Surface Electrochemical Modification Of WC-6%CO Substrate For Deposition Of Diamond Films By CVD

The application of diamond coatings on cemented tungsten carbide (WC-6%Co) tools wasthe subject of much attention in recent years in order to improve cutting performance and toollife. A well-known problem is the poor adhesion of the diamond films between diamond andsubstrates. WC crystals which occupied 94% of the substrate obstacle the acid removal of cobalt.Murakami's solution used for etching WC which got free obstacles for acid was appliedextensively. Our study found the Murakami's solution corrosion was so even that smaller crystalsof the substrate had been corroded seriously, which would do harm to the adhesion of the diamondfilms between diamond films and substrates. While the ingredient, tissue, structure, roughness anddefects of surface have marked influence on nucleation, crystal growth orientation, properties ofdiamond thin films. Based on these aspects, a new method for surface modification of cementedcarbide cutting tools using electrolytic polishing technology while the effects of different chemicalpretreatment procedures on WC+6%Co surface modification and some properties of diamondcoatings deposited by DC Arc Discharge Plasma CVD on the pretreated surfaces have beensystematically studied. We got the results as follows:(1)Comparing with the micrographs of finely grinded and semi-finished YG6 cutting toolspretreated with different techniques, the paper studied the micrographs of semi-finished YG6cutting tools systematically and obtained the proper etching time of these techniques primarily. Wealso studied the weight lose of WC, micro-hardness, etching depth, surface roughness ofsemi-finished YG6 cutting tools pretreated with different techniques and obtained correspondingcurves. The results indicated that direct current electrochemical pretreatment could enhance thesurface roughness, diamond nucleation, etching depth of cobalt, weight lose of WC, and improvethe adhesion of diamond films. (2)The micrographs of finely grinded and semi-finished YG6cutting tools pretreated with electrochemical pretreatment indicated that the structure of surfacewas a state of essential equality or equivalence. The difference was that removal of the finelygrinded YG6 cutting tools' cuticles needed more time. (3)There was no diamond film thatformed on the finely grinded YG6 cutting tools pretreated with alternating current electrochemicalpretreatment, but cluster of small round pellets formed. The cluster which did not cover the holesurface was considered as nanoscale diamond crystals or plumbago of layer structure. ACelectrochemical pretreatment was not proper for the formation of diamond films or improving theadhesion between diamond films and substrates. (4)There was diamond films that formed on thefinely grinded YG6 cutting tools pretreated with direct current electrochemical pretreatment.Nucleation density was higher compared to one-step and Murakami's solution pretreatment. Thediamond films were compact and particle size distribution of crystals was even. The average grainsize was about 1μm. (5)The adhesion between diamond films and substrate was better improvedcompared to one-step and Murakami's solution pretreatment. The conical indenter with 60Kg loadacting on diamond films indicated a good adhesion between the diamond films and substrates.With 60Kg load, the impress width of films extended to 150μm, and the surroudings of impressdidn't have evident cracks.