Abstract :
Dissimilar welding between cemented carbide and invar alloy was carried out using CO2 laser beam and argon arc as heat sources. η Phase was formed near WC–Co/weld interface and precipitations in the fracture were discovered. In order to disclose the microstructure and mechanical property, firstly, η phase’s morphology and composition at interface were investigated using backscattered electron imaging (BEI); and element diffusion across heat affected zone near WC–Co/weld interface was further studied. Secondly, bend strength values of butt joint with different welding parameters were tested by four-point bend strength experiment. Finally, WC migration mechanism was further discussed and the bend strength was measured. The results showed: (1) microstructures consisted of columnar crystals, cellular crystals, eutectic structure and fir-tree crystal and dendritic crystals. The columnar crystals were surrounded by lots of fir-tree crystals. (2) WC migration was driven by stirring effects of welds, high pressure of molten materials and ionized shielding gas, interface reaction and surface tension. (3) η Phases dispersion did not decrease bend strength of butt joint. And the maximum bend strength was 1493.56 MPa, which was attributed to NbC precipitations featured with super-fine fir-tree.
