The Influences Of Rare Earth Oxides And V₂O₅on Co-Cu-Sn Matrix Of CBN Tools

Research on the application of rare earth in superhard tools began in the1980s,from now on, researchers have carried out extensive research on the application of rare earth, including in Cu-based, Fe-based and Al-based superhard tools. The results showed that if the rare earth additive and bonder system were changed, the rare earth’s roles would different. So research on the performance of different rare earth additive in diverse bonder system appeared very necessary.This paper is focused on the effects of the types and amount of rare earth on the properties of metal bond and CBN composites. The basic formula of experiment is Co45-55Cu25-35Sn6-13Fe4-6,and make CeO2、La2O3、Y2O3、V2O5as additives. Study found that the hardness of the metal bond and CBN composites cannot be improved by joining in rare earth oxides, even which will be substantially reduced, but the flexural strength of the metal bond can be improved significantly. When the CeO2content is0.5-0.8%, La2O3content is0.6%,Y2O3content is0.2-0.5%, the flexural strength of metal bond increases a lot compared with the basic formulation, which is free of rare earth and whose flexural strength is451.9MPa.As for the flexural strength of CBN composites, only in case that La2O3content is0.8%and Y2O3content is0.2%,which is a little more than the basis formula’s.The roles of V2O5on the metal bond and CBN composites are very different from rare earth oxides.When the V2O5content is less than1.0%, the flexural strength of metal bond will between456.4MPa and551.4MPa,but the flexural strength of CBN composites essentially unchanged.By SEM and EDS analysis, Cu and Sn have been alloyed in CBN composites. Binder elements can be found in the CBN surface. Y2O3has highly dispersed in the matrix, so it "disappeared". When Y2O3content higher than0.75%, Cu-Sn alloying degree can be reduced. When V2O5content is0.3%,V2O5will initiate thermal decomposition, the pits caused by CBN dropping off,whose surfaces are smooth.In addition, V element is present in the CBN surfaces.