Arc Welding Of TiC_x-Cu(Al) Cermets As Well As Ti₃AlC₂ Ceramic

In this thesis,techniques of the arc welding without solder were investigated for jointing a TiC_x-Cu(Al)cermet material to another different TiC_x-Cu(Al)cermets or a copper alloy,as well as a bulk Ti₃AlC₂ ceramic material to a copper alloy.The elementary welding conditions including the current density,the arc time and the joining pressure were explored.Microstructures and phase compositions of the welded seam and the influence zone were observed and analyzed.The failure strength of the welded sample as well as the electrical resistivity and Vickers' hardness of the welded seam and the influence zone were tested.Further,the welding mechanisms as well as the effects of the microstructures and phase compositions of the welded seam and the influence zone on the jointing strength were discussed.Several creative outcomes were obtained as follows:1.The firm joint of TiC_x-Cu(Al)cermet to TiC_x-Cu(Al)cermet or to a copper alloy were actualized firstly by the arc welding technique without solder.2.The firm joint of the bulk Ti₃AlC₂ ceramic material to a copper alloy was also actualized firstly by the arc welding technique without solder.3.The arc welding mechanisms of TiC_x-Cu(Al)cermets and the bulk Ti₃AlC₂ ceramic were expounded firstly.4.The phase changing behavior of TiC_x contained in TiC_x-Cu(Al)cermets during the arc welding as well as effects of the microstructures of the welded seam and the influence zone on the joint strength and the electrical resistivity were expounded firstly.5.The partially dissolving reaction behavior of the welding interface of the bulk Ti₃AlC₂ to the copper alloy during the arc welding was found firstly.The research results showed that,under the proper welding conditions,the bonding strength of welded joints between TiC_x-Cu(Al)cermets evidently exceeded that of the base material.The joint strength of TiC_x-Cu(Al)to Cu(Mg)reached 95%of that of TiC_x-Cu(Al)cermet.Such high bonding strength can be attributed to the good fusion of metal phases in the welding end,the increase of the density of the welded seam and the influence zone,as well as the formation of the fined-TiC_x grains.Both of the welding current density and the arc time take significant effects on the fusion state of Cu(Al) phase as well as the phase transition behavior of TiC_x within the welded surface and the adjacent region;in addition,the joining pressure takes also a remarkable effect on the finally formed microstructures of the welded seam and the influence zone.The firm joint of the bulk Ti₃AlC₂ ceramic to copper alloy is mainly attributed to the high temperature dissolution reaction of Ti₃AlC₂ on Cu,resulting in the formation of transition region consisting of TiC_x phase and Cu(Al)phase.Under proper temperature, Al atoms and a small quantity of Ti from Ti₃AlC₂ bulk surface and the adjacent regions diffused to Cu,forming a Cu(Al)alloy phase containing Ti.The Cu(Al)alloy phase firmly bonded with TiC_x from decomposition of Ti₃AlC₂,which endows a strong bond between Ti₃AlC₂ and Cu alloy.Because of the significant differences of electrical resistivity and thermal conductivity between the bulk Ti₃AlC₂ and the copper alloy,the applied welding current and the arc time must be strictly controlled,to make sure that both the surfaces of Ti₃AlC₂ bulk and Cu alloy to generate a proper temperature simultaneously.The temperature in the welded surface formed under different welding currents and arc time,and the following applied joining pressures,have significant effects on the microstructure of TiC_x-Cu(Al)transition zone.At a lower temperature,the TiC_x phase generated in the TiC_x-Cu(Al)transition zone generally kept the original skeleton of the Ti₃AlC₂ grain,while at a suitable high-temperature,the formed TiC_x grains were mostly fine flake with a hexagonal shape,and dispersed uniformly in the network of the Cu(Al)alloy.With the temperature increasing in Ti₃AlC₂ bulk surface, the grain size of TiC_x was significantly increased.In general,the finer the TiC_x grains in TiC_x-Cu(Al)transition zone is,the firmer the bonding between Ti₃AlC₂ bulk and Cu alloy will be.The joining pressure takes also a remarkable effect on the microstructures and the density of the TiC_x-Cu(Al)transition zone formed finally.These creative outcomes and scientific cognizations provide a new technical approach and implement means for the manufacture of a part with complex shape by using the new TiC_x-Cu(Al)cermet and Ti₃AlC₂ ceramic materials,and thus,will effectively accelerate the engineering application of these new materials.