Nanocrystalline WC–Co materials have been the subject of interests and focus of research programs around the world for the past two decades owing to the expectations that the mechanical behavior of the material may improve significantly when grain sizes reduce to nanometer scale. However, although numerous technologies are available for making nanosized tungsten carbide powders, obtaining true nanocrystalline WC–Co (average WC grain size

Synthesis, sintering, and mechanical properties of nanocrystalline cemented tungsten carbide - A review

Diamondlike carbon (DLC) has been studied for many years as a wear-resistant material with low friction coefficient. Its tribological behavior is strongly affected by the tribotesting environment and is controlled by tribochemical effects, which may in turn be dependent on the technique used for the deposition of the films. New variations of DLC films, with various dopings, and new deposition methods have been investigated in recent years. The paper presents an updated review of the tribological properties of DLC and related materials, and discusses the mechanisms suggested for the explanation of the wear and friction behavior of these materials.

Tribology of diamondlike carbon and related materials: an updated review

In our recent studies, diamond-like carbon (DLC) films were found to possess low coefficient of friction (f < 0.1) and excellent wear resistance. The reduction in f was found to be consistent with wear-induced graphitization of the DLC structure. The purpose of the present work was to study the effect of load and sliding velocity on the frictional behavior and graphitization process occurring in DLC during wear. Pin-on-disc experiments were conducted on DLC-coated SiC substrates at sliding velocities between 0.06 and 1.6 m s−1 under 1 and 10 N loading levels using ZrO2 balls as the pin material. Analytical transmission electron microscopy was used to characterize the structure and microstructure of the wear debris after testing. The results showed that both sliding velocity and contact load influence the graphitization process. Higher sliding velocities increase the contact frequency and the rate of temperature rise that may facilitate the release of hydrogen atoms from the sp3 structure. Higher loading enhances shear deformation and transformation of the weakened hydrogen-depleted DLC structure into graphite [10]. The present findings are consistent with our earlier proposed wear-induced graphitization mechanism for these films. An equation was developed to describe the transformation kinetics of DLC into graphite as a function of sliding velocity and applied stress.

An investigation of the relationship between graphitization and frictional behavior of DLC coatings

Microstructural evolution in thermally sprayed WC-Co coatings: Comparison between nanocomposite and conventional starting powders

One of the main topics of the actual research in the field of cemented carbides concerns the development of new composites, with partial or total substitution of the traditional cobalt binder by other more economic and less toxic materials. Composites with partial substitution of cobalt by nickel and iron are currently entering in industrial production. However, the total cobalt replacement is envisaged and Ni–Fe or Ni–Fe–Cr alloys are being currently investigated for such a purpose. The actual knowledge on phase diagrams for WC and different binders will be extremely useful and opportune regarding the need to choose initial compositions leading to a desired final phase composition and to select adequate sintering cycle conditions. In the present review, the existent phase diagrams of W–C–M with M = (Co, Fe, Ni, Fe–Ni, Fe–Al, Co–Fe–Ni, Cr and Cr–Fe) are presented and discussed.

Cemented carbide phase diagrams: A review

Microstructure, hardness and toughness of nanostructured and conventional WC-Co composites

Diamond-like carbon (DLC) films were deposited on (100) silicon wafers and silicon nitride balls by RF plasma-assisted chemical vapor deposition at a pressure of 700 mTorr and a substrate temperature of 360 K. The friction coefficient and the wear rates were measured using a pin-on-disk tribometer in 40% humid and dry air. Friction coefficients are near 0.05 in all cases measured. In dry air, the wear of silicon nitride and steel against DLC is below measurement capability because of a protecting DLC transfer layer, and wear of DLC is 2.5 ± 10−8 mm3/Nm against silicon nitride and 6.5 ± 10−9 mm3/Nm against steel. In humid air, the DLC transfer layer does not adhere to the solids, and wear of both bodies is larger. Unmeasurable wear is obtained when DLC slides against itself in humid air; the wear rate is 5 ± 10−9 mm3/Nm in dry air. These results are interpreted in terms of the properties of a friction-induced transformation of the surface layer of DLC.

K. Jia

Papers

Microstructure, hardness and toughness of nanostructured and conventional WC-Co composites

Tribology of diamond-like carbon sliding against itself, silicon nitride, and steel