Study On Interface Strengthening And Thermal Damage Inhibiting Of Brazed Diamond With Rare Earth Doped Ni-based Filler

Brazed diamond tools have become an irreplaceable advanced processing tool due to high abrasive exposure,large chip space and good heat dissipation.However,different types of thermal damage caused by high brazing temperature and catalyst elements are the main factors that limit the comprehensive properties of diamond tools brazed with Ni-based fillers.In order to inhibit the thermal damage of brazed diamond tools with Ni-based filler and improve their properties,the Ni-Cr filler brazed diamond is selected as the research object,Ce and La are modified elements,and the method of theoretical calculation combined with experimental research is adopted to study the interface strengthening and thermal damage inhibiting of brazed diamond with rare earth doped Ni-Cr filler.The main researches are as follows:Firstly,the effects of Ce and La on the bonding behavior of diamond/Ni-Cr filler interface and diamond graphitization were studied by first-principles calculations.It is found that Ce and La atoms tend to segregate in the interface region near diamond,which is beneficial to isolate the diamond and Ni matrix,thereby weakening the catalytic effect of Ni element on diamond graphitization.The calculated interfacial separation work and interfacial energy show that doping Ce and La can effectively enhance the interfacial bonding strength and improve the interfacial stability between diamond and Ni-Cr filler,and doping Ce exhibits better effect.The diamond structures have no obvious distortion in doped interfaces,indicating that doping Ce and La can inhibit the graphitization of diamond.The electronic structure analyses show that the clean Ni-Cr/C interface mainly exhibits the ionic bond characteristics,while the doped interfaces present a mixture of ionic and covalent bonds between Cr and C atom,which may be the essential reason for the more stable doped interfaces.Secondly,Ce element with better modification effect was doped into Ni-Cr filler in the form of CeSi2 and the brazed coatings were prepared to study the influence of Ce doping on the microstructures and properties of brazed layers.It is found that the microstructure of brazed coatings with CeSi2-doped Ni-Cr filler is obviously refined,and a new phase CeNi3 forms in brazed layers.The microhardness of brazed coating with 2wt.%CeSi2-doped Ni-Cr filler reaches 774.8 HV,which is 89.2 HV higher than that of undoped coating,and its friction coefficient curve is relatively gentle and stable,and the wear quantity is minimum,showing the best wear resistance.The calculation results of elastic properties show that the new phase CeNi3 exhibits good plasticity and toughness but low hardness.Therefore,it can be concluded that the formation of CeNi3 phase is beneficial to improve the plasticity and toughness of brazed layer.Finally,the effect of Ce doping on strengthening interfacial bonding between diamond and Ni-Cr filler and inhibiting diamond graphitization was further studied by brazed diamond experiments.It is found that a layer of dense Cr3C2 compound is formed on surface of brazed diamonds with different contents of CeSi2 doped Ni-Cr filler,where Cr3C2 plays a bridging role and promotes the wetting and climbing of filler alloy to diamond.The Raman spectrum analysis results show that the graphitization degree of brazed diamond with CeSi2-doped Ni-Cr fillers is lower than that with pure Ni-Cr filler.The brazed diamonds with 2wt.%CeSi2-doped Ni-Cr filler exhibit suitable exposure,and the carbides on diamond surface exhibit the finer characteristic,which is beneficial to increase the contact area and reduce the stress concentration between diamond and filler alloy.Besides,the brazed diamonds with 2wt.%CeSi2-doped Ni-Cr filler remain relatively complete cutting edges and shapes after grinding test,showing the best wear resistance.