Mechanical properties and microstructure of pure nickel PAW and PAW-TIG welded joints

A plasma arc welding( PAW)-tungsten inert gas( TIG) hybrid welding process is proposed. And this paper investigated the microstructure and properties of pure nickel N6 joints by PAW-TIG hybrid welding. Compared with the conventional PAW method,the characteristic of PAW-TIG welding process is that there is no interaction between the two arcs.The addition of TIG can enhance the intrinsic high-efficiency peculiarity and the stability of the keyhole status of PAW. The joints made using PAW and PAW-TIG,respectively,were subjected to microstructural evaluations and tensile testing so as to analyze the effect of TIG arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that significant grain coarsening was observed in the weld metal( WM) and heat affected zone( HAZ)and it is found that the extent of grain coarsening increased with the addition of TIG arc. And the microstructure in hybrid joint,with wider weld width and the smooth surface,is coarser than in PAW joint. Furthermore,the microhardness and ultimate tensile strength( UTS) of hybrid joint is slightly lower than that of PAW joint. The fractograph observation shows that the fracturing mechanism of PAW joints ductile,while the hybrid welding joints exists as brittle-ductile fracture mode. The outcome of this work shows that in the condition of same deposited rate,TIG arc post-weld heat treatment can improve the welding efficiency and welding speed. The proposed PAW-TIG hybrid welding process is demonstrated to be suitable for welding nickel and its alloys in industry application.