Research On Glass Ceramic Bond For Diamond Grinding Wheel And Bonding Mechanism At The Interface Between Diamond And New Vitrified Bond

Diamond is the hardest substance in the nature;it has very high strength and excellent resistance to wear,so it is ideal material for manufacturing cutting tools or grinding products mixed with certain bond in order to process other hard materials such as tungsten carbide, Polycrystalline diamond compacts or engineering ceramics,magnetic materials.Because natural diamond is very rare and very expensive,it is difficult to meet the production demand in industry.At present,most diamond grinding compound used in the machine-finishing industry is man-made materials,which is synthesized at high temperature about 1773K and high pressure of 5-6GPa.However the diamond is difficult to be fixed because of its smaller grains.In order to use the diamond to carry on high precision process efficiently,the diamond grains are often prepared into grinding products mixed with certain kinds of bond such as the resin,the metal and the ceramic. Compared to other grinding products,ceramic bond diamond products have better application prospect because of their high longevity,high efficiency,good rigidity and lowest process cost.However diamond is easily oxidized in the air at higher temperature than 1023K,this will damage the structure of diamond.While ceramic bond products usually must be sintered at above 1473K for obtaining high union strength between diamond abrasive and bond.As a result,the ceramic bond which can meet the sintering demand of diamond in lower temperature and stronger strength with abrasives is difficult to obtain.This limits the application of ceramic bond diamond products in industry.Based on the chemical stability of diamond in high temperature and the property requirement of diamond to ceramic bond, Li₂O-ZnO-Al₂O₃-SiO₂ glass ceramics have been chosen as the bond in ceramic bond diamond grinding wheel.The relationship among composition,structure and property of glass ceramics has been investigated using DSC,X-ray diffraction,SEM,Infrared absorption spectra in this paper,including the effects of addition of Na₂O,B₂O₃ on the structure and property of glass ceramics,the effect of plating titanium on diamond crystal surface on the property of diamond,the soakage between diamond and vitrified bond in hugher temperature,the bonding status and bonding mechanism at interface between diamond and ceramic bond.The prescription of vitrified bond and diamond grinding wheel have been optimized by the experiment of grinding the cylinder of Polycrystalline Diamond Compact and back grinding of silicon ship.The main result as the following:(1)A new technology route that the ceramic bond diamond samples was buried in quartz sand and subsequently sintered has been presented, compared to the sintering technology of diamond crystals in the air or in the argon,which causes smaller structure destruction under same temperature-time curve.Generally,when diamond is sintered in the air, the oxidizing reaction starts to take place at 1023K.With the increasing of temperature,the oxidized degree rapidly increases and the anti-impacting strength of diamond decreases greatly.However when the diamond was buried in quartz and sintered,its oxidized degree lowered greatly and the anti-impacting strength did not obviously reduce.This discovery changed the idea of people that ceramic bond diamond products must be sintered below 973K to protect diamond from oxidization and offered more choice for the ceramic bonds with different property and prescription.(2)Glass ceramics was used as the bond of diamond products for the first time.According to conventional conception,the bond must have lower melting temperature than 973K and less viscousness so as to wrap diamond grains at sintering temperature.While glass ceramic is very difficult to be used in diamond products because of its higher melting temperature than 1373K and larger viscousness.In this paper,the Li₂O-ZnO-Al₂O₃-SiO₂ system glass and system glass ceramic have been prepared,the effect of addition of B₂O₃ and Na₂O on the properties of the glass and the glass ceramics has been investigation.The result shows that when Na₂O is added into Li₂O-ZnO-Al₂O₃-SiO₂ system,the viscousness of the glass decreased rapidly,but the softening temperature does not decrease obviously,and the coefficient of thermal expansion of the glass ceramic increases rapidly;when B₂O₃ is added into Li₂O-ZnO-Al₂O₃-SiO₂ system,the softening temperature of the glass decreases and the coefficient of thermal expansion of the glass ceramic increases with the increasing of B₂O₃ additions.To meet the property demand of diamond,18mol%is the best additions of B₂O₃.When TiO₂ or TiO₂+ZrO₂ is used as nucleating agent and a reasonable heat treatment is adopted,Li₂Al₂Si₃O₁₀micro-crystals with lower thermal expamsion coefficient is found in the Li₂O-ZnO-Al₂O₃-SiO₂ system bond.the glass ceramic has a coefficient of thermal expansion of 8.5×10^-6l/k,which is close to that of diamond,the drawing strength of 30.68 MPa,bending strength of 95.11MPa.This means that the bonding strength between diamond grains and this bond is very high.(3)when diamond is plated with titanium on the surface,titanium will be oxidized into Ti₃O₅ at higher temperature than 993K,the oxidization of diamond can be prevented because Ti₃O₅ is inert and compact;when the temperature increases to 1213K,Ti₃O₅ is transformed into TiO₂,which results in the disappearing of the protecting role and the decreasing of anti-impacting strength of diamond;Ti₃O₅ crystal is quartet crystal system(JCPDF:09-0309,a=3.754(?), b=9.474(?),c=9.734(?),Z=4,ρ=4.19)which has a similar structure to Al₂TiO₅(JCPDF:26-0040,a=3.593(?),b=9.439(?),c=9.647(?),Z=4,ρ=3.69) in the bond and can enter into the structure of vitrified bond,which causes decreasing of the surface energy between glass ceramic bond and diamond crystal.For B₂O₃-PbO-ZnO-SiO₂ glass bond,plating titanium has no obvious effect on improving the bonding strength between the bond and diamond grains.(4)The contact angle between vitrified bond and diamond crystal reduces with the increasing of temperature;when B₂O₃ exists in form of [BO₃],the surface tension of glass melting reduces,and the contact angle between vitrified bond and diamond crystal reduces;The additions of Na₂O offers more free oxygenions,increases the radio of O/Si and transforms complicated Si-O-Si network structure into smaller Si-O-Si group,which causes the increasing of the surface tension and the contact angle.(5)The diamond grinding wheel with the new vitrified bond has many advantages such as longer longevity(is as about 2.5—3 times as that of resin bond one or as 3 times as that of B₂O₃-PbO-ZnO-SiO₂ glass bond one),higher precision of PDC size(±0.01mm),higher efficiency (saving grinding time about 40%),hardly noise and little harm to grinder in grinding the cylinder of Polycrystalline Diamond Compact.Also this wheel can be used in import grinder for using in back grinding of wafer to substitute an import one.So the new vitrified bond has excellent property.