Liquid Phase Diffusion Welding Of Ti(C,N) To40Cr With Pulse Current Auxiliary

In this paper, Ti(C,N) and40Cr was connected by using AgCuTi/Cu/AgCu compositelayer material under conditions of liquid phase diffusion welding with pulse currentauxiliary and vacuum brazing. Researches showed that: The maximum of four-pointbending strength,229MPa, of joints was obtained at750℃,5min. The existence of pulsecurrent changed the distribution characteristics of Ag and Cu elements, avoiding theenrichment near the interface of ceramic/solder, thereby reducing the generation of thecompounds in the interface; reduced the diffusion activation energy of some elements, suchas active element Ti, interstitial C; and improved element diffusion rate.Using Cu53Zr47amorphous solder, the connection of Ti(C,N)-based cermet wasachieved under both liquid phase diffusion welding with pulse current auxiliary and vacuumbrazing. The results showed that: Zr performed excellent wettability to Ti(C,N)-basedcermet. Substitution reaction occurred between Zr and Al2O3, and Al was reduced to freeatom, significantly enhanced its diffusion ability; the reaction between Zr and Ti(C,N)-basedcermet promoted atomic diffusion in Ti(C,N)-based cermet, maked it easier for soldercomponent atom to diffuse into it, then to react with it; the highest average value offour-point bending strength was achieved by joint of900℃,6min under condition of liquidphase diffusion welding with auxiliary pulse current, its strength value was380.9MPa.Products of Zr in Ti(C,N)-based cermet and welding seam near cermet side weakened theresidual stress of joint, changed the distribution status of joint residual stress, and madestress concentration occurred at the interfaces of different microsturctures in brazing seam.Liquid phase diffusion welding with pulse current auxiliary of Ti(C,N) to40Cr havebeen conducted by using AgCuZr/Cu/AgCu as composite interlayer. The results showedthat the maximum bending strength,286.0Mpa, is obtained at the welding parameters of750℃,5min. Interface microstructures of it at ceramics side are Ti(C,N)/(Ti,Zr)(C,N)+Cu2(Zr,Ti)/Ag-Cu eutectic+CuTi/Cu3Zr/Cu9Zr2/Cu-based solid solution/Cu. With the rise ofwelding temperature, the width of welding seam increases, microstructures disperse,meanwhile, more and different layers of microstrucures appear; and there is a one-to-onecorrespondence between the sequence of Cu-Zr compounds in that joint and that of theintermediate phase in the phase diagram. Tensile stress concentration and compounds arethe main cause of the failure of joint, the microstructure composed of Cu51Zr14is the weaklink of welding joint. Interfacial high temperature effect exists in liquid phase diffusion welding with pulsecurrent auxiliary, the effect disappears with the melting of solder foils. Interface connectionmechanism is based upon the high temperature effect of the interface. Firstly, interface ofsubstrate/solder produce punctiform physical contact; secondly, contact point and its nearbyarea is melted to form liquid phase area and start wetting and spreading in the substratesurface; followed by liquid phase areas increase rapidly and interconnections form, and theinterfacial high temperature effect disappears when all solder foils have melted into liquidphase; finally, interface cools to the substrate temperature, then solid phase diffusionbonding began after brazing seam’s solidification.