Research On The Bonding Of CVD Diamond Thick Film

Diamond is a kind of substance with high level of hardness andwearability, as well as fine insulation and heat conductivity. Onaccount of these properties more and more diamond tools are appliedto industrial production. In the field of machining, diamond's join withother metallic substrates is the key for its further extension andapplication.This paper takes the join of CVD diamond thick film withcemented carbide (WC) substrate and materials of stainless steel as itsresearch object. Diamond film should be metalized at first and thenbrazed in vacuum furnace by Ag-Cu solder, or brazed directly by usingTi and Ag-Cu foil as filler metal. In this way the firm joining ofdiamond thick film with substrate is fulfilled. To overcome thenon-wetting between diamond and filler metal and get firm joint,theoretical study and experiment have been conducted systematically.The main results of this thesis are as follows:(1)For its excellent property of physics and chemistry, Ti isaffirmed as the best element to metalize diamond. By using XRD andSEM analysis, TiC can be produced. And the wetting and bondingbehavior of brazing is achieved through the function of TiC.(2)Diamond has great interfacial energy, so it is hard to wet itwith other metal alloy. The wetting condition of diamond and Ag-Cusolder can be greatly improved through the metallization of diamond.The wetting angle can be less then 10° in proper condition.The measuring result indicates that the wetting condition ofgrowing side is superior to substrate side or polished interface in thesame experimental parameter. So polishing is useless;The more thethickness of Ti layer is, the more the wetting condition is;Cleaning thesurface of diamond film and Ag-Cu solder can improve the wettingcondition considerably.(3)Draw test is the best way to assess the quality of brazing. Bothof the Shear strength and pull-off strength are studied in this paper.The shear strength of diamond film and diamond film, diamondfilm and WC, WC and WC is higher and higher successively. We cansee that the main problem lies in the weld of diamond film.We get the maximal strength 184MPa by brazing diamond thickfilm with WC at both sides. The shear strength increases and thenreduces along with the increasing of the thickness of Ti layer. Themost suitable thickness varies from 6.0μm to 10.0μm.Normally the diamond thick film is torn in the middle and itspull-off strength is no more than 88MPa. It is because that a greatmany of crystal boundaries and crystal defects exist in the interior ofdiamond film.(4)The distribution of all elements is analyzed by electron probemicroscopy analysis. Different from Ag and Cu elements whichdiffuse evenly, Ti is segregated at the side of interface of diamond film.