Study On Cu-Ni-Sn-Ti Active Filler Metal And Its Joining With The C-BN

The cubic boron nitride (c-BN) has some distinguished properties, such as extremely high hardness, good oxidation resistance ability and excellent physical, chemical properties and superior thermal stability. Especially the c-BN does not react with black iron-based alloys while the diamond will do. The c-BN is considered the alternative material of diamond by international materials community. c-BN products are very suitable for machining materials with high hardenss and great tenacity, such as iron-based alloys, titanium alloys and high-silicon aluminum alloys, and so on. c-BN is comprehensively applied to produce various tools or superabrasive against abrasion in the field of precision processing, stone materials processing, auto manufacture, mechanical processing, constructional materials, aviation, new materials processing, and so on. The range and field of application for c-BN is restricted due to the poor processing property of c-BN superhard material. In this paper, aimed at the difficult joining between c-BN and metal substrate, poor joining strength, working at high temperature and other issues, a new type of multi-component Cu-based active filler metal adding Ni, Sn and Ti elements is developed and the brazing mechanism of c-BN brazed with new Cu-based active filler metal is analyzed. The quadratic regression mixture experiment design method is adopted to optimize the composition of Cu-Ni-Sn-Ti active filler metal. The microstructure of the interface between c-BN and CuNi₅Sn_5.1Ti_11.1 active filler metal is researched by means of SEM, EDS and XRD, which reveal the interfacial formation mechanism. The distribution of interfacial residual stress is studied.According to the theoretical calculation of bond parameters and the experimental results, Ti elements are chosen as active elements of the Cu-based active filler metal for brazing c-BN. By the screen analysis of In, Sn, Al, Ag, Pb, Bi and Ga and other elements and the research on effects of In and Sn elements on the microstructures and properties of multi-component Cu-based active filler metal and the weldability of brazing c-BN, Sn elements are identified as alloy elements of the multi-component Cu-based active filler metal for brazing c-BN. Experimental results show that elements of new Cu-based active filler metal are Cu, Ni, Sn and Ti. Ti contents have effect on microstructures and properties of the Cu-Ni-Sn-Ti active filler metal and brazing c-BN. As Ti contents increase, the wettability of Cu-Ni-Sn-Ti active filler metal on c-BN is improved and the interaction between the filler metal and c-BN is intensified. The brittle compounds resulting from the interaction have an increase, which reduce the interfacial strength between the filler metal and c-BN. Therefore, the Ti contents in the filler metal need to optimize the design.By the method of extreme vertices design constrained by both upper and lower bounds, the composition of Cu-Ni-Sn-Ti active filler metal is optimized and the regression model of second order polynomial is established. The optimal composition of the Cu-Ni-Sn-Ti active filler metal is Ti:11.1wt.%, Sn:5.1wt.%, Ni:5wt.%, and margin is Cu. The melting temperature range of CuNi₅Sn_5.1Ti_11.1 active filler metal is 834.6-1000℃measured by differential thermal analyzer. The wetting angle of c-BN polycrystalline wet powder CuNi₅Sn_5.1Ti_11.1 active filler metal is 28-30°and the CuNi₅Sn_5.1Ti_11.1 active filler metal exhibits a good wettability on c-BN grains. During the process of brazing, Ti elements in the active filler metals interact with c-BN grains to achieve chemical metallurgical joining at the interface.The microstructures and mechanical properties of CuNi₅Sn_5.1Ti_11.1 active filler metal/ c-BN interface have been studied through changing processing parameters. The results show that, with the increase of the brazing temperature and the extension of the holding time, the interaction between Ti elements and c-BN enhances and new generating phases at interface increase, which have an important effect on the joining strength of CuNi₅Sn_5.1Ti_11.1 filler metal/c-BN interface. When vacuum degree is above 9.0×10-3Pa, brazing temperature is T=1100℃and holding time is t=10min, the interfacial joining strength is higher.The formation mechanism of the interface between CuNi₅Sn_5.1Ti_11.1 active filler metal and c-BN is discovered after the thermodynamics and kinetics analysis. During the brazing process, the chemical reaction occurs between active element Ti and c-BN. The compounds with certain metal and ceramic characteristics of Ti-N and Ti-B are pruduced, which play good transitional roles in the chemical and physical performance between CuNi₅Sn_5.1Ti_11.1 active filler metal and c-BN. The filler metal/c-BN interface realizes the chemical metallurgical combination. The structure of filler metal /TiN/TiB/TiB2/c-BN is formed at interface, helping to improve the interfacial joining strength.Residual stress and its distribution on CuNi₅Sn_5.1Ti_11.1 filler metal/c-BN interface are studied with finite element analysis method. The results show that the larger residual stress value appears at the highest contact point between filler metal and c-BN. The embedding depth of c-BN will affect the value and distribution of interfacial residual stress. In c-BN embedded in 35%-75% range, the interfacial residual stress increases with the increase of the embedding depth. In order to reduce the residual stresses generated brazing c-BN, ensure the c-BN strength requirements, the embedding depth of c-BN in the filler metal is feasible to be controlled at 30%-40% of the whole c-BN grain.