X.H. Zheng

Effects of Temperature on Microstructure and Tribological Performance of a-CNx Films Prepared by Pulsed Laser Deposition

a-CNx films were deposited onto silicon wafers at temperatures from RT up to 600 °C by using pulsed KrF excimer laser deposition. The composition, morphology and microstructure of the CNx films were characterized by X-ray photoelectron spectrum (XPS), scanning electron microscopy (SEM) and Raman spectrum. The tribological performance of the films was investigated using a ball-on-disk tribometer. With increasing the deposition temperature ranging from RT to 400 °C, the N content of films dropped from 36 at.% to 22 at.%, the ratio of N-sp3 C bonds, hardness and friction coefficient of the film decreased. Further increase of deposition temperature led to the lack of nitrogen and the increasing degree of order in ringed sp2 C=C bonds of the amorphous carbon film. The mechanical and tribological performances became worse. The film deposited at 300°C showed a low friction coefficient of 0.11 and a preferable wear resistance of 1.65×10–7 mm3 Nm–1 in humid air.

Microstructure and Tribological Performance of a-CNx /TiNx Composite Films Prepared by Pulsed Laser Deposition

CNx/TiNx composite films were prepared on high-speed steel (HSS) substrate by pulsed laser co-deposition process with the Ti/graphite combined targets and at a substrate temperature of 200 °C. The composition, morphology and microstructure of the films were characterized by energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). In the graphite/Ti range of 0.5–2.0 of the target, the composite films composed of TiNx, a-CNx and a small amount of metallic Ti. The TiNx disappeared in the films at a high graphite/Ti ratio of the target. The adhesion and tribological performance of the films were investigated using a conventional scratch tester and a ball-on-disk tribometer respectively. With increasing the graphite/Ti ratio of the target, the adhesion to substrate of the composite films deteriorated from 46 N to 26 N, and the friction coefficient drcreased from 0.23 to 0.17. The composite film deposited at the graphite/Ti ratio of 1.0 showed a low friction coefficient, good adhesion and wear rate of 3.2×10–7 mm3/Nm in humid air.

Preparation and Tribological Properties of Amorphous Ti/C Multilayers by Pulsed Laser Deposition

Amorphous Ti/C multilayers were prepared on titanium-alloy and silicon (100)-wafer substrates by pulsed laser deposition. Films with different Ti concentration were synthesized by changing the ablating time for Ti and C targets. The morphology and microstructure of Ti/C multilayers were characterized by scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). Both of the Ti and C monolayers were amorphous. The metallic Ti stimulated the formation of more amorphous carbon phase by reducing the sp2 aromatic bonds and elongating the C-C chain bonds. The tribological properties of Ti/C multilayers were investigated by ball-on-disk tribometer. The pure C film and the multilayers containing more than 68.8 at.% of Ti showed low wear resistance. The multilayer contained 36.8 at.% of Ti exhibited the lowest wear rate at 3.54×10–16 m3/N·m. The formation of carbon related interlayer and its effect on tribological performance of the films were discussed.