDC significantly lowers the friction coefficient of WC CDC synthesized from nanocrystalline WC has similar tribological properties to these of CDC grown on SiC