Chunting Wang

Plasma boronitriding of WC(Co) substrate as an effective pretreatment process for diamond CVD

Abstract Cobalt-cemented tungsten carbide (WC–Co) is a widely used material for making cutting tools. Coating these tools with a protective diamond film should improve their lifetime and performance. However, the deposition and adhesion of diamond films on this material are hindered by the presence of the cobalt binder. To overcome this problem, we have developed a simple substrate pretreatment method with plasma boronitriding. The addition of NH 3 to B 2 O 3 –H 2 plasma can prevent cemented carbide from being etched in the plasma pretreatment and the binder phase-cobalt in the surface of the substrate was passivated during the plasma boronitriding process. Raman spectra showed that our pretreatment method efficiently reduced the catalytic effect of cobalt that leads to the formation of a non-diamond type of carbon layer between diamond coating and substrate. Indentation tests on diamond coated tungsten carbide substrate showed that the adhesion of diamond films significantly improved with plasma boronitriding the surface of cemented carbide.

An analysis of the tribological mechanism of GLC film in artificial seawater

The tribological performances of the graphite-like carbon (GLC) films sliding against WC balls in distilled water (DW), artificial seawater (SW) and four types of saline solutions related to seawater were investigated. The GLC film was deposited by magnetron sputtering. The microstructure, mechanical properties and tribological performances of the GLC film were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, nano-indentation and reciprocating ball-on-disk tribo-meter. The results showed that the smooth, dense and hard GLC film with significant sp2-hybridized carbon exhibited good tribological performance with low friction and wear not only in distilled water, but also in seawater. The tribological performance of the GLC film in seawater was closely related to the nature and constitution of seawater, as well as the nature and performance of the counterparts. Bulky wear debris with hard particles would generate a three-body wear regime, which increases the friction coefficient and wear rate of the GLC film slightly in seawater environment. In contrast, the divalent metal salts of seawater can decrease friction and wear between the two contact surfaces. The synergistic effect led to a relatively higher friction coefficient and wear rate of the GLC film against the WC counterpart in seawater than that in distilled water.

Micro/Nanotexture Design for Improving Tribological Properties of Cr/GLC Films in Seawater

ABSTRACT Microdimples with different diameters and Cr/graphite-like carbon (GLC) films were fabricated on silicon by laser surface texturing and magnetron sputtering technology, respectively. The texturing effects on the microstructures and tribological performance in seawater were comparatively investigated. The results showed that both the friction coefficients and wear rates in seawater decreased with an increase in dimple diameter in the lower range and then increased with a further increase in diameter. The Cr/GLC film with an appropriate diameter of dimples (1.5 µm) is effective in enhancing the tribological properties due to entrapment of wear particles and seawater in the dimples. In addition, the roughness and graphitization contact area have obvious effects on the wear resistance. If the surface roughness is too high, the graphitization contact area will decrease, and the ratio of minimum aqueous film thickness to the surface roughness is so small that the load is almost totally borne by the boundary film.